Battery Payback Calculator

This calculator analyses your energy usage and estimates the payback period and savings for a home battery system based on your half-hourly electricity usage data and your chosen battery configuration.

Extra Details, Disclaimer and Privacy

What it does: The calculator uses your actual half-hourly readings for the last 12 months calculate how quickly a specific battery in a residential ESS setup will earn its money back. It provides some basic analytics of your provided energy readings. It presumes charging the battery from the grid at off-peak rates, and discharging during peak-rate periods to offset your most expensive usage. It takes into account any days where your usage is greater than the battery capacity and you would end up drawing from the grid to balance. You can input your expected annual usage growth. All calculations are based on your real usage patterns, so results are tailored to your home.

What it doesn't do: It does not consider any additional savings from solar generation or export tariffs. It doesn't consider whether your specified inverter has enough capacity to cope with the load from your house.

Defaults: The default values are for a Victron Multiplus-II inverter, a Cerbo GX, typical accessories, and a reasonable installation cost. The default tariff is set for Intelligent Octopus Go. The default batteries are three options from Fogstar Energy, which seem to have an incredible RoI and a 20kWh libbi option from MyEnergi

Disclaimer: This calculator is for informational purposes only and does not guarantee actual savings or payback periods. Actual results may vary based on changes in energy prices, usage patterns, and other factors.

Privacy: This web page does not store or collect ANY data. All calculations are performed in your browser, and no information is transmitted or stored. It's also open source, so you can review the code here. If you have any concerns, questions or suggestions, you can drop me an email.

Tariff Rates (per kWh)

Peak/Off-Peak Window

Annual Usage Growth

Battery Configurations

What do these terms mean?
Capacity (kWh)

The total energy the battery can store, measured in kilowatt-hours.

Capacity (Ah)

The total charge the battery can store, measured in ampere-hours. This is used to calculate how long it will take the battery to charge. Sometimes you have to dig into the datasheet to find this.

Charger Rating (A)

The maximum current (in amps) the battery can be charged at. Combined with the capacity in Ah, this tells us whether you'll be able to charge your battery within the offpeak window. This could be from the inverter or the battery, use the lower one.

Rated Cycles

The number of full charge/discharge cycles the battery is rated for.

Warranty (years)

The manufacturer's warranty period for the battery.

Cost (£)

The purchase price of the battery.

Extra Costs (£)

Any additional costs associated with this battery (e.g. installation, inverter, accessories, etc).

Battery 1
Battery 2
Battery 3
Battery 4

Energy Usage CSV

Please upload a CSV file containing the last full 12 months of half-hourly readings exported from Octopus Energy. This can be downloaded from the bottom of the MyEnergy page on your Octopus account.
The file must have the following columns:

Consumption (kwh), Start

Example:
Consumption (kwh), Estimated Cost Inc. Tax (p),Start,End
0.128000, 2.86, 2024-07-01T00:00:00+01:00, 2024-07-01T00:30:00+01:00
0.158000, 3.53, 2024-07-01T00:30:00+01:00, 2024-07-01T01:00:00+01:00
0.108000, 1.53, 2024-07-01T01:00:00+01:00, 2024-07-01T01:30:00+01:00
...
Each row should represent a single half-hour period.