How do I calculate the battery and inverter size I need?

More and more households are investing in a home battery to get more out of their solar panels, implement peak shaving, take advantage of dynamic tariffs, or become more independent of the electricity grid. But one question always comes up:

How big should my battery be and how much power should my inverter have?

In this blog post, we explain step-by-step how to calculate the correct battery capacity (kWh) and inverter power (kW). This way, you can be sure your home battery perfectly matches your consumption, installation, and future plans. Smart systems like the Enphase IQ Battery 5P demonstrate how modular power and capacity work together optimally.

Step 1: Determine your daily energy consumption

To determine your battery size, start with your average daily usage. You can find this on your:

• Annual statement from your energy supplier
• App for your smart meter
• Online portal of your energy supplier

Example:
Consumption per year = 4,000 kWh → average 11 kWh per day.

Note: You use more electricity in winter (heat pump, lighting), less in summer. Pay particular attention to your consumption on sunny days, as these are important for storage.

Step 2: Determine your daily solar production

The ideal battery is tailored to what you generate and do not use immediately.

Example:
A 10 kWp solar system produces 30–45 kWh on a summer day. Of this, you can use 10–15 kWh directly in your home. The rest (approximately 20–30 kWh) can be stored in a battery.

⭐ Rule of thumb:
The ideal battery can store at least one sunny afternoon's worth of excess power.

Step 3: How much do you want to consume yourself? (self-consumption)

The size of the battery depends on what you want to achieve:

• Do you mainly want to return less?
  Choose a battery that can store 50–70% of your solar production.
• Do you want to become more independent of the grid?
  Get a battery that can supply 100% of your evening and night consumption.
• Do you want to trade with dynamic rates or apply peak shaving?
  Additional capacity can then be financially interesting.

Step 4: Calculate the ideal battery capacity (kWh)

Scenario 1 – Increase only own consumption (basic)

0.5 – 1 × your daily consumption
At 11 kWh consumption → battery from 5–10 kWh

Scenario 2 – Nearly complete evening and night autonomy

1 – 1.5 × your daily consumption
At 11 kWh consumption → battery of 10–15 kWh

Scenario 3 – Dynamic contract, peak shaving or imbalance market

1 – 2 x your daily consumption
At 11 kWh consumption → battery of 10–20 kWh
Larger batteries pay for themselves faster through smart charging and discharging.

Scenario 4 – Off-grid or maximum grid independence

2 x your daily consumption + backup margin
At 11 kWh consumption → battery of 22–25 kWh

Step 5: Calculate the required inverter power (kW)

The inverter determines how much power your battery can supply or absorb.

• Capacity (kWh): how much energy you can store
• Power (kW): how quickly you can supply or charge energy

A 10 kWh battery is of little use if the inverter only delivers 1 kW. A good match is therefore essential.

How do you determine the correct inverter capacity?

Look at your peak loads simultaneously — how much power your devices are using at the same time:

Device	Average power
Induction hob	2–3 kW
Heat pump	1.5–3 kW
EV charger	3.7–11 kW
Washing machine	1–2 kW
Air conditioning	1–2 kW

Rule of thumb: choose an inverter with a capacity of 0.5 to 1 × your peak consumption, depending on how many appliances you want to use simultaneously.

Which battery is right for you?

Use our handy calculator