Turbines are now generally in the range of MW. What determines how much power a wind turbine can produce? A taller tower provides access to steadier winds, and larger blades capture more wind energy.
How much energy do wind turbines produce? Every wind turbine has a range of wind speeds, typically around 30 to 55 mph, in which it will produce at its rated, or maximum, capacity. At slower wind speeds, the production falls off dramatically. If the wind speed decreases by half, power production decreases by a factor of eight. On average, therefore, wind turbines do not generate near their capacity.
For example, if a 1. What is the typical capacity factor for industrial wind turbines? The average capacity factor for U. In it was What is the difference between capacity factor and availability? Without the wind, it is like a bicycle that nobody rides: available, but not spinning.
The second figure is availability, the amount of time that a turbine is not shut down. Neither figure expresses the amount of time that a wind turbine is actually generating electricity. How much of the time do wind turbines generate energy? Wind turbines generate electrical energy when they are not shut down for maintenance, repair, or tours and the wind is between about 8 and 55 mph.
Below a wind speed of around 30 mph, however, the amount of energy generated is very small. Are capacity factor and efficiency the same? The spinning blades of the turbine define a circle, with wind passing through the area of the circle being converted to energy. Remembering some basic high school maths, the area of a circle is pi x r 2. In this case r is the length of the turbine blades. This equation is important because it shows just how much the power and energy a turbine produces is dependent on the length of the blade.
If you double the length of the blade, you will get four times the amount of power and energy. Homes and commercial sites have space and regulatory considerations that limit the lengths of the blades. Large wind farms have much less restrictions and there is a continual push to make larger turbine blades and thus more powerful turbines. These things have all sorts of transport issues and are certainly not cheap!
Wind speed is obviously critical: the longer the wind blows at higher speeds the more energy the wind turbine produces. So how do we figure out how much wind is at a particular site? There are a few things that need to be considered when using such maps.
First is the height above ground. This has a massive effect on average wind speed, with wind increasing substantially as height increases. Three average wind speed maps of the United States are shown below, for heights of 10, 40 and 80m above the ground. These maps show just how important height is.
Take Nebraska, for example. At 10m above the ground, the average wind speed is about This is close to the edge of viability for a wind turbine. At 40m high, the average wind speed increases to about And at 80m, its up to The figure below shows a power curve for a commercial wind turbine with a rated power of W.
At a wind speed of 4. A massive difference in power output and therefore energy as the height above ground increases. Commercial wind farms with very large blades 80m plus have their hubs more than 80m high and thus can reach the higher wind regions. For smaller home and business systems, heights can be limited by local regulation, and of course economics.
Another factor that can be important when looking at average speeds is how constant the wind is. If the wind is reasonably constant then average wind speed is a good indicator. If, however, the site has mostly very light wind, but the average speed is boosted by frequent violent storms with wind speeds above the shutdown speed, then power and energy output will be much lower.
So how can we figure out how much energy to expect out of a turbine? We need this to evaluate the economic performance. The capacity factor, expressed as a percentage, is the actual energy output from a turbine over a year, divided by the energy output that would be obtained by the turbine operating at its rated power over a year.
If the turbine operated at 5kW for a whole year, the energy output would be 5kW x 24 hours per day x days per year equals 43, kWh. Suppose the turbine actually produced 20, kWh over the year. To run the economics of a wind turbine it is necessary to have an estimate of the capacity factor so we can estimate the amount of output energy.
The average wind speed combined with the power curve is one way of doing this. This estimation gets better with more constant wind. Today this urban Texas cowboy continues to crank out high-quality software as well as non-technical articles covering a multitude of diverse topics ranging from gaming to current affairs. How to Calculate Wind Pressure on Banners. How Do Wind Turbines Work? Wind Turbine Size Vs. How to Build a Wind Turbine for Kids.
Devices Used to Harness Wind Energy. Ways to Conserve Wind Energy. Plans to Build a Windmill. Homemade Windmills for Electricity. How to Calculate Fan Output. How Does an Anemometer Work? References Energy. Energy Information Administration: What is U. Electricity Generation by Energy Source?
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