kW (Kilowatt) explained
A kilowatt (kW) measures power — the rate at which energy is produced or consumed right now. One kilowatt equals 1,000 watts. When a solar installer quotes you a "4 kW system," they mean your panels can produce up to 4,000 watts of electricity under ideal sunlight conditions.
It's important not to confuse kW with kWh. Think of it like a hosepipe: kW is how fast the water flows, while kWh is how much total water you've collected over time.
For a typical UK home, a 3–4 kW system is the most common size. In sunnier climates like Australia or the American Southwest, the same system will generate more kWh per year simply because the sun shines longer and more intensely. System size in kW directly affects both upfront cost and annual savings.
- Small home (1–2 bedrooms): 2–3 kW system
- Medium home (3 bedrooms): 3–4 kW system
- Large home or EV charger: 5–8 kW system
Installers size your system in kW based on your annual electricity consumption (measured in kWh) and the roof space available. A larger kW system generates more electricity but also costs more upfront.