PES Solar 1 20 Full Mag Final

ASK THE EXPERTS: TECHNOLOGY Voyager FSLRS6 Patented Module Attachment Method TE: We have experience and capability TE: The majority of our focus has been in the process. This process is collaborative. This beyond that of a traditional tracker supplier. US, with some business in Europe and collaboration helps us be more transparent. We bring software design capability and Southeast Asia, however we have expanded engineering and construction expertise to offices in Australia, EMEA, and Asia. We’re Through this proactive collaboration we the table to be a full-service partner. That also bidding for several deals in Latin America hope to earn your trust, and build a lasting capability gives great flexibility to our and think it is definitely a ripe market for partnership upon it that can weather any customers. We see this flexibility 2P trackers. storm that may come our way. Every demonstrated in two ways. The first is the opportunity is an opportunity to learn and flexibility within our organization and the PES: What are your predictions for the improve. We don’t claim to know it all. No one second, the flexibility built into our solutions. solar/PV industry in general and your does. We are confident in our people and company in particular for 2020? their real-world experiences to understand Being flexible means, that we jump in with your needs, provide a plan of what we need to both feet with our partners, to design the TE: We see continued growth in the PV do and how to do it, and then execute it, to most optimized solution for lowest overall industry, especially as folks turn more deliver an optimized solution that exceeds balance of systems cost. towards trackers and 2P trackers in general. your expectations. Last year saw nearly 35 GW of tracker We do this by providing in-house expertise deliveries globally and we expect strong We are changing the way trackers are done with our supply chain, logistics, and growth over the next few years. As one project at time. We are listening to our operations teams. We organize Voyager mentioned above, we are targeting more customers, putting into practice their training before the EPC even gets to the site than 2 GW of deliveries in 2020. feedback, and adapting to market challenges. so they can get started and see productivity Here at FTC we look at things through the gains from day one. We customize laydown PES: Is there anything else you would like to following lens: yards and delivery schedules to support the add to the FTC Story? customer’s needs. We provide world class First do what is right for our partner construction experts with LEAN TE: FTC Solar may be a new company but our construction backgrounds to help advise/ team is not. I am proud of the industry Tailor solutions that optimize our train EPCs on site. pioneers that make up my team. They are partners projects committed to redefining the tracker PES: Where are your main markets and are experience. When I say that, I mean we just Collaborate consistently with our partners there any particular geographical areas don’t provide a customized solution to fit to enhance transparency where you are looking to drive your project. Anyone can do that. We further growth? redefine that experience by coming along www.ftcsolar.com side you as a partner and including you in our WWW.PESSOLAR.COM 51

ASK THE EXPERTS: MANUFACTURER Power up in all weathers Maria Stefanidou, Sales Director at Mounting Systems, gave PES Solar an interesting insight into the importance of racking systems. Just outside of Berlin, this German manufacturer supplies a whole range of products to our industry. The latest is for solar car ports. Read on to find out more ... Maria Stefanidou PES: Hi Maria, it’s a pleasure to welcome Maria Stefanidou: Mounting Systems is the you to PES. To start us off, would you like only racking system manufacturer in 52 PES SOLAR to give us a brief overview of Mounting Germany. Our production site is in Systems? Rangsdorf, 30 minutes outside Berlin, where

ASK THE EXPERTS: MANUFACTURER we produce a whole range of products for MS: As a business in the renewable energy PES: Could you tell us about some of the pitched and flat roofs as well as ground sector, sustainable trends and policies can structures you create for solar modules? mount including solar carports. have a huge impact on our business. The phasing out of fossil fuels and nuclear power MS: We offer a wide range of products and we Manufacturing products in-house means we will bring business opportunities for many are constantly in the process of developing are in full control of the system and the companies and industries on the one hand, new systems that will drive sales in the product: from the raw material all the way and independence in energy supply on industry forward. to the delivery to the customer. the other. This year we released the solar carports and Being a large manufacturer, we also make In many countries incentive programs are in we are also optimizing the trapezoidal rail parts for many other brands all over the place to support, homeowners for example, system, triangle system, as well as a new world, giving us a unique way into many to buy solar systems for their roof. As a flat-roof system. At Mounting Systems, we markets. We are selling our products with PV-manufacturer we excel this transition by always find a solution for every project, and if our Mounting Systems brand, as well as providing attractive systems for the we see demand for a new racking technology, private label. installation of PV modules. we are quick to engage the product management team. PES: We know that sustainable policies are We developed the solar carports to further becoming more of a requirement for provide solutions to help stakeholders chose One way to recognize one of our products is businesses and cities want to become to install green power options, may it be the module clamp, it has an inner-click greener, we wondered what effect this has homeowners, businesses or governmental technology and is used on all our systems. had on your solutions? institutions. PES: Are there a variety of designs or is it WWW.PESSOLAR.COM 53

ASK THE EXPERTS: MANUFACTURER Double charging station one fit for all, with just a variation in size? Between each foundation up to 6 cars can be good-looking solar carport in their driveway MS: I‘m pleased to say, we have developed 3 charged, where two thirds of the parking lots for an affordable price. versions for the 3 uses that we identified. can be equipped with a charging E-Port Wings, which are large scale infrastructure. The E-Port Home is offered as single and commercial sized areas such as airports, double for respectively one car and 10 solar supermarket, public parking lots etc. For E-Port Line, is for medium scale businesses panels or two cars with 15 solar panels. It’s these projects, getting the maximum output that want to have a charging infrastructure, also possible to have additional features is important, and so this is why we use a perfect for about 9-12 parking lots. The cars added such as led lights, preferred color and double-sided carport. As the name suggests will be parked on a line and two thirds of them more luxurious design for those who wants it has a foundation in the middle and covers, can be charged. the best of the best for their electric vehicle. through wing-like arms, both sides. E-Port Home, for the domestic small to We sell the E-Port Home through our trusted Single charging station larger households. Homeowners with one or wholesalers around Europe two cars, can now install a high quality and PES: Why are these important to the environment, customer and end user, what are the tangible benefits in terms of sustainability and cost reduction? MS: Cars need a parking space, and if that car also is electric, a charging infrastructure is needed. A solar carport serves multiple needs with one solution, it produced energy and protects the car from strong sun or rough weather. This multipurpose use on its own is valuable for a homeowner or a business owner, who wants to have a modern, cost-efficient and sustainable solution. Additionally, being energy independent gives freedom and can reduce fixed costs. PES: Who and where are your main customers? MS: Our strongest market is Germany, and we have an established presence in almost all the EU countries. Our sales strategy is transparent and loyal. Therefore, we limit our partnerships in each country to just a handful of wholesalers, supporting them with marketing, product trainings and handing over leads. 54 PES SOLAR

ASK THE EXPERTS: MANUFACTURER ‘The development of Mounting Systems has been really promising and we are determined to gain a higher share of sales in the European market.’ Developing strong partnership gives us the House with double charging station when they are deciding for a partner. benefit of long-lasting deals, where it’s easier to calculate production forecast. For next few months. The development of Mounting Systems has example, in 2019 we managed to deliver 95% been really promising and we are determined of all our products on time, which we only In addition to Spain we are also focusing on to gain a higher share of sales in the European managed due to the close communication Scandinavia, which is a slow market, but with market. New marketing campaigns and a with our partners. a big buying power and with strong focus on refreshed focus on our brand will support sustainable technologies. We are starting in that vision and bring a strong identity that all We also work with larger project companies Sweden, with the aim to eventually deliver stakeholders can recognize. (EPC). They work project for project and do our products to Denmark, Norway and not keep stock of our products, which can Finland. We have a new internal structure and a strong make it challenging to have accurate and supportive investor. So, we are focusing production forecasts. PES: What do you think will be the greatest on creating additional values for our opportunities and challenges for the solar partners. We have hired a complete product, For a manufacturer it’s very important to industry in the general and Mounting innovation and engineering team, with solar work with project-based businesses as well, Systems in particular, over the next experience and top engineering expertise. because the people working in project-based few years? businesses often are very knowledgeable We can already see promising results about the newest systems on the market, MS: From a sales perspective, the solar through creative and realistic product new market opportunities and upcoming industry sales channels are messy, which developments. challenges. We look at these partnerships as puts price pressure on racking producers and a source for market intelligence and a nice results in non-comparable pricing between www.mounting-systems.com way to develop a good network in the competitors. This can be frustrating for industry. customers, since they have no transparency PES: Geographically speaking are there any new markets you would like to break into? MS: Spain! Spain is a unique market due to the industry knowledge that is there, and that the market is finally recovering, after years with a very conservative policy, which stopped most of the solar industry over the past years. Now, finally the market is attractive to investors again, and due to the increasing pressure from the European Union to increase renewable shares in the grid, the market is recovering. This year we exhibited at the Genera fair in Madrid and was overwhelmed with the success. We really look forward to seeing the development the WWW.PESSOLAR.COM 55

TALKING POINT STR-21G Sun Tracker with MS-57 Pyrheliometer next to the MS-90 DNI Sensor at EKO Instruments Ami Solar Park, Japan Developing a new angle on solar irradiance Words: M ário Pó, PhD, lead scientist and Dmytro Podolskyy, Business Development Manager, both at EKO Instruments EU Our reliance on fossil fuels is ending. Not because we’ve run out of oil, gas, or even coal. Not even because the harmful environmental impact of these resources is finally, sadly, irrefutable; except to the most dogmatic of climate change deniers. No. Our reliance on fossil fuels is ending because of the advances we have made in renewables, wind, hydro, geothermal, and solar; especially solar. 56 PES SOLAR

TALKING POINT Dmytro Podolskyy Mário Pó, PhD application is equal to more energy produced; to more money saved, or earnt. Solar energy has always been integral to life from off-grid stand-alone photovoltaic (PV) on earth, and now through advancements in systems to Giga-Watt (GW) scale PV power Know your input, understand your output technology, increased efficiency, and the farms, or Concentrated Solar Power (CSP) hard truth of economics, solar is fast plants, and more. Their productivity is To define the efficiency of any solar becoming the definitive energy source of the defined by their ability to transform solar technology, we need accurate data on the next era in human civilization. radiation into electrical and thermal power input and output energy. That is, how much efficiently. Increased efficiency in any potential energy is available from the sun Solar technologies have broad applications, versus how much the system has produced. Knowing and fully understanding these two quantities is crucial in any solar energy installation, not just for process optimisation, but also in order to detect problems. Solar radiation, sunlight, is, however, a highly variable resource. Season, time of day, location, even the diffusion of light in the sky all impact on input and potential output. Diffuse and ground reflected solar radiation is increasingly being used to improve energy yields in more traditional installations. Bi-facial solar PV modules allow solar plant owners to harvest radiation from the sky, and also, from ground reflected light, increasing their total yields. Special ground engineering can also enhance the ground albedo, further increasing the amount of incoming energy to a bifacial solar panel. WWW.PESSOLAR.COM 57

