Solar Battery Calculator
A battery does not generate a single extra kWh. Its entire financial job is to change where those kWh go: away from a low-value export tariff and toward your own evening load. That means its value is almost entirely determined by…
What this estimate does
A battery does not generate a single extra kWh. Its entire financial job is to change where those kWh go: away from a low-value export tariff and toward your own evening load. That means its value is almost entirely determined by your utility's export rules, not by the hardware brochure. Under California's Net Billing Tariff, where new 2025–2026 applicants receive roughly 3.7–4.6 ¢/kWh for exports against retail rates near 30 ¢, storage can recover a meaningful share of the lost export value. Under full-retail net metering the same battery mostly buys backup power, because exporting already earns retail. This calculator lets you set capacity and $/kWh, then compare the 25-year result with the battery field set to zero.
Your inputs
Change any default to match your bill, your quote and your utility tariff.
Household and price
Roof and solar resource
Money, financing and 25-year assumptions
Your estimate
Federal residential credit (2026)
$0.
Itemized cost
Ownership comparison · 25-year net
| Cash purchase | — |
|---|---|
| Loan (after payments) | — |
| Lease / PPA (no upfront) | — |
| Loan monthly payment | — |
The cash and loan rows both exclude any federal credit. A third-party owner, not you, may claim section 48E.
Environmental scale
| CO₂ avoided in year one | — |
|---|---|
| Mature-tree equivalent | — |
| Gasoline car miles | — |
Uses 0.855 lb CO₂/kWh (U.S. grid average), 48 lb/tree/year and 0.89 lb/mile.
25-year cumulative net cash flow
Sensitivity to utility rate escalation
| Annual escalation | Payback | 25-year net |
|---|
Year-by-year cash flow
| Year | Production kWh | Bill savings | Maintenance | Net | Cumulative |
|---|
How this is calculated
Base self-consumption is 45% of generation. Adding storage raises the modeled share according to 45% + 0.55 × battery kWh ÷ average daily usage, capped at 95%. Self-consumed kWh are valued at retail and the remainder at the export credit. Battery cost is capacity × $/kWh, added to gross cost, with $0 federal residential credit in 2026. The cash-flow model then applies degradation, escalation and maintenance over 25 years. Note that we do not model cycle life, round-trip losses, warranty expiry, replacement, or time-of-use peak shaving — all of which can move a real result substantially.
A worked example
On a net-billing tariff with a 4.2 ¢ export credit and a 29.75 ¢ retail rate, each kWh shifted from export to self-use is worth about 25.5 ¢. A 10 kWh battery cycling most of that daily could shift a few thousand kWh a year — several hundred dollars of annual value — against an installed cost around $7,000 at $700/kWh. That is a long standalone payback, often beyond the warranty term, even though it improves the total system economics. Set battery kWh to 0 and compare the '25-year net' line: that difference is what the storage is actually worth in this model.
What this tool does not do
It does not model backup resilience, outage duration, critical-load panels, generator interaction, time-of-use arbitrage, demand charges, battery degradation, or replacement cost. It cannot tell you whether a warm-climate garage installation is acceptable. Resilience has real value that a dollar-only model will understate.
Practical checks before you compare quotes
- Compare the 25-year net with and without storage before deciding.
- Ask for the usable kWh, not the nameplate capacity.
- Check the warranty's throughput and end-of-life capacity, not just years.
- If your utility offers full-retail net metering, buy a battery for backup — and price it that way.
Common mistakes
- Assuming a battery increases generation.
- Valuing backup power at zero in a wildfire or hurricane region.
- Ignoring replacement cost inside a 25-year horizon.
- Applying the old 30% credit to storage.
Planning estimates only — not a quote, tax advice, legal advice or financial advice. State benchmarks are not your utility tariff. Verify every incentive with the program administrator and get at least three written installer quotes.
Frequently asked questions
Is a battery worth it in 2026?
Financially, it depends on the export tariff. Under net billing with ~4–8 ¢ exports and 30 ¢+ retail, storage does real work. Under full-retail net metering, energy-arbitrage payback is effectively never — you are buying backup.
Did the federal battery credit also end?
Yes for homeowner-owned systems. The §25D credit covering standalone and solar-paired storage ended December 31, 2025. A third-party-owned battery may still be part of a §48E commercial credit claim by the provider.
How large should the battery be?
For backup, size to critical loads rather than whole-house load. For self-consumption, a capacity near your typical evening consumption is usually more efficient than a very large pack that rarely fills.
Does the model include SGIP or other battery rebates?
No. California SGIP and utility programs are income- and territory-dependent with waitlists. Enter a confirmed dollar amount in the utility rebate field.
Sources and further reading
- HelioCalc methodology and calculation kernel
- IRS FS-2025-05 (2026 federal credit rule)
- EIA Electric Power Monthly, Table 5.6.A, August 2026