The paradox of seasonal storage
A home battery shifts daytime solar surplus to the evening or night. Its capacity and losses make it short-term storage, not seasonal storage. Winter production depends on the roof and weather; a large battery does not create missing energy.
Step 1: Calculate your nightly consumption
Record consumption by hour rather than promising self-sufficiency from March to October. Example: 6 000 kWh/year with 40% consumed in the evening and at night gives 2 400 kWh/year, or about 6.5 kWh per day as an annual average. A usable capacity of 7 kWh can be a starting point to test, including losses, reserve and seasonal variation.
Step 2: Check production surplus
Measure the surplus actually fed into the grid through metering or monitoring. If a day provides only 3 kWh of surplus, that surplus alone cannot fill a 10 kWh battery. Simulate charging and discharging over the year to estimate useful cycles and savings.
The quick rule: ratio 1:1 and its adaptation
An initial guide of 0.8 to 1 kWh per kWp would give about 8 to 10 kWh for 10 kWp of panels. Adjust this using the hourly profile. Thresholds of 1.5 kWh/kWp or 0.5 kWh/kWp are not universal limits: the contract, uses and charging source can change the result.
The alternative: Storage in other forms
Before adding storage, compare hot-water control and vehicle charging during solar production. Thermal storage depends on volume and permitted temperatures; follow the system instructions. Energy stored in the car is for driving and powers the home only if the vehicle and installation explicitly support that function.