WIND TURBINES
THE POWER TO GENERATE
Domestic scale wind turbines have dropped off the front pages of late. A couple of years ago it seemed that every celebrity or rising politician was having a roof-top wind turbine installed. Sales of small roof-mounted machines from your local DIY shed brought the Government’s grant funding scheme to its knees. We don’t hear so much about them now, perhaps because it has become clear that they don’t work.
Let’s be clear, the right wind turbine in the right location is a great idea and will produce lots of energy. Energy that can be sold to the grid, produce an income for the owner and reduce CO2 emissions. But any wind turbine in a bad location is a waste of space. And town centre roof tops are always bad locations.
A survey carried out by Encraft Ltd monitoring the performance of 26 turbines over a 12 month period has proved this. The survey was “an open-access project to provide independent and objective data on the performance of rooftop wind turbines on real sites in the UK” – which is a quote from their web site www.warwickwindtrials.org.uk/2.html
What this 2 year long project, meticulously recording data from sites from Aberdeen to Cornwall, showed was that small wind turbines bolted to roof-top locations with very little wind will not produce very much energy. By “real sites” it seems they mean sites with no wind. It also showed that the power-curve information provided by wind turbine suppliers was not accurate in urban locations. Which is perhaps not surprising given that the manufacturers will have tested their machines in rural locations, possibly even locations with some wind.
This project measured the wind speed at each site, found that it was below recommended levels but erect a wind turbine anyway and reported that the turbine was not producing much energy. They say that madness is repeating the same action and expecting a different result. These guys did it 26 times. And the project was funded by the public purse, which makes MP’s expenses seem quite reasonable.
The Encraft report conclude that “Overall the trial has painted a picture of an industry and technology that is still at development stage and is likely to make a tangible contribution to energy and carbon saving only on the most exposed sites and tallest buildings.” It could be argued that the industry knows very well that exposed sites and windy conditions are necessary for a wind turbine – that piece of knowledge has been in the public domain since Roman times. In 5 years as a renewable energy consultant I have found only one supplier that stuck wind turbines where-ever the customer wanted – the one you could buy at the local DIY shed. In my experience there are good and bad wind turbine suppliers, some more rigorous in their site testing than others. I know of none that would have erected a turbine in most of the sites selected for this survey.
The report conclusions continue “The combination of this reality, aggressive and over-optimistic marketing by some suppliers, and the enthusiasm and credulity of the market (and regulators) has potentially led to an unfortunate outcome where the wind industry as a whole is in danger of suffering from a setback in credibility.” It might be argued that it is not the industry that lacks credibility but rather this survey.
There is an immutable law that an annual average wind speed of more than 5 metres per second (m/s) is necessary for a wind turbine (any wind turbine) to produce enough energy to justify putting it up. The DTI provide a very handy national wind speed database at
www.berr.gov.uk/energy/sources/renewables/explained/wind/windspeed-database/page27326.html
Typing in a grid reference will return a set of figures showing the annual average wind speed for the given location. Anyone doing this will notice almost immediately that the wind speed is faster the high off the ground you are. For my own home the wind speed at 10m above ground level (AGL) is 4.8m/s, at 25m AGL 5.3m/s and at 45m AGL 5.8m/s. That means that my wind turbine would need to be about 20m high to get into wind good enough to give good production. The reason is that the ground creates drag, slowing the wind down. Drag is also created by trees, building and other obstructions – including roofs. The wind is slowed when it passes over a single roof, it is slowed even more when it passes over a town-full of roofs. What the database does not know is that my house is surrounded by trees and in a hollow on a hillside. It is actually protected from the wind. The nearest good location is about 200m from the house – a fact that would be apparent without any testing of the wind, but testing the wind is always essential.
To repeat, wind turbines are great in the right location but you need to establish exactly how good your site is. The best, if not only, way is to monitor the wind. The Wind Prospector from Wind And Sun Ltd (www.windandsun.co.uk) will tell you exactly what production you can expect from any wind turbine. But you don’t even need that to tell you that if you live in a single-storey house in the centre of town a wind turbine ain’t gonna work.
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