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Energy, and electricity in particular, has several different units of measurement that can be more than a little difficult to understand, but I’m going to go ahead and try.

First up is the British Thermal Unit (BTU). The BTU is a measure of heat energy (not electricity). One BTU equals 252 calories, and will raise one pound of water one degree Fahrenheit. It is about equal to a match or a burning candle.  One barrel of fuel oil (42 gallons) offers 140,000 BTUs of energy. To produce one million BTUs you would need one of the following:

80 lbs of coal

250 lbs of hardwood

11 gallons of propane

7 gallons of #2 diesel fuel oil

293 Kilowatts of electricity (more on this below)

BTUs are generally measured in quads (one quadrillion BTUs). The world uses about 400 quads a year and the United States uses about a quarter of that, or 100 quads.

Electricity has three basic units of measurement; voltage-measured in volts; current-measured in amps; and, resistance-measured in ohms. A good way to understand these units is to think of a hose. The voltage is equivalent to the water pressure; the current is equivalent to the flow rate; and the resistance can be compared to the hose diameter.

Power is the rate at which energy is generated and consumed and is measured in watts. Watts are the product of volts and amps. 1000 watts is one kilowatt, and 1 million watts is a megawatt.  California currently has 500 megawatts of solar power, spread over 50,000 solar participants.

A watt-hour is equal to the work done by one watt acting for one hour. For example, a 100 W light bulb that is on for one hour uses 100 watt-hours (or .1 kilowatt hours). Your energy utility measures your use in kilowatt-hours.

One last term that is useful to know is “load.” A “load” is anything on the electrical circuit that draws power. Your refrigerator, TV, and electric toothbrush are all examples of loads. And the fact is, we have just gone over a “load” of information!

Posted by Danny Kennedy

Danny Kennedy co-founded Sungevity and now serves as strategic advisor. He is an internationally recognized opinion leader on climate and energy issues. He is the author of Rooftop Revolution: How Solar Power Can Save Our Economy - and Planet - from Dirty Energy (2012), a book that has been described as the clean energy manifesto for the next greatest generation.