The Science and Economics of Repowering
New multi-megawatt solar installations are growing rapidly, which is great news for the environment and the economy. With that growth comes falling prices, both for power purchase agreements (PPAs) and solar gear including PV modules, inverters and other equipment.
But what about the people reading this article who got into large scale solar earlier in the game, with PV plants now between five and ten years old, or perhaps even older? How are your PV assets performing now? It’s quite likely there is significant untapped potential in those assets that could provide you increased returns on your existing portfolio by boosting yield and decreasing operating costs.
There is sound science behind how you can do so, the application of which will have some very significant economic benefits.
Turning your central inverter into a string inverter
One of the great debates in the solar industry at the moment is the one over central versus string inverters. Settling this debate is beyond the scope of this article. What is in the scope of this article is explaining that one of the arguments string inverter advocates make in favor of their application is their more granular maximum power point tracking or MPPT. For those unfamiliar with this term, MPPT refers to the technique for determining the maximum amount power a PV module can produce.
Central inverters generally offer one maximum power point tracker for the entire PV array that feeds into them. For example, say a 500 KW PV array has 84 strings connected to a central inverter with one MPPT (MPPT can also stand for maximum power point tracker or the software and hardware that actually does the maximum power point tracking). That means the central inverter looks at each string in the array as if they were the same from a power production perspective. The problem, particularly in aged PV plants, is that those strings are anything but the same in this regard. This lack of similarity is called mismatch.