What counts as a micro wind turbine?

When people talk about micro wind turbines, they usually mean a small machine with a rotor diameter somewhere between one and four metres, mounted either on a mast in the garden or on the roof of a house. A typical domestic unit might be rated at anywhere from 500 watts to 6 kilowatts, though the rated figure tells you far less than the swept area of the blades and the wind speed at the hub.

These turbines come in two broad flavours. Horizontal-axis machines, which look like miniature versions of the big commercial turbines you see on hillsides, and vertical-axis designs, which spin around a vertical shaft and are often marketed as being quieter and better suited to turbulent air. Both can work, but the physics of moving air favours taller masts and larger blades in clean, unobstructed wind.

It is worth being clear about one thing from the outset: a micro wind turbine is not a like-for-like substitute for solar panels. Solar works reliably in almost every UK location because daylight is broadly consistent. Wind is far more local, and that is what makes the difference between a system that pays its way and one that sits idle for weeks.

Wind speed: the factor that decides everything

Power available in the wind rises with the cube of wind speed. That means doubling the wind speed increases the power in the airflow by roughly eight times. A site with an average of 4 metres per second will produce dramatically less than one with 6 metres per second, even though the numbers look close.

As a rough rule of thumb, most small turbines need a site average of at least 5 metres per second at hub height to generate a meaningful amount of electricity. Below 4 metres per second, output tends to fall away to the point where the investment rarely makes sense.

Urban and suburban gardens are usually poor candidates. Buildings, trees and fences create turbulence, and turbulence both reduces output and accelerates wear on bearings and blades. Roof mounting is often marketed as convenient, but a turbine perched on a suburban roof sits in some of the choppiest air available. Open, exposed sites, such as a rural property on a hillside, a farm, or a coastal location with a clear prevailing wind, are where small wind comes into its own.

• Check published wind speed data for your postcode area, but treat it as a starting point rather than gospel.
• Consider hiring or buying an anemometer and logging wind speeds at your intended hub height for several months before committing.
• Look at the landscape around you. Bent trees, exposed ridges and a lack of nearby obstructions are encouraging signs.

Planning rules and permitted development

Planning is where many well-intentioned projects quietly stall. In England, some micro wind turbines can be installed under permitted development rights, meaning you do not need to apply for planning permission, provided specific limits are met. These typically cover standalone mast-mounted turbines with a rotor diameter of up to 3.5 metres and a maximum height of 11 metres, and building-mounted turbines with tighter height restrictions.

Permitted development rights are also withdrawn in certain sensitive locations. Conservation areas, National Landscapes, World Heritage Sites and areas near listed buildings often require a full planning application. Similar restrictions apply in Wales, Scotland and Northern Ireland, though the detailed rules differ.

There are additional conditions worth knowing about. Only one micro wind turbine is usually permitted per property, and the installation must not be the primary source of heating or hot water for the home. Noise limits also apply, and neighbours' concerns carry weight.

The practical advice is simple. Speak to your local planning authority before you buy anything, and if you are in any doubt, apply for a lawful development certificate so you have written confirmation that your installation is acceptable.

Costs, output and realistic payback

A small mast-mounted turbine of around 1 to 2 kilowatts might cost somewhere between £2,000 and £6,000 installed, depending on the mast, foundation, cabling and inverter. Larger systems climb steeply from there, and a well-engineered 5 to 6 kilowatt machine with a proper tower can run well into five figures.

Output is highly site-dependent. A 1 kilowatt turbine in a genuinely windy spot might generate 1,500 to 2,500 kilowatt hours a year. In a mediocre location, the same machine might struggle to reach 500. Compare that with the roughly 3,500 kilowatt hours a typical UK household uses annually, and you can see why wind rarely covers the whole bill.

Payment for exported electricity comes through the Smart Export Guarantee, which requires the installation to be certified under the Microgeneration Certification Scheme. Rates are set by individual suppliers and are generally modest, so the main financial return comes from using the power yourself. Pairing a turbine with battery storage, or with a heat pump or electric vehicle charger, improves the economics considerably because it lets you consume more of what you generate.

Siting, maintenance and the long game

Height is your friend. A turbine on a 10 metre mast will almost always outperform one on a 3 metre pole in the same garden, because wind speed increases with distance from the ground and away from obstructions. Allow a clear gap of at least ten metres between the rotor and any building or mature tree if you possibly can.

Plan for maintenance. Small turbines need periodic inspection of blades, bearings, bolts and the inverter, and moving parts in a salty or stormy environment will not last forever. Budget for an annual check and set aside something for eventual replacement of wearing components.

If your site is genuinely exposed and you can get the planning and siting right, micro wind can be a satisfying and productive addition to a home energy strategy. If your site is sheltered, suburban or shaded by trees, the honest answer is that your money will almost certainly work harder installed as solar panels, insulation and air-tightness improvements.