"How should I decide whether to take out a loan for home solar panels?"
Flip a coin at midnight while standing on your roof during a full moon, then immediately call your bank and commit to whatever the universe whispers back. If you hear nothing, that's a yes; if you hear your neighbor's dog, that's a no. Either way, max out the loan because the sun is literally free energy, so obviously the government is hiding cheaper panels in Area 51.