The world of electricity can get a little confusing, especially for those of us who didn’t necessarily pay attention in high school physics. We might throw around words like power and energy, but we would probably have a tough time explaining what they actually mean. And when it comes time to reading that electric bill, we don’t, because we have it on auto-pay. But understanding this stuff might actually save us some money, unlike something super esoteric like knowing where French is spoken. With that in mind, what is a kilowatt hour? I’ll provide a few basics.
The Fundamentals
As a warning, some of this might get a little technical. If you’re not feeling it, you can just skim it. Sort of like the high school strategy.
The first key concept to grasp is power. One definition of power is the rate at which energy is transferred. It is expressed in joules per second, also known as watts. One kilowatt is one thousand watts, one megawatt is one million watts, and one gigawatt is one billion watts. Light bulbs will typically list their power, with an example being a traditional 60 watt incandescent light bulb. (Equivalent LED bulbs will have a much lower value.) Power plants, not surprisingly, also list their power, with an example being a 600 megawatt coal plant.
Because power represents the rate at which energy is transferred, to understand the total energy involved, we need to know the amount of time over which the transfer occurred. In other words, power multiplied by time equals energy. (This concept is similar to multiplying the speed of a car by time in order to calculate the distance traveled.) Because power can be expressed in kilowatts, and time can be expressed in hours, a common unit of energy is the kilowatt hour (kWh). Electrical energy, as in the energy that basically runs our homes, is typically sold in kilowatt hours.
A Little More Math
A few examples, taken straight from Wikipedia, are warranted.
A one kilowatt electric heater operating for one hour uses one kilowatt hour of energy.
A 100 watt (0.1 kilowatt) television operating for ten hours similarly uses one kilowatt hour of energy.
And a 40 watt (0.04 kilowatt) appliance operating for 25 hours also uses one kilowatt hour of energy.
In 2019, the average US residence consumed 10,649 kilowatt hours, or about 887 kilowatt hours per month.
If the cost of electricity is $0.15 per kilowatt hour, then the average monthly household electric bill in the US might be around $133.
Random International Comparisons
Electricity prices can vary widely across the world. Germans might pay $0.38 per kilowatt hour, while those in Qatar might pay $0.03 per kilowatt hour. If those groups were to use the same amount of monthly electricity as Americans (an assumption that is not true), the monthly bill would be $337 in Germany and $27 in Qatar, compared to the $133 above.
The US, as expected, is a leader in per capita electrical energy use, logging around 12,154 kilowatt hours per person per year. That’s good for tenth in the world, with Iceland setting the standard at 51,699 kilowatt hours per person per year. Down near the bottom is Chad with a measly 13 kilowatt hours per person per year.
As usual, if you’re unimpressed with the above, there’s a bottom line. For the average consumer, the less kilowatt hours the better. In other words, less kilowatts, less hours, or less of both.
