See how much a home battery saves by storing cheap off-peak (or solar) energy and discharging during expensive peak time-of-use hours. Calculate daily and annual energy-arbitrage savings, account for round-trip losses, and find your battery's payback period.
Peak-shaving & arbitrage savings
Many U.S. utilities now charge time-of-use (TOU) rates — electricity costs far more during peak evening hours than overnight. A home battery (like a Tesla Powerwall, Enphase, or LG unit) lets you store cheap energy — either from your solar panels or low-cost off-peak grid power — and discharge it during expensive peak hours, shaving the priciest kilowatt-hours off your bill. This is called energy arbitrage or peak shaving.
The savings per cycle equal the peak energy you avoid buying, minus the cost (and round-trip losses) of charging the battery. Because batteries are only about 85–95% efficient, you need to store a bit more than you get back. With a 13.5 kWh battery cycled once daily, a $0.45 peak vs $0.12 off-peak spread can save several hundred dollars a year. This calculator factors in usable depth of discharge, round-trip efficiency, and your local rates to show daily savings, annual savings, and how long the battery takes to pay for itself.
The bigger the rate spread, the more a battery saves. Steep TOU plans make storage far more valuable.
Batteries return ~85–95% of stored energy. The calculator accounts for the energy lost charging.
Charging from your own solar at near-zero cost maximizes the spread and the savings.
The federal residential clean-energy credit and state/utility rebates cut battery cost and shorten payback.
As more American utilities roll out time-of-use (TOU) pricing, "is a Tesla Powerwall worth it," "home battery payback," and "solar battery savings calculator" have become top searches for U.S. homeowners. A home battery stores cheap off-peak or solar energy and discharges it during expensive peak hours, shaving the priciest kilowatt-hours off your bill. This calculator quantifies that energy arbitrage — daily savings, annual savings, and how long the battery takes to pay for itself.
Savings depend on your peak-to-off-peak price gap, round-trip efficiency, and how often you cycle. In high-rate states like California (and on steep TOU plans elsewhere), a battery paired with solar and the 30% federal residential clean-energy credit can deliver a compelling payback. Enter your real rates to see if it pencils out.
A 13.5 kWh battery cycled once daily on a plan with a $0.45 peak and $0.12 off-peak rate (90% efficiency) saves roughly $1,560 per year by discharging during peak hours. Against an $11,000 installed cost after incentives, the payback is about 7 years — shorter where the peak/off-peak spread is bigger.
U.S. homeowners with solar panels or time-of-use electricity plans evaluating a home battery (Tesla Powerwall, Enphase, LG) for energy arbitrage, peak shaving, and backup power.
Sizing home battery storage starts from what you actually need it to do, and the two goals demand very different capacities. Backup during an outage requires covering only essential circuits for a set number of hours. Time-shifting solar, by contrast, requires storing the daytime surplus for evening use, which is usually a larger figure. Nameplate capacity overstates what is available: usable energy is reduced by depth-of-discharge limits protecting battery life, and again by round-trip efficiency losses of roughly 10% converting in and out of storage.
Usable capacity = Nameplate × depth of discharge × round-trip efficiencyBackup sizing = essential load (kW) × hours requiredSolar shifting = daily surplus generation not consumed on siteBatteries needed = requirement ÷ usable capacity per unitwhere:
Assumptions: Capacity in kWh is energy; the inverter's kW rating limits how much can be drawn at once. A large battery behind a small inverter cannot start a well pump or air conditioner regardless of stored energy.
Find the real usable capacity, then test it against both use cases.
Result10.94 kWh usable — about 14.6 hours of essential loads
The gap between 13.5 and 10.94 kWh is why sizing from nameplate capacity leaves people short. Note also the inverter constraint: a 5 kW inverter cannot run a 3 kW air conditioner plus a well pump surge, however much energy is stored behind it.