TALKING POINT Different solar cell technologies are also EKO sensors, mapped to solar irradiance more sensitive to various components of the solar spectrum. ‘Perovskite’ solar cells, for instance, absorb the shorter wavelengths of the solar spectrum more efficiently. Whereas ‘Solar Tandem’ cells combine more than one spectrally selective material, potentially overtaking traditional Silicon solar modules for efficiency. Monitoring irradiance in all its components is essential to the effective planning, and management of a solar power plant. Individual instruments can be deployed as part of a solar monitoring station to measure each component. For example, a solar monitoring station with an automated tracker, a pyrheliometer that is always pointing at the sun and two pyranometers, one shaded by a special shading ball or disc and one unshaded, can together measure Direct Normal Irradiance (DNI) and Diffuse Horizontal Irradiance (DHI) simultaneously. The second pyranometer measures Global Horizontal Irradiance (GHI) independently providing redundancy in the measurement data in case one of the sensors becomes soiled, or out of level; the error in the data can be easily detected by evaluating the radiation closure. Such a system is the most precise way to measure solar irradiance provided that all WORKING PRINCIPLES: TITLING, ROTATION, DETECTION. sensors are properly calibrated, and the tracker has the highest pointing precision Left. Sensor schematic: and reliability. However, this sort of system a. Direct solar beam isn’t always the most practical solution. a b. Rotating mirror: reflects the beam to the detector Whether due to budget constraints, or c. Pyroelectric detector: measures pulse simply a lack of space, a more compact d. Titled angle: optimized to latitude option is sometimes a necessity. c 5V 2 ‘Tracker-less’ Alternatives b 2 There are several solutions available on the 1 market that can measure at least two components of solar radiation, and calculate 0V the third. d For example, two pyranometers, a shaded and unshaded one, could be used to measure 3 GHI and DHI, enabling the calculation of the DNI. The shading can be provided by a Above. MS-90 Beam: shadow ring or an automated rotating 1. Analog output shadow band. However, these methods often 2. Peakvalues proportional to Direct Normal Irradiance require high maintenance and have relatively 3. Time approx. 15 sec. high measurement uncertainties due to the fact that the shading elements cover a much POSITIONING: ORIENTATION larger part of the sky than the shading ball on a full-sized solar monitoring station; this can Northern hemisphere N lead to errors in the measurements of diffuse MS90 oriented to the equator S and global irradiance. Equator Another challenge to the accurate calculation of DNI is the often-high variability Southern hemisphere in atmospheric conditions at most sites. The MS90 oriented to the equator composition of air is changeable, its humidity, the presence of aerosols and To measure DNI the EKO MS-90 sensor body is set up with a fixed tilt optimized according to the location latitude. The direct beam is airborne particles such as dust, sand, soot, Hroeflwecittewd otortkhse:stehnesoMr hSe-a9d0byDaN45I°Stieltnedsorortating mirror. Each revolution of the mirror has a period of 15s, reflecting the direct beam radiation to the sensor head once every period. A pyroelectric detector then measures the signal pulse, which is proportional to DNI. 58 PES SOLAR

TALKING POINT MS-90 Plus+ fog, ice crystals, smog, and even sand can all The MS-90 accurately measures DNI without accurate measurement of GHI due to its low affect the dispersal of solar light. a sun tracker. The spectral sensitivity of the thermal offset and fast response time; sensor covers a wide spectrum from 300 to making it possible to measure fast changes So, while ‘tracker-less’ solutions can be a 2500nm; enabling accurate measurements in irradiance. practical alternative, they have traditionally of DNI for both PV and CSP applications, as been regarded as ‘second-best’. In an well as in meteorological observations. And And with no external moving parts the MS-90 industry where the accuracy of the as it’s calibrated outdoors using a Plus+ is easily installed and maintained. monitoring solution, and in turn the pyrheliometer, not in the lab, the MS-90 DNI efficiency, and economic viability of an Sensor is traceable to the World Radiation Find out more about the MS-90 Plus+ and application are paramount, second-best Reference (WRR). other solar monitoring solutions. simply isn’t good enough. Meet the MS-90 Plus+ Contact [email protected] A Unique Solution We’ve combined the unique internal rotating www.eko-eu.com That’s why EKO Instruments developed the mirror design of the MS-90, with our MS-90 DNI Sensor a new approach featuring industry-leading, fast response, Class A Mário Pó, PhD is lead scientist at EKO a unique internal rotating mirror design that MS-80 Pyranometer and original C-Box Instruments EU, and received his can measure DNI without requiring a smart interface, to create the MS-90 Plus+. A doctoral degree at the University of separate tracker. The distinct shape of the new, total solar irradiance solution. Lisbon. His areas of expertise include mirror reflects the direct solar beam to a very photovoltaic systems, solar irradiance fast pyroelectric detector, allowing the Additional features include an integrated measurements and instrumentation. MS-90 to measure direct radiation without GPS receiver, enabling the C-Box to calculate the whole unit tracking the sun as a much the diffuse component of the irradiance Dmytro Podolskyy is Business larger solar monitoring station would. based on the DNI data from the MS-90 and Development Manager at EKO the GHI data from MS-80; plus, a MODBUS Instruments EU. He graduated from TU We measured the MS-90 against reference 485 RTU output for easy connection to any Delft with a degree in Applied Physics and pyrheliometers at the National Renewable digital data acquisition system. Nanotechnology and has since gone on Energy Laboratory (NREL) in Colorado, USA; to support industrial solar initiatives and successfully demonstrating the accuracy and The MS-80 Class A Pyranometer with a wide scientific research projects around the viability of this unique solution. spectral range also provides the most world. WWW.PESSOLAR.COM 59

TALKING POINT Inspired by Mars Atonometrics was founded in Austin, Texas, in 2007, with the mission to provide high-quality test and measurement equipment to the small but growing photovoltaics industry. The company founders came from a long background in test and measurement equipment for the semiconductor industry. The experience of the management team included over 30 years of R&D, product development, sales, marketing, and manufacturing. The company’s first products included light This experience in the PV industry led the followed by calibrated reference cells for soaking systems and IV measurement company to develop products for cost-effective irradiance measurements. systems for PV module manufacturers and operational PV plants. The company’s first test labs. These products have been soiling measurement system was Soiling: the accumulation of dust and other installed in factories and labs worldwide. introduced in 2010 and that product was contaminants is a significant concern for photovoltaic (PV) solar power plants. 60 PES SOLAR

TALKING POINT Soiling affects solar power generation by developed, keeping in mind the costs of There are several methods for measuring blocking sunlight from getting to the solar cleaning which vary significantly by soiling losses at PV plants. Atonometrics, is panels. It causes worldwide solar industry cleaning method and plant location. The a leader in the field and has been providing power losses of 4 to 7%, with decision of how often and when to clean is PV irradiance and soiling measurement corresponding revenue loss in the an economic one, increases in revenue due systems for over 10 years and has over multibillion-dollar range. And some to cleaner solar panels should exceed 1,000 systems installed in over 30 countries locations, such as the Middle East, can losses due to soiling. worldwide. The most common PV soiling experience soiling losses of 50% or more measurement method is based on the during dust storms. Since soiling losses are highly variable and comparison of two PV devices such as solar have plant-specific impacts, panels, reference cells, or a combination. Soiling occurs primarily because airborne instrumentation is needed to measure particulate matter settles onto the soiling losses on site. At operational power One device is regularly cleaned, either surfaces of solar panels and sticks to them. plants, ongoing measurement of soiling automatically or manually, and the other The rate of soiling accumulation, usually loss is an important component of device is allowed to soil naturally like the discussed in terms of the daily increase in performance monitoring. At solar panels at the site. Comparing the power loss in between cleanings, varies pre-construction sites, soiling loss soiled device to the clean one yields the between 0.1 to 1.0 percent per day, measurement is an important part of impact of soiling loss. These methods depending on the amount and type of resource assessment for future power plant require some labor and maintenance costs, dust in the air, wind speeds, humidity, and performance prediction. either in manually washing a clean reference other conditions. The total soiling loss continues to grow until a cleaning or rainfall event occurs. Soiling is a location-specific phenomenon. Not only are there are clear differences in soiling rates between geographic regions, but even on the local scale there can be significant differences in soiling rates depending on local surroundings. Soiling rates can even vary significantly across a single PV power plant, perhaps due to a road, farm, or factory on one side of the plant or due to prevailing winds. Studies have reported up to 3% performance variations across a single plant due to location-specific soiling rates. For PV power plant sites without regular rain, cleaning strategies need to be 2 0.040 0.06 0.036 0.055 0.039 0.05 1 0 Distance (km ) 0.039 Average Soiling Rate (%/day) -1 Wind 0.061 0.028 0.045 0.04 -2 0.025 0.035 -3 0.03 FARM 0.065 -4 -4 -3 -2 -1 0 1 2 3 Distance (km ) Variation of soiling rates measured by 8 soiling sensors, distributed within a utility-scale solar power plant. Multi-year average daily soiling rates in %/day, shown in text and by circle radius in figure, are highest near the edge of the plant immediately down-wind of a farm. Soiling rates could be up to 2x the averages, as shown by the outer circles at each sensor location. WWW.PESSOLAR.COM 61

