INDUSTRY I BALANCE OF SYSTEM
shifted their focus to balance-of-system (BOS) improvements and overall system advances to make solar arrays more efficient, cost-effective and ultimately achieve higher return on investments (ROI).
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Array managers have to look at maximizing yield out of every system component to ensure the entire system operates at an optimum level to improve ROI and reliability. This trend is already apparent as panel and inverter manufacturers tout expanded warranties, operations and maintenance (O&M) teams sign tighter contracts to assure minimum power production guarantees, and banks insist on improved system monitoring as a condition of financing.
This is where new technology and improvements in monitoring and optimization solutions are vital in order to manage array efficiency.
Until recently, conventional monitoring options have been limited to the inverter level, and sometimes sub-array level, for large- scale arrays. More recently, although still rare, string-level options have entered the field. These solutions tend to produce more data, but suffer from a lack of precision and the ability to provide actionable information. They only aggregate sections of the array. Therefore, these solutions can only point to sections where there may be possible performance impairments and aren’t able to tell you what the problem is, how to fix it and even more importantly, if it is cost-effective to fix. In essence, array owners and operators are potentially throwing away money and don’t even know it. The next-generation systems, processes, and procedures used to design, commission, monitor, manage and maintain these larger PV assets are evolving into a more integrated and cost-effective operational framework. New management tools provide the site operator with intelligent and actionable O&M information, delivering value far beyond today’s largely passive and opaque monitoring solutions.
These new approaches to site management are open, flexible and scalable; enabling rapid deployment into both new and existing PV power plants, independent of equipment type, site design, wiring topology, and array size.
Monitoring success Until recently, most new array owners have not been offered, or taken advantage of, these new monitoring and optimization options. However, the effectiveness, affordability and availability of these technologies are becoming much more attractive. The industry is approaching the point where large-scale solar assets will not be considered without it.
The Clarity monitoring and optimization system, developed by Solar Power Technologies, discussed below, is one of the current solutions on the market that addresses these needs. But first, it is worth taking a closer look at how traditional monitoring options lead to low system performance.
ith module prices continuing to drop, PV developers and solar industry watchers have
Clarity System monitor in-situ
Current Problems with Performance A commonly used measure of solar array health is the Performance Ratio (PR) – the ratio of the actual energy produced from a solar array compared to its theoretical capability. The closer the array gets to a 1.0 PR, the better it performs. In practice, a PR of 1.0 is not achievable due to unavoidable DC wiring losses, temperature effects and DC-AC conversion losses, but new and well maintained large-scale arrays can achieve levels of around 0.80. Therefore, you often see the DC-side overbuilt by 20-25 percent to provide a defined AC power rating.
In reality, most systems are not maintained at the 0.80 level. A study of large arrays of varying age and locations showed that the actual average was 0.66, with the lowest at 0.38.1
Most of the
energy loss in solar arrays is due to faults and impairments within panels and the interaction of those panel impairments within and between strings. Energy loss from a single panel fault can be multiplied two to ten times, depending on the type of fault.
Inverter, sub-array and even string monitoring systems do not see most of these losses. They aggregate the array into large sections of panels, and assuming that most panel faults are evenly distributed across an array, they will rarely identify faults and almost never pinpoint them such that action can be taken.
Why? Most inverter, sub-array and string-level monitoring systems use sensing technology that limits their measurement accuracy to plus or minus five percent. This might be okay for sensing large catastrophic faults such as open circuits, blown fuses and dead strings, but is insufficient when trying to identify array impairments, most of which occur at the panel-level and are distributed throughout the array, pulling down aggregate performance significantly, but not showing up in a monitoring system that is only able to sense 5.0 percent variations between array sections. For instance, how do you monitor panel original
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