The romance and reality of urban wind power

Its now possible to buy a 200 watt micro wind turbine for $449 from Jaycar electronics. A couple of years ago they were even including a four meter tower with the wind turbine. If you live in a windy flat spot with no trees or houses upstream of the prevailing wind it’s a bargain. But don’t waste your money buying one of these and putting it on top of your suburban house, in your backyard or on top of your office building.

Encraft in the UK have published the results of a trial on the operation of 26 building mounted wind turbines with a combined 168,950 hours of operation. The purpose of the trial was to see how grid connected small wind turbines performed on a range of building types and locations. It was undertaken in 2007 and 2008. A range of turbines from different manufacturers were tested, with capacities from 400 to 1,250 watts. The report includes photos of each installed turbine. Looking at the photos it becomes pretty obvious that the wind turbines that performed the best were mounted high, well above surrounding buildings.

The gist of the report comes in paragraph three “as anyone who knows anything about wind power will attest, urban environments and building mounting is probably the most challenging context in which to try to make wind power work.” The report then goes to show that the average availability factor of turbines in the trial was 0.85%, improving to 4.15% if turbines which were switched off or broken were taken into account.

At a 4% availability factor a 200 watt turbine would only produce 70kWh a year, about 20% of the energy used by a small energy efficient fridge. At a 1% availability factor that drops to under 20kWh. Take off the power that the generator might use and the effective power output could be zero.

The report notes that many of the turbines on the best sites (high rise) were turned off because of noise complaints.

Encraft say that the “technology is still at a development stage and is likely to make a tangible contribution to energy and carbon saving only on the most exposed site and tallest building.”

A couple of years ago I researched putting a small wind turbine on my surburban house. Someone from the wind industry advised that for the turbine to work it had to be twice as high as the nearest obstruction. Otherwise the air would be turbulent, reducing output and leading to early failure. I figured that building a 50 meter tower in my backyard and getting the necessary planning permit wasn’t worthwhile. And of course it also helps if you live in a windy location.

With this rule of thumb in mind it becomes obvious pretty quickly that urban or surburban wind generation in most cases just isn’t viable with current technology. And the UK study proves it. Maybe emerging technologies that may be able to operate better in turbulence may prove more useful in urban environments, such as the linear wind generator.