TALKING POINT Soiling Ratio 1.00 0.98 Mar Apr May Jun Jul Aug 0.96 0.94 0.92 0.90 Feb 10 Rain (mm ) 5 Cleaning Aug 0 Apr May Jun Jul Feb Mar Top: soiling ratio the fraction of actual system power to expected clean-state power, measured by a soiling sensor at a site in California, showing varying soiling losses over time with rain and cleaning and heavy build-up in summer months. Bottom: Rain and cleaning events at the site. device or in periodic refilling of a water tank the budget or on-site personnel to install Along the way, Atonometrics has become for automated cleaning. soiling measurement technologies, but that the recognized technical experts in PV test is changing with the introduction of new and measurement technologies. This is All-optical low-maintenance techniques are techniques. evidenced by over 30 published technical a recent development in soiling papers at the industry’s leading measurement technology. Atonometrics Soiling measurement is becoming conferences, workshops, and magazines. has developed a compact, easy-to-use increasingly important to optimize PV In addition, the company has over 20 issued measurement device called Mars™. This is a power plant performance and revenue. and filed patents. camera-based technology that requires no The conclusion is that soiling measurement maintenance and no calibration technologies are very cost-effective and To date, Atonometrics has installed several procedures. It is a completely hands-free newer optical technologies, such as Mars™, thousand products in over 30 countries and operation when installed. enable soiling measurements on a wide 6 continents worldwide. scale worldwide. The name for Mars came from a www.atonometrics.com conversation with technologists at The National Aeronautics and Space Administration (NASA), inspired by the idea of serving remote locations for which any maintenance, or calibration procedures would be difficult. Any sensors eventually deployed to Mars would have to be fully autonomous since maintenance technicians are difficult to find on Mars. So, the Atonometrics’ optical soiling sensor’s name was conceived with future Mars missions in mind. Mars™ was introduced to the market in 2018 and has since been installed in many PV plants worldwide. The low-cost, maintenance-free, and calibration-free aspect of good optical technologies has expanded the market for soiling measurement systems to smaller installations including commercial rooftops. Previously, these installations did not have 62 PES SOLAR

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TALKING POINT Explaining PV plant monitoring to IEC 61724-1 Words: Clive Lee, Technical Sales & Services Manager, Kipp & Zonen Reliable measurement of solar irradiance, and other environmental parameters, is crucial to accurately calculating the performance ratio (PR) of a solar energy plant. IEC 61724, published in March 2017, is the latest and most comprehensive international standard to address these issues. But what does it mean? IEC 61274-1 Photovoltaic system performance analysis that rely upon the data methods, and terminology for the performance - Part 1: Monitoring also serves collected, IEC TS 61724-2 and IEC TS performance monitoring and analysis of solar as the basis of two standards for 61724-3. Part 1 outlines equipment, energy PV plant systems; from irradiance 64 PES SOLAR

TALKING POINT input to AC power output. It is applicable to fixed angle, single-axis tracking and dual-axis tracking conventional PV modules and to concentrator (CPV) systems. It does not currently cover bifacial installations. For Classes C and B, it is acceptable to estimate some measurements from other nearby and reliable data sources, but these are rarely available. For Class A all parameters must be monitored at the site. The types of sensors required for each monitoring system (station) depend largely upon the application. Measurement of Diffuse Normal Irradiance (DNI) and Diffuse Horizontal Irradiance (DHI) is included in the standard for specific purposes, but here we will concentrate on the measurement of Global Horizontal Irradiance (GHI) and Plane-of-Array irradiance (POA) and other key meteorological (weather) parameters. Communication and Connection IEC 61724-1 PV plant performance monitoring classifications The industry standard for data for use with the analog inputs of low-cost polycrystalline silicon cells typically drops by communication within PV plants is now industrial data loggers. around 0.5% per °C temperature rise, 2-wire RS-485 with Modbus® RTU protocol, compared to the standard test condition of using individually addressable inverters and Class C Monitoring System 25°C. At 45°C in the sunshine the output monitoring equipment on a small number of could be 10% lower. This is not a fault; it is a data bus loops. Distributed sensor power is • POA irradiance – any type of thermopile characteristic that needs to be measured 12 or 24 VDC. pyranometer, PV reference device or accurately and taken account of in PR photodiode sensor; to be recalibrated as calculations. Recent inverters, hubs and gateways often per the manufacturer’s requirements. have no analog inputs. There may be no field This type of monitoring system is largely data logging, all the devices connect back to • Ambient air temperature – for an indication intended for commercial rooftop the site supervisory control and data of the effect on module efficiency, installations to give an idea of the PV acquisition (SCADA) system for storage, although it is much better to monitor the installation efficiency where there are no analysis and visualization by the plant module temperature directly. significant performance-related financial monitoring software and for remote access. and contractual implications. Where a digital output is not available from a The efficiency of monocrystalline and device, a 4-20 mA signal is usually preferred Class C irradiance sensor with compliant module temperature sensor WWW.PESSOLAR.COM 65

TALKING POINT Class B Monitoring System Pyranometer measuring plane of array (POA) irradiance • G HI and POA irradiance – ISO 9060:2018 ventilated solar radiation shield to prevent utility-scale PV plants often have significant Spectrally Flat Class B pyranometers or PV build-up of static air. contractual under-performance penalties. ‘reference’ devices with measurement The uncertainty of the hourly irradiance uncertainty ≤ 8 % for hourly irradiance • W ind speed – affects surface cooling of the totals will be around 6-8% and this is not totals (photodiode sensors are not modules. good enough for meaningful PR calculations acceptable); to be recalibrated every that will satisfy all stakeholders. It is unlikely 2 years. • Rainfall – to correlate with power that stakeholders will see a necessity to generation loss due to water on the install 6 module temperature sensors per Heating is required if condensation and/or modules. monitoring system. frozen precipitation, including dew, will affect the irradiance measurement on more than Class B is not likely to be popular because 14 days per year. Ventilation of pyranometers is optional, but in many locations (particularly where cleaning is infrequent) soiling can be a significant issue. External ventilation units blow filtered clean air over the pyranometer dome to reduce the deposition of dirt, dust and other soiling contaminants and reduce the frequency of cleaning that is needed. They also include the option of heating the airflow to prevent dew forming on the dome, evaporate rain droplets and melt frost. • PV module temperature – 6 sensors per system, distributed along the strings, for temperature correction of PR. As the number of modules in a string increases the loading along the string and the temperature of the cells varies. There are strict IEC guidelines regarding sensor position, thermal conductivity of the fixing and overall accuracy of the measurement. • A mbient air temperature – for historical trending analysis, the sensor must have a Pyranometer with ventilation and heating unit 66 PES SOLAR

TALKING POINT Class A monitoring system: GHI and POA pyranometers, weather station, soiling monitors Class A Monitoring System trending analysis. technology monitors the loss of light transmitted through the glass and, for any • GHI and POA irradiance – ISO 9060:2018 • R ainfall – to correlate with power type of module, the effect on power Spectrally Flat Class A pyranometers or PV generation loss due to water on generation can be calculated from the reference devices with measurement the modules. manufacturer specifications. This type of uncertainty ≤ 3 % for hourly irradiance soiling monitor requires no maintenance and totals (these genuinely ‘reference’ cells • Snow – to correlate with power generation is only cleaned at the same time as the typically cost more than an equivalent loss if this is an issue at the location. modules around it. pyranometer); to be recalibrated every year. • Soiling ratio – if the power loss is > 2 %, to Different areas of a large PV plant get dirty at inform when module cleaning is advisable. different rates and multiple monitors can Heating is required if condensation and/or provide a soiling map of the plant. By frozen precipitation will affect the irradiance An all-in-one weather station with a single comparing the opportunity cost of lost measurement on more than 7 days per year, mounting and power/data connection is a energy production with the cost of cleaning ventilation of pyranometers is mandatory. In convenient way to monitor all the the O&M staff can decide when, and where, practice this means that heating and meteorological parameters other than solar to clean modules on a site-specific basis. ventilation are always required. See the irradiance. Typically, these also monitor air comments for Class B regarding the pressure and relative humidity and calculate The uncertainty of the hourly irradiance advantages of an external ventilation unit to the dew-point, which is useful to correlate totals will be around 3 % (daily total typically reduce dome soiling. with reduced yield. The wind speed and within 2 %) which is very suitable for reliable direction sensor are ultrasonic with no plant PR calculations. Class A monitoring • PV module temperature – 6 sensors per moving parts. requires that the irradiance sensors are system, distributed along the strings, for cleaned at least once per week and temperature correction of PR; as described Unlike a tipping bucket rain-gauge, a radar recalibrated every year and the air for Class B. precipitation sensor does not need regular temperature and module temperature cleaning and outputs data in real time, to sensors are to be recalibrated every 2 years. • A mbient air temperature – for historical correlate with the power generated, and it There is a cost associated with this. trending analysis, the sensor must have a can detect whether the precipitation is rain Therefore, it is possible that a PV plant might ventilated solar radiation shield. (liquid) or snow (solid). be specified with Class A monitoring equipment but that the O&M procedures are • Wind speed – affects surface cooling of A soiling monitor that can be mounted not compliant. the modules. alongside PV modules or within an array gets dirty at the same rate as the surrounding • Wind direction – for historical modules. An optical soiling measurement WWW.PESSOLAR.COM 67

TALKING POINT Number of Plant Monitoring Systems IEC 61724-1 minimum number of monitoring systems by plant capacity IEC 61724-1 refers to the designed AC power and the standard requires that pyranometers criteria for Secondary Standard, it is now capacity of the plant for the recommended respond evenly over this range and are termed Spectrally Flat. If the 95 % response minimum number of monitoring systems, on ‘spectrally flat’. For this reason, it does not time is less than 0.5 second, it is Fast the basis that all the PV modules are installed allow ‘photoelectric’ sensors, such as silicon Response. Fast Response Class C is typical at the same orientation and that there is no cells and photodiodes, because of their for the analog output of a photodiode sensor redundancy or back-up monitoring. restricted and uneven spectral response. without amplification. Where sites have varying module angles, for The most noticeable change in ISO Radiometers with RS-485 Modbus® RTU serial example over hillsides or in valleys, there 9060:2018 is the classification names: data communication usually update values in should be more POA pyranometers and the output registers every second and soiling monitors; some orientations could be Class C → Class B → Class A therefore are not ‘fast response’. This is also East and some West. true of most amplified analog pyranometer The standard now allows photoelectric outputs due to noise ISO 9060 – The Standard for Pyranometer sensors. If a pyranometer meets the 1990 reduction filters. Performance ISO 9060 ‘Solar energy - Specification and classification of instruments for measuring hemispherical solar and direct solar radiation’ defines what is a pyranometer, and what is a pyrheliometer for measuring DNI. IEC 61724-1 refers to ISO 9060:1990 because it was developed and published before the standard was updated in November 2018, which ‘de facto’ replaces the earlier edition. The 1990 version specifies pyranometer performance in order of improving performance as: Second Class → First Class → Secondary Standard Radiation from 350 to 1500 nm is the critical wavelength range for photo-voltaic materials Kipp & Zonen pyranometer ISO 9060:1990 and 2018 classifications 68 PES SOLAR

