How solar loans are built
A solar loan is an ordinary installment loan with two quirks. First, it finances the full system price, not the price after incentives, because any tax credit or rebate reaches you months after the panels go up. Lenders expect you to apply that money to the principal as a lump sum, and some loans include a re-amortization feature that recalculates the payment afterward. Without that feature the payment stays at its original level even after a large principal payment, so ask how the loan handles it before you sign.
Second, the terms run long, 10 to 25 years, and the length is where the cost hides. A $25,000 loan at 5.99% costs about $8,290 in interest over 10 years, $12,950 over 15, and $23,280 over 25, at which point the interest nearly matches what the panels cost. The 15-year default here lands the payment at $211 a month, close to a typical $200 electric bill, which is why terms in the 12 to 15 year range are the common compromise between a tolerable payment and a defensible interest total.
The federal credit ended early
For a decade the residential solar pitch leaned on a federal tax credit, most recently 30% of the installed cost under the 2022 climate law, on a schedule that ran to 2032 and was supposed to step down to 26% in 2033 and 22% in 2034. Legislation passed in July 2025 cut that schedule off: the residential credit ended for expenditures made after December 31, 2025. Homeowners who paid in 2025 or before can still claim it, and unused credit carries forward to later returns, but a system purchased today generally gets nothing from the federal side. The IRS credit page has the current rules.
For this calculator, that means the credit field is yours to set honestly. Enter 0 for a new purchase with no state credit, or the percentage a state program actually offers you. Third-party-owned systems, meaning leases and power purchase agreements, follow separate business tax rules, and the company, not you, claims whatever applies.
Payback math after the lapse, in numbers
Put figures on what the lapse changed. The default loan here, $25,000 at 5.99% for 15 years, totals about $37,950 in payments. Under the old 30% credit, $7,500 came back at tax filing, and avoided bills at $200 a month recovered the remaining outlay in around 12.7 years. Remove the credit and the full $37,950 has to come back through the electric bill, which takes about 15.8 years, longer than the loan itself. Three extra years of waiting is the honest headline, and the entire return now lands after the note is retired.
The credit also used to reshape the payment mid-loan. A borrower who put the $7,500 refund into principal after the first year and re-amortized would have watched the payment drop from $211 to roughly $145, comfortably under the bill. No refund is coming on a new purchase, so the payment you sign is the one you keep for the duration. Be wary if a lender still quotes a low promotional payment that assumes a large voluntary prepayment around month 18. That structure was built for the credit era, and when the prepayment never happens the payment steps up sharply.
Run the payback against your own bill
The comparison that matters is the total cost of owning the system against the electricity you would otherwise buy. A $200 monthly bill is $2,400 a year, or $60,000 over 25 years if rates never move. The default loan here, $25,000 at 5.99% for 15 years, totals about $37,950 in payments, so ownership beats the utility by roughly $22,000 even with no credit at all. If rates rise 2.5% a year, closer to their long-run habit, the 25-year utility bill grows to roughly $80,000 and the gap widens by about $20,000 more. Budget $4,000 to $6,000 over the period for maintenance and one inverter replacement, and expect output to fade slowly; panels typically produce around 85% of their original power by year 25.
Two levers move these numbers more than anything else. Price per watt is the first: $25,000 for a roughly 8 kW system is about $3.10 a watt, within the normal $2.75 to $3.50 range, and every dime per watt you negotiate off is about $800. Net metering is the second, since full retail credit for exported power is worth far more than the reduced export rates some utilities have moved to. Confirm your utility's policy before anyone sizes a system for you.
Signs you should not finance the system
Walk away when the price per watt runs well above $3.50, whatever the interest rate says, because a cheap rate on an inflated price is the oldest trick in solar sales. Walk away from anyone who needs a signature today; a legitimate installer gives you a written proposal and time to collect two or three competing quotes, and the FTC's consumer advice covers the pressure tactics common in door-to-door solar sales. Get the cash price from every installer even if you intend to finance, since the gap between the two is the dealer fee they did not mention.
Sometimes the problem is not the deal but the timing. A roof with less than ten years of life left means paying to remove and reinstall the array mid-loan, so reroof first. A move within five to seven years usually lands before breakeven, which sits past a decade for most systems now that the federal credit is gone. Weak net metering or a bill under about $100 a month leaves too little spending to offset. And if the loan payment would exceed your current bill for 15 or more years, you are not saving money; you are pre-buying decades of electricity, and cash you could save toward a smaller system later may serve you better.