Your electricity system consists of different parts. For example: solar panels, batteries, your central electricity supplier and your electric car. The current between these elements varies and must therefore be regulated.

Your system consists of an electricity grid connection that sometimes supplies cheap and sometimes expensive power. You want to charge your power storage system when the sun is shining and use it when power is expensive. If your electricity network fails, the power in your storage must be used immediately and without disruption. If the sun shines too little, your electricity storage must be filled when the power is cheapest. If you are completely off-grid and there is no sun and the electricity storage is empty, the generator must be started. If there is too much capacity in the summer and the storage is full, you preferably want your car to be charged because returning power to the central electricity grid yields little.