Solar Battery Calculator (USA)
Size a home battery and see what it actually returns. Get your net cost after the federal tax credit, how long the battery runs your critical loads in an outage, annual bill savings, and the year you break even.
| Yr | Rate | Usable kWh | Bill savings | Annual total | Cumulative net |
|---|---|---|---|---|---|
| Calculate to see schedule | |||||
How to Use the Solar Battery Calculator
Size a home battery and see what it returns — net cost after incentives, backup runtime, bill savings, and the year you break even — in four steps.
Enter your home energy use
Set monthly usage in kWh or dollars, your electricity rate, and the share of that usage you want backed up. Add how often outages hit, how long they last, and what an hour without power costs you.
Configure the battery
Choose the primary purpose — backup, solar self-consumption, or time-of-use shifting — then set nominal capacity, usable depth, round-trip efficiency, and warranty cycles and term.
Add costs & incentives
Enter cost per kWh or paste a total quote, set the federal tax credit and any state or utility rebate, then choose the analysis period, rate increase, and yearly capacity degradation.
Read your result & save it
See net cost after incentives, backup runtime for your critical loads, annual savings, payback, levelized cost of storage, and a year-by-year schedule. Then download the branded PDF.
What’s Included
Everything you need to judge a home battery on both fronts — resilience during outages and dollars on the bill.
Net cost after incentives
Takes your gross install cost — from a quote or capacity times cost per kWh — and nets out the federal credit and any rebate to show what you actually pay.
Three operating modes
Model backup power, solar self-consumption under net billing, or time-of-use bill shifting — each with the right savings math instead of one generic formula.
Backup runtime for your loads
Works out how many hours the usable capacity runs your critical load, and whether that covers a typical outage — the number most sizing tools skip.
Usable capacity & losses
Separates nameplate from usable depth and applies round-trip efficiency, so the energy you can actually count on is never mistaken for the label on the box.
Degradation & service life
Fades capacity each year and caps life by warranty cycles and term, so the projection reflects a battery that ages rather than one that never wears out.
Levelized cost, schedule & PDF
Reports payback, ROI, and a levelized cost per kWh stored, flags the break-even year in a year-by-year schedule, and downloads a branded two-page report.
By the Numbers
A quick snapshot of what this calculator covers under the hood.
backup · solar · TOU
editable
per kWh, editable
with degradation
no sign-up needed
Built for the Question “Is a Battery Worth It?”
Whether you want backup for outages, more value from your solar, or savings from a time-of-use rate, the calculator sizes the return.
Outage-prone homeowners
Tired of losing power? Set your critical load and typical outage length to see how many hours a battery keeps the essentials running — and whether it covers a full outage.
Solar owners under net billing
Exporting solar for pennies? A battery lets you use that energy at retail instead. The self-consumption mode shows the gap it closes between export credit and your rate.
Time-of-use bill shifters
On a plan with steep peak rates? Charge off-peak and discharge on-peak. Enter both rates and your cycles per year to see what the daily spread is worth.
Size a Battery That Pays Off
Seven habits that make your numbers realistic — and keep expectations honest.
- 1Set an honest critical load share. Backing up the whole house drains a battery fast. Target the essentials — fridge, lights, internet, well pump, maybe one AC zone — and your runtime estimate becomes realistic instead of aspirational.
- 2Work from usable capacity, not nameplate. A battery only delivers its depth-of-discharge times its round-trip efficiency. The usable and delivered figures are what actually run your house, so watch those, not the label.
- 3Don’t ignore round-trip losses. Every kWh you store loses roughly 8–14% coming back out. Leaving efficiency at 100% overstates both backup runtime and bill savings, so use the real figure from the spec sheet.
- 4Under full net metering, expect little bill savings. If your utility credits exports at your retail rate, a battery has almost no arbitrage to capture — its value is backup and resilience. The savings case strengthens under net billing or time-of-use plans.
- 5Match the mode to your rate plan. Choose self-consumption if you export solar cheaply, time-of-use if you have a big peak-to-off-peak spread, and backup-only if resilience is the whole point. The right mode changes the answer.
- 6Confirm current tax-credit and rebate eligibility. Incentives shift, and the federal picture changed for 2026. Set the credit field to what actually applies to your purchase, and add any state or utility rebate you’ve confirmed.
- 7Account for degradation and warranty limits. Batteries fade a couple of percent a year and are warrantied for a set number of cycles. Entering both keeps the later years of the projection from overstating what an aging pack delivers.
Frequently Asked Questions
Answers to the most common questions about sizing a home battery and what it’s worth.
How long will a home battery run my house?
It depends on how much of the house you back up. Runtime is the battery’s usable, deliverable energy divided by your critical load. A 13.5 kWh battery with 95% usable depth and 90% round-trip efficiency delivers about 11.5 kWh; if your backed-up loads average 0.5 kW, that’s roughly 23 hours, but if you back up the whole house at 2 kW it’s closer to six. This calculator asks for your critical load share and average draw, then reports the runtime and whether it covers a typical outage — the honest answer instead of a single headline number.
What’s the difference between the three operating modes?
They match how the battery earns its keep. Backup only assumes the battery sits charged for outages, so its return comes from the value of avoided outage time. Solar self-consumption captures energy your panels would otherwise export cheaply and lets you use it at your retail rate — the savings are the gap between your rate and the export credit. Time-of-use shifting charges when power is cheap off-peak and discharges during expensive on-peak hours, so savings come from the price spread and how many cycles you run. Pick the one that describes your situation and the math changes to suit.
Will a battery actually lower my electricity bill?
Sometimes a lot, sometimes barely — it hinges on your rate structure. If you’re on full retail net metering, exported solar already earns your full rate, so a battery has almost nothing to arbitrage and its value is mostly backup and resilience. Under net billing, where exports pay only a few cents, storing that energy to use at retail can save real money. On a time-of-use plan, the peak-to-off-peak spread is the lever. Run the mode that matches your plan and the calculator shows the bill savings honestly rather than assuming a battery always pays.
What are usable depth and round-trip efficiency?
They’re the two haircuts between the number on the box and the energy you actually get. Usable depth, or depth of discharge, is how much of the nameplate capacity the system will draw down — modern lithium batteries allow 90–100%. Round-trip efficiency is energy out divided by energy in after inverter and conversion losses, typically 86–92%. A 13.5 kWh battery at 95% depth and 90% efficiency delivers about 11.5 kWh per cycle, not 13.5. The calculator applies both so runtime and savings reflect real, deliverable energy.
Is there still a federal tax credit for home batteries?
The federal picture changed, so confirm your own eligibility with a tax professional before relying on a number. The 30% Residential Clean Energy Credit (Section 25D) that covered owned solar and battery storage expired for systems placed in service after December 31, 2025, so a battery you buy with cash or a loan in 2026 no longer qualifies for that credit. Third-party-owned systems on a lease or PPA can still tap a federal credit on the installer’s side, passed through as lower payments, and several states and utilities run their own battery rebates. In the calculator, set the federal tax credit field to what actually applies to your purchase — for a 2026 cash or loan buy that’s 0% — and add any confirmed rebate.
How do payback and levelized cost of storage work?
Payback tracks your yearly savings — bill savings plus any outage value — against the net cost until they’ve repaid it; the year-by-year schedule flags the break-even year, and savings fade as capacity degrades and grow as rates rise. Levelized cost of storage divides the net cost by the total energy the battery delivers over its life, giving a cents-per-kWh figure you can compare against what you’d otherwise pay the utility. If that levelized cost sits below your rate, the stored energy is cheaper than grid power; if it’s above, the battery’s case rests more on backup value than on bill arbitrage.