Electricity becomes easier to understand when you separate two ideas: how quickly energy is being used, and how much energy is used over time.
A 5 kW appliance can use energy quickly. If it runs for two hours, it uses 10 kWh.
Power is the rate
Power describes how quickly a device is transferring or using energy. It is measured in watts (W), or more commonly kilowatts (kW). A fast EV charger has a higher power rating than a household wall socket because it can deliver energy at a higher rate.
Energy is the total
Energy is power multiplied by time. It is measured in kilowatt-hours (kWh), the unit you see on an electricity bill. A 1 kW heater running for three hours consumes 3 kWh.
Why it matters at home
Solar panels are often described by their power output in kW. Home batteries are described by their stored energy capacity in kWh. A system can therefore have a 6 kW solar array connected to a 10 kWh battery.
| Question | Use | Example |
|---|---|---|
| How fast? | Power (kW) | A 7 kW EV charger |
| How much? | Energy (kWh) | A 10 kWh home battery |
| How long? | Time (h) | Charging for 2 hours |
Sources & further reading
SmartGridTwin guides are written for curious readers and reviewed for clarity. Technical references will be linked here as each guide is expanded.