TALKING POINT ‘By comparing the opportunity cost of lost energy production with the cost of cleaning the O&M staff can decide when, and where, to clean modules on a site-specific basis.’ Different module orientations require extra POA pyranometers ISO 9060:2018 states that the new demonstrate that it meets the requirements https://webstore.iec.ch/publication/33622. classifications are ‘roughly corresponding’ to of the standard. This means that if a the classes from 1990 and there are some Secondary Standard pyranometer did not www.kippzonen.com significant differences in the way that have these individual tests carried out, and it specifications are defined. However, in met the new limits, it cannot be ‘updated’ to This article is an excerpt from general, a pyranometer that met the 1990 Class A without the additional testing being ‘Solar Energy International Standards’, Secondary Standard requirement should carried out. a whitepaper produced by Kipp & Zonen meet the 2018 Spectrally Flat Class A to explain the standards most frequently requirements. Many people involved in the solar energy used in solar energy: ISO 9060, IEC sector have heard about this standard 61274-1, ISO 9846/9847 and ISO/IEC Note that Class A pyranometers must be but do not appreciate what it covers. 17025. You can download it at individually tested for temperature response We strongly recommend purchase of the www.kippzonen.com/standards and directional response (cosine error) to document from the IEC Webstore at WWW.PESSOLAR.COM 69

September 14-17, 2020 Anaheim, CA Mark your calendars SPI, ESI, and North America Smart Energy Week will be returning to Anaheim, California this September 14-17. With the energy industry having been heavily impacted by the market downturn, we will continue striving to keep our industry strong, resilient, and together with informative content and promising business opportunities. LEARN MORE AT: smartenergyweek.com POWERED BY

ASK THE EXPERTS: TRACKERS Yield is king High Seismic over River Cobble in Chile WWW.PESSOLAR.COM 71

ASK THE EXPERTS: TRACKERS PES had a great catch up with Mark Kingsley, CEO of Alion Energy, California. Leaders in solutions for trackers and O&M robotics and currently enjoying the bifacial surge in our industry. Although the current Covid 19 situation presenting some challenges, he has no doubt about the future opportunities. Mark Kingsley been better. tracker designs and hence uses much less steel while being up to 7x stiffer. PES: Hi Mark, it’s a pleasure to welcome PES: Please could you tell us about your you to PES Solar. Would you like it begin tracker solutions? So, clients save on land, shipment, drilling, by giving our readers a brief overview of assembly and O&M. Concrete is always local Alion Energy? MK: The design goal was to enable and avoids duties. unsubsidized solar PV to compete directly Mark Kingsley: Alion Energy is a total with combined cycle gas turbine economics. PES: How do the trackers cope in difficult solutions provider for bifacial trackers and To accomplish this, we needed to extend the environments and unusual terrain? O&M robotics. Our brand promise is ’The solar project useful life, whilst ensuring Most Power from PV’ as we use integrated maximum generation. MK: We avoid drilling through the use of design to combine reflective foundations and slip-formed or precast ballasts. We have cleaning robotics, with a patented A-frame + The supporting technologies include slip flexible couplings between each 5, 6 or ballasted tracker. System design optimizes formed concrete foundations to eliminate 8-module table and this enables the tracker our tracker’s steel content to <18 metric tons subsurface corrosion. These foundations row to follow the landscape sinusoidally. The per MWp, which allows for both a stronger enable construction on sites closer to design also works well on active clays or in and cost competitive design. interconnects including: sites that are sloped, frost heave conditions. rocky or filled with corrosive clays, or on PES: Would you say the solar/PV industry is caliche and karst formations. They also A durable bifacial reflector made from expanding at the moment? function as a bifacial diffusion reflector and a concrete as opposed to cloth, plastics or driving surface for our robotics platform. small rocks, stays cleaner and hence more MK: Very much so. Bifacial has finally arrived Taken together our design lets you build effective in harsh environments. in force and our industry’s economics vs where you want and keep your arrays clean Furthermore, our robot platform may be alternative sources of energy have never while maximizing bifacial gains. configured to read site albedo and treat the foundation area to ensure maximum bifacial PES: Why are trackers so important in gains. our industry? PES: Can you tell us about the typical life MK: ‘Yield is king’…. Energy generation is in expectancy of a system? the denominator of all levelized-cost-of- energy calculations. Trackers x bifacial MK: The accepted useful life on an modules x reflective foundations x O&M unreinforced concrete slab is 50 years. Our robotics deliver the highest kWh/kWp. foundations do not suffer from subsurface corrosion, or face tree roots, overloading PES: What are the technical advantages of from delivery trucks, or the salt ingress to your trackers and are there any cost steel reinforcements that can harm urban implications to the clients? concrete pavements. So, we remain inspired by the 1,800-year-old unreinforced concrete MK: We handle the much heavier 450Wp+ used in the roof panels of The Pantheon 27.5kg module formats better than other in Rome. designs in longer 145 module rows. This means less TCUs. Unlike traditional direct Our mechanical design will never gallop and torque-tube based designs, we can stow at we offer extended warranties on our 0º and not flutter or gallop. This results in structure, as well as C4/C5 corrosive lower overturn loads and hence the lowest environment upgrades. So, with good mass ballast designs. Our A-Frame is more maintenance practices, including motor and mechanically efficient than traditional controller spares, we intend our design to 72 PES SOLAR

ASK THE EXPERTS: TRACKERS % Gain from Bifacial PERC Modules @ Test Site Energy Yield Increase from White Reflec8ve Founda8ons @ 1.30m Tracker Height Baseline Bifacial Gain Set by Background Albedo 0.30 Bifacial 2L Monofacial 1P Control % Gain 2L Front Side Soiling→ 24% Rainy Day → 24% N38.6º W121.7º 22% 20% Module Level Wh,DC/day / kW,DC,peak 0.25 Painting foundation significantly improved +12% 18% bifacial gain on cloudy or rainy days 16% Mar-8 to 14% 0.20 +7% 17% May-05 12% Cloudy Day → 10% Feb-14 to >8000 8% 0.15 Mar-2 Data Points 6% 4% 8% 2% Bifacial Gain Sunny 0% Day ↓ Cleaned→ 0.10 0.05 0.00 Green Grass & + Exterior Acrylic ⛄\" Grey Concrete White Paint ‘Tropical Snow’ 2222000022220000////2222////12129494 22222000002222220000002/////0/33333/////313122/500505 2020/4/4 222000222200002///0/444///4121/9469 2020/5/1 COMPANY CONFIDENTIAL last through two PPAs and a repowering. At PES: We would like to hear about Alion’s avoids the ruts created by repeatedly driving end of life the concrete can be reground and offerings with respect to cleaning trucks and tractors between rows. reused and does not need to be dug out from solutions. How do these differ? the earth. Another difference is our system has both MK: A critical difference is our cleaning dry and wet cleaning capabilities. A robot PES: What about monitoring? How is robots ride on the concrete foundation rail as may dry-brush off sand, however liquids are this done? opposed to on the PV module. Other robots required to effectively remove organic often require additional racking and deposits. These organics range from seabird MK: Our controllers follow broadly adopted intertable bridges. Hence, while other PV guano to industrial or agricultural carbons. Zibgee enabled communication protocols robot designs must be very lightweight in that connect with the PV plant SCADA. order not to damage PV cells, our robotic PES: What are the benefits to the client of Wired solutions for cold environments are platform can be heavy and carry fluids and autonomous cleaning solutions? also available. inspection equipment. Our system also MK: To sum up, cleaning robots are an Bifacial Reflective Foundation Reduces Overhead Lift Demands WWW.PESSOLAR.COM 73

ASK THE EXPERTS: TRACKERS Spot dry and wet robot insurance tool to know you will meet your galloping sensitivities seen in some company in particular for 2020? debt service coverage ratio on a low priced 2-in-portrait designs. PPA. Low PPA prices equate to a lower MK: More excitement and grey hair as we all tolerance for energy losses. Affordably PES: Where are your main markets and are fit 10 months of projects into the last 6 increasing cleaning frequency minimizes there any particular geographical areas months of 2020. Accelerated by the these losses. where you are looking to drive further COVID-19 shock, I see a general shortening growth? of supply chains, with a continued drive to Robotic cleaning economics are driven by component localization, plus a renewed asset efficiency. In the Alion Energy system, MK: Our team operates globally outside of focus on leaner construction practices. As to two workers, with two transfer carts and four mainland China. We focus on the following technology we will continue to add capability robots can clean up to 20MWp per night. use cases: to our robotics platform. The workers remain at the end of the rows and ping-pong robots back and forth to each • R ocky, corrosive, dusty desert Forecasting further ahead, coal’s demise is other. No need to follow the robots down a environments from Chile to the clear. The improving economics and row or lift them over gaps and obstacles. Middle East. response speed of PV + storage spell Cleaning head position is actively controlled continued change for gas turbines in 2020. by LIDAR and both dry and wet cleaning • L ittoral sites with hurricane, cyclone or Within 5 years new gas turbines will either modes are possible. Longer rows allow for typhoon-force winds and often with clay or burn hydrogen or be relegated to mobility- faster cleaning as inter row transfers are limestone soil challenges. related applications such as ships and minimized. aircraft. This will further shake our legacy • Areas with >50% average cloudiness. energy ecosystem. Although one can fully automate row-to-row This as our reflective foundations drive transfers with a rail, most sites have more bifacial gains >15% under diffuse irradiation Harnessing the nearly free energy from sub amoeba-shaped boundaries and hence we conditions. This includes project sites 2¢/kWh solar will drive additional business offer electric transfer carts. from Maine to Malaysia. Bifacial modules, model innovation and geographic disruption. boosted by a reflective foundation, now I am optimistic for our future as PES: Why should prospective clients choose allow tracker economics to win in Northern opportunities abound. your solutions, what makes AlionEnergy Europe. This as 30% yield improvements stand out from the competition, what are overcome high land costs and lower Stay healthy, we all have lots more to do the benefits in terms of cost and tariff rates. in renewables. performance? • Brownfields such as shuttered coal www.alionenergy.com MK: Better LCOE from a differentiated and interconnects ash dams or landfills. holistic design meant to last. We optimize the full bifacial equation and eliminate the PES: What are your predictions for the solar/PV industry in general and your 74 PES SOLAR



