THE WIND POWER BOOK
(Page 7 of 9)
EDITOR'S NOTE: Paperback copies of The Wind Power Book by
Jack Park can be purchased from Mother's Bookshelf, P.O.
Box 70, Hendersonville, North Carolina 28791 for $11.95
each. Another book that should definitely be a part of any
prospective windpower user's library is a new treatise by
Donald Marier (editor of Alternative Sources of Energy
magazine) called Wind Power for the Homeowner: A Guide to
Selecting, Siting, and Installing an Electricity-Generating
Wind Power System ...also available—for $12
.95—from Mother's Bookshelf. (Please include 95d for
shipping and handling.)
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ENERGY AND POWER
A clear distinction must be made between energy and power
...two different but closely related quantities. Briefly,
power is the rate at which energy is extracted, harnessed,
converted, or consumed. It equals the amount of energy per
unit time, or
Power =
Energy
Time
An equivalent relation between these entities is
Energy =Power X Time
The amount of energy extracted or consumed is therefore
proportional to the elapsed time. For example, a typical
light bulb draws 100 watts of electrical power. One watt (1
W) is the basic unit of power in the metric system, Leave
the light bulb on for two hours, and it will consume 200
watt-hours (100 watts times 2 hours equals 200 watt- hours,
or 200 WH). Leave it on for ten hours, and it consumes
1,000 watt-hours, or one kilowatt-hour (1 KWH), the more
familiar metric unit.
In the English system, energy is measured in foot-pounds,
British Thermal Units, and a host of other units that don't
concern us here. One foot-pound (1 ft.-lb.) is the amount
of mechanical energy needed to raise one pound one foot
high. One British Thermal Unit (1 BTU) is the
amount of thermal energy needed to heat one pound of water
1°F. Power is most often measured in horsepower and in
BTU per hour. One horsepower (1 HP) is the power required
to raise a 550pound weight one foot in one second:
1 horsepower = 500
Foot-Pounds
Second
Note that the units of power are expressed in units of
energy per time, as one would expect.
Conversions between metric and English units require that
you know a few conversion factors, For example, one
horsepower equals 746 watts ...and one kilowatt-hour is
equal to 3,413 BTU. Thus,
100 W =
100
HP= 0.134 HP
746
10,000 BTU =
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