The Truth About Wind Turbines

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 rooftop wind turbine installed. Sales of small roof-mounted machines from local DIY sheds brought the Government’s grant funding scheme to its knees. We don’t hear so much about them now — perhaps because it has become apparent that they don’t really 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 rooftops are always bad locations.

A survey carried out by Encraft 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,” according to its website (warwickwindtrials.org.uk).

What this two-year-long project, meticulously recording data from sites from Aberdeen to Cornwall, showed was that small wind turbines bolted to rooftop locations with very little wind will not produce very much energy. By “real sites” it seems it means 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 erected a wind turbine anyway) and then reported that the turbine was not producing much energy.

The Encraft report concluded 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 fives years as a renewable energy consultant, I have found only one supplier that stuck wind turbines wherever 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.”

There is an immutable law that an annual average wind speed of more than 5m per second (m/s) is necessary for a wind turbine (any wind turbine) to produce enough energy to justify putting it up. The BERR provides a very handy national wind speed database at berr.gov.uk.

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 higher 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, buildings 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 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.

The Trials Explained

The Warwick Wind Trials began in 2007, with the intention to monitor 26 rooftop wind installations on a variety of urban and rural sites over 12 months. The sites ranged from Aberdeen to Cornwall with ten in Warwick, and locations including three tower blocks, a number of gable-end installations in different contexts, a steel framed building and a timber frame eco house.

What the trials proved without a doubt is that in the wrong location, wind turbines are pointless, but, more worryingly, that manufacturers’ claims can be at times misleading. Matthew Rhodes, MD at Encraft, explained: “What the Encraft Warwick Wind Trials have shown is that in the case of wind power, while the manufacturer’s published data might be true under perfect laboratory conditions, in the vast majority (more than 90%) of real-life building-mounted situations, actual performance will be at best 20% of this.”

My Wind Turbine Success Story

Derek Matthews (ABOVE) installed a FuturEnergy turbine in his and wife Anne’s rural Bromsgrove home three years ago. A perfect location for a turbine, it forms part of a comprehensive domestic renewable energy system, integrating with a series of motor-driven solar water heater panels. None of the electricity generated by the turbine is wasted. With priority given to maintaining the charge in the batteries, any excess electricity is used to power a series of specially modified freezers and fridges. After this, any additional surplus electricity is used to assist the solar panel in pre-heating the water feeding the hot water cylinder, and water can be diverted for bathing purposes, or for use with a dishwasher and washing machine both modified to run from the hot tank only.

Your Turbine Checklist:

To work out whether it is worth investing in a wind turbine, first read on and check that all of the following is true for you:

• You live in a rural location — turbines simply will not work in builtup urban areas

• You have enough room for one — typically you need double the length of the mast

• There are no large buildings and/or trees nearby that will affect the wind speed

• You have used the wind speed calculator at berr.gov.uk — you need an annual wind speed of at least 5m/s to justify a turbine

• You have tested the wind speed yourself using the Wind Prospector from Wind and Sun Ltd

• You have checked with the local authority that you are likely to be granted planning permission

• You are prepared for the fact that ‘pay back’ time could be many years

ABOVE: A pole-mounted wind turbine in an exposed location, like this from Tech2000 (LEFT), will yield far better results than one on a rooftop in a built-up area (RIGHT).

Further reading:

• Six Steps to an Energy Efficient Home
• Renewable Energy Systems
• Eco Logical

Voice your opinion about Wind Turbines in the Homebuilding Dicussion Forum