THINK TANK The have-it-all synergy between monitoring & aerial data for solar PV Words: S tanislas van der Vaeren, Founder and Customer Innovation Manager, SITEMARK Every company that owns solar plants wants to generate the highest return. In order to achieve this, the system’s maintenance teams need to constantly ensure the optimal functioning of all system components, especially the panels and inverters. A solar monitoring system enables you to be informed of your PV system’s performance. 76 PES SOLAR

THINK TANK The industry standard: solar site minimum requirement, detecting and How does the addition of aerial inspections monitoring identifying panel faults in large solar systems fill these gaps? can be a complex process. Monitoring It offers information about energy systems help detect low-performing areas, The solar PV system is a yielding asset that consumption and generation as well as but finding the specific panel that harms the should provide investors with a maximum possible damage to your solar system. It’s string output requires more time and return every year. Detecting and addressing important to monitor your solar assets in advanced testing devices. By utilizing the poorly performing panels through visual data some manner. Without monitoring, it is best of both worlds with system monitoring inspections and analysis helps maintenance impossible to determine if your solar panels and aerial data inspections, asset owners can and asset managers maintain site are operating at their full capacity. improve the performance of their systems performance for the system’s lifetime. So and maintain yields over time. how do you streamline the process and While system monitoring is considered a manage your solar assets effectively? Aerial site surveys with their software analytic tools are the most reliable, comprehensive and cost-effective approach. Drone inspections that cover 100% of the modules with a thermographic scan are the most efficient way to get a complete analysis of a site, and to identify what the monitoring systems cannot. As a cost saving measure, it is currently becoming less common to do string monitoring. Without string monitoring, it is particularly important to have the thermal drone scan. However, even with string monitoring, locating the weakest module on the string in utility scale projects is a difficult and often inefficient mission. But by using aerial data gathered from drones, now the asset owner can prioritize corrective maintenance in conjunction with the O&M. If inspections don’t cover 100% of the WWW.PESSOLAR.COM 77

THINK TANK modules or produce a snapshot-in-time Thermal view of a solar site with anomalies identified and analyzed report, you are unable to track the history of inspections and compare them year greater portfolio returns. hotspots, multi-point hotspots, and single or over year. double broken bypass diodes. What is Another pertinent example is GiraSol interesting is that the customer had noticed By using visual data technology and a web Renewable Energy, a leading consulting firm the low performance of the system from platform, comparing history is simple and that covers multiple services for the PV and their monitoring system, even before the you have a verified track record performance Renewable Energy market in Israel. aerial scan. But now, through the web of the site. Capturing and visualizing the platform, they were able to obtain a complete aerial data is not about drones but taking Girasol recently performed an aerial snapshot of the site. The most important data science to the next level. Since working thermographic scan for a client’s rooftop being an estimate of the loss of production with an aerial data platform enables users to site. After gathering and uploading the due to the faults. Through this information, compare inspections side by side and over images, over 200 panels with different faults the customer began a claim process with the time, you can make a verified assessment of were found. Among the faults were single panel manufacturer. the health of your site. The aerial data analytics platform is capable Real-world examples using this synergy of analyzing most common faults on the solar as a service site including PID, inactive strings, hotspots, bypass diode faults and panel connection The EU’s largest solar PV asset owner is boxes defects. All the gathered data is Enerparc AG. Enerparc has been closely available to the user via a web platform on a following the rapidly developing landscape map configuration of the site. The faulty for aerial inspections and platforms available panels are detailed on the map and the for managing PV sites. In 2020, over one GWp original site design can be uploaded and of their solar assets will be inspected by layered so maintenance teams know the drones equipped with high resolution visual exact location of the faulty panels. This cameras and thermographic sensors. allows the fault handling to be prioritized according to the cost severity and areas of The captured aerial data will be processed the site that are underperforming. and analyzed using the Sitemark Fuse platform. Powered by AI, the platform This analysis is automated and filtered for identifies and analyzes PV module anomalies the user. With the web platform and a mobile at the cell, module and string level. All while app, the technicians that do the corrective offering state-of-art features that optimize maintenance don’t need to search through maintenance work and ultimately, result in the original plant diagrams to determine location of the defective panels in order to replace them or make any repairs. This makes their work much more efficient, an added value for both the O&M and Asset owner. Evaluating your aerial data options If your objective is to capture and visualize the most accurate and quality output available in the industry today, then a full visual and thermal orthomosaic of your site is 78 PES SOLAR

THINK TANK your best option. Ensure no anomalies are • T hermal cause classification in 12 Sitemark missed with easy auditing of the detection categories i.e. open string, PID, quality. The final report includes deeper Potential PID, single bypassed substring, Sitemark is a world-leading aerial data context into your site such as loss estimation double bypassed substring, diode, open analytics company active in over 30 and cause classification for a single source panel, missing panel, multi hotspot, countries within the energy, construction, of truth. hotspot, junction box, unknown mining and agricultural industries. Another choice, ideal for larger sites is a • V isual Cause Classification in 9 Through the use of aerial data, Sitemark is photo-based data capture solution which categories i.e. soiling, physical, advancing the development of locates site maintenance issues and their vegetation, unknown, fuse, shadowing, ground-breaking technologies and causes on a photo level. Acquiring the data is dropping, inverter, wiring artificial intelligence that fuse the faster, enabling cost efficiencies especially physical and digital worlds. for the larger sites. The final report also • T emperature deltas includes critical context into your site’s Our products and services enable users health providing a single source of truth. • L oss estimation to improve their understanding of their assets and make better decisions while Both options are suitable for O&Ms, EPC • L ink to source visual and thermal image increasing the efficiency and profitability contractors and asset owners. The bottom of their field operations. line and true benefits come from the thermal Conclusion scan. While the visual RGB is interesting and Girasol helpful, it offers no insight into the All stakeholders in the solar site lifecycle have productivity of the actual panels. the same goal - maximize yield over the GiraSol Renewable Energy is a leading Additionally, even with a basic report listing lifetime of the asset. Ideally, you need to be consulting company covering multiple poorly performing panels, without analysis of evaluating the health of your site from the aspects of the PV and renewable energy the defect and priority by loss estimation, it is data and basing your decisions on a single market in Israel. very difficult to determine what is urgent and source of truth. Even after panel faults and what is just ‘nice to have’ regarding site anomalies are identified, you need to Girasol’s mission is to empower its clients health and optimization. prioritize and correctly evaluate the urgency to extract the best performance possible for repairs, which can be especially from their renewable energy investment. What exactly does an aerial site inspection challenging with larger sites. For optimal deliver? yield, the complementary pairing of site To achieve this goal, Girasol has monitoring plus annual aerial inspections partnered with leading global companies • D rone-captured visual and thermal delivers the most efficient and cost-effective to provide the highest quality products single images approach. and services to the PV industry. • G eo-located solar anomalies, each www.sitemark.com including: WWW.PESSOLAR.COM 79

TALKING POINT Grid feed-in at high-voltage level: a case study Midden-Groningen © Goldbeck Solar Grid integration is a key issue in the expansion of renewable energies throughout Europe. The requirements for power generation plants at all voltage levels have changed significantly with the pan-European harmonisation of grid connection requirements and the resulting adaptations to the national foundations. The aim of the EU regulation is to create a stable electricity grid throughout Europe in order to further increase the share of renewable energies with respect to climate goals. 80 PES SOLAR

TALKING POINT These new regulations close the gap, complexity and scope. The requirements for transmission system operator TenneT TSO particularly in the area of verification, which power plant control, especially for voltage B.V. previously presented a grey area at the and reactive power control, were high and project level: manufacturers attested the verification process to ensure grid code Case study: Zonnepark Midden-Groningen themselves with a manufacturer’s compliance was comprehensive. declaration that ensured that their power The 103 MWp solar park ‘Zonnepark plant controllers fulfilled the necessary With the pan-European harmonisation of Midden-Groningen’ near Sappemeer is the requirements. Project-specific uncertainties grid connection conditions in accordance first solar park in the Netherlands to be during commissioning were the result. With with EU Regulation 2016/631 Requirements directly connected to the national the new network code throughout Europe a for Generators (RfG) and the national transmission network. It covers an area of new step has been made. implementations, the requirements for grid approximately 116 hectares in the north- integration of renewable generation plants east of the Netherlands. Its total capacity of Creating a solar power plant in the three-digit have increased. Even though both the 103 MWp can cover the annual electricity megawatt range such as Midden-Groningen technical requirements and the compliance consumption of around 32,000 households. with feed-in at the high voltage level is a verification procedure were already at a very challenge that is unparalleled in its high level in the grid area of the Dutch The solar power is fed in at a high-voltage level (110 kV), while the point of common WWW.PESSOLAR.COM 81

TALKING POINT ‘We are glad to have found a competent and very experienced partner for power plant control in meteocontrol.’ coupling is located about five kilometres Deniz Urla, Head of Engineering & Design at extensive verification through project- from the power plant. From the very Astronergy points out: ‘The multi-stage specific simulation and measurement of the beginning, the project team coordinated with compliance verification procedure for power plant control not only confirmed once the transmission system operator TenneT obtaining the final operational notification again, the high quality of metecontrol’s TSO B. V. to ensure the best possible from the grid operator was very controller simulation model, but also showed project-specific implementation of the comprehensive and complex in this project. how crucial project-specific Grid Code power plant control. We are glad to have found a competent and Compliance (GCC) services are for the very experienced partner for power plant success of the project. Joining forces for success control in meteocontrol.’ The possibility of adding project-specific The ‘Zonnepark Midden-Groningen’ project Project success relies on innovative solutions functions to the meteocontrol Power Plant was a milestone in terms of size and and project-specific engineering. The Controller (PPC) based on the standardised requirements for all the companies involved. 82 PES SOLAR

What we can learn from the sun: when it comes out, it shines. #StaySafe PHOTOVOLTAIC MONITORING • PROJECT ENGINEERING meteocontrol.com TECHNICAL CONSULTING • SOLAR POWER FORECASTING

