Wind Turbines: Are They Worth it?

Whether David Cameron ever changes the face of British politics remains to be seen, but he has already had a huge impact on one small branch of British industry domestic wind turbine suppliers. Back in January 2006, he decided to give his Notting Hill house an eco makeover and the element that caught the popular imagination was the installation of a roofmounted micro wind turbine.

"It'll never work, There's no payback, It'll be too noisy," were some of the kinder comments aimed at Camerons project - and these were being voiced by reputable wind turbine manufacturers, not just anxious neighbours. Cameron had to apply for planning permission for his wind turbine and in doing so opened himself up to all manner of neighbourly criticism. However, in July the permission came through and the nation waits with bated breath to find out what the Camerons make of their new toy.

What it has done is put wind turbines on the agenda in ways they have never been before. The question many readers will be asking is: Should I be considering one for my project? Well, perhaps you should...

Understanding wind speeds

Average wind speed data is absolutely critical in determining how much power a wind turbine will produce. This is because the power output increases exponentially in relation to wind speed. Taking data from the website of wind turbine supplier Windsave:

• at 3 metres/second or less, it (in common with almost all wind turbines) doesnt rotate and produces no power
• at 4.6m/s, it generates just enough power to light a 60watt bulb
• at 7m/s, it produces 200watts
• it peaks at 12m/s (around 30mph), where it generates over 1kW of electricity, but that is only ever going to be achieved on exceptionally windy days
• at wind speeds much higher than this, it cuts out as a safety feature

Now, obviously all sites experience a multiplicity of wind speeds throughout the course of a year; but, in general, sites with low average wind speeds will have far more calm days and far fewer windy days so the total amount of wind energy available to harvest is much lower. So, knowing your average wind speed is critical to working out your likely power yield.

Wind speed data is freely available at www.bwea.com, maintained by the Department of Trade & Industry. The wind speed data is stored by grid reference. If you don't know your grid reference, there is a converter which will work it out for you if you type in your postcode. If you use this, you require the LR result, which you have to amend slightly before you key it into the database. Its all a little bit fiddly but worth it.

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The wind speed data is given for each grid reference at three different heights, being 45m, 25m and 10m above ground level. Note that the higher you go above ground level (agl), the higher the average wind speed. For instance, for my own address the figures are:

• 6.4m/s at 45m agl
• 5.9m/s at 25m agl
• 5.1m/s at 10m agl

This tells us something useful. The higher you go, the more wind energy there is available and the more electricity you will be able to generate. Now, a domestic wind turbine is realistically never going to be more than 10m above ground level. This low level figure is what should be used to calculate your likely power output. In contrast, the commercial wind farms are building turbines 100 metres high.

Size Counts

As a rule, the larger and taller your wind turbine, the better the investment. Whereas the small micro turbines mounted on walls or roofs will struggle to produce any meaningful amount of power or to have any sensible payback, the commercial wind farms will pay for themselves within four or five years, as each one is capable of producing 400,000kW of electricity each year.

If you happen to own a farm near a major power line, a giant 2MW turbine could represent a fantastic investment for you with mouthwatering returns. However, its an option open to very few of us.

Small Wind Turbines: There is an intermediate option that represents a more realistic proposition, especially to selfbuilders with a little land. There is a range of small turbines, rated at outputs anywhere from 2.5kW to 6kW, that produce sensible amounts of power, enough to export to the grid, and when grants and subsidies are taken into account, to represent moderately attractive investments. The 6kW Proven wind turbine, for instance, has been shown to produce more than 10MW per annum (equivalent to the power requirements of a very large house) for an outlay of around £20,000. Subtract from this a £5,000 installation grant and add onto the income roughly £500 per annum by way of the Government Renewable Obligation Certificates, and you are looking at a 12-year inflation-proofed payback. And thats on a site with a measly 5.1m/second average wind speed. A windy spot would reduce this payback period dramatically.

To make financial sense, most small wind turbines have to be connected to the grid via a special meter. This allows you to export surplus electricity when its windy. For a long time, the electricity companies dragged their heels on this issue and were reluctant to make microgeneration grid connections, but now, not only will companies provide an export meter, they have at last started to pay for microgenerated electricity at rates close to what they sell it for. Both EDF and Powergen have recently introduced export tariffs of around 8p per unit.

However, one downside not often realised is that a grid-connected wind turbine stops producing power when there is a power cut. This is a safety feature in order to allow repairs to be carried out on the grid cables. The only way around this is to have your turbine-generated electricity fed into batteries, an expensive option not usually recommended unless your site is completely off grid.

Micro Turbines

If the launch of a product was well timed to catch hold of a captive market, it has to be Windsave's (windsave.com) deal to sell its wall-mounted turbines through B&Q for £1,500, including installation. Windsave's product is not the first of these micro turbines - and it was not the one selected by David Cameron for his home - but it is the most high profile and it looks as though it will capture a significant share of a new market. The Windsave turbine is being assembled in Livingston in Scotland at a plant which is capable of turning out around 1,000 units per week. It anticipates shifting around 18,000 in its first year of trading, following the ground-breaking deal with B&Q. The basis of the Windsave concept is that it is very quick and simple to install. The customer has to pay in advance - always a big benefit to a start-up company - and is then subject to a site survey to see if their house is suitable for a Windsave turbine. If it isn't, the refund is handled promptly by B&Q. Subject to planning permission (which can still be a problem in some areas), the turbine is installed on the windward wall and the resulting power is delivered via a unique Plug & Save unit which just plugs in via an existing wall socket. No attempt is made to sell any surplus onto the grid. Its a very simple product.

