Which home battery do I need?
The right capacity follows from your evening and overnight consumption, not from your annual total. We calculate it in three steps, show which size suits which household and explain why power in kW matters as much as capacity in kWh.
The most common mistake when choosing a home battery is calculating from annual consumption. A household using 3,500 kWh a year does not need 3,500 kWh of storage, nor a tenth of it. What you store is only the part of your consumption that falls in the hours when your panels produce nothing. That makes the calculation smaller and more concrete than most people expect.
Short answer: how many kWh do you need?
For most Dutch households the answer is between 5 and 15 kWh. A two-person household without a heat pump and without an electric car gets through almost every evening on 5 to 8 kWh. A family of four with a normal usage pattern sits around 10 kWh. With a heat pump your evening and overnight consumption doubles in winter and 15 kWh or more becomes realistic. If you also charge a car at home, a battery expected to cover that fully is rarely economic: a car takes more in a single charging session than a complete home battery holds. The rule of thumb closest to practice is this: take the amount of power you use between sunset and sunrise, and pick the battery size just above it.
Work out your evening consumption in three steps
Step one: take your annual consumption in kWh from your energy statement and divide it by 365. A household on 3,500 kWh comes out at about 9.6 kWh a day. Step two: estimate which part of that falls outside daylight hours. For a typical household where nobody is home during the day, that is around 60 to 70 percent, so roughly 6 to 6.7 kWh. If you work from home or run the washing machine during the day, it is lower, closer to 45 percent. Step three: add what runs overnight regardless, such as cooling, ventilation and standby loads, usually 1.5 to 3 kWh. If you land on 7 kWh, a battery of 8 to 10 kWh is the right size: a little above your calculation, because you never use the full nominal capacity.
Want to be precise? Almost every smart meter records quarter-hour values that your energy supplier shows in its app. Look at an ordinary weekday in November and add up what passes through the meter between 17:00 and 07:00. That number is your real storage requirement.
Which size suits which household
The table below translates the calculation into situations. It assumes a household with solar panels that uses the battery mainly to consume daytime generation in the evening. The middle column is the capacity you are looking for; the right-hand column is what that costs here as a complete system including inverter and meter, including VAT and excluding installation.
| Situation | Capacity | Complete system from |
|---|---|---|
| Single or couple, apartment | 3.5 to 5 kWh | € 2,022 |
| Couple, terraced house, no heat pump | 5 to 8 kWh | € 2,969 |
| Family of four, normal consumption | 10 to 12 kWh | € 3,561 |
| Family with a heat pump | 14 to 16 kWh | € 5,562 |
| Detached house, heat pump and home charging | 20 kWh and up | € 7,292 |
Nominal capacity is not usable capacity
The label states the nominal capacity, for example 10.24 kWh. What you get out of it daily is less, for two reasons. First, the battery management system does not let the pack run fully empty; the depth of discharge, or DoD, is usually between 90 and 95 percent on LFP batteries. Second, every cycle loses energy converting DC to AC and back. On a good system that round-trip efficiency is around 90 percent. So budget roughly 80 percent of nominal capacity as usable daily energy: from a 10 kWh battery you use about 8 kWh. Manufacturers who quote only the nominal figure are not being dishonest, but the comparison only holds once you apply the same correction to both brands.
kWh or kW: the other number that matters
Capacity in kWh says how much energy fits. Power in kW says how fast it can come out. The two are often confused, which produces systems that are big enough on paper but cannot handle the peak in practice. An induction hob, a kettle and a hairdryer together draw around 5 kW; if your system only delivers 3.6 kW, the grid makes up the difference and you buy power at exactly the most expensive moment. For an average household 3 to 5 kW of discharge power is enough. If you want to keep running during a power cut, you need not just power but an inverter with a backup function, and that is a separate feature that many systems do not have.
