Shopping for Solar? Get to Know Kilowatts and Kilowatt-Hours
Knowledge is power, and knowledge about the power you use at home can turn you into a more skilled solar panel shopper.
Solar panels convert sunlight into electricity. If you're thinking about getting solar panels of your own, you'll want to understand just how that electricity works.
The science and infrastructure that bring nonstop electricity to our homes is something most of us don't think much about, much less talk about. But if you're consulting with solar companies about installing panels on your roof, you'll have to start. And to do that, you need to know the jargon.
Terms like kilowatt, megawatt, kilowatt-hour and more are important when you're shopping for a solar panel system. And even if you don't have solar panels, you'll want to understand kilowatt-hours, an important measurement on your electricity bill.
If you're intimidated by the lingo, don't fret. Here's a quick breakdown of some of the measurements used in the solar and energy industry and what you need to know as a homeowner.
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What are watts, kilowatts, megawatts and gigawatts?
When you want to understand energy terminology, you have to start with the most basic unit. A watt is a unit of power. It measures the rate at which energy is generated or consumed.
A watt is simply defined as the flow of one joule of energy per second, according to Jake Edie, an adjunct professor at the University of Illinois Chicago. Edie teaches a course on clean energy in the electric grid.
A practical way to grasp this concept is to think of a joule as the amount of energy required to lift an apple by 1 meter, Edie told CNET.
How to convert to kilowatts, megawatts and gigawatts
Converting watts to kilowatts, megawatts and gigawatts is simple multiplication.
Kilowatts and megawatts are simply multiples of watts, Edie said. One kilowatt equals 1,000 watts, and one megawatt equals 1,000 kilowatts or 1 million watts. Converting between these units is as simple as multiplying or dividing the given metric by 1,000.
To convert from watts to kilowatts: Kilowatts = watts / 1,000
To convert from kilowatts to megawatts: Megawatts = kilowatts / 1,000
To convert from megawatts to gigawatts: Gigawatts = megawatts / 1,000
For example, if you have a power output of 15,000 kilowatts, you can convert it to megawatts by dividing it by 1,000: 15,000 kilowatts / 1,000 = 15 megawatts. You can convert it to gigawatts by dividing again by 1,000: 15 megawatts / 1,000 = .015 gigawatts.
To convert from gigawatts to megawatts: megawatts = gigawatts x 1,000
To convert from megawatts to kilowatts: kilowatts = megawatts × 1,000
To convert from kilowatts to watts: watts = kilowatts x 1,000
For instance, if you have a power output of 1 gigawatt, you can multiply by 1,000 to find out how many megawatts you have. Multiply by 1,000 again to get kilowatts and again to get watts.
1 gigawatt = 1,000 megawatts = 1,000,000 kilowatts = 1,000,000,000 watts
How big are gigawatts?
Gigawatts (and megawatts, really) are only relevant on the scale of the grid. When people talk about states or countries transitioning to green energy, they're talking about gigawatts. When we're talking about your home, we're talking kilowatts.
What are kilowatt-hours?
Kilowatt-hours, meanwhile, measure energy rather than power. The distinction can be hard to visualize, Edie said.
Edie uses the analogy of a water pump. The power of the pump is how much water it can pump in a certain amount of time -- say, 5 gallons an hour. The amount of water pumped depends on how long the pump is operating. One with the power to pump 5 gallons per hour, if left on for 2 hours, will pump 10 gallons of water.
In terms of energy, a solar panel might have a rating of 500 watts. That means in an hour, it would generate 500 watt-hours of energy -- or half of a kilowatt-hour. If it operates for 2 hours, that's one kilowatt-hour of energy produced.
How to understand your energy usage in kilowatt-hours
If you're considering installing a solar system, it's crucial to understand your current energy usage in kilowatt-hours. This knowledge empowers you to make an informed decision when comparing solar panels. In addition, your utility bills provide a clear picture of your monthly energy consumption, allowing you to track and manage your usage effectively.
For example, most homeowners' energy consumption surges from June to August due to increased air conditioning usage during the summer heat. Similarly, homeowners with electric heaters see similar spikes in the winter due to the cold weather. By analyzing these usage patterns, you can identify peak energy times and evaluate how solar panels can optimize energy efficiency.
Many household appliances provide power ratings (in watts) on their labels or user manuals. To calculate the energy consumed in kilowatt-hours, you can multiply each appliance's average usage time per day by its power rating. This calculation lets you identify the devices that contribute the most to your overall energy usage. The US Department of Energy offers an online calculator for this purpose.
Alternatively, Silicon Valley Power, the community-owned electric utility in Santa Clara, California, provides an extensive table listing the typical energy consumption of various household appliances, which can be used as a reference guide. Here are some approximate energy consumption values for standard household devices according to Silicon Valley Power:
Typical appliance power consumption
| Appliance | Detail | Estimated energy usage |
|---|---|---|
| Air conditioning | Central (3 ton - 12 SEER) | 3.0 kWh per hour |
| Refrigerator | Energy Star 14 cubic feet | 34.5 kWh per month |
| Washing machine | Energy Star qualified | 1.90 kWh per load |
| Television | 60- to 75-inch LED 4K | 0.15 kWh per hour |
| Computer | Laptop | 0.02-0.05 kWh per hour |
| Medical equipment | Sleep apnea machine | 0.2 kWh per hour |
What to know about kilowatts when buying solar panels
If you're trying to figure out how much power your solar panels need before purchasing a system, start by checking out your utility bill. Find how many kilowatt-hours you use monthly and divide that by the number of days. That will give you your average daily usage. Then, divide that daily usage by how many hours of sunlight, or peak sun hours, you get in a day, on average (four or five is a good ballpark figure for the contiguous US). You'll have the power rating you need for your solar panels to keep up with your energy needs.
If your area gets the equivalent of five peak sun hours per day, 1 kilowatt of solar panels would generate five kilowatt-hours of energy in a day. If you use 25 kilowatt-hours of energy on a typical day, 5 kilowatts of solar panels will meet your needs.
There are other factors to consider -- your panels will generate more electricity during the day and little to none at night, necessitating either a connection to the grid for net metering or a solar battery. And to navigate both of those decisions, you'll need a working knowledge of kilowatts and kilowatt-hours.
Correction, June 6: This story initially used the wrong unit of measurement for the energy needed to lift an apple by 1 meter. It is a joule.
Correction, Aug. 18: This story originally presented some statements as direct quotations that were actually paraphrases of what the individual cited had said. Those passages have now been rendered appropriately as paraphrases.
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