Solar battery: calculate whether the extra investment makes sense
A battery can store solar power for later, when the house needs it. It does not increase the panels’ production. The calculator therefore examines the battery’s extra value by comparing the same installation and the same consumption with and without storage.
Worked example
- Nearest town: Aarhus
- Direction: South
- System size: 6 kWp
- Slope: 35 degrees
- System loss: 14 %
- Household consumption: 4,000 kWh/year
- Usable capacity: 5 kWh
- Max. charge and discharge power: 5 kW
- Overall efficiency: 90 %
- Price paid for electricity: 2.00 DKK
- Sale price: 0.50 DKK
- System price: 30,000.00 DKK
- Lifetime: 10 years
Added value of the battery
1,850 DKK per year
Charged 1,423.2555 kWh · delivered 1,280.93 kWh · loss 142.3256 kWh · payback about 16.2142 years
Even consumption over the day and one typical year from PVGIS (EU JRC); no degradation and no charging from the grid.
What is the stored electricity worth?
When electricity is stored, there is less to sell in the hour it is produced. Later the battery can replace a purchase from the grid. The difference between these values must cover losses, operation and the investment itself.
The battery’s capacity is not a measure of daily savings. It must also be charged with relevant surplus and discharged when there is a need. Power limits and reserve can limit the energy you actually shift.
How to use the battery calculator
Use the same starting point in both scenarios
Keep the same solar installation, household consumption and prices. Enter the battery’s usable capacity, efficiency and price including the necessary equipment. Add the expected lifetime and any replacement.
Example of losses in storage
If you store 10 kWh with a total efficiency of 90 per cent, at most 9 kWh can be delivered back under the simplified assumptions. The lost energy must be included in the economics, as must the value of the electricity you could otherwise have sold.
Look at both smaller and larger batteries. A larger store can cost more without being used correspondingly more. The result shows the economics of the chosen model; an installer must also assess the installation’s compatibility and the actual installation conditions.