Wind power

Wind power

Catch the wind

The UK is the windiest country in Europe. Because of this, wind farms are a great way for us to meet our energy needs without creating carbon emissions. Small wind turbines can be effective, but must be very carefully placed in order to reduce carbon emissions or be cost-effective.

CAT has been using wind turbines since we started in the 1970s, and you can see examples and displays around our visitor centre. Our books and short courses on DIY wind turbines are based on the robust designs of Hugh Piggott (Scoraig Wind).

When harnessing the wind, two key factors make a big impact – the size of the rotor and the speed of the wind captured.

How big does a wind turbine need to be?

The smallest turbines, costing a few hundred pounds, are fine for charging up a 12volt battery in a boat or caravan. However, to produce an output similar to a domestic solar PV roof, a much larger turbine would be needed.

When you double the diameter of a rotor it makes the swept area twice as big. This means that very small turbines can’t capture much wind. A rotor diameter of about 1 metre could give you a few hundred kWh per year – about the same as one solar panel. To get as much energy per year as a whole solar roof array, you’d need a rotor about 4 metres across.

How important is wind speed?

Doubling the wind speed will give eight times as much power. This means that if you get half as much wind as expected, you’ll only have one-eighth as much power to harness. Because of this, putting a turbine in the windiest possible position is vital.

Many sites are not windy enough – especially at a small scale. Wind speeds increase significantly with height, so even small turbines need to be mounted on a high tower, away from buildings and trees. Those obstacles will create turbulence that reduces power output and increases wear and tear.

Where should I put a wind turbine?

An ideal site is a smooth hilltop with a clear open stretch – at least in the prevailing wind direction. Towns & villages don’t usually have open stretches like this, which is why they’re usually bad sites.

Before spending thousands of pounds on a wind turbine, we strongly recommend spending a few hundred on decent measuring equipment – such as a mast and data logger. Be wary of relying only on an online database that gives wind speeds for a given postcode or map reference. These don’t account for the local conditions that a small turbine will be affected by.

Can I put a wind turbine on my roof?

We strongly advise against mounting turbines on rooftops or buildings, as they will receive only weak and turbulent winds. Several field trials have found that building-mounted turbines perform poorly, producing only a small fraction of the energy they would produce if properly sited. A turbine that does not spin will not save you money or reduce carbon emissions. In addition, turbines can resonate in the wind and produce vibrations, which can damage the structure of the building.

How much does a wind turbine cost?

A turbine plus tower and installation will typically cost between £2,500 and £6,000 per rated kilowatt (kW). When calculating installation costs it is important to factor in the tower and other system components.

Turbines are built to operate without much maintenance, but some moving parts of the turbine may have to be replaced during its lifetime of around 20 years.If an inverter is needed, then this is likely to need replacing within the life of the turbine.

How much will it pay back?

Whatever you can use directly will save you about 16p per kWh, based on current electricity prices. At the moment, the situation with exported electricity is unfortunately not clear.

The feed-in tariff (FIT) incentive scheme closed to new installations in April 2019. We don’t yet know what payment may be available under the proposed Smart Export Guarantee (SEG). This is a scheme that would pay you a fair rate for any electricity exported to the grid. It would require a suitable type of smart meter that is able to measure exported electricity (which many first generation smart meters cannot do). Unfortunately this ‘smart export’ scheme has not been finalised in time to replace the feed-in tariff and so there will be a gap with no payments available at all. Once we have more details we’ll update this page with some estimates.

Community Power

Large-scale wind turbines can harness the much stronger winds on hilltops, away from towns. Investing in a big community owned wind turbine is therefore usually the best way for most of us to benefit from wind power.

Find out more

See our questions and answers section below, and the books we sell. You could also come for a day visit to CAT or attend one of our short courses.

Although the feed-in tariff scheme has ended, you can still use the Microgeneration Certification Scheme (MCS) listings of accredited installers and products. You can also contact us if you’re looking for some specialist installers of small off-grid systems.

Related Questions

How much power will a wind turbine produce?

The ‘rated power’ of a wind turbine, given in kilowatts (kW) is the power produced at its ‘rated’ wind speed. This speed is quite high – often 10 or 12 metres per second. Different turbines have different rated wind speeds, so don’t just go by the rated power when comparing them.

