Okay, so what is the difference between power and energy? What are watts, joules, kilowatt-hours and BTUs?
These may not be ‘Frequently Asked Questions,’ but they ought to be, because power and energy are Frequently Confused Concepts. Power is the rate of energy release at a given instant in time. Energy is power integrated over time. Power is measured in watts, kilowatts and horsepower. Energy is measured in joules (watt-seconds) or kilowatt-hours. A power level of one watt that continues for one second equals one joule; the integrated energy from a 100-watt light that runs for 60 seconds equals 6000 joules. 4.18 joules equal 1 calorie, which is enough energy to raise the temperature of one gram of water by one degree Celsius. In U.S. industry, thermal energy is sometimes measured in BTUs (British Thermal Units). A BTU is the energy it takes to raise one pound of water one degree Fahrenheit. One BTU equals 1,055 joules. One horsepower equals 746 watts.
