How much a residential wind turbine can generate depends on a number of factors – wind speed, local environment and turbine size are just three of them. Having said that, it is possible to make an estmate of what a particular turbine is likely to produce in a certain location. It’s not a precise science, but you can get an idea.

Firstly, a well sited turbine will typically generate on average around 10% of its rated output over a long period of time. This may seem low, but you need to consider how the what the power rating actually represents. The rating of a geneator gives its MAXIMUM output, at the optimum wind speed. Output increases with the cube of the wind speed, so doubling the wind speed increases output by 8 times. And obviously the wind speed varies from day to day, and from hour to hour. Manufacturers obviously want to sell their product in the best possible light, so they quote the rated output at just about the fastest useable wind speed that the turbine can handle. All turbines have a cut-out, so that if the wind speed is too high they are not damaged by spinning too fast. So the reason for the 10% average accounts for the fact that the wind is unlikely to blow at the fastest safe wind speed continuously 7 days a week, 52 weeks a year.

You’ll have noticed that I said ‘a well-sited turbine’ can produce around 10% of the rated power. Siting is incredibly important. It’s important to look at wind speed maps for your area to get an idea of the average you could expect over the year. Most sources think that 4.5m/sec (or 10 mph) is around the minimum average level you need to make a home wind geneartor worthwhile. Even if the wind maps look promising, you should seriously consider monitoring the actual wind on your proposed site for at least 3 months using a wind meter to make sure that the numbers really do stack up.

You also need to consider the very local environment. If there are large trees or buildings nearby, they can make the airflow turbulent at up to twice the height of the obstruction. And turbulent air greatly reduces the power generated. In this were the case you would need to have the turbine at twice the height of the obstrustion to stand a chance of generating what you anticipate. This is why some oranisations suggest that the best place for a residential wind turbine is in open country – ideally on a plot of land around 1 acre with no obvious obstucions nearby. This may going too far, but you need to be aware that a more enclosed environment will increase the required height of the turbine.

The height above the ground of the turbine also need to be thought about. Increasing the height by just 5 metres (16 feet) can increase the output by around 30%. But obviously this would need to be offset against the increased cost for a taller mast, whether local building codes allow such high masts, and the likely increased impact upon your neighbours.

If you can find a suitable site it is possible to generate decent amounts of electricity from a residential wind turbine. And many countries have utility tariffs which make it financially attractive to sell excess electricity back to the grid. Even with expensive, fully installed systems consumers can expect to achieve a payback of investment in under 10 years, and some people have reported payback times of 5 – 7 years. The key is to research your site properly before buying a system to make sure it will achieve what you want it to. The tales of home wind turbines not generating any where near the amount of electrcity which was expected are nearly all caused by ignoring the important details about the correct siting of the turbine. Some basic research at the beginning can save a lot of heartbreak in the following years!

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