The classic Simplified Surplus Compensation allows the electric company to pay you a small amount for the surplus kilowatts you inject into the grid, deducting them from your monthly bill. The problem is that this discount has a legal cap: the monthly energy cost cannot be negative and, moreover, it does not allow for deducting fixed quotas (tolls and basic electricity taxes).
To solve this, what the sector calls the Virtual Battery (or solar wallet) has emerged, a commercial service offered by various energy retailers.
What exactly does it consist of?
Imagine that, because you are traveling for a week, your panels generate much more energy than you consume. With the virtual battery, the economic value of all that injected electricity is accumulated in euros in a balance or "virtual wallet." At the end of the month, the accumulated balance is used not only to reduce the consumed energy cost to zero but also to pay almost the entire fixed term. Thanks to this, many installations manage to issue electric bills where they pay literally 0 euros.
Furthermore, if you own a second residence sharing the same electric utility, the balance generated by your primary home's panels can be used to also reduce the vacation home's tariff.