Solar & EV Payback Calculator
How many years until solar or an EV pays for itself.
Optional. Annual utility-rate inflation.
Optional. Annual loss of output (panels ~0.5%/yr).
Optional. Used for the net present value.
Simple payback
- Payback yearescalation + degradation
- Year 8
- Net present value
- $25,086.64
Estimate. Savings are modelled year-by-year with utility-rate escalation, panel degradation, and discounting; NPV is net of the up-front cost.
How the solar payback calculator works
The calculator answers two questions: how long until the savings repay the up-front cost, and what the whole project is worth in today’s money. You give it the net cost after incentives, your first-year savings, and a horizon in whole years. You can also set a yearly escalation (how fast your savings grow as utility prices rise), a yearly degradation (how fast output fades), and a discount rate for the present-value calculation.
Simple payback is the flat ratio simplePayback = netCost / annualSavings. The more realistic figure models each year separately on an end-of-year basis: savings_t = annualSavings * (1 + escalation)^t * (1 - degradation)^t for each year t. The calculator adds these up year by year and reports the first whole year where the running total reaches the net cost. The net present value is npv = sum( savings_t / (1 + discountRate)^t ) - netCost. If degradation is left blank it defaults to 0.5 percent per year, a common figure for solar panels; for an EV you would set it to zero.
Worked example
A homeowner installs solar with these inputs:
- Net cost after incentives: 18,000
- First-year savings: 1,400
- Escalation: 3 percent per year
- Degradation: 0.5 percent per year
- Discount rate: 4 percent
- Horizon: 25 years
Year-one savings are 1,400 * 1.03 * 0.995 = 1,434.79. Year two is 1,400 * 1.03^2 * 0.995^2 = 1,470.44, and each year grows from there. The running total crosses 18,000 partway through year 12 (cumulative savings reach 19,776.95 by the end of year 12).
| Result | Value |
|---|---|
| Simple payback | 12.86 years |
| Escalated payback year | 12 |
| NPV over 25 years | 11,083.55 |
Simple payback is 18,000 / 1,400 = 12.86, but because savings rise faster than the panels fade, the modelled payback lands a year sooner. Over the full 25 years the project is worth about 11,084 in today’s money beyond what it cost.
How to use it
- Enter net cost after every rebate and tax credit you will actually receive, not the quoted price.
- Set first-year savings from your real bills: avoided utility spend for solar, or gas minus charging cost for an EV.
- Use escalation to reflect how fast your utility or fuel prices have risen; 2 to 4 percent is a common range.
- Set degradation to 0 for an EV, or leave it at the 0.5 percent default for solar panels.
- Pick a discount rate equal to the return you give up by spending the cash now.
- Match the horizon to your warranty or how long you plan to keep the system.
Limitations
This is an estimate, not financial advice. It assumes your savings, escalation, and degradation rates hold steady for the whole horizon, which real utility prices and weather will not. It does not model financing interest, maintenance or repair costs, inverter or battery replacement, resale value, or changes to tax credits and net-metering rules. Savings beyond the horizon you set are not counted, and a single wrong input (especially first-year savings) moves the result a lot. Treat the output as a planning guide, confirm the figures with written quotes, and speak to a qualified professional before committing.
Frequently asked questions
Why is the escalated payback year sometimes sooner than simple payback?
Simple payback assumes your savings stay flat forever at the first-year amount. When you add a utility-rate escalation, each later year saves more than the first, so the running total reaches your net cost in fewer years. Panel degradation pushes the other way, but a typical 3 percent escalation easily outweighs a 0.5 percent degradation, so the escalated payback usually arrives earlier.
What net cost should I enter for solar?
Enter the price after every incentive you actually receive: federal or national tax credits, state or utility rebates, and any sign-up bonuses. The figure should be the real cash dent to your finances, not the sticker price. For an EV, use the purchase premium over the gas car you would otherwise buy, after any purchase credit.
How do I estimate first-year savings for an EV?
Subtract your expected annual charging cost from what you would have spent on gasoline for the same mileage, then subtract any difference in maintenance and insurance. The result is your net first-year saving. Charging at home overnight is usually far cheaper than public fast charging, so the rate you assume matters a lot.
What discount rate should I use for the NPV?
Use the return you would otherwise earn on that money. If the cash would sit in a savings account, a few percent is reasonable; if it would pay down a mortgage or sit in index funds, use that rate instead. A higher discount rate lowers the present value of distant savings and makes the project look less attractive.
Does the calculator account for the panels wearing out at the end?
It models gradual output loss every year through the degradation rate, but it does not assume a hard failure at the end of the horizon. Set the horizon to match the equipment warranty or your planning window. Savings beyond that horizon are simply not counted, which keeps the estimate conservative.