What is the difference between kW, kWp and kWh?

kWh (kilowatt-hour) is a measure of electricity use (or generation) over time. A 1kW (kilowatt) load running for 1 hour will use 1kWh of electricity. Similarly, a 1kW generator running for 1 hour will generate 1kWh. Electricity is bought and sold in kWh (often termed "units"). kWp is used solely when expressing the nameplate rating of a PV module or array (see above). The actual instantaneous output of an array is measured in kW and the energy production over time is measured in kWh.