Home Battery Capacity Calculator: How Many kWh Do You Need?

Why calculating capacity matters

The capacity of your home battery (expressed in kWh) determines how much energy you can store. Choose too small and you'll still lose surplus solar power. Choose too large and you'll pay for capacity you don't use. The right capacity depends on your consumption pattern, the size of your solar panel installation and your household composition.

In this article, we give you the rules of thumb, worked examples and tables to determine the ideal capacity for your situation. You only need your annual consumption and the number of solar panels.

Step 1: Determine your daily consumption

The average Dutch household consumes approximately 2,800 kWh per year, or about 7.7 kWh per day. But actual consumption varies considerably between households. Factors that play a role:

• Household size: a single person uses ~2,000 kWh/year, a family with children 3,500-5,000+ kWh/year
• Electric car: adds 2,000-4,000 kWh/year to your consumption
• Heat pump: adds 3,000-6,000 kWh/year
• Working from home: approximately 300-500 kWh extra per year
• Electric cooking: approximately 200-400 kWh extra per year

Step 2: Calculate your daily surplus

The battery capacity you need is largely determined by the difference between your solar power generation and your actual consumption at that moment. In practice, you only use 30-40% of your solar power directly during the day. The rest is surplus. Here is an indicative table:

Rule of thumb: choose a battery capacity equal to 60-80% of your daily surplus in summer. In winter you produce less, but electricity prices are higher — the battery is then also charged via dynamic tariffs.

Step 3: Consider your consumption pattern

It's not just the amount of consumption that matters, but also when you consume. This determines how much energy you draw from your battery in the evening and at night.

Working from home during the day

If you're at home during the day, you use more solar power directly. You then need less battery capacity because there is less surplus. A battery of 3-5 kWh is often sufficient for households with home workers and 8-12 solar panels.

Not at home during the day

If you're away during the day (work, school), virtually all solar power is surplus. Here you need a larger battery to capture it all. Expect 5-10 kWh for an average household with 10-14 panels.

Family with high evening consumption

Cooking, washing machine, dryer, TV, lighting: families with children consume the most between 17:00 and 22:00. A battery of 8-15 kWh is then needed to cover the evening peak.

Worked example

Suppose: you have 12 solar panels (4.8 kWp), consume 3,500 kWh per year and are not at home during the day.

Common mistakes when choosing capacity

These are mistakes we see regularly:

• Choosing too small: a 2 kWh battery with 14 solar panels is a waste — you'll still lose most of your surplus
• Forgetting winter production: in winter you produce only 20-30% of your summer capacity. An oversized battery won't be fully charged by solar power (but it will be via dynamic tariffs)
• Ignoring future consumption: planning an EV or heat pump? Factor those extra kWh into your choice
• Not thinking modularly: choose a system you can expand later as your consumption grows

Conclusion and advice

The right capacity depends on your specific situation. As a rule of thumb: a battery of 5-10 kWh is suitable for most households with 8-14 solar panels. For larger installations or households with an EV/heat pump, we recommend 10-20 kWh.

Unsure about the right capacity? Use our free savings calculator or request personal advice. We'll help you make the optimal choice.