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If you have solar and a time-of-use (TOU) rate, the best battery is the one that lets you schedule when it charges and discharges, delivers enough continuous power for your evening loads, and fits your utility’s export and interconnection rules. The Tesla Powerwall 3, FranklinWH aPower 2 and Enphase IQ Battery 10C are the three we compare, using manufacturer documents and published analyses as of October 24, 2026. We did not test them. See how we pick products.
Before you buy for the spread alone, read the math below. In our worked example it is real but small.
What a TOU battery earns
Our time-of-use guide uses Idaho Power’s 2026 optional TOU rate for on-site generation customers: a summer on-peak kWh costs 29.9185¢ and an off-peak kWh costs 7.4797¢. It also uses a midday export value of 3.4¢ per kWh for illustration. We rely on that guide for the tariff figures and did not re-pull the tariff today.
Formula (our math): value per stored kWh = (round-trip efficiency × on-peak price) − (price of the energy you stored).
Inputs: 90% round-trip efficiency (an assumption, not a manufacturer figure), 29.9185¢ on-peak, 3.4¢ for the solar kWh you give up exporting.
- 0.90 × 29.9185¢ = 26.93¢
- 26.93¢ − 3.4¢ = 23.53¢ per stored kWh
Scale it (illustration): shifting 10 kWh a day on summer on-peak days. Idaho Power’s summer period runs June 1 to September 30, Monday to Saturday except holidays. By our count that is about 103 days in 2026 (122 days, minus 17 Sundays, minus July 4 and Labor Day).
- 10 kWh × $0.2353 = $2.35 a day
- $2.35 × 103 days = about $242 for the summer
That ignores the rest of the year, battery degradation and any demand charges. Against installed prices in the five figures (see below), TOU arbitrage alone is a slow payback, which is why we do not pitch a battery as a bill-saver by itself. See our payback guide for how to build your own estimate.
Quick picks
| Best for | Battery | Capacity | Continuous power | Warranty |
|---|---|---|---|---|
| Most output for evening loads | Tesla Powerwall 3 | 13.5 kWh (nominal) | 11.5 kW | 10 years |
| Big single unit to cover a long peak window | FranklinWH aPower 2 | 15 kWh | 10 kW | 15 years / 60 MWh |
| Enphase microinverter homes | Enphase IQ Battery 10C | 10 kWh | 7.08 kW | 15 years / 6,000 cycles |
Sources: Tesla, FranklinWH, Enphase. A fuller comparison is in Powerwall vs Enphase vs FranklinWH.
What to look for on a TOU rate
Schedule and mode control
You need to tell the battery when to charge and when to hold energy for the peak. We did not verify each manufacturer’s TOU scheduling features in the documents we read, so ask your installer to show the app or controller settings for your exact tariff before you sign.
Enough kW for the evening
Peak windows are when ovens, dryers, air conditioners and EV chargers run together. If continuous output is lower than your simultaneous load, the grid covers the difference at peak prices. Compare the continuous kW above to your own load.
Enough usable kWh for the window
Idaho Power’s summer on-peak runs 7 p.m. to 11 p.m., four hours. Hours covered = usable kWh ÷ average kW. A 2.5 kW evening load over four hours needs 10 kWh.
Export rules
Some utilities pay different export credits by hour. Hawaiian Electric’s credits in our TOU guide are 13.5¢ for daytime exports on Oahu and 32.9¢ from 5 p.m. to 9 p.m. Where evening exports pay well, discharging to the grid in the peak can beat self-use. Check your tariff and see export credit rates by utility and net metering by state.
Round-trip efficiency
Our example assumes 90%. We did not find a round-trip efficiency figure in the manufacturer documents we read for all three batteries, so treat 90% as an assumption and ask for the datasheet figure.
Product notes
Tesla Powerwall 3. 11.5 kW continuous, 13.5 kWh nominal, 10-year warranty, integrated solar inverter per Tesla’s pages, UL 9540 and related listings per the datasheet. Strength: output. Weakness: shortest warranty here. Approx. price: $998 per kWh (EnergySage, Apr 2026); about $15,000 median installed with solar (Solar.com, Sept 2026). Check price
FranklinWH aPower 2. 15 kWh, 10 kW, 15 years or 60 MWh, IP67. Strength: capacity for long windows. Weakness: UL listing not stated on the product page we read. Approx. price: $1,177 per kWh; about $17,250 median installed with solar. Check price
Enphase IQ Battery 10C. 10 kWh, 7.08 kW, 15 years up to 6,000 cycles. Strength: pairs with Enphase microinverters; modular. Weakness: lower output; highest per-kWh price in EnergySage’s table. Approx. price: $1,404 per kWh; about $14,250 median installed with solar. Check price
Price sources: EnergySage (updated Apr 29, 2026) and Solar.com (updated Oct 1, 2026, before incentives). Prices checked October 24, 2026.
Who should skip a battery for TOU savings
- Your peak and off-peak prices are close.
- Your peak window is short and your evening load is small.
- You already shift loads (laundry, dishwasher, EV charging) into cheap hours.
- Your utility is switching to a flat or net-billing structure that changes the value; check the latest rules.
Incentives
The IRS says the residential clean energy credit is not available for property placed in service after December 31, 2025. Utility demand-response or battery programs may still pay for discharge during grid events; ask your utility. Use Rates by State to find your state’s page.
Buying checklist
- Get your tariff’s hourly prices and your own hourly use from the utility.
- Estimate shiftable kWh per day by season.
- Confirm the battery can follow your schedule and your utility allows it.
- Compare continuous kW and usable kWh to your evening load.
- Ask for datasheet round-trip efficiency and warranty terms.
- Get three installed quotes and compute payback with your inputs.
Limitations
The Idaho example is an illustration, not a forecast; tariffs change, and our efficiency figure is an assumption. We did not verify each battery’s TOU features. This is not financial or tax advice.
Sources
- Time-of-Use Rates and Solar (Solar Examiner, Oct 8, 2026; Idaho Power and Hawaiian Electric figures)
- Tesla datasheet · FranklinWH · Enphase
- EnergySage · Solar.com · IRS
Frequently asked questions
Is a home battery worth it on a time-of-use rate?
It depends on the price gap between your cheapest and most expensive hours, how many days the gap applies, and the battery's cost. In our Idaho Power example the summer on-peak arbitrage is worth roughly $240 a year on 10 kWh a day, which on its own does not repay a typical installed battery. Backup value and other programs may change the answer.
What battery features matter most on a TOU rate?
The ability to schedule charging and discharging by hour, enough continuous power (kW) to cover your evening loads, enough usable energy (kWh) to last through the peak window, and compatibility with your utility's interconnection and export rules.
Should I charge my battery from solar or the grid?
Whichever costs less per stored kWh after efficiency losses. If exporting midday solar pays little, storing it is cheap; if grid off-peak power is cheaper than your export credit is worth, grid charging can also work, where your utility allows it. Check your tariff and interconnection agreement.
Are there federal tax credits for batteries on TOU rates?
The IRS says the residential clean energy credit is not available for property placed in service after December 31, 2025. State and utility programs may apply; confirm with your utility and a tax professional.