The power output at lower wind speeds will be substantially less. For an overview of the performance of a turbine, look for a ‘power curve’ – a graph of power output against wind speed.

wind turbine power curve

Domestic wind turbines are typically rated between 1kW and 10kW. A very small turbine for use on a boat might be rated at only 100 to 200 watts.

Many factors affect how much energy you’ll get, but a conseravtive rule of thumb is that a 1kW turbine on a reasonably good site could generate 1000kWh over a year. On a better site, an annual output of 1500kWh per rated kW could be possible.

 

 

What is a windpump?

A windpump is used for raising water from a borehole to provide a water supply or irrigation. The design uses a fairly large multi-bladed rotor, mounted on a high tower.

Over the last 150 years or so, windpumps have been popular in America and Australia to provide water for agriculture. More recently, windpumps have been used in developing countries.

They are quite site-specific, requiring a steady moderate wind to start up and keep turning, so you’ll need to monitor and evaluate the site to properly size one.

Wind pumps have a relatively low capital cost and long lifetime (about 25 years). They are good for off-grid sites, as they’re entirely mechanical – no need for electricity to run a controller, for example. However, they do require a 6-monthly service, and the pumping efficiency drops off in high wind speeds.

A wind pump could cost about £3,000 (with complete installation up to £10,000) but is a cost-effective solution for a large scale application. A 3.5 metre diameter rotor operating in a windspeed of 3 metres per second could pump 45,000 litres a day from a depth of 5 metres.

For more information, CAT’s eco store sells the book How to Build a Wind Pump. If you need to find a supplier, get in touch and we can send you some contacts.

How can I pump water using wind or solar power?

A renewable energy technology could be ideal for pumping water where there is no mains electricity available, as a grid connection may be expensive and a diesel generator noisy and polluting.

Sizing a pump

The two main factors to consider when seeking a suitable pump are the flow rate – the amount of water that the pump will deliver, and the head – the height through which it will raise the water. These are related, as increasing the head will decrease the delivered flow. It’s important to minimise bends and other friction losses in pipework, as navigating these will require greater pressure, and as pressure and head are directly related, this effectively means a greater head.

Manufacturers’ technical data sheets will give the performance range of each pump, with graphs showing optimum combinations of flow and head. A pump sized properly to your needs will operate most efficiently. Suction pumps are limited to a depth of a few metres, so to draw water from a well or borehole, you’ll almost certainly need to lower in a submersible pump. Pumping wastewater or sewage necessitates one designed to handle drainage or effluent.

Small electric pumps for circulating water could cost tens of pounds, whilst those for drawing water from a well or borehole supply are likely to be a few hundred pounds. The main cost will be providing power to the pump, particularly when off-grid. Therefore, do first take all appropriate water-saving measures (such as spray-head fittings, mulches on plants to minimise water loss, etc) as these easily pay for themselves in the energy saved by reduced demand.

Off-grid electric pumps

Meeting a year-round water demand with a renewably-powered pump may require a combination of PV panels and a wind turbine, as this will balance energy production over the year. Sunshine and wind are naturally intermittent, so you may need some form of storage. Pumping water up to a tank (with demand then fed by gravity) during sunny or windy periods is more efficient than transferring the energy to batteries. If storing lots of water, you’ll need to balance the costs of a large tank (and supporting structure) against the costs of batteries (and their environmental impact and toxicity). An inexpensive control system can pump when needed, and otherwise divert power to batteries, giving extra backup facility.

The price of a small-scale renewable energy system will depend on the power and the maximum capacity needed. A very rough estimate is around £5 to £10 per installed watt. Siting generating equipment close to the pump minimises the cost and power loss incurred by cabling. As small turbines and PV panels usually produce power at 12 or 24 volts, a low-voltage pump would enable you to do without a costly inverter (for stepping up to 240 volts).

Mechanical pumps

For larger-scale pumping applications, you can avoid the losses in electrical systems by using mechanical power directly. See for example the question on our wind power page about wind pumps, or the question on our hydro power page about hydraulic ram pumps.

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