What's a Watt?
Energy and Power Conversion Calculator
We are confronted every day by the notions of Energy and Power:
Cars and motors are sold by Horsepower, lightbulbs
by Watts, natural gas by Therms, electricity by Kilowatt-Hours, and
air conditioners by Tons or BTUs per hour. Is Energy the same as Power?
If not, what's the difference, and how do all of these units relate to each other?
It's really simpler than it looks. You can think of Energy as a "stuff" that can't be created or destroyed,
but can be converted in form. The form might be a moving mass,
light, heat, an elevated mass, particular chemical combinations, or
electricity in a wire. Power is simply the rate at which energy is converted (for example, a Watt is one Joule per Second).
Here are some of the ways that you will see Energy and Power represented: Modify the value
in any box and see what happens...
The following table illustrates how various energy storage systems would store this amount of energy:
Always remember that, in every energy conversion,
some of it goes where you want it, and some
goes elsewhere (usually heat). The ratio of what you want
to the amount that you start with is called efficiency.
Here are some typical efficiencies encountered in everyday
- burning fossil fuel to get useable heat - about 85%
(running a gas-fired water heater, or making steam
to power a turbine...some heat goes up the smokestack).
- burning fossil fuel to get electricity - about 33%
- sunlight to electricity in a PV cell - about 10%
- putting electrical energy into a battery (charging it)
and pulling it back out: about 90%
- converting electrical energy into mechanical energy
with an electric motor about 85%
I have made considerable effort to present correct information.
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