Part of the guide Home battery, EV charger and electric heating
Short answer: for an average household using 2,500 to 3,500 kWh a year with 8 to 12 solar panels, 5 kWh is the size that gives the best return: enough to cover evening and night-time consumption from your own solar power, small enough to be charged and discharged almost every day. The calculation: take your daily consumption (annual consumption divided by 365, usually 7 to 10 kWh), work out what share of it falls outside sunshine hours (60 to 70 per cent) and take that as the battery size, limited by what your panels have left over on an average day. If you come out above 10 kWh, that is almost always due to a heat pump or an electric car, and then a larger system or a second module pays off. In our shop 5.12 kWh (Marstek Venus E 3.0) costs €1,099 and 10 kWh (Venus E Max) €2,399.
Step 1: your daily consumption and when you use it
A home battery earns its money by letting you use the solar power you have left over during the day in the evening instead of exporting it. So it is not about your total consumption, but about the share you use when the sun is not shining. For a household that is out at work during the day that is 60 to 70 per cent; for someone who works from home or combines a home battery with a heat pump, 40 to 50 per cent.
| Annual consumption | Per day | Outside sunshine hours (65%) | Battery |
|---|---|---|---|
| 2,000 kWh (1 to 2 people) | 5.5 kWh | 3.6 kWh | 2 to 5 kWh |
| 3,000 kWh (family) | 8.2 kWh | 5.3 kWh | 5 kWh |
| 4,500 kWh (family with heat pump or induction hob and many appliances) | 12.3 kWh | 8 kWh | 5 to 10 kWh |
| 6,500 kWh (family with heat pump and electric car) | 17.8 kWh | 11.6 kWh | 10 kWh or more, if the panels can supply it |
Your smart meter or your energy supplier's app shows your consumption per hour; add up the hours from 18:00 to 08:00 on a few ordinary days and you have the real figure.
Step 2: what your solar panels have left over
The battery can only charge with power you do not use straight away. Ten 400 Wp panels produce 20 to 25 kWh on a summer day and 1 to 3 kWh on a grey winter day. In spring and autumn, the months that count most, 10 panels typically leave you 5 to 8 kWh a day after daytime consumption. A 5 kWh battery is then full every day; a 15 kWh battery would stay half empty for three quarters of the year. Rule of thumb: 1 to 1.5 kWh of battery per kWp of panels. So for 4 kWp, 4 to 6 kWh; for 8 kWp, 8 to 12 kWh.
If you have no panels, a battery can only pay off with a dynamic energy tariff: charge cheaply at night or around midday, discharge during the expensive evening hours. That yields less per kWh than your own solar power and requires a battery that can respond to hourly prices.
Step 3: charging and discharging power
Besides capacity (kWh), power (kW) counts: how fast the battery can charge and deliver. An average household draws 300 to 800 W in the evening, with peaks of 2 to 3 kW when the oven or kettle goes on. The Venus E 3.0 delivers a maximum of 2,500 W, the Venus E Max 3,600 W; higher peaks simply come from the grid. Charging works at the same power: at 2,500 W, 5 kWh is full in two hours, ample for a sunny afternoon. More power is only useful for a large household or a 3-phase connection with many appliances running at the same time.
Waarom te groot slechter rendeert dan te klein
The saving per kWh of battery is highest for the first kilowatt-hours: they are used almost every day. Each extra kWh is filled on fewer days a year. In the Netherlands a 5 kWh battery makes 250 to 300 full cycles a year; a 15 kWh battery with the same panels perhaps 120. The price per kWh of storage does fall with larger systems, but not enough to make up for that. So rather choose a battery you can expand: a second Venus E next to the first when the car or the heat pump arrives.
| Model | Capacity | Power | Price | Suitable for |
|---|---|---|---|---|
| Marstek Venus E Mini | 2.0 kWh | 800 W | €659 | Klein huishouden, appartement, 4 tot 6 panelen |
| Marstek Venus E 3.0 (collection in Alblasserdam, Netherlands €1,100) | 5.12 kWh | 2.500 W | €1,099 | Family with 8 to 12 panels; the standard choice |
| Marstek Venus E Max | 10 kWh | 3.600 W | €2,399 | Heat pump or electric car, 14 panels or more |
| 2 × Venus E 3.0 | 10.24 kWh | 5.000 W | €2,258 | Expanding in stages; two socket circuits needed |
Prices including VAT and P1 meter, September 2026. All models can be found under · ; you connect the plug-and-play models yourself, see Plug-and-play or fixed home battery.
Worked example: family with 10 panels
Annual consumption 3,200 kWh, 10 panels of 400 Wp (3,500 kWh yield). Without a battery this family uses about 30 per cent of its solar power directly and exports 2,450 kWh. With a 5 kWh Venus E 3.0, self-consumption rises to about 60 per cent: 1,000 to 1,200 kWh a year less to buy. With a supply tariff of €0.28 and an export rate of €0.05 to €0.08, that saves €230 to €270 a year, and where net metering ends or does not apply the saving is higher still. That puts the payback period at five to six years. The full calculation, including export charges, can be found in What a home battery costs now that net metering is ending.
Frequently asked questions
Can I expand later?
With the Marstek Venus E series you place a second unit next to the first; both work together with the same P1 meter. With fixed systems with an inverter, it depends on the number of battery modules the inverter can handle.
Hoeveel kWh heb ik nodig zonder zonnepanelen?
Then choose based on your evening consumption and a dynamic tariff: 5 kWh covers the expensive hours from 17:00 to 21:00 for most households. The return per kWh is lower than with your own solar power.
Is 5 kWh enough if I have a heat pump?
In spring and autumn yes, in winter no: that is when the heat pump uses the most and the panels produce the least. A bigger battery helps little then, because there is nothing to fill it with. Choose 5 to 10 kWh and expect to use grid power in the winter months.
How much is lost during charging and discharging?
Ten to fifteen per cent over the whole cycle. Of 5 kWh of solar power charged, 4.3 to 4.5 kWh comes back into the home. This is included in the worked examples.