Solar Loan Calculator

What a solar loan really finances

A solar loan spreads the upfront cost of a rooftop or ground-mounted photovoltaic system over a fixed term so you can own the panels instead of paying the full installed price at once. Ownership is the key word: with a loan, the system is yours, which means you keep any tax credits and the long-run energy savings — unlike a lease or power-purchase agreement (PPA), where a third party owns the array and you simply pay for the power or rent the equipment. This calculator models the loan itself: enter the financed amount, the APR, and the term to see your fixed payment and the true cost of borrowing.

Solar loans come in two flavors. A secured solar loan (often a home equity loan or a loan that places a lien on the system) usually carries a lower rate but ties the debt to your home or the equipment. An unsecured solar loan funds faster and adds no lien, but the rate is higher and hinges on your credit. Either way, the math the calculator runs is the same fixed-rate amortization.

How to use this calculator

Enter the system cost financed — the installed price minus any down payment — along with the APR from your quote and the term. Solar loans commonly run 10 to 25 years. The tool returns your fixed monthly payment, the total interest, and a downloadable amortization schedule. Because many homeowners use a tax credit to pay down the balance early, it is worth running the calculator twice: once on the full financed amount and once on the lower balance you expect after applying the credit.

How it's calculated

The payment uses standard amortization. Each month, interest is charged on the outstanding balance and the remainder of your fixed payment reduces the principal, so early payments are mostly interest and later ones are mostly principal. The payment depends only on the amount financed, the monthly rate (annual APR divided by twelve), and the number of payments. Note that a very low advertised APR sometimes comes with a dealer or origination fee baked into a higher system price — so always compare the total installed price, not just the rate, across installers.

Payment versus savings: cash-flow positive?

The number that matters most for solar isn't the payment in isolation — it's the payment compared with the electric bill the panels offset. If your monthly loan payment is less than the utility bill the system replaces, the project is roughly cash-flow positive from day one: you pay the lender instead of the utility and come out slightly ahead each month, then own free electricity once the loan is paid off. If the payment is higher than your current bill, the system still builds long-term value but costs you cash flow in the early years.

A worked example

Suppose a system is financed at $25,000 with a hypothetical 7% APR over 15 years. The monthly payment is roughly $225. If your average electric bill is around $180, the loan costs about $45 a month more than your current bill in the early years — but that gap can close as utility rates rise over the loan's life. Now suppose you qualify for a federal solar tax credit and use it to pay the balance down to about $18,000 in year two. Re-running the loan on that lower amount drops the payment well below your old utility bill, tipping the project firmly cash-flow positive. Confirm the current credit percentage and your eligibility with a tax professional — the rules and rates change.

Loan vs. lease vs. PPA

Tips and common mistakes

Get quotes from several installers and compare the all-in installed price, not just the monthly payment or APR. Watch for dealer fees folded into the price to subsidize a low headline rate. Don't oversize the system beyond what your roof and usage justify — a bigger array means a bigger loan. Be realistic about energy savings, which depend on your location, roof orientation, shading, and local utility rates. And never bank on a specific tax-credit amount until a tax professional confirms you qualify and tells you the percentage in effect for your tax year.