Energy vs. Power

Energy and Power often seem like interchangeable words, for instance in “energy storage” and “power storage.” Yet they are very different!

Power is measured in MW (or W, or kW, or even GW!). It refers to how much you can power simultaneously across all the demand you have without dropping frequency or voltage. All your appliances are rated by their power.

For instance:

  • if you live isolated from the grid and use your own diesel generator (terrible idea btw, please switch to Solar PV and a storage system) with a rated output power of 8.5kW,
  • you can power your 5kW central air conditioner and your 3.5 kW clothes dryer at the same time, but you had better not turn on your 3kW electric oven on top of that or you’ll be in trouble!

Energy, on the other hand, is measured in kWh, and represents the amount of power you use multiplied by the amount of time that that you use it.

For instance, if you use your 3.5kW clothes dryer for one hour, you spent 3.5kWh of energy. Your electrical bill will show a $ charge for 3.5kWh. Your electrical utility charges you in function of the energy you use.

You can also look at it from the other direction, and say that power is the rate at which you use energy.

Why is it important? Power measures the speed at which you can distribute energy to the greed, while energy tells you how much capacity you have in total. They are linked by the Energy to Power Ratio.