Solar Savings Calculator

How to Use This Calculator

1. Enter your monthly electricity bill — the average dollar amount you pay, ideally from a recent statement.
2. Select your state. The calculator loads state-specific average peak sun hours and electricity rates automatically.
3. Choose your daytime home usage — this sets what fraction of solar power you consume directly versus export to the grid.
4. Optionally enter your actual electricity rate in cents per kWh if your bill shows it — this overrides the state average.
5. Optionally enter your usable roof area in square feet to check whether your roof has enough space for the estimated system.
6. Open Advanced options to edit the model assumptions: system cost, panel degradation rate, electricity escalation rate, system efficiency, and inverter replacement cost.
7. Click Estimate Savings. The result shows year-1 annual savings, net cost, payback year, 25-year savings, and a sensitivity table showing how payback shifts across cost and escalation scenarios.

How the 25-Year Model Works

Unlike flat estimates that multiply year-1 savings by 25, this calculator models each year individually. Two forces work in opposite directions:

Panel degradation (default 0.5%/yr) reduces annual production. A system producing 10,000 kWh in year 1 produces about 8,800 kWh by year 25 — roughly a 12% reduction over the system's life.

Electricity rate escalation (default 2.5%/yr) increases the value of each kWh you produce. U.S. residential electricity rates rose at roughly 2.5% annually from 2000–2023 (EIA). Escalation outpaces degradation, so savings grow each year in dollar terms — making the 25-year projection more favorable than a flat model suggests.

The model also subtracts a one-time inverter replacement cost ($1,500 by default) at year 12 — a real expense most calculators ignore.

Self-Consumption and Net Metering

Solar panels produce most power around midday. If nobody is home during the day, most production gets exported to the grid rather than consumed directly. This matters because most states no longer credit exported power at the full retail rate.

The self-consumption ratio (50–80%) represents what fraction of production you use on-site. The rest is exported at the net metering export rate — which varies by state policy from the full retail rate (full net metering) down to 35% of retail (partial net metering, e.g. California NEM 3.0) or a wholesale floor of about 3¢/kWh (no net metering). Selecting "Mostly home" (80%) vs "Rarely home" (50%) can shift the effective blended rate by 20–40% in partial-metering states.

The Payback Sensitivity Table

The sensitivity table shows payback years across nine scenarios — three system cost levels (your quote ±15%) and three electricity escalation rates (pessimistic 1%, your setting, optimistic 4%). The center cell is always your scenario. Green cells indicate payback under 8 years; orange and red cells warn of slow payback scenarios.

This table answers the most common homeowner question: "What if my installer quote comes in higher? What if electricity rates stay flat?" No other consumer solar calculator shows this — it's usually buried in spreadsheet models that installers charge for.

Costs and the Federal Tax Credit

The installed cost uses $3.00 per watt as a national midpoint (DOE/SEIA 2024 range: $2.75–$3.50). The federal Investment Tax Credit (ITC) reduces this by 30%, giving the net cost. The ITC is a dollar-for-dollar reduction in federal income taxes owed — not a deduction — and applies to systems installed through 2032. Homeowners with no federal tax liability receive no ITC benefit.