TALKING POINT controller blue’Log® XC also provides driver of the blue’Log® X-Series, meets the feedback, such as that received from Luca customers with the advantage of a reliable requirements of high protocol variety with a Simonetti, who was the senior project and flexible system. maximum level of flexibility. Regular updates manager at Goldbeck Solar: ‘A successful continuously expand the compatibility of the project of this magnitude again confirms our The Power Plant Controller (PPC) enables the system for a sustainable, future-proof confidence in meteocontrol when it comes to comprehensive and precise control of active solution. The graphical user interface allows grid integration and grid code compliance of and reactive power as well as the voltage of easy and efficient commissioning. large solar parks.’ heterogeneous PV power plants. meteocontrol has already had a power- Solutions for complex issues and changing A high-precision power analyser records all generating system (PGS) controller with the market conditions help to ensure reliable and grid parameters during operation. This component certificate required for German practicable implementation in large-scale enables fast and stable control at the point of medium (VDE-AR-N 4110) and high voltage projects even in difficult circumstances. The common coupling and continuous (VDE-AR-N 4120) since May 2019. products and services of meteocontrol can measurement of the power quality. be a decisive factor for a successful grid Functions can be added to the standardised connection. The flexible, modular and scalable features power plant controller on a project-specific offer various advantages. basis. Thus, enabling the development of a ‘The extensive verification through tailor-made power plant controller system project-specific simulation and Export limitation for avoiding grid for any international PV project. Simulation measurement of the power plant control bottlenecks, demand-based reactive power models, which can be provided for the Power confirms the high quality of our simulation control according to characteristic curve, Plant Controller in common development model. The simulated control behaviour highly dynamic frequency stability and environments, such as DIgSILENT reflects the real characteristics of the plant process data exchange in real-time with the PowerFactory and PSS/E, are becoming control very well. When our customers grid operator - the Power Plant Controller increasingly important, especially for large receive a Power Plant Controller, they are offers a wide range of functions for reliable solar power plants. In order to be able to receiving a reliable, future-poof and grid integration of PV power plants. The evaluate the control behaviour of the active extremely maintenance-friendly system,’ range of functions can be flexibly expanded and reactive power control as early as in the states Markus Holzapfel, Product Manager and adapted to any system topology on a planning phase, the simulation model at meteocontrol. project-specific basis. All interfaces have validated to FGW TG4 can be used for system a modular design and thus allow for high certification purposes. www.meteocontrol.com scalability. The meteocontrol team was very happy to be Regardless of whether it is a mixed park or a part of this project and about the positive heterogeneous portfolio, the all-in-one 84 PES SOLAR

A different angle on accuracy. The MS-90 Plus+ is your total solar irradiance measurement solution. Combining the unique internal rotating mirror design of the MS-90, with our industry-leading MS-80 Pyranometer, and new C-Box smart interface. Designed for accuracy, built to last. + + = DNI, GHI and DHI + = DNI www.eko-eu.com | [email protected]

TALKING POINT Combining highest throughput and precision in IV measurements of high-efficiency bifacial silicon solar cells Abstract: we analyze available measurement time in a sun simulator in highest- throughput production of silicon solar cells. We explain how this time is distributed on the different measurements, which need to be performed to characterize a solar cell. For high-efficiency solar cells, we elaborate how it is possible to reduce the required measurement time to determine their IV characteristics such that throughput requirements can be met in all cases. We find that a combination of voltage sweep speed adaptation and advanced hysteresis evaluation is suited for highest throughput without compromising measurement accuracy even for highest-capacitance heterojunction (HJ) cells. Introduction To allow such short cycle times, handling and for a device to achieve quasi-steady-state measurement times need to meet strict conditions after a change in operating Modern solar cell production lines run at high requirements. conditions, a prerequisite for accurate power throughput with cycle times of 1 s or below. rating of solar cells, increases. During IV For the near future, cycle times as low as At the same time, Si-solar cell efficiency is measurements, the applied voltage is varied 800 ms, translating to a throughput of up to constantly improving, thereby increasing cell from 0 V to open-circuit conditions and 4500 wafers/hour, have to be achieved on a capacity due to higher effective charge beyond, i.e. the operating conditions are single line of a solar cell tester and sorter. carrier lifetime. As a result, the required time modified drastically. 86 PES SOLAR

TALKING POINT Thus, the time that is necessary to measure the steady-state IV curve of highest V cells like HJ cells or TopCon OC cells on n-type material may reach several seconds. The recent breakthrough of bifacial solar cell technology adds another challenge. In addition to the light IV measurement at standard test conditions (STC front), STC rear and true bifacial measurements are performed routinely in solar cell production, thereby tripling the light IV measurement time. The three requirements, long measurement times, an increasing number of measurement types and highest throughput, represent a conflict of objectives. A solution that sacrifices measurement precision is no option. Therefore, this conflict of objectives can only be solved using advanced solutions. We analyze the available time for a light IV © halm measurement in high-throughput production of modern bifacial devices and Figure 1a: Time breakdown of a cycle for a solar cell IV measurement in production. One cycle comprises a transport, explain measurement strategies which a contacting, a measurement and a decontacting step. allow obtaining precise steady-state IV Figure 1b: The bottom sketch shows the split-up of the measurement step into different measurement types. The curves even for highest-capacity HJ cells time spans marked in dark blue are net measurement times while those marked in light blue represent additional within the available time. time that is necessary to switch between measurement types. Timing analysis elements are closed in order to achieve measurements need to be performed. electrical contact required for the Finally, the contacting elements are opened Figure 1 shows one measurement cycle measurements. again. With the next cell transport sequence, including handling time in a typical station During the measurement time (contacts the next cycle starts. Due to mechanical of a sun simulator for electrical closed, no cell movement), the actual restrictions, wafer transport and contacting measurements like IV, electroluminescence time cannot be minimized endlessly. In (EL) or thermography. The cycle splits into Voc  Isc modern production lines 550 ms for all three different tasks, which need to be performed steps at a cell size of 210 mm is already at the sequentially. First, the cell is transported into edge of the mechanical feasibility. the measurement position, then the contact Isc  Voc Step Time [ms] Transport 330 Contact 120 Measurement 250 Steady state Decontact 100 Adv. hysteresis Sum 800 Table 1: Example for a time breakdown for one cycle of a solar cell measurement. The handling time sums up to 550 ms leaving 250 ms for the actual measure- ment. A total cycle time of 800 ms is assumed (4500 wafers/h). © halm 330 ms are required for wafer transport and about 120 ms for contacting and 100 ms for Figure 2: Current-voltage characteristics of a high-efficiency solar cell (Voc 734 mV). The I → V and the decontacting. This leaves as much as 250 ms OC for all measurements. Please note that 550 ms V I SC handling time is an assumed optimum. OC → SC sweeps are performed within 28 ms. The root cause for the deviation of these curves from the A throughput of 4500 wafers/h allows for 250 ms of measurement time. Obviously, steady-state curve is explained in the text. longer measurement times reduce the throughput, while shorter times leave room to increase it. WWW.PESSOLAR.COM 87

TALKING POINT 6.2 the IV measurement time in the two cases of I V V I SC OC OC 6 → sweep and → SC sweep. The cell has Voc  Isc linear sweep an open-circuit voltage of 734 mV and thus a Pmpp [W] 5.8 very high capacitance. The results are displayed in Figure 3. Two horizontal lines represent the desired accuracy level +/-0.2% around the 5.6 steady-state efficiency. Measurement results should ideally lie 5.4 within these lines. Otherwise, the accuracy requirements are not met. It is obvious that 5.2 Isc  Voc linear sweep all measurements are quite far out, even for measurement times as large as 100 ms. At 40 ms measurement time, the 5 measurement-time limit determined above, 0 20 40 60 80 100 120 a deviation of larger than 4.5% from the steady-state value is observed which is far © halm Sweep time [ms] beyond any precision requirements. Figure 3: IV measurement results for a HJ solar cell for sweep times up to 100 ms using a linear voltage ramp. Sometimes it is proposed to adapt the State-of-the-art measurements that are increased during the voltage sweep, the voltage sweep speed during the necessary to characterize a bifacial solar cell capacitance is loaded and the current that is measurement time in order to achieve more allowing process and quality control include necessary to charge the cell capacitance is precise measurement results. The sweep not delivered to the cell terminals. speed is reduced close to VMPP to decrease • 3 -level light IV (STC rear, true bifacial, STC the transient effects and increased at low front) for bifacial cells Similarly, when the voltage is decreased, the voltages. Using such an approach, the cell capacity is discharged. The discharge deviation between steady-state • dark-forward IV current is additionally delivered to the cell measurement result and transient result can terminals and current values higher than the be decreased as displayed in Figure 4. • dark-reverse IV and steady-state value at the same operating condition are measured. As the effect can be However, even with optimized settings, the • electroluminescence measurement attributed to the cell capacitance, the deviation from steady-state at 40 ms sweep differences between the measured IV curves time is still larger than 1% and at 100 ms Having only 250 ms for the total and the steady-state curve increase with measurement time the steady-state value is measurements, no measurement times increasing cell capacitance and faster sweep missed by 0.5%. larger than approximately 40 ms are allowed rate. As fast sweep rates are necessary for for the three light IV and the dark-forward high-throughput measurements, advanced The solution to achieve the desired accuracy measurements, the ones that are affected by solutions are required for precise IV cell capacity. This leaves approximately 90 ms measurements of high-efficiency solar cells. in short measurement times is the usage of for reverse IV and EL measurements, switching times between the measurements To analyze measurement accuracy under the two sweeps performed in one single flash, and handshake communication. time limitations presented above, we perform IV measurements of a HJ cell as a function of sweeping from I → V f irst and then back A breakdown of the total of 250 ms OC measurement time into the different SC from VOC→ ISC. In this way, two IV curves are measured. The difference between the two curves is characteristic of the cells transient behavior. It can therefore be used to individual measurements, as well as switching times and communication time, is shown in Figure 1b. Data evaluation 5.8 Voc  Isc linear time is not shown as the data evaluation is 5.7 performed in parallel to the handling time. Measurement Strategies In the following, we focus on optimizing the Pmpp [W] 5.6 Voc  Isc optimized measurement time of the light and dark- forward IV measurement. Current-voltage characteristics of a high-efficiency solar cell are shown in Figure 2. It shows the IV curve of 5.5 a measurement with a forward voltage sweep from 0 V to V (I → VOC) and with a reverse OC SC V V (VOC ISC). voltage sweep from OC to 0 → In 5.4 Isc  Voc linear addition, the steady-state IV curve is shown. 5.3 Isc  Voc optimized 0 The I → V cur ve shows a lower FF and the OC © halm V SCI OC → SC curve a higher FF compared to the steady-state curve. This can be attributed to 20 40 60 80 100 120 Sweep time [ms] the minority charge carriers, which are stored in the silicon volume, usually referred to as cell capacitance. Accordingly, this cell P MPP capacitance is not constant but varies with Figure 4: values achieved in single-sweep measurements with optimized non-linear and linear sweep the cell voltage. When the voltage is settings. Even at 100 ms sweep time, the desired accuracy is not reached while at 40 ms the deviation is still larger than 1%. 88 PES SOLAR

cetisPV cell tester line High precision Class A+A+A+ measurement systems for PV cells • Available for large solar cells • Applicable for all kinds of up to 220 mm x 220 mm solar cells including PERC, • Enabling measurements at heterojunction, busbarless standard and true bifacial test and bifacial cells conditions • Future-proof and upgradable • Fastest high precision IV, EL due to modular design and hot-spot measurement up to 5000 cells/h

