Domestic wind turbines have dropped off the radar recently but turbines continue to be a viable option for some. There are several factors to consider first, including:
- wind speed
- location
- planning consent
- noise and flicker
- connecting to the grid
- efficiency
- maintenance and durability
- cost
Wind Speed
Domestic wind turbines need plenty of ‘clean’ wind, ideally uninterrupted and blowing constantly from a single direction.
The general rule is that a site needs an annual average wind speed of more than 5 metres per second (m/s) to be productive and preferably more than 6m/s. An estimate of 5m/s at 10m above ground level might well be 6m/s at 25m above ground level.
To decide if your site is suitable, consult a database of annual average on-shore wind speeds.
If you want a more accurate wind speed data, you’ll need an anemometer (Omega produces them for around £400). The anemometer must be in the right location and at the right height to be of any value, and in place for a full year to get the full annual average wind speed.
Where to Place a Wind Turbine
Useful wind is affected by topography and obstructions, as well as speed. Strong wind that is disrupted by trees or tall buildings will not do.
The turbine also needs to be:
- 10m above any obstacle within 200m – ideally in ‘clean air’ that is undisturbed by turbulence or directional shift
- at least 1.5 times its height away from any building, road, footpath, bridleway, telephone or electricity lines or anything that can be damaged if the turbine falls over
- in a spot that does not ‘cause offence’ to neighbours (typically, noise offence), listed buildings or national parks
How Much Does a Wind Turbine Cost?
The bigger the wind turbine, the more expensive the costs. A 5kW wind turbine would be usual for a domestic installation and will cost around £20,000-£25,000. Add to that the cost of preparing the site, erecting the turbine, laying cables to the grid connection and planning consent, and the final cost could reach £30,000-£40,000.
A good 5kW wind turbine, such as the Britwind R9000, will:
- produce around 10,000kWh per year with an average wind speed of 6m/s, almost enough for two average households
- attract a Feed-in Tariff of 8.26p/kWh and export tariff of 4.8p/kWh — a return of £1,310 per year
- have a total capital cost of £30,000
- have a payback of at least 23 years.
Another option might be a tiny turbine, like the FuturEnergy Airforce1 1kW machine. This:
- costs around £1,200, with total installed costs of £2,000
- will usually not need planning consent
- will not annoy the neighbours
- can be fitted on a scaffold pole
- will produce around 2,000 kWh with a 6m/s wind speed
As this is not grid connected there is no Feed-in Tariff and all the production must be used on site. This gives the electricity a value of 15p/kWh as it displaces electricity bought from the grid. Returns are about £300 a year — a potential payback of seven years.
Do I Need Planning Consent for a Wind Turbine?
Wind turbines need planning consent. They will almost always attract objections, usually from neighbours. The process can be expensive and time-consuming, covering:
- plans
- drawings
- ecological and bat surveys
- highways
- visual impact
- noise surveys (for anything over 10kW)
Noise and Flicker
Potential noise is the usual objection, with little cause. Wind turbines are not silent, but as there must be some distance between the turbines and any houses, there is little perceivable noise.
Flicker can be a real nuisance and can affect people with epilepsy. It is caused by the blades passing in front of the sun and making the sunlight appear to flicker to anyone ‘downstream’ of it. To avoid it, the turbine needs to be positioned so that it is not directly between the sun’s path and any neighbouring properties.
Connecting to the Grid
The UK electricity grid is nearing maximum capacity and in some areas, like the south coast of England, it is already at capacity. In these areas it may not be possible to connect the turbine to the grid. Even when it can be connected, upgrading a grid connection can cost thousands or tens of thousands of pounds.
Connection, with no upgrade, is usually possible for generators with a capacity below 4kW. This needs to be checked with the grid operator before any other plans are made.
There is an argument that turbines need to be 5kW or more to justify the investment. However, a 1kW-2kW machine that is not grid connected will do all that a normal household needs.
Wind or PV?
Assume a wind speed of 6.5m/s and a capacity of 2kW:
Installed costs: around £4,000
Maintenance: £200 per year
Production: 3,800 kWh per year
Value of production: All used on site, no FiTs £570
Assume a south-facing roof and a capacity of 3.9kW:
Installed costs: around £5,000
Maintenance: £50 per year
Production: 3,200 kWh per year
Value of production: 40% used on site. FiTs at 4.11p. Export at 4.8p. £360
Efficiency
The rated output of a wind turbine is what the turbine is called, for example, a 10kW turbine. This reflect its optimum wind speed, in this case, usually something between 10m/s to 12m/s, which is a fairly strong wind.
More important are the start-up and shut-down wind speeds:
Start-up speed is the speed needed to start generating and is a key factor to production. The lower the figure the better. Anything around 2m/s is useful.
Shut-down speed is another matter. Some wind turbines ‘flat line’ their output at their rated output until the wind reaches its ‘survival’ speed. A 10kW wind turbine with a survival wind speed of 30m/s will continue to produce 10kW as the wind speed increases from 12m/s to 30m/s before shutting down. The maximum output of that 10kW turbine may be a bit more than 10kW, up to 12kW.
The turbine will have the necessary controls to ensure that the blades turn no faster and the generator is asked to do no more than 12kW. Others will not have these controls and will shut down when the optimum wind speed is exceeded. The ability to continue producing electricity in low and high wind speeds is critical to efficiency and to financial returns.
Maintenance and durability
Wind turbines are complicated bits of kit with many mechanical components, which will fail. Smaller, cheaper wind turbines do not have any monitoring systems so owners may not immediately be aware that they are not producing electricity.
The nacelle (the working part of the equipment) is at the top of the mast, and this needs to be taken down to ground level to be maintained or repaired, which will be expensive.
Wind turbines have a warranty period, typically 10-20 years. Make sure you read the small print: some manufacturers might cover parts only. This means that the owner pays for labour and for dropping the nacelle, and can only use parts supplied by the manufacturer. This effectively makes the warranty valueless.
Conclusion: Are Wind Turbines Worth it?
There are better ways to make money than from domestic-scale wind turbines, and changes in tariffis mean that the usual 5kW and 10kW turbines are less viable than they used to be. A small 1kW-2kW wind turbine might be the answer. This would be improved by adding battery storage to the system, like a Sunamp or Telsa system at about £3,000.
Case Study: “It’s a Great Success!”
Simon and Annie Winstanley installed a wind turbine on their hillside Dumfriesshire plot — and are delighted with the results (pictured at the top of this article).
Simon and Annie’s cutting-edge self build should be a benchmark for low-carbon design. The airtight structure is insulated to PassivHaus standards and uses mechanical ventilation with heat recovery, with heating topped up by underfloor heating fuelled by an air-sourceheat pump; triple-glazed NorDan windows are orientated to maximise on passive solar gain.
All of the green hardware is, however, discreet and the only evidence that this is a green house is the turbine from Segen, which cost £10,000 and generates supplementary electricity for the house.
So, what are the economic benefits of these energy-efficient measures? “The house costs £10 a week to run — for everything,” says Simon.
