But in this case, the panels produce (hopefully) a pretty constant annual amount of electricity, and the price I get is a fixed amount, so it seems that calculating IRR is easy.
Your calculation is presumably for a fairly long term. In the long term prices don’t remain fixed, things break down, need maintenance, etc. For example, hail might damage some of your panels. Or your roof might start to leak and the presence of the panels will substantially add to the cost of repairing it.
Your calculation is presumably for a fairly long term. In the long term prices don’t remain fixed, things break down, need maintenance, etc. For example, hail might damage some of your panels. Or your roof might start to leak and the presence of the panels will substantially add to the cost of repairing it.
Excellent. I had an overly-simplistic mental model in which the panels would last until they fail.
But yes, unexpected costs that are nonetheless below full price of the panels are a real possibility.