The solar energy industry has come of age. Operations and maintenance of existing PV plants worldwide could well exceed 200 GW by the end of 2016. The shift in emphasis from building newcapacity towards optimising the existing fleet is being heralded by a greater focuson safety and asset value. But this evolution is threatened by inertia – doing things the way they have always been done. Oscar Fitch-Roy and Ragna Schmidt-Haupt of DNV GL, the leading global energy advisor, identify several elements of a modernised and holistic approach to solar operations and technical asset management.
The solar PV industry has continued to promise a brighter future with dramatic growth in solar generated energy. Looking back, the dramatic cost reductions we are seeing today are a result of tireless innovation and continued investor confidence in this fast growing industry. Breakthroughs in technology, manufacturing, project development, construction, due diligence and new financing mechanisms are just some of the areas that have continued to spur this industry forward.
As a significant global power generation technology today, the focus of the solar industry has changed. While global installed capacity continues to grow, focus has now shifted towards optimising asset value and conducting proper operations and maintenance of existing solar PV plants.
Optimising the value derived from solar assets requires a top-to-bottom re-think. By combining cutting-edge analyses with hands-on experience and knowledge, owners and operators can make solar operations and asset management smarter and more highly coordinated. But like any transition, changes in technology and practice must overcome inertia, the strong tendency to do things the way they’ve always been done. In this article we describe some of the technologies and practices that are moving solar operations and asset management forward.
Three key areas for modernisation of solar operations and asset management include (1) updating energy production estimates, (2) transforming operational data into intelligence and (3) performing physical inspection of installed systems. Each of these areas is reviewed in greater detail below.
Updated production estimates
The volume of energy produced can be considered to be the single most important factor in determining the overall success of a solar asset. This is also the parameter that is most widely communicated with various stakeholders. A pre-construction energy production estimate is valuable in determining the initial financing requirements. However this value, based on theoretical assumptions, is often challenged when the solar asset is entering its operational phase. There is an obvious benefit in making use of this data at the point of re-financing or change in ownership to more accurately predict the energy production for the remaining lifetime of the asset.Statistical techniques allow the historical production data to be combined with irradiance data collected at the same time to refine the forecast of future energy production. Deviations between pre and post construction estimates could range anywhere from 5 to 20 per cent depending on how the solar plant was designed and is being operated. Updated energy estimates that are validated by site measurements in mature markets such as France, UK, Italy, Germany and the US has typically twice the confidence of a pre-construction estimate.
Transforming operational data into intelligence
Besides providing more accurate energy production estimates, operational data from solar projects collected 24 hours a day, seven days a week can offer early warnings of potential problems.
The first area where operational data can be transformed into intelligence is by analysing the changes in the performance ratio (system yield vs reference expected yield – a measure of the overall conversion efficiency of the system). Analysing this data over time facilitates easy detection of grid failure, invertor failure, sensor failure and even design flaws. Decomposing the fluctuations in performance ratio can reveal several phenomena such as unexpected shading, differential mismatch, high soiling levels, defective strings or inverters, excessive module degradation, potential induced degradation, power and utility limitations.
Project performance is not just a question of efficiency but also availability (i.e. the proportion of time that the plant is available to produce power. Here availability also includes analysing the down time of the utility grid and other key components such as inverters. While compiling detailed availability data is considered as good practice, it can also be used to benchmark individual system components and track overall system performance.
Furthermore, other parameters such as module temperature, open circuit and maximum power point voltage can be used to identify problematic performance and diagnose areas for further investigation. While a number of these analyses may not directly lead to full resolution of operational issues, they can make solar systems more intelligent in predicting problem areas in the future, thereby improving investor confidence at the point of re-financing or transfer of ownership.
When advanced analysis of operational data indicates potential problem areas, the next logical step is to physically inspect these areas. Physical inspections here could involve various levels of detail as required – from high level visual inspections to identify any issues with the general maintenance of the asset and Balance of System, down to detailed end of warranty or root cause analysis inspections.
Problems that are frequently identified through physical inspections are when the PV modules are underperforming, i.e. the labelled power is higher than real power, or when low quality monitoring systems are identified. A visual inspection is a simple but extremely valuable way to identify anomalies that could be a result of shading, cracks in solar cells, yellowing of PV modules due to the degradation of EVA encapsulated, delamination or “snail trails” on modules.
More specialised inspection services such as using thermographic analysis (through infra-red imaging) is beneficial in identifyingtemperature spikes that would otherwise go undetected during visual inspections. These temperature spikes could be caused by defects in components such as modules, connections, combiner boxes, inverters and both DC and AC cabling connections. Possible problems identified may be defective bypass diodes in the modules or high impedance electrical connections. This analysis can be followed up by measuring the I-V curve (current vs voltage) for strings or individual modules to further isolate an underperformance issue.
A systems approach to solar operations and asset management
While each of these focus areas discussed above is individually important for improving solar PV performance, optimal asset management and effective operations truly arises from understanding the inter-relationships and interactions between the various focus areas. This should be achieved bya standardised framework of recommended best practices and through a systems-thinking approach. Combining various standards to achieve a single recommended practice towards solar operations and asset management is a major challenge for the industry today, but the benefits are clear: such a holistic approach would be an important step towards ensuring long-term sustainability of the solar industry.
Case Study A
Location: Gujarat, India
Reason for review: Underperformance
Technical issue: Potential-Induced Degradation (PID)
and safety risks
Possible solution: Recommendation to grounding of negative DC pole and off-set box (applies positive voltage during night) and use pyranometer for reliable irradiation data
Value of improvement: 2-3% production increase.
Case Study B
Reason for review: recalculation of energy production
(financing contract condition)
Technical issue: Underperformance of a large amount of modules (>10%)
Possible solution: Replacement of modules (not likely) and/or Liquidated Damages from the manufacturer.
Value of improvement: 7-8% lower PR, translating to
(>100 k € recovered revenue pa)
Possible solution: replacement of modules (not likely) and/or Liquidated Damages from the manufacturer.
DNV GL in the Energy industry
In DNV GL we unite the strengths of DNV, KEMA, Garrad Hassan, and GL Renewables Certification. DNV GL’s 2,500 energy experts support customers around the globe in delivering a safe, reliable, efficient, and sustainable energy supply. We deliver world-renowned testing, certification and advisory services to the energy value chain including renewables and energy efficiency. Our expertise spans onshore and offshore wind power, solar, conventional generation, transmission and distribution, smart grids, and sustainable energy use, as well as energy markets and regulations. Our testing, certification and advisory services are delivered independent from each other. Both authors are part of the global Strategy & Policy Advisory team for Renewable Energies.Ragna Schmidt-Haupt is based in DNV GL’s Singapore office – the Clean Tech Centre - and Oscar Fitch-Roy is working from the UK.