The terms “power” and “energy” are often inter-changed in everyday speech but their meanings are very different. Before going any further, I think it is important to understand this difference.
When thinking about a journey, it is clear to everyone that “distance” and “speed” are not the same. After a few moments’ thought, most people will agree that:
Distance (in miles) = Average Speed (in miles/hour) × Time_of Journey (in hours).
In the world of electricity, “energy” is related to “power” in just the same way. So: Energy (in kWh) = Power (in kW) × Time_forWhichTheApplianceWasOn (in hours).
If a 2 kW heater (its power rating) were to be switched on for a period of 1 Hour (time), then 2 kWh (of energy) would be consumed. Similarly, if a PV installation were to generate electricity at a constant rate of 1 kW (power), and this situation were to be maintained for a period of 17 Hours (time), then 17 kWh (of energy) would have have been generated.
In the same way that “Speed is the rate at which Distance is covered”, i.e. miles per hour, so “Power is the rate at which Energy is consumed or generated” i.e. kWh per hour, or just kW. In the material which follows about the measurement of mains electricity, it is often helpful to think of power as the rate at which energy flows. (from openenergymonitor.org )