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What are the disadvantages to borrowing money for energy conservation measures / solar panels?
If you sell the property before the ten years are up, the panels might have declined in value more than the amount you owe declined.  In the original post's situation, this is a negligible risk. Suppose (for the sake of argument) that each year's panels are 10% better than the previous year's panels.  Even if the panels lasted forever, and even if the price you could sell the power for stayed the same, then the value of your panels should decline 9% per year.  If the panels are financed at a 4.5% APR for 10 years, your principal should decline by 8.1% in the first year. A second risk is that the solar panels might be ugly, or might go out of fashion.  When selling a home, "curb appeal" matters.  If potential buyers do not like how your home looks with the solar panels, you might not be able to get as much money for the house if you have to sell it. A third risk is that the loan might harm your credit rating, or otherwise restrict your ability to borrow.  Even though this deal does not impinge on your disposable income, a bank might think that it raises your debt-service-to-income (DTI) ratio.  This could theoretically prevent you from refinancing your home, or raise the interest rates on potential loans you might want to take out. A fourth risk is that the installation process might damage your home in a way that causes expensive damage.  Water leakage and electrical fires can potentially destroy homes.  You need to have the solar system competently installed. A fifth risk is that the solar power system might make it harder to maintain or replace your roof.  Will your roof need to be replaced during the life of the solar power system?  If so, consider options that do not force you to throw away the solar power system prematurely.