What is the difference between power and energy?
We often see people getting confused as to the difference between power and energy. The difference is distinct and actually quite simple and easy to understand.
Think of it this way. If a dam is holding back a lake full of water, the power rating of the dam is the rating of the generator. The energy rating of the dam is based off of the power rating AND ALSO the amount of water in the lake. Energy is accumulative, power is only an instantaneous rating.
In another example we can take a car with 100 horsepower. This car has 100 horsepower, but that doesn’t tell us how far it will go, or how much energy it holds. Basically, this is the fuel capacity of the car. If it can run at 100 horsepower for 1 hour, that is 100 horsepower-hours worth of energy. If it can run at 100 horsepower for 10 hours, that is 1000 horsepower-hours worth of energy.
In the solar industry, the solar panels and inverter is comparable to the engine of the car, or the generator of the water dam. The amount of sun that shines on the panels, and for how long the sun shines on the panel, determines how much energy the system produces. For this reason, a solar system installed in Arizona will produce far more energy than a solar system installed in Montana, even if the power rating of the solar systems are exactly the same.
When we add batteries to a system, these are also comparable to the gas tank of the car or the amount of water in the lake. The battery has a power rating (how much power can be charged or discharged without causing damage) but it also has an energy rating, which calculates the power rating of the battery along with the storage capacity. If we combine them together, we get an energy rating.
Terminology
Below are a few examples of the units used when referring to power and energy in the solar industry:
- Watts = Power
- KW (Kilowatts) = Power. Simply watts times 1000
- KWH (Kilowatt hours) = Energy. This is the amount of power times the duration that power was used. If a 100 watt light bulb is on for 10 hours (100 watts x 10 hours) this will use 1 kilowatt hour (1000 watt hours) of energy.