TALKING POINT ‘We have shown that Pmpp [W] 5.6 advanced hysteresis in combination with an Voc  Isc optimized optimized sweep form allows for meeting this 5.55 requirement without sacrificing measurement Advanced hysteresis accuracy.’ 5.5 5.45 5.4 Isc  Voc optimized 0 20 40 60 80 100 120 © halm Sweep time [ms] Figure 5: Measurement results including advanced hysteresis analysis (blue diamonds). Even for very short measurement times, all efficiency values fall within the band of desired accuracy. Note: The results from the linear sweep do not fall into the range displayed in this graph. calculate the true steady-state IV curve, Conclusion sacrificing measurement accuracy. The based on the measured curves and the Modern high-throughput solar cell production required flash pulse length of 40 ms for each Figure 5knowledge about the physical origin of the requires fast measurements that are observed splitting between them. performed in no more than about 250 ms. As measurement condition of a highly capacitive several measurements are needed for solar cell This is performed by the h.a.l.m. advanced characterization, in particular for bifacial bifacial solar cell (rear STC, true bifacial, front hysteresis approach. Please note, as two devices, the maximum allowed measurement sweeps are required for each measurement, time for one IV measurement is about 40 ms. STC) allows for two voltage sweeps to the available sweep time in a 40 ms flash segment is reduced to about 17 ms per We have shown that advanced hysteresis in determine the I → V and the VOC→ I sweep. Figure 5 displays the results achieved combination with an optimized sweep form OC using advanced hysteresis evaluation in allows for meeting this requirement without SC SC combination with an optimized voltage sweep ramp, together with the single sweep curve. A sophisticated algorithm that uses results already shown in Figure 4. both curves together with a physical model For all measurement times from 2x8 ms up two results in an IV curve that precisely matches 2x100 ms, the results closely agree with the the steady-state IV curve. steady-state value and fall within the band of desired accuracy. This demonstrates how the www.halm.de precision of fast measurements on highly capacitive devices is increased using advanced © halm hysteresis analysis. Deviations from the desired steady-state value are only observable Figure 6: Sketch of the light IV measurement sequence of a bifacial solar cell using single-flash hysteresis for at very short measurement times. For these conditions, distortions in the IV curves at all three measurement conditions. The bottom graph shows the irradiance levels of the front and rear flash as voltages below VMPPare observed for high- capacitance devices, which is why very short a function of time. As can be seen, the first measurement is performed at rear STC, the second at true bifacial sweep times are not recommended by h.a.l.m. for such measurements. conditions and the third at front STC. Within each flash level, the IV characteristics are determined with a Accordingly, we recommend our customers forward (ISC → V ) and a reverse (VOC→ I SC) sweep (single-flash hysteresis). to use the whole 40 ms measurement time OC for highest-capacitance solar cells. This ensures precise measurement results and delivers not only the steady-state output power but also the whole steady-state IV curve and thus allows precise determination of important cell parameters like series resistance or diode saturation currents. A time diagram of the three light IV measurements for a bifacial cell is presented in Figure 6. As can be seen, all light IV measurements of a bifacialFsioglaurrceell6can be performed within 120 ms. 90 PES SOLAR

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ASK THE EXPERTS: CHARGERS AND CONTROLLERS Proud technical creativity Bill Mellema, Director of Engineering and Brad Berwald, Product Manager and Technical Training Manager, at Morningstar Corporation, met up with PES to bring us up to date on the solutions offered by this innovative, employee owned company. Here the workers are proud of their products and provide only the highest quality and efficiency to the market. They have a balanced portfolio: residential, industrial and off-grid and keep a keen eye on the markets to see where improvements are possible. Read on, you’re sure to be impressed. 92 PES SOLAR

ASK THE EXPERTS: CHARGERS AND CONTROLLERS Bill Mellema Brad Berwald PES: Hi Brad and Bill, it’s a great pleasure to Bill Mellema: We have over 20 patents and a that category. You have an unusually wide to welcome you to PES Solar. We have dozen trademarks, leading the field in range of controllers, something like 40 worked with your company for quite a few off-grid power conversion technology. Our models in eight lines, other companies may years now, and are sure our readers would low turnover and long-term team approach have two or three in comparison. Why did be interested in a brief overview of foster an environment where technical you diversify so much in this area? Morningstar, so shall we begin with that? creativity thrives, resulting in an IP portfolio that’s very broad and comprehensive for a BB: Well, it was really in response to demand. Brad Berwald: So, we’ve been the solar company our size. Morningstar’s patents Several examples: there are industrial users charging experts for the off-grid PV industry cover areas which include thermal who need controllers that can operate under for over a quarter of a century, and, unlike engineering, mechanical design, charging hazardous conditions, such as in oil and gas many other companies, have the same and control, advanced electronic topologies, production facilities or mines. There are management and ownership. In fact, we’re safety systems, and more. strict international safety requirements for employee-owned, which is the main reason electrical products in those environments. we’re so focused on maintaining the PES: With energy storage becoming such a So, we responded with our SunSaver and industry’s lowest hardware failure rate and growing area, how has that affected what SunKeeper charge controller lines which are highest reliability. Our own individual system designers are looking for in solar rated for what’s called Class 1, Division 2/ reputations ship with every product. charge controllers and inverters? Groups A&D use. BB: The growth of energy storage affects This ensures they are approved for use where power electronics in a number of ways. For ignitable concentrations of flammable gases, one, system set-up is more complex. liquids or vapors may be present, including Installers have to deal with variables such as Acetylene, Propane, Gasoline, Naptha, absorption, float, equalizing voltages, time Benzene, Butane, Ethyl Alcohol, Acetone and and temperature compensation factors, Methane. This makes it easy for industrial high-voltage disconnect/reconnect for the users to use solar electricity in a variety of battery and low-voltage disconnect/ locations and conditions. reconnect for loads, all critical settings to battery health and longevity. These are We make another SunSaver version called highly important, because with the costs of the Duo, designed for RV/caravan and marine PV modules getting lower than ever, a use with two batteries. Another is our battery bank is now often the single most SunLight controller, specifically designed for expensive part of a system. solar-powered lighting applications including streetlamps and parking areas. There’s a saying in solar installation: ‘any problems in your design you’ll learn about in The Essential Series, another line, was your batteries first.’ No one wants to learn developed to make Morningstar quality that very expensive lesson! Advanced available to a wider audience, with more basic battery chemistries also present new versions of our ProStar controllers. All of our challenges. For example, lithium batteries controllers are available in different can be damaged if one attempts to charge amperage ranges and some in different them under cold conditions. So, it’s voltages, so if you’re as serious about charge incumbent on the systems’ electronics, controllers as we are, your line naturally most notably the charge controller, to be expands to meet diverse user needs. ‘smart’ enough to anticipate errors and minimize any problems. PES: You’re getting into inverters now, what’s behind the progression from solar PES: Morningstar is unique, in that it controllers to inverters, and what do these started as a charge controller company and different devices have in common? for more than 25 years focused its efforts in BM: Having over 25 years of experience in WWW.PESSOLAR.COM 93

ASK THE EXPERTS: CHARGERS AND CONTROLLERS Minas TS MPPT TriStar 600V fanless solar controller building best-in-class charge controllers specification. Over-spec components are into advanced batteries including lithium actually had direct application to the inverter even more critical in a high-voltage power- faster than conventional designs, increasing we conceived, for four reasons. conversion platform such as an inverter. system autonomy, or the ability to go for longer periods using stored electricity. It also The first is our background in proprietary Finally, we build everything around superior addresses fear of obsolescence with a unique software architecture, which extracts the thermal design. Morningstar is the only solar ReadyRail expansion system, where the user maximum performance possible out of every electric manufacturer that does not use fans can snap-in ReadyBlocks to add individual processor on-board our to cool high-power electronics. Fans have communications and control, generator controllers. This means they are able to three problems in charge controllers. They support, battery management and other provide more power and maintain constant make the system inefficient, because they features. output because, unlike competitor designs, require power to run and are a parasitic load. they don’t need to ‘drop down’ and then They suck dust, dirt and debris into the PES: We are hearing a lot about off-grid recalibrate as incoming power changes. A insides of components, which shortens their solar in rural and industrial projects, do you principle which also applies to the new life. And they can fail because they have see the solar industry shifting to off-grid MultiWave inverter/charger. moving parts. and hybrid systems in other sectors? The second is an internal layout based on BB: The thermal design excellence behind BM: It is inevitable and in fact is underway. performance instead of economics. Morningstar’s charge controllers is integral Look at the state of California in the United Morningstar internal circuitry is laid out in a to the unique design of the MultiWave States, where utilities are promising years, way that makes the most engineering sense, inverter/charger: it stands alone in its power perhaps decades, of ‘managed outages’ to as opposed to the cheapest to manufacturer class without needing a cooling fan. mitigate wildfire risk. There’s as much solar and produce. This greatly improves Mean electricity in California as there is in the rest Time Between Failures (MTBF), maintains PES: What innovations and benefits to the of the country, but because it’s almost all signal integrity, increases efficiency, and customer can Morningstar bring to this grid-tied with no back-up it’s useless during reduces excessive heat, all of which improve well-established category? outage conditions. performance and dependability. BB: Even before it gets to the customer, or So, there’s been a surge of interest in Third, we use higher-quality, ‘over-spec’ end-user, it brings benefits: MultiWave installing new systems with battery back-up components. If Morningstar used the same weighs a lot less than comparably powered and even upgrading existing systems with quality components as our competitors, we inverters, making it much easier for installers energy storage, through AC and DC coupling could still achieve better performance and to handle. This is due to its high-frequency schemes. It may be a cliché that ‘necessity is reliability with our software and electronic electronic design which reduces a lot of the the mother of invention,’ but it’s one helping design advantages. But instead we ‘over- heavy internal components typically drive the energy storage business in many spec’ critical components to create hardware associated with inverter/chargers. For the sectors right now, and we don’t see that to take full advantage of our design. user, they can expect an exceptionally stable, slacking off. reliable inverter with very high peak By oversizing key parts, we achieve an efficiency across a wide load range. PES: Geographically speaking are there any industry-beating hardware failure rate of less new markets you would like to break into? than 0.4%, and are the only manufacturer It also has unprecedented charging who publicly publishes this kind of capability, and is able to ‘stuff’ electricity BB: It’s not so much new geographic 94 PES SOLAR