Low voltage or high voltage
Home batteries come in two flavours. Low-voltage systems work at around 48 volts and are the rack models you see in server cabinets; they are cheaper per kWh, broadly compatible and easier to expand. High-voltage systems work between roughly 200 and 700 volts, are more efficient at higher power levels and are what most brand-tied systems from Huawei, BYD and GoodWe use. For an average household the difference in yield is small; the difference in price is not. In practice the choice is made by your inverter: it is either low voltage or high voltage and accepts only batteries from the matching family. If you are buying everything new, low voltage is the cheapest path and high voltage the one with the most brand support. Which brands fall into which category is set out in the brand comparison.
Will this battery work with my inverter?
This is the question that goes wrong most often and costs the most when it does. A hybrid inverter only accepts batteries the manufacturer has approved and that exist as a profile in its firmware. Connect an unapproved battery and the battery management system will not communicate with the inverter, the installation will not pass inspection and the warranty lapses on both sides. That is why every battery product page here lists which inverters are supported, and on the complete systems the combination is already fixed. If you already have an inverter, first find the exact model on its rating plate, because manufacturers ship variants that look identical but support a different battery family. If you are unsure, send us the model number before ordering. Which battery brands are released broadly and which are supported by only a single inverter manufacturer, we worked out in which inverter fits which home battery.
Starting small and expanding later
Modular systems let you start with the smallest module and add units later, which sounds attractive on a limited budget. There are two catches. The first is that expanding requires modules from the same series and preferably the same production batch; a new module alongside one that has been cycling for three years drags the whole string down to the level of the weakest. The second is that the inverter has to be sized for the final capacity from day one, otherwise you end up replacing it anyway. If you do phase your expansion, do it within about two years and buy the inverter large enough immediately. If you already know you want 15 kWh, buying it in one go is almost always cheaper per kWh.
Where is the battery allowed to go?
Most home batteries are meant for a dry, frost-free indoor space: a utility room, outbuilding or garage. The operating range on most LFP batteries is 0 to 50 degrees when discharging, but charging below zero causes damage, so an unheated shed is a bad idea. If you want to mount outdoors, check the IP rating: IP65 is jet-water resistant and suitable outside, IP20 or IP21 is strictly indoors. Also look at weight and mounting method. A 10 kWh wall unit quickly weighs 100 kilos and needs a load-bearing wall; larger systems stand on the floor. Every product page lists IP rating, temperature range, weight and mounting method as separate specifications, so you can check this before you order. How many models actually may not charge below zero, and how heavy they are per capacity class, is counted in installing a home battery.
Frequently asked questions
How many kWh of home battery do I need at 3,500 kWh a year?
About 8 to 10 kWh. From 3,500 kWh a year you use around 9.6 kWh a day, of which roughly 60 to 70 percent falls outside daylight hours. Add the overnight base load and you arrive at about 7 kWh you want to bridge. Because only around 80 percent of nominal capacity is usable, you pick a battery of 8 to 10 kWh.
Is a 5 kWh home battery enough?
For one and two-person households without a heat pump, usually yes. You draw about 4 kWh from it per evening, which covers normal evening consumption. If a heat pump runs or you charge a car, 5 kWh is too small and you will regret it within a year, because expanding afterwards costs more than buying bigger up front.
What is the difference between kW and kWh on a home battery?
kWh is how much energy the battery holds, kW is how much power it can deliver at once. A 10 kWh battery rated at 3.6 kW can deliver 3.6 kW for nearly three hours. If your household draws more than that at peak moments, the grid makes up the difference. For an average household 3 to 5 kW is sufficient.
Can I add a home battery to existing solar panels?
Yes, in two ways. If you already have a hybrid inverter, you simply add the battery, which is by far the cheapest option. If you have a plain string inverter, an AC-coupled battery inverter is added alongside your existing installation, without having to replace it. What the battery alone costs is set out in the cost guide.
Can a home battery go in the garage or outdoors?
In a dry, frost-free garage usually yes; outdoors only if the battery is rated at least IP65. Charging at temperatures below zero damages LFP cells, so an unheated shed is not advisable. Check the IP rating, the temperature range and whether the model is wall or floor mounted on the product page.