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Domestic Wind Power

I have always wondered about the idea of installing a windmill on my roof. Without highlighting the companies I have been looking at the figures quoted by those companies that provide the windmills.

One says:
How much energy does it generate?
The xxx will generate around 10,000 kWh per year in a good wind site of 5.8m/s average. This is equivalent to five low-energy houses’ electricity demand, or the electrical needs of a twenty man office (i.e. lights, computers, servers, printers, faxes and phones)


Lets apply a bit of physics to this. kWh is a KiloWatt Hour. It is a measure of energy rather than power. If you have a single bar of an electric radiant heater (1 kW) on for an hour that provides the energy of a kWh.

If we even the figures out to calculate the average power we have to divide 10,000 by 365 days and then 24 hours. That gives you a power of 1.1 kW. Not actually as bad as it could be, but clearly not enough to power a 20 person office unless most of the equipment is kept off. (even if you multiply it up to 5kW by working hours.)

There is then the issue of having an average windspeed of 5.8m/s.

Wind Power has its role, but energy efficiency is the top priority.

Comments

Joe Otten said…
There is considerable skepticism towards micro turbines from such worthies as the Centre for Alternative Technology.

In some locations they will work, but the typical suburban rooftop gets too little wind and too much turbulence. A wind speed survey is recommended.

But with £1600 turbines appearing in B&Q next month, there is a risk of a big mis-selling problem.
Tom Gray said…
For readers, there is a lot of information on small wind turbines available from our Web site.

Regards,
Thomas O. Gray
American Wind Energy Association
www.awea.org
www.ifnotwind.org
ecofx said…
Office hours do indeed end up as approx. 20% of the year, so you can multiply up by five, thus your calculation of 5kW for 20 people (250W per worker) during those hours is reasonable. This is 250W per office worker.

The biggest drains on power are computers plus peripherals and lighting, but 250W average is easily manageable, even without power management considerations.

The turbine you quote figures for (without naming it) is of a new vertical axis blade design, isn't it? To be able to get an average of 1.1kW out of a turbine, a conventional turbine would have a rated power of about 5kW, have a swept area of about 20 sqm, and be in a windy area on a decent mast to get above other air-flow obstructions.

The first production model of this new turbine seems to have a smaller swept area, but could perform more efficiently at (almost) roof height, so for windy locations these claims may also be reasonable.

According to the DTI, Moseley and Yardley get 5.3 and 5.2 m/s average wind speed at 10m off the ground, respectively.

However, although I am a supporter of wind power, consider your environment, John.
Go to the 'products in development page' to see a scale diagram of the turbine's size. I think even a 2.5 is a bit big for compact residential areas. But on a high mast (less noise at ground level), they would be fine at allotments, school playing fields etc.

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