How it works

We model your home hour by hour for a year, price every hour on your utility's 2026 rates, then add up 25 years. Rates and costs checked Oct 6, 2026.

1. Your roof

Google's Solar API gives us your roof's faces (pitch, direction, area), where panels fit and what each one would make in a year, with the date of the aerial imagery. No imagery means we assume a typical roof and say so in the report.

2. When the panels produce

The timing comes from PVGIS, the European Commission's solar model, on NSRDB satellite weather. On one 4.7 kW Northern California array we measured for a year, it was within about 1% of the real output. PVGIS (opens in a new tab)

3. When you use power

Your bill, worked backwards through your rate plan, gives annual use. Without one we use a typical home for your area (statewide about 7,553 kWh a year) energy.ca.gov (opens in a new tab), spread over the year with a regional load shape, plus overnight car charging if you have an EV.

4. Your bill, every hour

Power you use yourself saves the full retail price. Power you export earns that hour's Net Billing Tariff credit, locked for 9 years pge.com (opens in a new tab). PG&E and SCE add a small ACC Plus bonus on exports for 2026 applicants: PG&E $0.0088/kWh pge.com (opens in a new tab), SCE $0.016/kWh sce.com (opens in a new tab). SDG&E gives none to standard homes.

Homes already on NEM 1.0 or 2.0 keep it for 20 years from turn-on, and adding a battery doesn't change that. A state battery rebate or more than 10% (or 1 kW) of new panels moves you to the Net Billing Tariff pge.com (opens in a new tab).

5. Twenty-five years, then the verdict

Each year we add the savings (rates rise, panels fade a little), subtract what you pay (price, loan or lease payments, an inverter replacement) and discount to today's dollars. Above zero beats doing nothing. The verdict follows net value, and says so when it's close.

2026 rules we account for

No federal credit for panels you own

The 30% credit (IRC 25D) ended for spending after December 31, 2025 (P.L. 119-21, section 70506). We use 0%. irs.gov (opens in a new tab)

Leases can still carry one

The company that owns your panels can claim 30% (48E) if the system is running by December 31, 2027, or construction started by July 4, 2026. You only see it in the lease price, so we compare the two. seia.org (opens in a new tab)

The battery rebate is closed to most homes

We count SGIP as $0/kWh. selfgenca.com (opens in a new tab) Income-qualified homes can apply to an equity budget that is waitlisted or nearly spent. selfgenca.com (opens in a new tab) Grid-support payments (DSGS) are counted as $0/yr. efiling.energy.ca.gov (opens in a new tab)

What we don't model

• Roof condition. If it needs replacing within ten years, do that first.
• Panel upgrades, trenching, HOA rules and unusual permit costs.
• CARE and FERA discounts. On one of them, solar saves less than shown.
• Community choice suppliers (MCE, CleanPowerSF, SVCE and others). Their prices are close to the utility's, not identical.
• Export rates after the 9-year lock ends.
• Backup value in outages. A battery can be worth it for that alone.

A number looks wrong for your home? Run it and check each assumption against your quotes.