Even though its simple and relatively cheap, a wallmounted wind turbine is not for the faint-hearted. So few have been fitted that the product hasn't developed a track record and no one knows how they will perform or if they will cause problems to the occupants or their neighbours. If they are too noisy in operation, they can be locked off but that rather defeats the point of fitting one in the first place. However, the key question for most people is whether they will ever produce a sensible amount of power. Windsave suggests without promising that its turbine is capable of generating enough electricity to reduce your electricity bill by a third. But a close inspection of the likely power outputs indicates that this is only going to happen for customers with a very small power demand who happen to live in a very windy location. Even on its most optimistic estimates, Windsave is not suggesting that you'd get more than 1MWh per annum from its turbine, replacing 80% of metered electricity. That's only ever going to be a third of the consumption of a small house with low demand.

The average UK home now consumes around 4MWh per annum and many larger family homes regularly consume twice as much as this without using any electric heating. However, to get even 1MWh per annum from your roof turbine, you have to be living in a pretty windy spot. Windsave says that this output is achievable at average British wind speeds of 5.6 metres/second. Whilst this may be the average across the whole country, the major population centres are almost invariably lower than this, often down below 5.0 metres/second, and the power output from low average wind speeds is much lower. Even using the data from Windsave's own website, you can extrapolate a total annual power output from a turbine in London of 0.2-0.4 MWh. In terms of electricity bills, thats maybe a £15-30 saving each year. These are pretty miserable-looking returns. But even so, with an installation cost of £1,500, less a £500 grant and a possible £50 a year subsidy, it is conceivable that a Windsave turbine could pay for itself in 15 years. In a windy location the payback would be shorter. However, these are big ifs and the truth is that anyone buying a roofmounted turbine today is taking part in an experiment rather than buying into established technology.

What Are the Potential Benefits?

In the UK we have 40% of Europes total wind energy; but its still largely untapped and only 0.5% of our electricity requirements are currently generated by wind power. Wind power is proportional to the cube of the winds speed, so relatively minor increases in speed result in large changes in potential output. Individual turbines vary in size and power output from a few hundred watts to two or three megawatts (as a guide, a typical domestic system would be 2.5-6 kilowatts, depending on the location and size of the home).Wind speed increases with height so its best to have the turbine high on a mast or tower. The ideal siting is a smooth-top hill with a flat, clear exposure, free from excessive turbulence and obstructions such as large trees. However, small-scale building-integrated wind turbines suitable for urban locations are currently being developed and will be available to install in homes and other buildings within the next few years. Knowledge of the local wind is critical to designing a wind energy system and predicting output. For domestic installations, a good source of information on local wind speeds is the NOABL database which can be accessed from the British Wind Energy Association (bwea.com). You can also collect primary information by setting up your own monitoring mast to record wind speed. An ideal way of doing this is with an anemometer. You can buy one online for around £120. Planning issues such as visual impact, noise and conservation issues also have to be considered. System installation normally requires permission from the local authority.

Background

Wind turbines per se are nothing new. Weve been using windmills to grind corn and to lift water for centuries and, more recently, wind turbines have been used to generate small amounts of electricity for boats and caravans. It was, however, the Danes who started the major push towards generating electricity from the wind in the 1980s, both at the domestic level and later using the giant 2MW wind turbines that are used to build wind farms. In common with many other countries, Britain is now embracing commercial wind farms, but the interest in domestic turbines is quite new. Chris Gooding has been installing both wind turbines and solar electric roof panels since 1984 through his business Solar Energy Alliance (solarenergyalliance.com). For many years, the bread and butter of this business was selling solar-powered lights and toys but in the past year it has all changed dramatically. "I can more or less pinpoint the day," says Chris. "It took off when there was a dispute between Russia and the Ukraine about gas prices and Russia turned off the supply for a few days. Suddenly people everywhere became twitchy about energy security and the phone hasn't stopped ringing since with potential customers enquiring about wind turbines and solar electric roof panels." Set against a background of trebling oil prices and the North Sea gas reserves going into decline, this event seemed to have acted as the jolt needed to kick-start a wind turbine boom.

Wind Turbine FAQs

Is my house suitable for a wind turbine? Is there access? Is there enough room for a wind turbine? Typically, you need double the length of the mast. Check wind speed. Any average wind speed above 4.6 metres/second can use wind power to generate electricity but the higher the speed, the better. Also check your individual situation. If large buildings and/or trees are nearby, wind speeds will be affected.

Will I need planning permission? The situation with planning permission remains problematic and different local authorities have different views. Planning permission may well be required but is unlikely to be an issue unless the neighbours object.

Grants are available. England,Wales and N. Ireland use the Low Carbon Buildings Programme: lowcarbonbuildings.org.uk or 0800 915 0990. Grants are £1,000 per installed kW up to a maximum of £5,000 or 30% of the installation cost, whichever is the lower figure.

Scotland: 0800 138 8858 - grants available of up to a maximum of £4,000 are available on 30% of the installed cost.

What about Government subsidies? The Government pays a subsidy to all generators of renewable electricity, whether grid connected or not. This is known as the Renewables Obligation Certificate or ROC. The value is driven by market forces but is currently around 4.5p per kWh or unit of electricity, equivalent to 45 for a megawatt hour.

Can I sell back excess electricity to the grid? Wind turbines tend to produce either nothing at all or too much electricity for domestic use alone. It therefore makes sense to connect all but the smallest turbines to the grid and get paid for exporting your surplus. You will require an export meter and an export tariff rate agreed with your power company. Not all sites are suitable for grid connection: this is subject to survey.

Visit the BERR wind speed database at berr.gov.uk to find the average wind speed in your area.

Further Reading:

• Feed-in Tariffs Explained
• Self-sufficiency: A Green Dream or Reality?
• How to Give Your Home an Eco Makeover