Self-consumption optimization
Use more of your PV power yourself instead of feeding it in cheaply.
The battery buffers PV surplus instead of exporting it to the grid at the lower feed-in tariff, and releases it again when the purchase price is higher than the feed-in tariff.
Example: 50 kWp PV system (around 50,000 kWh of yield per year), self-consumption rate raised from 25% to 65%. That is about 20,000 kWh you use yourself instead of feeding them in. At a purchase price of 25 ct/kWh against a feed-in tariff of 6 ct/kWh (19 ct difference) that is around €3,800 of additional savings per year.
This way you use a much larger share of your PV power yourself instead of handing it over at the lower feed-in tariff.