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Solar calculator

Estimate the right residential solar system size for your home — and what it will cost, save, and pay back. Currently supports the United States, Germany, India, and the United Kingdom. Numbers are 2026 indicative ranges; use them as a starting point, not a final quote.

Your inputs

Country

US state

Fills in your state's average electricity rate (EIA) and solar production (PVWatts). You can still edit both.

Average monthly electricity bill ($)

Electricity rate ($/kWh)

Solar production factor (kWh per kW per year)

Typical: US 1300–1700 (south sunnier) · Germany 950–1050 · India 1400–1700 · UK 850–1000

Installed cost tier

$3,000–$5,200 per kW installed (Berkeley Lab, 2024 installs before incentives)

No federal credit for systems you own installed after Dec 31, 2025 (IRS, 25D ended)

Estimated results

Annual electricity used: 11,000 kWh
Recommended system size: 7.6 kW
Gross installed cost: $26,552
Net cost after incentive: $26,552
Estimated annual production: 11,000 kWh
Annual electricity bill savings: $1,980
Simple payback: 13.4 years
15-yr loan payment (7.5% APR): $246/month
vs. avoided bill: $165/month
25-year net savings: $22,948

Estimates only. Actual prices vary by installer, state/region, system specification, and time. Get three independent installer quotes before any commitment.

US defaults and sources

Residential electricity price: State average when you pick a state; US average 18.19 cents/kWhEIA Electric Power Monthly, Table 5.6.B (year-to-date through August 2026, preliminary) · checked Oct 27, 2026
Solar production per kW: Modelled for one major city per state when you pick a statePVWatts v8 (National Laboratory of the Rockies, formerly NREL): fixed roof mount, 20 degree tilt, south-facing, 14% system losses, NSRDB typical-year weather (2020; 2023 for Alaska) · checked Oct 27, 2026
Installed price range, all host-owned home solar: $3.0/W (20th percentile) to $5.2/W (80th percentile); loan-financed median $4.7/WBerkeley Lab, U.S. Distributed Solar and Storage 2025 Data Update · checked Oct 27, 2026
Federal credit for buying solar or a battery (25D): None for systems installed after December 31, 2025IRS FAQs on Public Law 119-21 · checked Oct 27, 2026

How this calculator works

The calculator uses your average monthly electricity bill and local electricity rate to estimate your annual kWh consumption. It then divides that by a country-specific production factor (sunshine hours weighted by tilt and shading) to recommend a system size in kW. Installed cost is computed from country-specific 2026 per-kW price ranges (lower, mid, premium tier); incentives are applied as a percentage (India PM Surya Ghar) or noted explicitly (Germany 0% VAT, UK 0% VAT). The US has no federal credit for homeowner-owned systems installed after December 31, 2025, so none is subtracted; if you are weighing a lease, use the solar lease vs buy calculator. Loan terms use 2026 country-typical APR and tenor.

What the inputs mean

Country — sets currency, default electricity rate, default production factor, installed cost range, and incentive treatment.
Monthly bill — what you pay your utility on average. Don't use your highest summer bill or lowest winter bill — use the annual average.
Electricity rate — your blended retail rate per kWh. If you have time-of-use rates, use the average.
Production factor — how many kWh a 1 kW system produces per year in your location. US south: ~1700; US northeast: ~1100; Germany: ~1000; India: ~1500; UK: ~950. Adjust if your roof has significant shading or non-optimal orientation.
Cost tier — picks the lower, mid, or premium end of the 2026 country installed-cost range. Most buyers land in mid.
Include incentive — toggles whether the calculation subtracts the country-typical incentive from gross cost. Shown only where a purchase incentive exists (currently India).

Important caveats

These are estimates, not quotes. Real installer pricing varies 25–40% on identical hardware.
The production factor uses an annual average. Real production has seasonal variation, weather variation, and degradation over time.
The 25-year savings number assumes electricity rates stay flat. Most US, EU, and Indian households have seen real-rate inflation of 2–5%/year, which means actual savings are usually higher.
Loan payment assumes country-typical APR and tenor — your actual loan offer depends on your credit, lender, and current rates.
India incentive is capped at ₹78,000 per PM Surya Ghar rules; for systems above 3 kW the percentage is effectively lower than the headline.