A battery can help lower a household’s electricity costs. By connecting it to a virtual power plant, it can also – together with other connected batteries – generate revenue by selling flexibility services to several participants in the power system. Our calculations show that such combined use in the first half of this year could have roughly quadrupled profitability for Finnish customers compared with savings resulting only from the battery system’s built-in functionality.
When you buy a battery — whether it’s connected to CheckWatt or not — it often comes with built-in functionality that optimizes the usage of the battery based on the electricity consumption in your property. For example, the battery can store surplus solar electricity for later use. For customers with hourly electricity pricing, there is sometimes also an option to configure the battery to optimize usage based on electricity prices. At CheckWatt we call these use cases behind-the-meter services.
When you connect your battery to CheckWatt’s virtual power plant, you can combine these use cases with selling flexibility services, i.e. front-of-the-meter services. These include, among other things, ancillary services to help Fingrid maintain frequency in the power system, and local flexibility that allows the local grid owner to avoid peaks and connect more customers to the local grid.
Comparison of revenue from two batteries with different operating modes
Here we compare revenue for two batteries with different operating modes. In the first case — similarly to CheckWatt’s recommended operating mode, Currently Optimized — the battery delivered the ancillary service FCR-D while, within a limited span of the battery’s charge level, also storing solar energy and performing electricity arbitrage,charging at lower prices and using energy at higher prices.
In the second case, the battery’s entire capacity was used to store solar energy and perform electricity arbitrage. These services can often be done with the battery system’s built-in functionality, similarly to CheckWatt’s other operating mode, Self Consumption. In this scenario there is no delivery of ancillary services.
For both operating modes, we assume the system has perfect forecasting of electricity prices as well as hourly electricity consumption and production. The outcome is therefore idealized on the basis that the battery does what is most optimal each hour. We assumed the customer has hourly electricity pricing, a 10 kW solar system, consumes around 16,000 kWh per year, and pays average fees to the electricity retailer and grid company.
In practice, conditions for a specific household and potential savings will vary. For ancillary-service prices, we used market prices from Fingrid and deducted a safety margin in bidding as well as percentage fees to CheckWatt and the installer.
Earnings by operating mode during January-June 2025
| Battery system | Behind-the-meter services only | FCR-D + CheckWatt AI |
| 10 kW / 10 kWh | €169 | €668 |
| 10 kW / 20 kWh | €245 | €766 |
Price development on the ancillary service markets
CheckWatt continuously works to add more services to our virtual power plant and to optimize usage of a battery as market prices and regulations develop.
The clearest trend in the Finnish ancillary services markets in the first half of the year is the increasing market prices for mFRR (manual Frequency Restoration Reserve). mFRR addresses the difference between forecasts and actual outcomes in power trading — a need that grows in systems with a larger share of renewable generation which is harder to forecast. In Sweden, CheckWatt began to deliver mFRR in May. We are currently working to enable also Finnish customers to deliver the service.
Additional benefits for the electricity system
In addition to improved revenues, the services enabled through CheckWatt’s virtual power plant also create direct benefits for the electricity system. Ancillary services help manage imbalances and disturbances in the power system, and local flexibility is a precise tool for handling the most strained hours in the power grid.
In this way, they contribute to increased stability in the electricity system, reduce costs for grid expansion, enable the continued growth of affordable renewable electricity generation, and facilitate society’s electrification which is necessary to transition away from fossil fuels.
