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A watt is a measure of electric power. Technically, it's a derived measure of the
rate of transfer of conversion of energy, defined as one joule per second. The same
measure can therefore be applied to other forms of energy besides electricity. For
example, a person weighing 100 kilograms climbing a 3-
Other definitions of the watt as a measure of energy conversion include: A watt is the rate at which work is done when an object with a velocity of one meter per second maintains that velocity against an opposing force of one Newton.
A watt is the rate at which work is done when current equal to one ampere runs through
In practice, the watt is normally used as a measure of electric power potential at any one time. It measures the electricity consumption of appliances (e.g. a one hundred watt light bulb), and this refers to the intensity of power used by the appliance at any given moment that it is in use.
We also speak of the output of electrical production in watts, meaning the amount
of power the source can produce at any one time. Multipliers of the watt (kilowatt,
megawatt) are in use to describe larger-
A terawatt is a measure of energy (especially electricity) equal to one trillion watts. It is, of course, a great deal of power production. The total energy consumption of human society all over the world is measured in terawatts and in 2006 was estimated to be some 16 terawatts.
The most powerful lasers ever developed have produced energy measured in terawatts, but only for extremely brief periods of time. The total amount of solar energy striking the earth is estimated to be 174,000 terawatts, which is of course more than enough to supply all the energy needs of humanity many times over (although we cannot cover the entire planet with solar panels, and so can make use of only a small fraction of this available energy, most of which must be used to grow plants instead).
A common confusion involves the difference between watts (and the multiples of this
unit such as the terawatt) and watt-
Home energy bills usually measure energy consumption in watt-
The world's total energy consumption as of 2006, assuming it was constant throughout
the year at an average consumption of 16 terawatts, would have been 140,160 terawatt-
The difference can also be important for energy production. A laser that produces
energy in the terawatt range but only for a tiny fraction of a second is not generating
much power measured in watt-
More practically, a home energy system that generates, say, 2000 watts of power at
peak times generates much less than that times 24 in watt-
As stated above, the sunlight striking the earth provides far more power than the entire power consumption of humanity. Practical use of this power is however limited by the amount of surface available for capturing sunlight to produce electricity, and also by the efficiency of photovoltaic cells and other methods of converting sunlight into electricity, none of which approach 100 percent conversion (which is, of course, physically impossible).
Most sunlight must go to supporting the biosphere by providing energy for the growth of plants. But one big advantage of solar power is that it can be produced from surfaces already in use for other things, such as the rooftop solar and other buildings. The total area available for solar energy use would provide power well into the terawatt range.
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