Home Battery Storage Savings Calculator

How it is calculated

The model is day/night arbitrage: charge at the off-peak price, discharge at the peak price. Enter the usable capacity in kWh, the round-trip efficiency in percent, the number of full cycles per year (not per day), the peak and off-peak prices per kWh, and the battery cost. To deliver 1 kWh at peak you must buy 1 / efficiency kWh at night, so saving per cycle = capacity × (peak price − off-peak price / efficiency). Then annual saving = per cycle × cycles and payback = cost / annual saving in years. If the spread is too small to cover the losses the tool returns no result. Solar self-consumption, degradation, battery lifetime, standby losses and tariff changes are not modelled.

Common mistakes

• Entering cycles per day (such as 1) instead of per year: the field is yearly, so 1 gives about $2 of saving a year and an absurd payback.
• Entering the nameplate capacity instead of the usable capacity: batteries cannot be fully discharged, so the saving is overstated.
• Entering efficiency as 0.9: it is read as 0.9 %, which makes the saving negative and the result empty.
• Using the average tariff instead of the actual peak and off-peak prices: the saving depends on the gap between them.
• Ignoring degradation and the warranty period: a payback close to the battery's lifetime means it may never pay for itself.