Because your electric bill goes up every year as the utility keeps asking for return on equity (assuming investor owned utility, math might be different if you're in an electric coop). A solar PV system will produce power for 25 years at a minimum at a fixed cost. Like a mortgage that is fixed versus rent that is not.
It's the equivalent of a bond investment with potential subsidies at the utility, state, and federal level (solar is no longer subsidized, but batteries still are).
> 25 years at a minimum
So long as the roof itself lasts that long. People who are mid-cycle on their existing roof should not install solar until they get to the next replacement. This is where I am, and why I do not have rooftop solar. I expect to get 15 additional years from my roof, and there's no guarantee I will have hit the break even point by then. Plus, solar installers will not warranty a mid-cycle roof against leaks, so if something goes wrong that quickly eats into your cost savings.
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