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TOU Battery Optimizer Calculator

Enter your Time-of-Use rate schedule and battery size — get optimal charge/discharge timing, daily savings, and battery payback period.

TOU rate schedule
¢/kWh
¢/kWh
¢/kWh
Battery & home
kWh
%
kW
kWh/day
TOU optimization results
Save $5.63/day — $2055/year
24-hour TOU schedule
0
6
12
18
Peak (5h) 51¢Off-peak (8h) 12¢Shoulder (11h) 24¢
Usable battery capacity12.2 kWh
Charge during off-peak13.5 kWh
Discharge during peak12.2 kWh
Peak load shifted5.2 kWh
Daily cost — without battery$6.41
Daily cost — with battery$0.77
Monthly savings$168.94/mo
Annual savings (arbitrage)$741/yr
Annual savings (solar offset)$1314/yr
Est. battery cost (LFP)$10,800
Battery payback period5.3 yrs
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How to Use This Calculator

Enter your TOU rate schedule

Find your Time-of-Use rates on your utility's website or on your monthly bill. Enter the peak, off-peak, and shoulder rates in cents per kWh. Then set the start and end hours for each period. Most utilities define peak as 4pm–9pm on weekdays; off-peak as 11pm–7am. If your plan has only two tiers, enter your standard rate for the shoulder field.

Enter your battery and home details

Enter your battery's nameplate capacity in kWh (not usable capacity — the calculator applies round-trip efficiency automatically). Enter round-trip efficiency: LFP batteries like Powerwall 2 and Enphase IQ Battery run 90–92%; older lead-acid systems run 70–80%. If you have solar, enter your system size — this adds daytime self-consumption savings on top of the arbitrage calculation.

Read the results

The 24-hour color-coded timeline shows when your battery should charge (green = off-peak) and discharge (red = peak). The results show daily and annual savings from shifting load out of peak hours, plus solar offset savings if applicable. The battery payback period assumes a $800/kWh all-in installed cost for LFP — adjust mentally if you paid more or less.

The Formula

Usable kWh = Battery Capacity × Round-trip Efficiency Charge kWh = min(Battery Capacity, Off-peak Hours × 3.3kW charger rate) Discharge kWh = min(Usable kWh, Charge kWh × Efficiency) Peak Load Shifted = min(Discharge kWh, Peak Consumption) Daily Arbitrage Saving = Shifted kWh × (Peak Rate − Off-peak Rate) Daily Solar Saving = Solar Daily Gen × Daytime Offset Rate Annual Savings = (Daily Arbitrage + Daily Solar) × 365 Battery Payback = Battery Cost ($800/kWh) ÷ Annual Savings

The model charges the battery at a typical 3.3kW AC rate during off-peak hours, then discharges during peak hours to serve home loads that would otherwise draw from the grid at the peak rate. The spread between peak and off-peak rates is the arbitrage opportunity — wider spreads mean faster payback.

Example

Maria — PG&E E-TOU-C customer in Sacramento

Maria has a 13.5 kWh Powerwall 2 (90% efficiency) and a 6kW solar system. She's on PG&E's TOU-C plan: peak 51¢/kWh (4–9pm), off-peak 12¢/kWh (11pm–7am), shoulder 24¢/kWh. Her home uses 25 kWh/day.

Battery13.5 kWh Powerwall (90% RTE)
Peak window4pm–9pm at 51¢/kWh
Off-peak11pm–7am at 12¢/kWh
Solar6 kW system

Optimal schedule

Charge from grid11pm–7am at 12¢ → 12.2 kWh
Discharge to home4pm–9pm, ~11 kWh at 51¢
Peak load shifted~4.3 kWh
Daily arbitrage saving$1.76/day
Annual battery savings~$640/yr
Annual solar savings~$350/yr
Battery payback~10.9 years

CA's wide peak-to-off-peak spread (39¢ differential) makes TOU arbitrage genuinely worthwhile. Maria's Powerwall pays for itself in ~11 years on arbitrage alone — add solar self-consumption savings and backup value, and the economics become much more compelling.

FAQ

TOU (Time-of-Use) arbitrage means charging your battery when electricity is cheap (off-peak, typically overnight) and discharging it to power your home when electricity is expensive (peak, typically 4–9pm). The profit is the spread between peak and off-peak rates, minus round-trip efficiency losses. On PG&E's TOU plan, that spread is 39¢/kWh — one of the highest in the country. On AZ SRP, the spread is only 13¢/kWh, making arbitrage less attractive.
The larger the spread between peak and off-peak rates, the more money you make per kWh shifted. California utility plans (PG&E, SCE, SDG&E) have the widest spreads — up to 39¢/kWh on PG&E E-TOU-C, making them the best for arbitrage. New York ConEd offers up to 25¢ spread. Texas and Arizona plans typically have smaller spreads (10–17¢) but TOU batteries still provide backup value and solar optimization benefits that improve the economics.
Yes, significantly. With solar, the battery has two revenue streams: (1) arbitrage — charge during off-peak grid hours, discharge during peak; (2) solar self-consumption — store excess midday solar generation that would otherwise be exported at low net-metering rates, then use it during peak hours to avoid buying expensive peak power. California's NEM 3.0 policy, which pays very low export rates (~5¢/kWh), makes solar + storage self-consumption especially valuable since storing solar for peak self-use is worth 4–10× more than exporting.
Round-trip efficiency (RTE) is the percentage of energy you get back out of a battery compared to what you put in. A 90% RTE battery loses 10% as heat during each charge/discharge cycle. For arbitrage, this means you need the peak-to-off-peak rate spread to exceed your loss rate. If off-peak is 12¢ and RTE is 90%, the effective cost of off-peak energy delivered is 12¢/0.9 = 13.3¢. You still profit as long as peak rates exceed 13.3¢ — which they do in all major TOU markets.
Yes — most modern home batteries have built-in TOU optimization modes. Tesla Powerwall uses "Time-Based Control" and can download your utility's rate schedule automatically. Enphase IQ Battery uses "Cost Savings Mode" and integrates with utility APIs. SolarEdge Home Battery and Generac PWRcell have similar features. You enter your peak/off-peak hours and the system automatically charges and discharges at optimal times. Some systems (Tesla, Enphase) also support dynamic rate APIs that adjust in real time.

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