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Rooftop and Urban Wind

May 4, 2007
Paul Gipe

Roof Top Over the Top in Britain


Has something happened to the water in Britain since they privatized the water companies? Someone should check because the British government has gone berserk.

In an article in the Guardian Terry Slavin reports on a British government program to subsidize micro wind turbines with capital grants of 30% of the installed cost for roof top or so-called urban wind installations. In the land of Margaret Thatcher, the Quota model, and neo-liberalism, the British are resurrecting an incentive program that failed 30 years ago in the misguided hopes that it won't fail this time. It didn't work then, it won't work now.

Capital subsidies are one of the worst if not the worst policy mechanism for spurring the development of renewable energy. Of course, this assumes that the British government wants to actually produce renewable energy from this program. That's not certain, especially as details emerge on the companies hoping to take advantage-in all senses of the word-of the program and consumers who are anxious to join the renewable revolution sweeping the globe.

British consumers are being poorly served by their government at best and at worse they are being led to the roof top altar for ritual slaughter.

I've written elsewhere why roof top mounting of micro wind turbines-of any wind turbine-is a bad idea, so I won't go over the same ground again. But I will take a quick peak at the outlandish claims of some of the British companies greedily eyeing the so-called roof top market.

Renewable Devices' Swift

Something never felt right about the Swift from the very beginning. The sales pitch is aggressive, not as over the top as some, but aggressive all the same.

For example, just look at these specs for a wind turbine with only a 2.1-meter diameter rotor (swept area of only 3.5 m2).

  • Rated power output: 1.5 kW
  • Annual Power Supplied: 2000 - 3000 kWh
  • Design enables use of turbine in turbulent air flows
  • Silent mast mounting technology eliminates unwanted vibration to building . . .

Whoa, "silent" mounting. That's a tip off all is not well in the land of Shakespeare. No wind turbine is silent or vibration proof.


Update December 8, 2008: Renewable Devices now claims that their Swift turbine will produce only 2,000 kWh per year "Dependant on siting of turbine". Indeed. For the size of the Swift, you'd need an average annual wind speed of at least 7 m/s (15 mph) to produce that much electricity. This assumes that the turbine is one of the best performers in its class and that has not been substantiated. In fact, there is very little published data on the actual performance of the Swift turbine.


Using a standard power rating for small wind turbines (see my books for details), this small turbine should only have a rating of 600 watts-not 1,500 watts! That's a rotor loading of 433 watts/m2, 1.16 times the much over-rated AirX.

But it gets better. Renewable Devices says it's turbine will produce 3,000 kWh per year at an average wind speed of 5 m/s. More like 1,000 kWh/year under those conditions for a turbine of that size and that's if everything works right-consistently. More likely only 750 kWh/year.

Whatever they're smoking at Renewable Devices, it must be good, very good. It surely is not legal.

Windsave's WS 1000

Windsave is no better. The 1.75-meter diameter turbine should have a standard power rating of 500 watts and not 1,000 watts claimed. Their estimate of annual generation is high too. I find the noise measurements for the Windsave particularly difficult to accept without seeing a full report. The rotor loading of 400 watts/m2, is "only" 1.5 times the much over-rated AirX.

Stewart Russell's commentary on Windsave. Stewart knows what he's talking about. He's a pro.

Stealthgen D400

Of course this wonder qualifies for stealth because it's so small its practically invisible. It should be on a sail boat-for which it was designed.

The 1.1-meter diameter machine should be rated at 190 watts. Will it produce the 660 kWh per year claimed? Half of that, maybe. Probably a lot less in an urban environment.

Conclusion

What's the take-away message here? Check the water. Someone's poisoning the British. Call Miss Marple. She better get on it right away before more damage is done and they actually start installing these over-hyped little devils.


Wind Speed Measurement over a roof top in Edinburgh, Scotland by Hugh Piggott.


Andy Mahoney's Rooftop Mounting Failure at http://navitron.org.uk/forum/index.php?topic=942.0


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