Today, with so much interest in electricity, whether it be via household solar systems or more recently electric vehicles (EV’s), the confusion between power and energy, is understandable. Here, hopefully, we can sort out the confusion.
Power: is that force which moves vehicles, heats our water, powers our electronic devices and so on.
Energy: is the result of that force acting over time which is the work done.
Keeping in the electrical domain, power has the units, in the metric system, of watts (W), thousands of watts (kW), millions of watts, megawatts (MW) and so on. In electric vehicles, electrical power from the battery produces that force which propels the vehicle down the road.
Interestingly to go twice as fast we need to provide eight times as much power to overcome the aerodynamic drag of the vehicle moving through the air.
The result of that application of electrical power over time to move the vehicle, i.e. work done is called energy which is the electrical power applied multiplied by the time for which that power is applied.
Moving to an example with heating water. We heat a 2 litre jug of water from 20 degrees centigrade to boiling point at 100 degrees centigrade. The jug has a heating element that dissipates or consumes 2 kW of power. The water will take 5 minutes to heat to boiling point and will consume 190 Wh or 0.19 kWh of energy. The work done in heating the water is 0.19 kWh of energy.
A final point.
That 14.52kWh required to heat the water in our hot water tank is quite a lot of energy; enough to drive our Tesla model 3 for about 100 km. And at a cost of around 16 cents/ kWh in the middle of the night will amount to $2.38 (16 x 14.52 = 2.38). Even allowing for the fact that we usually don’t start with a cold tank every day the water heating costs for Australian households is considerable.
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