When we see the symbol “kWh” on our utility bills, we may assume that it’s some mysterious mathematical or metaphysical entity, and ignore it altogether. Actually, kWh simply means kilowatt-hours, and it’s a basic measurement of energy. Understanding kilowatt-hours helps us understand our electrical bill, while also helping us look smart when people start talking about heavy topics like renewable energy or carbon footprints.
It starts with a watt.
Obviously, kilowatt-hours have something to do with watts. A watt is a unit of power. In technical terms, a watt is a current of one ampere, pushed by a voltage of one volt. Volts x amps = watts.
“Kilo” is from the Greek, meaning “thousand.” Just like a kilometer is 1,000 meters, a kilowatt is 1,000 watts of power. A megawatt is equal to 1,000 kilowatts – or 1 million watts. Household power is generally measured in kilowatts, while large-scale power plants measure in megawatts or even gigawatts.
Energy is power generated over time. To understand the power/energy relationship, think of the wattage powering a household device. Your refrigerator may have a lot of power (wattage), but that power is useless to you if it only works for one second. You need your fridge to keep working 24 hours per day. Thus, kilowatts don’t mean much in a practical sense, unless we see their performance over time.
Energy companies base their services around kilowatt-hours, which are 1,000 watts of electrical power, over the course of one hour. Kilowatt-hours are measurements of energy, and you’ll see them abbreviated as kWh (big W, and little k and h).
Energy and power. Not the same thing.
Most people use the terms energy and power interchangeably, but that’s technically incorrect. They’re related… but not the same.
Energy is the capacity to do work – literally the ability to move something over a distance. For example, it takes energy to move your car down the road. In the gym, it takes energy to lift weights over your head. It also takes energy to produce light by moving an electron through the filament of a light bulb.
Energy can be measured in joules, BTUs, newton-meters, and calories. But when we’re talking about electrical energy, we talk in terms of watt-hours or kilowatt-hours. Energy measures the total quantity of work performed.
Power (or wattage) is the rate of producing energy – it’s a measurement of energy per unit of time. If a device is very powerful, it can do lots of work in a short time – more quickly than a less-powerful device. A powerful gust of wind might blow your lawn chair across the patio in a second. A light breeze might nudge that same chair across the patio, too, but it would take all day. If the chair moved across the patio, the power level was different, but the overall energy use was the same.
What do kilowatt-hours mean to me?
Your electricity bill is calculated in kWh’s – per day and over the course of the month. The less kWh’s your household utilizes, the smaller your electrical bill. Therefore, kilowatt-hours translate into money moving out of your pocket. Reducing kilowatt-hours helps you hold onto that money. Before you buy new appliances, compare kilowatt-hour capacity. Energy-efficient models will save you money.
When a whole community, country or planet reduces kWh’s, the savings are even more dramatic. Less energy consumption equals less greenhouse gas emissions, so energy efficiency is imperative for the health of the environment. Energy efficiency also ensures more resource availability for generations to come. For Americans, it means less dependence on foreign power sources – and thus greater national security. Of course, energy efficiency is good for the economy, too. Americans who care about energy conservation are spurring innovation in the manufacturing of efficient devices, and saving a grand total of more than $500 billion a year.