Can renewable energy sources power the world?
Can renewable energy sources power the world?

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Can renewable energy sources power the world?

2.2 Efficiency and capacity factor

When energy is converted from one to another, what comes out is never as much as what goes in. The ratio (usually expressed as a percentage) is called the efficiency of the process:

percentage efficiency = (energy output/energy input) x100

Some types of energy conversion can be really efficient, for example up to 90% in a water turbine; others very low - around 10-20% in a typical internal combustion engine.

If you’re trying to assess an energy generator’s productivity in practice, one useful measure is its capacity factor (CF):

capacity factor = actual energy output over time / maximum possible output

The period of time can be a year, a month, a week or an hour. The units for the output quantities can be kWh, MWh, GWh, etc., and the capacity factor can be expressed as either a fraction or a percentage. The time period to which the capacity factor relates (a year, a month, a week etc.) should be stated.

Have a look at a couple of examples:

Activity 1

What would be the annual capacity factor of a 1 MW plant running constantly at a full rated capacity for one year?


One year = 365 days x 24 hours = 8760 hours in a year or so, the annual capacity factor = 8760 MWh / 8760 MWh = 1 or 100%

Activity 2

A 1 MW wind turbine generated 3000 MWh last year, so what would its annual capacity factor be?


We have already worked out that there are 8760 hours in a year, so: annual capacity factor = 3000 MWh / 8760 MWh = 0.342 or 34.2%


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