Solar ROI Calculator

Solar installer proposals are optimized to close deals. They lead with the best-case numbers: peak sun hours, full retail net metering, maximum incentives, lowest financing rates. These aren’t lies. They’re just the rosiest version of a scenario that depends heavily on your specific situation.

The three variables that installers most often present optimistically are solar production estimates (often using NREL peak sun hours without adjusting for your specific roof orientation and shading), net metering credits (which vary enormously by state and utility, and have been cut in several states in recent years), and electricity rate escalation (installers often assume 3–4%/year; your actual future rates may differ).

This calculator lets you model your own assumptions. Change the net metering policy from full retail to avoided cost and watch the payback period extend. Lower the electricity rate escalation from 3% to 1%. The realistic scenario (not the optimistic one) is the one worth paying the most attention to.

Payback period tells you when you break even. Lifetime return tells you what you actually make. These are different numbers, and both are worth understanding.

A 10-year payback on a $14,000 system (after ITC) sounds reasonable. But over a 25-year system life with 2.5%/year electricity rate escalation, that same system might generate $35,000 in total savings, a net benefit of $21,000 and a 150% ROI on the net investment. The back half of the system life, after payback, is where the real financial return accumulates.

This is also why financing matters so much. A $20,000 solar loan at 6.9% over 20 years costs $11,000 in interest, nearly doubling the true cost of the system. The advertised “zero down, positive cash flow from day one” pitch usually relies on electricity escalation assumptions that may not materialize.

Cash purchase maximizes your return. If you don’t have the cash, a shorter-term loan (10–12 years) at a competitive rate is usually better than a 20-year solar loan. A HELOC at current rates is often cheaper than manufacturer-sponsored financing.

Net metering is how your utility credits the excess electricity your solar panels send to the grid. Under full retail net metering (still the standard in most states), you get a credit equal to your full retail rate for every kWh exported. If you pay $0.15/kWh, you receive $0.15/kWh for each kWh your panels send back.

Not all states offer full retail net metering. Some pay the utility’s avoided cost (wholesale rate, typically $0.03–$0.06/kWh, or about 25–35% of retail). A few have eliminated net metering for new systems entirely. California’s NEM 3.0, implemented in April 2023, cut export credits by roughly 75% for most customers, extending the payback period for new installations by 2–4 years.

Net metering policy is determined at the state and sometimes utility level, and it can change after your system is installed. This calculator uses your state’s current default policy, but verify your specific utility’s rules before purchasing.

Solar makes the most financial sense when you have a high electricity rate ($0.15+/kWh), good sun exposure (southwest, southeast, or flat south-facing roof), own your home and plan to stay at least 7–10 years, have federal tax liability to use the 30% ITC, and live in a state with favorable net metering.

Solar is harder to justify when your electricity rate is very low (Louisiana at $0.08/kWh, for example), when significant roof shading reduces production, when you plan to sell the home in under five years, or when your state has moved to avoided cost or no net metering.

The payback period is also sensitive to installation quality. A system that underperforms due to poor installation, panel orientation, or inverter issues will have a longer real-world payback than the modeled one. Get multiple quotes, check installer reviews and certification (NABCEP certification is the gold standard), and read the warranty terms carefully.

One last thing: solar adds value to your home in most markets. A Lawrence Berkeley National Lab study found solar panels increase home values by approximately $4/watt on average, roughly the net system cost. This benefit is outside the calculator’s scope but worth factoring into your total decision.