Virtual battery or physical?
A virtual battery is an accounting product of your electricity supplier: it credits your surplus and deducts it later, for a monthly fee. A physical battery actually stores the surplus. The calculator shows what gets the most out of your surplus.
Inputs
Calculation assumptions, you can adjust them
Suppliers' virtual batteries with your surplus, per year. Rates from the suppliers' price lists, verified on 16 September 2026.
| Supplier | Package capacity | Value of 1 kWh | Fees per year | Net benefit |
|---|---|---|---|---|
| Greenlogyfrom 1 July 2026 quarter-hours with negative prices are not credited | no limit | 0.1800 € | 36 € | 518 € |
| SSEsaving only on the supply price, 12-month commitment | 6,000 kWh | 0.1800 € | 161 € | 394 € |
| VSEvalue equals the supply price of 0.1096 €/kWh | 3,000 kWh | 0.1096 € | 191 € | 138 € |
| ZSE FlexiFlexi: value by time of generation, 0.036 €/kWh excl. VAT around midday | no limit | 0.0354 € | 36 € | 73 € |
Result
Feed-in or sharing of surplus: 169 € a year. Virtual battery, Greenlogy: 518 € a year. Physical battery, annual saving: 459 € a year
You generate 7,700 kWh a year, with a surplus of 3,080 kWh. Below are three different things: two annual flows without an investment, and a battery you buy.
- Feed-in or sharing of surplusgross income at 55 €/MWh
- 169 € a year
- Virtual battery, Greenlogynet of fees of 36 €, 3,080 kWh credited
- 518 € a year
- Physical battery, annual savinggross saving, 3,000 kWh through the battery at 85 % efficiency
- 459 € a year
- Physical battery, gain over feed-ingross saving 459 € less the 165 € feed-in given up on 3,000 kWh
- 294 € a year
- Physical battery, investment10 kWh × 350 €/kWh
- 3,500 €
- Physical battery, simple paybackfrom the gain over feed-in, excluding degradation, service and the value of backup power
- 11.9 years
Indicative calculation from the suppliers' rates verified on 16 September 2026. A virtual battery is an accounting product of the supplier, not a storage unit: ZSE now offers Flexi, which prices the electricity you deliver by time band, VSE values stored electricity at the supply price, SSE saves only on the supply price and Greenlogy does not credit quarter-hours with negative market prices from 1 July 2026. The first two rows are annual flows without an investment; a physical battery has an investment, a limited life and also works as backup during an outage. The result therefore does not crown a winner.
How a virtual battery works
Surplus from your solar PV goes into the grid and the supplier credits it to your account. When you draw electricity later, part of it is deducted from the account. Not a single kWh is stored; it is a billing arrangement for the energy component, and you keep paying distribution charges on what you draw.
Every supplier has a different package: capacity in kWh per year, a monthly fee and an efficiency, meaning what share of your surplus is actually credited. Unused surplus expires at the end of the period.
The terms change. From 1 May 2026 ZSE no longer lets you draw energy for free at public ZSE Drive chargers but at a 35 % discount off the day tariff, while its home Flexi battery values the energy by time of generation. Greenlogy introduced a monthly fee of €3. That is why the calculator keeps the rates in its assumptions, where you can adjust them to your current contract.
When a physical battery wins
With higher surplus and evening consumption: a battery from 7 kWh uses 80 to 90 % of the stored surplus at home, independently of the supplier and its fees.
When you need backup: a virtual battery does not help during an outage; a physical one keeps selected circuits running when it is wired for it; the design decides what stays powered.
For businesses almost always: reserved capacity, peaks and the spot market are jobs for a physical battery controlled by EnergoMind, not for an accounting product.
Questions we get asked
1Which virtual battery is the best value?
It depends on the volume of surplus and on whether you are a customer of that supplier. For smaller volumes Magna is often attractive, for larger ones SPP; ZSE, SSE and VSE have packages based on PV capacity. Compare the monthly fee with the annual saving and take the 2026 changes into account.
2How much does a virtual battery cost?
The monthly fee typically ranges from €2 to around €12 per month depending on capacity and supplier. Storing surplus is usually free, but on drawdown you pay distribution charges, roughly €0.06/kWh, on top of the energy component.
3What changes for virtual batteries in 2026?
From 1 May 2026 ZSE applies a 35 % discount off the day tariff when you draw energy at ZSE Drive chargers instead of the earlier free drawdown, and its home Flexi battery values energy by time of generation. From 1 July 2026 Greenlogy introduces a fee of €3 per month and does not credit surplus during negative-price periods. Levies on the sale of surplus have also been added.
4Which pays off more, a virtual or a physical battery?
A virtual battery needs no investment, but it is a paid service without backup and with changing terms. A physical battery costs more upfront, but it really stores energy, serves as backup and is independent of the supplier. With higher self-consumption and for businesses, the physical battery usually wins.
5Will I use all the surplus stored in a virtual battery?
At the end of the billing period unused surplus is reset to zero. You do not pay for it, but it is not paid out either. Set the capacity and package according to your real consumption.
6What is electricity sharing and how does it differ from a virtual battery?
Electricity sharing through an aggregator registered with OKTE EDC (the Slovak energy data centre) buys surplus at a fixed price, for example €55/MWh, and works as an add-on to your existing contract and to a virtual battery. A virtual battery stores surplus for later drawdown, usually with a monthly fee and restrictions.
A battery design for your system
Tell us your PV capacity, electricity supplier and whether you have surplus. Pavol Kaprál will get in touch by the next working day.
Family homes: Ing. Pavol Kaprál
pavol.kapral@energovision.sk
+421 911 700 727