[robocat]

If you have a mortgage then you are effectively borrowing $23k from the bank for the period of your mortgage - so the total interest could be a significant chunk of money.

Assuming that you have some leeway to pay your mortgage off quicker (depending on your exact terms).

[sagarm]

Homeowner mortgage rates are well below the long-run return on e.g. the S&P 500. A solar system is just another alternative investment option.

[hilbertseries]

How does interest factor in here? Your mortgage is fixed with the bank.

[seabrookmx]

If you pay off your mortgage quicker you pay less interest. Not sure what you mean by "fixed".

Atleast where I live a standard 25 year mortgage can be paid off in ~10 if you were to double up your payments, because all of the additional money you're paying comes off the principal. Thus, the non-interest portion of the payment has _more than_ doubled.

[girishso]

OP means he could have prepaid the $23K of mortgage, instead of spending on the solar system.