Independent energy math
Enter a ZIP for a real answer, computed from published figures for your state. Holding a quote? Change the system size and the price per watt to match it.
In California, a system at per watt, offsetting a monthly bill at per kWh under , pays back in
9.2 years
at these inputs.
Every boxed value above is editable. Tap one to put your own figure in, and the answer changes as you type.
Computed from 5 published state figures (EIA, NREL and DSIRE), each shown with the date it was published. 1 more is worked out from the figures in the sentence, and 9 are starting values this site sets, also listed. Federal credit: off (expired 2025-12-31). Turn it on for a pre-2026 install or a lease.
| Sun hours | 1,825/yr | DSIRE 2025-01 / NREL PVWatts, 2025-01-01 |
|---|---|---|
| State incentive | $0 | DSIRE 2025-01 / NREL PVWatts, 2025-01-01 |
| Analysis period | 25 years | Site default |
| Federal tax credit | off (expired 2025-12-31) | Site default |
| Utility rebate | $0 | Site default |
| SREC revenue | $0 | Site default |
| Used on site | 80.0% | Site default |
| Export credit rate | $0.0800 (stated rate, see source) | DSIRE 2025-01, NEM 3.0 avoided cost, 2025-01-01 |
| Annual usage | 5,630 kWh (from the bill) | Computed from the monthly bill and rate |
| State | California | Site default |
A simple payback is the net cost divided by the first year’s saving, so financing terms and long-run effects like panel degradation never reached this number. They change the lifetime picture in the full calculator.
| Panel degradation | 0.5%/yr | Site default |
|---|---|---|
| Inverter replacement year | year 12 | Site default |
| Inverter replacement cost | $1,500 | Site default |
| Rate escalation | 2.5%/yr | Site default |
| Purchase method | cash | Site default |
| Loan rate | 5.5%/yr | Site default |
| Loan term | 15 years | Site default |
| Down payment | $0 | Site default |
| Loan amount | none (cash purchase) | Site default |
A heat pump does not always beat a gas furnace, and solar does not always pay for itself. When the math says so, the tools say so. Nothing here is paid for by an installer, and no result is routed to anyone.
Electricity and gas prices come from the EIA, sun hours from NREL, and incentives from DSIRE. Each figure carries the date it was published, because some states are refreshed more often than others and pretending otherwise would be dishonest.
Model your system size, local electricity rates, and incentives to find your break-even year and 25-year return at your inputs.
Size the battery bank, solar array, charge controller, inverter, and fused wiring for an off-grid van from your real appliance loads.
Compare the full cost of a heat pump against a gas furnace across climate zone, fuel prices, and state and utility rebates.
See the combined payback for every gas-to-electric upgrade, with IRA credit stacking, appliance by appliance.
Compare gas, hybrid, and electric over 5 to 10 years of real ownership cost, not just the sticker price.
Also here: personal finance calculators for Compound Interest, Cost of Waiting, Debt Payoff, FIRE Number, Savings Rate, and Emergency Fund.
For educational and illustrative purposes only. Not financial, tax, or investment advice. Results depend on the accuracy of your inputs and on assumptions that may not reflect your actual situation. ForestMatters is not a registered investment advisor. Full disclaimer.