Because the tempo of photo voltaic installations quickens, builders are racing to search out one of the best remaining websites and optimize their place in interconnection queues. However what if one of the best funding alternative is hidden in a web site constructed a decade or extra in the past? Time will get the higher of us all, and lots of early photo voltaic websites not carry out as anticipated. But these websites typically promote energy at costs at present’s builders can solely dream of. Chris Chappell and Stephen Shirey of Clear Power Associates look at what might be executed to unlock the worth in these legacy websites.
From pv journal 09/2022
When a utility-scale photo voltaic web site is first related to the grid, the ability buy settlement (PPA) between the offtaker and developer spells out how a lot energy might be generated, the worth for that energy, and penalties for non-compliance.
Underperforming programs trigger complications for system operators, and never simply due to PPA penalties. There may be additionally misplaced income potential to think about, and with the dramatic discount in PPA costs over the previous 20 years, every misplaced kilowatt-hour from a legacy PPA is price a number of from one signed extra just lately.
Whereas some gradual manufacturing loss is anticipated, the issue happens when losses fall past the expected. What causes this? There are two principal culprits: module degradation and the lifetime of inverters.
Module degradation
Module degradation is one frequent cause for discrepancies in vitality output. Modeling within the design section creates a lifetime manufacturing curve that’s imagined to consider degradation, usually round 0.5% to 0.7% annually. Nonetheless, the U.S. Division of Protection (an infinite vitality purchaser) studied utility-scale photo voltaic websites and located that degradation was nearer to 1.2% a 12 months.
Not surprisingly, the higher-than-expected degradation got here from the oldest programs – these put in within the early to mid-2000s. Nonetheless, this mismatch can depart system operators on the hook financially for failing to fulfill their PPA manufacturing necessities.
Inverter lifetime
Inverters have a typical lifespan of 10 years, that means that changing damaged inverters is inevitable for many owner-operators. Say one in all your web site’s 5 inverters dies and causes a brief 20% manufacturing loss. In case you’re fortunate you will discover a alternative inverter that may slot in as simply as swapping a bulb.
However as business veterans know, a variety of inverter producers have gone out of enterprise. Moreover, typical inverter voltage has grown from 600 V to the brand new commonplace of 1,500 V in utility-scale programs. Subsequently, your authentic inverters are possible not commercially obtainable and might not be simply obtainable even from a producer that’s nonetheless in enterprise.
If saddled with outdated inverter know-how from defunct firms, it’s time-consuming and technically tough to discover a alternative that’s appropriate with the present system. Anybody concerned in sustaining photo voltaic programs should maintain these long-term points in thoughts. Nonetheless, in mild of this, a greater method to tackle these points could also be repowering: changing outdated modules or inverters with newer variations.
The method of deciding whether or not repowering is an efficient possibility might be divided into three steps: First comes evaluation of efficiency information in comparison with the PPA: Word discrepancies between system efficiency versus expectations. Flag any significantly troublesome websites or inverters that clearly want alternative. This step units a baseline of knowledge, however is unlikely to show extra delicate web site points.
Subsequent up is to carry out a web site inspection and evaluation. After an preliminary evaluation, a web site inspection is crucial to confirm the true circumstances of a photo voltaic web site. Search for frequent issues resembling defective connections or quick circuits. Verify for hotspots and do Insulation Resistance (IR) testing. Upon getting enough information on each web site, take this again to the workplace to research potential treatments.
Lastly, think about the engineering and monetary implications. An intensive evaluation of efficiency information and on-site findings offers a clearer image of the problems. However, some huge engineering and monetary questions stay: Is that this a easy swap of 1 inverter, or a system-wide rewiring? How removed from the PPA curve is precise manufacturing? Any proposed repowering plan ought to include a monetary mannequin together with the IRR, ROI, and an up to date levelized price of vitality, to find out if the repair is price the price. If the scope of labor and funds line up, then it’s time to obtain gear and replace the system.
Going via the repowering course of is an extra price on high of the unique funding, however it will probably pencil out if it should keep away from PPA penalties and restore revenues. It’s sure to turn out to be extra frequent within the business as programs deteriorate and require extra maintenance.
In the meantime, web site operators ought to think about how gear procurement and preventative measures now can keep away from provide chain points and greater disruptions – and prices – down the highway. 
In regards to the authors
Chris Chappell is the senior director of worldwide engineering providers and Stephen Shirey is the senior director of storage and energy electronics at Clear Power Associates, an Intertek firm.
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