Capacity factor is the ratio of the actual productivity of a wind farm to its rated capacity. Let’s understand what is meant by rated capacity and actual capacity. We will also try to understand why there is a difference between the two and what its effect on wind power production is.
Rated Capacity
Rated capacity is nameplate rating or capacity of each wind turbine multiplied by the number of hours in a year. Nameplate rating of a wind turbine is the amount of power that it can generate under ideal conditions. It is the maximum power that can be generated theoretically. The rated capacity is also called installed capacity.
Real Capacity
Real capacity of a wind farm is its actual productivity. It is calculated by taking an average over a long period of time, typically a year. The main reason for real production of a wind farm being less than the rated capacity is availability of wind. Wind speeds do not remain constant, but vary with the time of the day, changing season, local weather conditions, etc. Production of electricity is possible only if wind speed is between 8 kph to 54 kph. Anything lower or higher cannot be used.
Capacity Factor Values
Nameplate ratings are expressed in watt. Productivity of a wind farm is also in watt. Since capacity factor is the ratio between the two, it has no units. It is expressed in percentage. Normally a wind farm’s capacity can be anywhere between 15 and 50%.
Improving Capacity Factor
Capacity factor of a wind turbine can be improved by improving its design and ability to produce electricity for a wider range of air speeds. If we talk of wind farm productivity, it can also be improved by increasing the height of windmills. Productivity increases by 34% if the height of the windmill is doubled. This is because at greater height there is less turbulence in the atmosphere and less obstructions as compared to the ground. However, air density decreases with height, which takes away some power from the wind.
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The concept behind the capacity factor, which we discussed just now, applies to all renewable energy resources, like solar energy, biomass, etc. Real production of electricity by wind farms is less than the theoretical maximum that can be achieved. To ensure maximum utilization of wind power, this gap has to be reduced more and more.
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