ASK THE EXPERTS: CHARGERS AND CONTROLLERS Sunsaver 20L 037 rate! So, assuming that green environmental since we have a pretty balanced portfolio of values coincide with clean energy, lead-acid regions and markets to serve. When the markets, but new applications for off-grid enjoys a compelling value proposition in residential sector shows signs of weakness, solar. Depending on the region, our products terms of its contribution to the eco-system. for example, industrial, rural and commercial intended for one type of customer, often find PES: What makes your products standout applications often pick up, and vice-versa. a new market when used someplace else. from the competition, why should So, we’re looking at some immediate Our Essential Series is an example. It’s customers choose you? challenges and opportunities of a more Morningstar quality and performance, with BB: It’s easy to get over-excited about this technical nature. a reduction in communications and other type of question and run on, but If we had to features including certifications. boil it down to one thing something that one The challenge in my view is the expanding of our own customers said recently in an adoption of Lithium batteries for energy In developing countries, it serves a lower- on-line review says it better than we ever storage. This will require smoother and more priced market segment for general off-grid could: ‘Morningstar is the second charge effective integration, charging support, no solar electric systems. But in developed controller I bought, and the one I should have unified interface, and monitoring. Our Energy countries it serves consumers and the leisure purchased first.’ That says it all! Storage Partners program is a step in that market, specifically RV/caravan and marine PES: What do you think will be the greatest direction, where Morningstar and selected systems. opportunities for off-grid solar in the next battery brand partners collaborate and few years, and the greatest challenges, for provide pre-determined settings, which PES: There is rapidly growing interest in Morningstar and the industry in general? make it easier for installers to design lithium lithium batteries, along with applications BM: Perhaps we see the geopolitical and storage into new systems or drop lithium for them, as well as other advanced storage economic picture for solar a bit differently, batteries into existing ones. chemistries today. Do you see this replacing lead-acid technology or co- TriStar MPPT multiple BB: For me the opportunity is lower cost PV, existing with it? And what special which means systems can and will get bigger, requirements come with adopting or with higher capacity chargers and inverters switching to lithium storage? scaling accordingly. This will mean significant, additional hardware sales. BM: Like a lot of innovations, it isn’t an ‘either/ or’ proposition. Lead-acid has advantages in The challenge: evolving code standards addition to cost, including wider tolerance for domestically, the drive for safer systems will temperature extremes and uniform safety require novel and cost-effective solutions. among the various configurations. They have This is true in industrial as well as residential disadvantages as well. Lead-acid batteries can systems. Morningstar has some experience have their life dramatically shortened by a here, with charge controllers specifically system that keeps them in ‘partial state-of- designed and rated for use under hazardous charge,’ for example, whereas the life-span of field operating conditions. lithium batteries is actually increased under those conditions. As with anything, it’s The opportunity: data access, or more application-centric, and there are applications specifically making sense of data i.e. big data. where lead-acid may be a better choice. The challenge of reliable remote connections affects this; expect to see more embedded So, we’d paraphrase a famous author and data systems that don’t require constant state that ‘reports of lead-acid’s death are connectivity to be effective. greatly exaggerated, we see the two types not only co-existing, but complementing www.morningstarcorp.com each other in some instances. One other thing: as far as recycling goes, it’s a long-established saying that lead-acid batteries are a poster child for success in that area, industry data shows a 99% recycling WWW.PESSOLAR.COM 95

COMMENT: TECHNOLOGY Are we about to experience a DC boom with the growth of solar plus storage? Words: H anan Fishman, CEO Alencon Systems, USA In case you missed it, Bloomberg New Energy Finance just revised its already bullish estimates for the growth in storage deployments upward – again, predicting a 122-fold boom in the installation of stationary energy storage over the next two decades. For its part, solar continues its high double-digit growth, making it the fastest-growing form of new generation. Hanan Fishman well together. Pairing storage with solar Storage, it does seem a rather unintuitive allows solar to move from an intermittent way to connect to a DC source (PV) to a DC Solar plus storage is rapidly entering the source of energy to a dispatchable one. load (storage). As logic would dictate, there is vernacular of popularly associated words and Achieving the base-load reliability storage another method to combine solar and will no doubt soon be joining the ranks of offers solar will be a major step to allowing us storage – DC coupling. peanut butter and jelly and ham and cheese in to achieve our renewable energy goals and frequent use. Like those classic culinary combat climate change. DC coupling vs AC coupling combinations, solar and storage just go so Besides for their more frequent Unlike AC coupling, with DC coupling, Solar concatenation, solar and storage share and Storage are connected on the DC side of another feature common: They are both DC the inverter. This means the DC-current never energy sources, batteries are actually both has to be converted to AC current through a DC sources and loads. When the sun’s rays solar inverter and then back to DC through a hit solar panels, they generate DC current. second battery inverter in order to charge the Batteries store energy in DC. Of course, our battery. In a DC coupled system, a second distribution grid transmits power in AC. inverter is replaced with a DC-DC optimizer, a Amazingly though, most collocated solar and device that manipulates DC voltage and storage projects today connect the solar current on the input to a different level of DC panel and the batteries on the AC side of the voltage and current on the output. In the ‘old inverter, a technique referred to as ‘AC days’ of solar and storage, these devices were coupling.’ With such a topology, the energy also known as charge controllers, though generated from the Solar panels needs to those devices are puny and wholly make a long ‘round trip’ from the PV field, inappropriate for today’s larger scale solar and through an inverter back through another storage deployments. DC-DC optimizers are inverter before arriving at the battery. needed to DC couple solar and storage because batteries typically require a different While AC coupling still represents the most level of DC voltage to charge and discharge common way of connecting Solar and themselves than PV generates. 96 PES SOLAR



COMMENT: TECHNOLOGY ‘One of the hallmarks of our products is that they feature galvanic isolation, a technique that creates electromagnetic isolation between the input and output.’ In reality, DC-coupling has a number of 3. F ewer roundtrip losses: roundtrip losses Additionally, there is not a lot of equipment advantages over AC-coupling, including: are the amount of energy lost as power to choose from to deploy DC-coupled passes from the energy source into the systems at scale. As a result, today, large 1. R educed cost: optimizers can cost less batteries and back out again when that scale DC-coupled solar plus storage systems than inverters and an additional set of AC energy gets put onto the grid. In the are still talked about more than they are switchgear, so you can save money on a DC-coupled concept, there are fewer actually installed. DC-coupled system by needing less conversions, typically about half as much equipment. loss as an AC coupled system. Making DC-coupling a reality 2. Increased energy yield: coupling solar and 4. More ITC: for systems built in the United Here at Alencon Systems, we build DC-DC storage on the DC side provides a States, when charging your storage on the optimizers that can be used to DC couple significant opportunity to increase the DC side, 100% of the cost of the storage solar and storage. One of the hallmarks of our yield of your PV assets, particularly if you system can be deducted for investment products is that they feature galvanic have a high DC to AC ratio, i.e. more PV tax credit (ITC) purposes. Claiming ITC on isolation, a technique that creates panel capacity than name plate inverter AC coupled systems can be difficult if not electromagnetic isolation between the input capacity. When a PV plant has a DC impossible. As the cost of storage is and output. overbuild, PV capacity can be ‘clipped’ significant, taking this deduction can when DC energy production exceeds that appreciably improve the ROI of a solar plus As more DC-coupled projects come to of the inverter. storage deployment. fruition, engineers are rapidly beginning to understand why using a galvanically isolated By coupling PV and storage on the DC side, 5. R etrofit Possibility for Existing PV DCDC converter is critical to a successful and this excess DC capacity can be diverted Systems: DC-coupling batteries does not cost-effective deployment. Galvanic directly to the battery. As a result, such a change the AC rating of existing PV plants; isolation offers system designers a great deal system can better divert PV energy at times thus, it can be quite possible to retrofit of flexibility in choosing grounding schemes of higher supply and lower demand to be existing PV plants with storage without for both the solar and storage part of the available during times of higher energy having to alter their interconnect system. Additionally, having galvanic demand and low solar energy supply (i.e. agreement. isolation offers a great deal of added safety evening time). This phenomenon of an to these systems. Galvanically isolated overabundance of PV energy on the grid If DC-coupling is so great, why isn’t DCDC optimizers also allow wide voltage during the midday is known as the ‘Duck everyone already doing it? gaps between PV and batteries to be easily Curve’ for the shape of energy demand bridged onto the same DC bus. curve relative to solar production. In the paragraphs above, we lay out some pretty compelling benefits for DC-coupling of In short, having a galvanically isolated DCDC The shape of the curve resembles a duck solar and storage over AC coupling. This begs optimizer can be the difference between and shows the imbalance between peak the question: If DC coupling is so great, why talking about DC-coupling and successfully demand and renewable energy supply. isn’t being deployed more frequently – yet? deploying such systems and unlocking their DC-coupling is particular helpful method myriad technical and economic benefits for flattening out this curve by syphoning The answer to that question is nuanced, explained here. more of that extra PV generation in the however one reason is that it isn’t particularly middle of the day and allowing it to be well understood by industry because it has www.alenconsystems.com discharged later. not yet been deployed extensively. 98 PES SOLAR



TALKING POINT Decarbonizing energy in time of crisis and beyond Words: Dan Ibbetson, Managing Director, Global Products & Technology Reliability and speed of response are essential to effectively managing or preventing a crisis - especially when it comes to power supply and temperature control. This has been clearly demonstrated by the While some industries, such as aviation and manufacturers are changing production lines outbreak of COVID-19 with countries across retail, have limited operations to reduce the to increase the volume of respirators, the world needing to rapidly put in place the spread of COVID-19, other sectors have antibacterial products and PPE available, necessary infrastructure to combat the virus joined forces to support relief efforts. while data centres are under strain to and subsequently dealing with the wider Temporary field hospitals and testing support the greater demand caused by economic consequences of the health crisis. facilities are being built in a matter of days, at-home working. This results in drastically 100 PES SOLAR