What is a kWh (kilowatt-hour)?
3 min read below · SolarFast knowledge base
A kilowatt-hour (kWh) is the energy a 1,000-watt appliance uses in one hour. How to convert watts to kWh and read your use on your annual statement.
A kilowatt-hour (kWh) is the energy a 1,000-watt appliance uses in one hour. It is the unit you pay your electricity in and the unit your solar panels' output is counted in.
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What is a kilowatt-hour?
A kilowatt (kW) is power: how hard something draws electricity at a given moment. A kilowatt-hour (kWh) is energy: power times time. A 2,000-watt kettle running for half an hour uses 1 kWh. Your annual statement shows your total use in kWh.
The formula is simple: kWh = (watts × hours) / 1,000. A 500-watt appliance running for four hours uses 2 kWh. That lets you estimate what a device costs per year, as long as you know how long it typically runs.
kW, kWh and kWp apart
The three abbreviations look similar but measure different things. kW is power at a moment, kWh is energy over time, and kWp (kilowatt-peak) is the peak power of your solar panels together. The power per panel is listed in watt-peak (Wp).
| Unit | What it measures | Example |
|---|---|---|
| kW | Power (moment) | A charger draws 7 kW while charging |
| kWh | Energy (power × time) | That charge session uses 15 kWh |
| kWp | Peak power of panels | Ten 400 Wp panels = 4 kWp |
4 kWp produces roughly 3,400 to 3,600 kWh per year in the Netherlands (rule of thumb 0.85 to 0.9 kWh per Wp). This rule of thumb matches the yield figures of Milieu Centraal.
How much kWh does a household use?
Use varies a lot per household. Family size, appliances, a heat pump or an electric car determine how many kWh you need per year. Two homes next to each other can easily differ by a factor of two.
The best starting point is your own annual statement or smart meter. There you see how many kWh you actually use. We use that figure to size your solar panels. A heat pump or charger pushes use up significantly; factor that in if you are planning ahead.
kWh and solar panels
Your panels' output is also counted in kWh. To go from the wattage on your roof to kWh per year, multiply total watt-peak by roughly 0.85 to 0.9. That is a rule of thumb for the Netherlands; your actual yield depends on orientation and shade.
Concrete calculation examples, a monthly split and what it saves on your energy bill are on our page about solar panel yield and return. Want to know how many kWh you need? Start with your annual statement and request a quote via solar panels.
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Frequently asked questions
What is the difference between kW and kWh?
kW is power at a moment, kWh is energy over time. A 1 kW appliance running for an hour uses 1 kWh.
How many watts is 1 kWh?
1 kWh is 1,000 watts for one hour. A 2,000-watt appliance running for half an hour also uses 1 kWh.
How do you calculate kilowatt-hours?
Multiply power in watts by the number of hours and divide by 1,000. A 500-watt appliance running for four hours: (500 × 4) / 1,000 = 2 kWh.
What does kWp mean?
Kilowatt-peak is the peak power of your panels together. Ten 400 Wp panels are 4 kWp. The rule of thumb of 0.85 to 0.9 kWh per Wp converts that into kWh per year.
Where do I see my use in kWh?
On your supplier's annual statement and on your smart meter. We use that consumption to size your system.
We apply this every day
The same knowledge you're reading here, we put to work for households across the Netherlands.