Panels, solar battery and virtual battery: how to balance them
A system that really saves has three pieces: the panels, which produce; the solar battery at home, which moves the day's sun to the night; and the virtual battery, which saves the surplus in euros. None is enough on its own: a solar battery and virtual battery work better together, with the panels behind them. Here's what each one does and how to balance them to what you use.
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What's the difference between a solar battery and a virtual battery?
| Panels | Home battery | Virtual battery | |
|---|---|---|---|
| Stores | nothing | kWh | euros |
| Works | in the day | evening and night | sunny months |
| Saves you | daytime electricity | the expensive hours | the rest of the bill |
| Depends on | roof and consumption | what you use in the evening | the tariff |
Why do they need each other?
- The panels produce in the day, and in summer, too much. What you don't use at the time goes to the grid and is discounted from the bill. But the law sets a cap: the surplus can only discount what the energy you buy that month is worth (Royal Decree 244/2019, article 14, checked on 27/10/2026). In the sunny months it's easy to go over that cap, and what goes over is lost.
- The virtual battery saves what goes over the cap. With Naturgy's, for example, that surplus is credited at €0.06 per kWh before taxes, in a balance that pays your next bills (their website, checked on 27/10/2026).
- The home battery moves the midday sun to the evening and the night, when electricity is more expensive. But without a virtual battery, in summer it's worth little: compensation already brings the energy on the bill to zero, and storing more sun doesn't lower it further.
What does each combination do?
- Panels alone lower the bill by what you use while the sun is out. In summer, what goes over the legal cap is lost.
- Panels and a virtual battery: that surplus is saved in euros and pays the darker months, including the power charge and taxes. In the sunniest months, the bill can come out at zero.
- Panels and a home battery, without the virtual one: it saves less than it seems. In summer the surplus already goes over the cap, and storing more sun doesn't lower the bill; it works mostly in the darker months.
- All three together: the home battery covers the expensive evening and night hours all year, and the virtual one saves the summer surplus. That's why the home battery performs better with a virtual one behind it.
Month by month: who does what
- From November to March there's less sun and the house uses more: the surplus doesn't cover the month's energy. That's where the home battery makes the difference, skipping the expensive hours for you.
- From April to October there's sun to spare, and that's when the virtual battery works: it saves in euros what the law doesn't let you offset, and pays the power charge and taxes with it.
How long does the summer balance last? It depends on what you use and how many panels you have: it can last until October or November. With a home battery it lasts longer, because the house buys less in the expensive hours and spends less balance.
How do you balance them to your consumption?
The panels: the ones your consumption makes use of
Panels are sized to what your house uses in a year, counting what's coming (a car, a heat pump), so that there's a surplus in the sunny months to fill the virtual battery.
But more panels aren't always better. If the surplus is much more than what the house uses in the darker months, the balance grows without being spent, and a balance that isn't spent saves nothing.
The home battery: by what you use in the evening and at night
Its savings come from the expensive hours. With the home tariff (2.0TD), peak runs from 10:00 to 14:00 and from 18:00 to 22:00 on working days; with daytime sun, the one that matters is the evening. The more you use at that time and at night, the more it saves. Saturdays, Sundays and national holidays are off-peak all day: there it hardly counts.
If your tariff has no virtual battery, do the maths carefully: in summer, the home battery saves little.
The virtual battery: by the tariff
Not all tariffs have one, and not all work the same. Before choosing, check three things:
- whether the balance pays the whole bill, including the power charge and taxes, or only the energy;
- how much they pay you for the surplus;
- what happens to the balance if you change company or account holder. With Naturgy it resets to zero, and it expires five years after the last bill that made it grow.
And compare by the whole year's bill, not by what each piece saves: with a tariff without a virtual battery, the home battery can save more euros and still leave you with a more expensive year.
What about the income tax deduction?
A home battery is included in the energy-efficiency deduction for the work if it goes with new panels: up to 60 % in a house, if you're the owner and the energy certificate after the work lowers non-renewable primary energy use by at least 30 %, or leaves the house in band A or B (Spanish Tax Agency, 2025 Income Tax Manual, checked on 27/10/2026).
A battery on its own, without new panels, doesn't qualify: the certificate counts the energy you produce, not the energy you store.
We balance the three pieces around your bill
With your bill and your roof we tell you how many panels you need, whether a home battery pays off and which tariff suits you, without inflating anything.
Work out for free how many solar panels you need and whether a solar battery and virtual battery pay off in your home.
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Frequently asked questions
What's the difference between a solar battery and a virtual battery?
The home battery stores kWh in your house and uses them that evening and night, in the expensive hours. The virtual one saves in euros the surplus the law doesn't let you offset and discounts it from your next bills, including the power charge and taxes.
How long does the summer balance in the virtual battery last?
It depends on what you use and how many panels you have: it can last until October or November, and longer with a home battery. If the surplus is much bigger, the balance grows without being spent and saves nothing.
Does a home battery pay off if I already have a virtual battery?
It performs better with the virtual one than without it: the virtual battery takes care of summer, and the home battery of the expensive hours the rest of the year. What matters most is how much you use in the evening and at night on weekdays.
Does a home battery on its own qualify for the income tax deduction?
No. The deduction requires the energy certificate to improve, and a battery without new panels doesn't improve it. If it goes with new panels, it's part of the deduction for the work.
Solariña
We design and install solar self-consumption systems for homes all over Galicia, mainly in the province of A Coruña. Every study starts from your bill and your measured roof; the work is done by an authorised installer, who signs the electrical certificate, and the energy certificates are signed by a qualified technician. If something doesn't pay off for you, we'll tell you.