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W, kWh, V and Ah in plain English — and how they relate.
Watts (W) measure power — how fast something uses energy *right now*. A LED bulb sips 10W; a fan heater gulps 2,000W. The golden formula: Watts = Volts × Amps.
Kilowatt-hours (kWh) measure energy — power over time, and what your electricity bill counts. Run 1,000W for one hour and you've used 1kWh. Everything in system sizing comes back to "how many kWh per day do I need?"
Volts (V) are electrical pressure. Small DIY systems run at 12V or 24V (safe to work on); UK mains is 230V (never DIY). The inverter converts between the two.
Amp-hours (Ah) describe battery capacity *at a stated voltage*. A 100Ah 12V battery stores roughly 1.2kWh (100 × 12 = 1,200Wh). That's a day of lights, laptop and phone charging — but only about 35 minutes of a 2kW heater.
Once these four click, every spec sheet in the solar world becomes readable.
From EcoPowerful — plain-English DIY solar & wind guidance for UK homes, with a free instant system plan builder. Guidance is general; 230V fixed wiring always needs a qualified electrician. Last updated 2026-06-13.