Time of Use Battery Savings Calculator: What Peak Shifting Saves

A time of use battery savings calculator values each cycle as the peak-price power you avoid minus the cost of the energy you stored, then multiplies by cycles per year. With the defaults, a 13.5 kWh battery shifting energy from 8¢ to 45¢ per kWh 300 times a year saves about $1,316 a year and pays back $16,000 in about 12.2 years.

How to use the time of use battery savings calculator

1. Usable battery capacity. From the spec sheet. Default 13.5 kWh, the median home battery installed with solar in 2025 (LBNL, 2026 (opens in a new tab)).
2. Peak price you avoid. Your evening on-peak rate. Default 45¢ per kWh.
3. Value of the energy you store. The off-peak price if you charge from the grid, or the export credit you give up if you charge from solar. Default 8¢.
4. Full cycles per year. Default 300. Weekday-only peak plans give fewer.
5. Battery price. Installed. Default $16,000.
6. Advanced: Round-trip efficiency (90%) and Battery rebates ($0).

The results show yearly savings, savings per cycle and simple payback. A break-even line chart and a 15-year cash-flow schedule (with rates rising 3% a year and battery capacity falling 2% a year) can be downloaded as CSV. The scenario table compares your inputs, weekday-only cycling at 250 cycles, and a peak price 10¢ higher.

How the calculation works

Energy delivered   = usable kWh × round-trip efficiency
Savings per cycle  = delivered kWh × peak price − usable kWh × stored-energy value
Yearly savings     = savings per cycle × cycles per year
Simple payback     = (battery price − rebates) ÷ yearly savings
15-year schedule   = yearly savings × 1.03^(year−1) × 0.98^(year−1), added to −net cost

Assumptions that match the code:

• Every cycle is a full cycle at the same prices.
• All delivered energy displaces peak-price purchases; no exports at peak are modeled.
• Simple payback uses first-year savings only; the schedule adds the fixed 3% rate growth and 2% capacity fade.
• No payback is shown if savings per cycle are zero or negative, which happens when the price gap is too small to cover efficiency losses.

Worked example

Default inputs: 13.5 kWh, 45¢ peak, 8¢ stored-energy value, 90% round trip, 300 cycles, $16,000, no rebates.

• Delivered: 13.5 × 0.90 = 12.15 kWh, worth 12.15 × $0.45 = $5.47.
• Stored energy cost: 13.5 × $0.08 = $1.08.
• Savings per cycle: $4.39. Yearly savings: $1,316. Simple payback: 12.2 years.
• In the 15-year schedule, the running total is still −$2,267 after year 10, turns positive in year 12 and reaches about $5,097 after year 15.

Second example, charging from solar under net billing: suppose your plan's peak price is 38¢, you give up a 4¢ export credit to store solar, you cycle 330 days a year, and the battery costs $15,000 with a $1,000 rebate.

• Savings per cycle: $4.08; yearly savings: $1,345.
• Simple payback: 10.4 years on $14,000 net; the 15-year schedule ends about $7,565 ahead.

A cheaper stored-energy value can matter as much as a higher peak price.

What your result means

If simple payback is well inside the battery warranty, shifting alone may justify it. If payback runs past the warranty, the battery is mostly a backup purchase, and bill savings are a bonus. Our guide on whether solar batteries are worth it weighs both.

In California, test the full solar-plus-battery picture with the NEM 3.0 calculator and read our California NEM 3.0 guide. For outage needs, size storage with the solar battery size calculator.

Rules that change the answer

• California Net Billing Tariff. Since April 15, 2023, new PG&E, SCE and SDG&E solar customers earn hourly avoided-cost export values and must take a high-differential electrification time-of-use rate (CPUC D.22-12-056 (opens in a new tab)). Low midday export values make the stored-energy value small, which helps batteries.
• Other time-of-use solar tariffs. Some utilities outside California also pair new solar customers with time-of-use rates. Check your utility's solar tariff for its peak hours and export rule.
• Full retail net metering (for example, Florida's investor-owned utilities) leaves little price gap to capture, so shifting saves little.
• Federal credit. As of October 2026, 25D does not cover batteries installed after December 31, 2025 (IRS (opens in a new tab)).
• Rebates. California's SGIP residential budgets were mostly closed or waitlisted as of October 2026 (SGIP (opens in a new tab)).
• Backup reserve. Keeping part of the battery for outages reduces usable capacity for shifting; see our home battery backup guide.

Common mistakes

• Using the retail rate as the stored-energy value when charging from solar under net billing.
• Assuming 365 cycles when peaks only apply on weekdays.
• Forgetting round-trip losses.
• Using total capacity instead of usable capacity.
• Comparing payback with the panel warranty rather than the battery warranty.

Limits of this calculator

This is an educational estimate. It assumes one peak price, one stored-energy value and identical cycles all year, and it ignores demand charges, seasonal rate changes, partial cycles and how your utility credits battery exports. Check your exact rate schedule and the battery's warranty terms before relying on the result.