Three names sold as if they were the same thing, and they are not. Only one actually stores energy: the physical battery. The ‘virtual battery’ is an accounting entry with your supplier, and compensation is the discount set by RD 244/2019. Here is each one, plainly, as part of the solar panel study we do house by house.
The key difference: a physical battery is your own equipment, the ‘virtual battery’ is a commercial product from your supplier, and simplified compensation is the legal framework that applies by default. They do not compete on equal terms: the first two sit on top of the third.
A unit in your home that stores real kWh.
You store the energy you do not use at midday and use it at night. It is yours: it works with any electricity supplier and stays with you if you switch company. With the backup option it can also keep your lights on during a power cut.
An accounting credit with your supplier. There is no equipment.
The company records the value of the surplus not offset within the month and deducts it from later bills. It usually comes with a lock-in period, fees or terms that the company itself sets and can change. It can suit some people, but sign knowing what it is.
What RD 244/2019 sets out for installations up to 100 kW.
Your surplus is deducted from each month's bill, with a cap: the discount never exceeds the value of the energy you consumed that month. No money is paid out. At most, the energy term drops to zero. What each kWh is worth depends on your tariff.
It is not a battery. It is an accounting wallet: the supplier records the value of your leftover surplus and deducts it from later bills. It stores no kWh, gives no power in an outage and is not yours. If it were called a ‘surplus piggy bank’, nobody would mistake it for equipment.
The company sets the terms. Lock-in periods, monthly fees, limits on how much you can accumulate, or what happens to the credit if you switch supplier: all of that is in the contract, and the company can change it under its own terms. With a physical battery you do not depend on that small print.
It can suit some profiles. A second home that exports a lot and consumes little, or a household not yet ready to invest in a battery, can get value from it. We do not dismiss it out of hand: we ask that you sign up knowing what it is, comparing the full offer and not just the name.
Before signing, look at the whole package. The price of the kWh they charge you, the price of the surplus they credit you, and the lock-in. Sometimes the ‘virtual battery’ comes with an expensive tariff that eats the benefit. In how to read your electricity bill we show you where to look.
Because the solar hours tend to be worth less and less. The more panels there are in the country, the more energy is left over at midday, and the further the price sinks just when you are producing. For many hours of the year, the midday kWh trades at very low values. Exporting cheap and buying dear at night is the worst of deals.
A battery turns that around: you store the kWh when it is worth little and use it when buying it is expensive. The market has already done this sum. According to UNEF, 61% of the households that installed solar in 2025 fitted a battery from the start, and residential storage nearly doubled in a year.
That does not make a battery compulsory. If your house consumes mostly during the day, it may not pay off for you yet, and we will tell you so just as plainly in the study. What each exported kWh earns today, supplier by supplier, is in our surplus tariff comparison.
If the grid goes down, your panels shut down too. That is the inverter's anti-islanding protection: it disconnects for the safety of the crews repairing the line. The blackout of 28 April 2025 showed it across the whole of Spain. Neither panels alone nor a ‘virtual battery’ give you power during an outage.
The only option that does is a physical battery with a backup function, installed with that function enabled and with the circuits chosen in advance: fridge, lights, router, whatever you decide to keep running. Not every battery has it and not every installation is wired for it. If it matters to you, it goes in the study and the system is sized for it.
No. It is a credit to offset against bills from that same supplier. It is not money in your account, and the terms for using it, accumulating it or keeping it if you leave are set by each company in its contract. Read them before signing, especially the lock-in period.
Yes, and it is the usual setup. You consume your own production first, the battery stores what is left over and, if you still export something to the grid, that remainder is offset on the month's bill according to your tariff.
On the open market, in 2026, most offers sit between 0.04 and 0.10 euros per kWh, with fixed-price offers commonly around 0.06. On the regulated PVPC tariff the price is hourly and follows the market. We compare offers on our surplus tariffs page.
Only if it is a battery with a backup function and the installation has been set up for it. Without that function, a grid outage shuts everything down, battery included, because of the inverter's anti-islanding protection. A virtual battery, not being equipment, gives you no power in any case.
Battery or not, and what size, is decided from your hour-by-hour consumption and your roof's real production. We do that calculation in the study, with numbers we hand you signed. If the sums do not favour you, you will see that in writing too.
A Captia Technology company. Chartered, qualified engineers.