The right home battery capacity is not automatically equal to annual electricity consumption or solar panel power. A battery operates within daily cycles. You therefore need to understand how much energy is normally left over during the day and how much you consume once solar production has fallen.
For many households the best battery is not the largest one, but the smallest capacity that can regularly be charged and discharged usefully. Start with our home battery calculator for a personal indication.
Capacity in kWh and power in kW
- Capacity in kWh is the amount of energy stored. A 5 kWh battery could theoretically provide 1 kW for five hours.
- Power in kW is how quickly the battery charges or discharges. Higher power supports larger simultaneous loads but does not increase storage.
Think of a water tank: kWh is the size of the tank; kW is the flow rate through the pipe. Both need to suit your home.
Step 1: determine daily grid export
Use your energy supplier, P1 meter or solar inverter app to review representative days. Avoid sizing only from one exceptionally sunny day. Ideally, review several weeks in spring and autumn and note daily export.
If you normally export 6 kWh on useful solar days, a 10 kWh battery cannot be filled completely with your own solar energy. Charging from the grid can still be intentional, but that is a different use case.
Step 2: determine evening and overnight use
Calculate consumption from the end of solar production until the following morning. Include cooking, heat pumps, appliances, ventilation, home working and EV charging. A battery that stores 8 kWh while evening use is only 3 kWh will frequently retain unused energy.
A practical starting point is:
suitable usable capacity ≈ the lower of daily grid export and evening/overnight consumption
This is a rule of thumb rather than exact system design. Battery reserve, conversion loss, weather and app strategy reduce the amount that can actually be used.
Step 3: account for seasons
Summer often brings high solar surplus but lower evening demand. Winter demand is higher while solar production is lower. Do not size only for peak summer days. A battery that completes useful cycles across spring and autumn can be more sensible than a much larger system filled only on a few days.
A dynamic tariff can allow grid charging during cheaper periods, but price difference is not profit. Include charging losses, taxes, contract rules and battery wear.
Examples
Limited surplus
A household exports 3 to 5 kWh on a normal sunny day and uses 4 kWh in the evening. A compact battery around 2.4 to 5 kWh may make more sense than 8 or 15 kWh. A Zendure SolarFlow 2400 AC+ or a system around 5 kWh could be relevant, subject to power and installation requirements.
Average surplus and higher evening use
A household regularly exports 7 to 10 kWh and consumes 6 to 8 kWh between evening and morning. An 8 kWh system such as the Zendure SolarFlow 3000 Mix AC+ or Zendure SolarFlow 4000 Mix AC+ may fit better.
Start with 5 kWh and expand later
The EcoFlow STREAM AC 5000 starts at 5.024 kWh and can reach 15 kWh within one base unit plus expansion batteries. Staged expansion helps avoid buying unused capacity on day one.
These examples are not remote product advice. Maximum power, the distribution board, placement and P1 compatibility are equally important.
Why annual use alone is insufficient
Two households with the same annual consumption can have very different profiles. A heat pump that runs mainly at night, an EV charged in daylight or frequent home working changes the result. If only an annual statement is available, use it as a first estimate and refine the calculation once P1 or interval data are available.
Solar architecture matters
Some batteries include a direct MPPT solar input. Others, including the EcoFlow STREAM AC 5000 and Zendure Mix AC+ models discussed here, work on the AC side with an existing PV inverter. Check how the battery integrates with your current system, not only how many kWh it stores.
If you do not have solar panels, read home battery without solar panels.
Check connection and P1 measurement
Maximum product output is not automatically safe through any socket. Check the circuit, wiring, protection and other appliances. Ask a qualified electrician to assess hard-wired or uncertain installations.
A compatible P1 meter lets the system monitor import and export. Reliable Wi-Fi, correct app permissions and an available or correctly split P1 port matter. Follow our installation checklist.
A simple selection order
- Measure daily export and evening/overnight use.
- Choose capacity that can regularly be filled and emptied.
- Check required charge and discharge power.
- Decide whether future expansion matters.
- Check the connection, P1 compatibility, Wi-Fi and placement.
- Compare warranty and current total price, including accessories and installation.
Then explore all plug-in home batteries or bring your measurements to our showroom.
Currency
This guide was reviewed on 27 August 2026. Products, tariffs and rules can change. Calculations are indicative and do not guarantee savings or a payback period.
