The fact that the return is not compounding makes a very large difference here.

$16,500 returning 10% of the original principle per year isn’t a great investment. 25 years you have $41,000 + 25 yr old solar panels.

$16,500 returning 10% compounding over 25 years gets you $162,000 + the $16,500 principle.

Considering opportunity cost spread evenly over 25 years, those panels cost over $5000 per year.

There are plenty of reasons to go solar, but return on investment is not one of them.