Borders Energy Farming Forum

The UK has about 40% of Europe's total potential wind energy. However, we only meet 0.5% of our electricity requirements from windpower.

Technology

Site requirements

The amount of energy produced depends on the wind speed. Therefore, it is important to pick a development site very carefully. Wind speeds generally increase with height above sea level. The ideal siting is a clear exposure free from excessive turbulence and obstructions such as large trees, houses or other buildings. Some turbines can be roof mounted - however these turbines are smaller and the wind is much more likley to be turbulent, which will lead to very poor performance and even structural damage. A well positioned, pole or tower mounted turbine is likely to be a far better option.

Estimating energy production

The stated size (in kW) is the power a turbine produces when the wind is blowing in ideal conditions - not too weak and not too strong. The relation between wind speed and power output for a 20kW turbine is shown in the graph.

As a rule of thumb, a turbine on a good site in the UK will deliver on average about 25-30% (known as the capacity factor) of its rated capacity over a year. So a 10kW turbine will provide on average about 3kW of electrical power. Over the course of a year (8760 hours) the number of "units" (kWh) produced will be roughly.

Knowledge of local wind speeds is vital. A starting point for information is the NOABL wind speed database that can be accessed from British Wind Energy Association. However, this is very general. To assess specific local conditions, wind speed can be monitored by an anemometer, which are available from around £120. Some turbine installers may offer windspeed monitoring as part of a feasibility survey. The table below links wind speeds to the Beafort scale.

Relating wind speed (m/s) and energy generation to obervable conditions
Beaufort number	Wind Speed (m/s)	Description	Land conditions	Energy Generation
0	0 - 0.2	Calm	Smoke rises vertically
1	0.3 - 1.5	Light air	Wind motion visible in smoke.
2	1.6 - 3.3	Light breeze	Wind felt on exposed skin. Leaves rustle.
3	3.4 - 5.4	Gentle breeze	Leaves and smaller twigs in constant motion.
4	5.5 - 7.9	Moderate breeze	Dust and loose paper raised. Small branches begin to move.	A viable site will usually have an average wind speed of at least 6 m/s. Sites with average speeds of 7m/s or more are considered very good
5	8.0 - 10.7	Fresh breeze	Smaller trees sway.
6	10.8 - 13.8	Strong breeze	Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult	Peak output obtained from most small to medium scale turbines
7	13.9 - 17.1	Near gale	Whole trees in motion. Effort needed to walk against the wind.
8	17.2 - 20.7	Gale	Twigs broken from trees. Cars veer on road.
9	20.8 - 24.4	Strong gale	Light structure damage.	Power production may stop to protect the turbine
10	24.5 - 28.4	Storm	Trees uprooted. Considerable structural damage.	Power production may stop to protect the turbine
11	28.5 - 32.6	Violent storm	Widespread structural damage.
12	32.7 - 40.8	Hurricane	Considerable and widespread damage to structures.	Turbine may be damaged. Typical turbine survival speeds are between 30m/s and 50 m/s.

Planning

Seek advice of the planners at an early stage. Planning permission is required for all but the smallest installations. At commercial scale, the planning decision may be "called-in" by the Scottish Executive for Ministerial decision rather than by the local authority. National planning guidance should be examined.

Economics

The table below shows some indicative costs for a range of sizes of turbine. The costs are for the complete turbine installation

Turbine size	Typical installed cost	Maximum SCHRI grant available
6 kW	£18 000	£4 000
10 kW	£24 000	£4 000
15 kW	£40 000	£4 000
20 kW	£45 000	£4 000

These vary depending on the site, and prices can change subject to demand. Global demand for tubines has been high, and there may be a lead in time while a turbine is manufactured.

Once installed, operation and maintenance costs are low. Typically a turbine will require a service once per year.

Income and savings

For a guide to ROCS and selling energy back to the national grid, see this fact sheet from Proven Energy

Some example costings and payback times are shown below. These are indicative: the economics depends strongly on the individual site windier sites could pay-back in a few years while poor sites may not pay back over 20 years. Also - the biggest savings come from savings on your electricity bill, so in tubrines will be financially more attractive for larger users of electricity.

Installed capacity	Installed cost (incl VAT @5%)	Energy production/year	Annual saving on bill	Annual income from ROCS	Income from sale of electricity	Payback time	Annual CO2 Savings
kW		kWh					kg CO2
6	£14,000	15768	£1000	£631	£231	9	6780
10	£20,000	26280	£1000	£1,051	£651	10	11300
15	£36,000	39420	£1000	£1,577	£1,177	14	16951
20	£41,000	52560	£1000	£2,102	£1,702	13	22601
Assumptions Assuming 30% grant, up to maximum of £4 000 Assuming 30% capacity factor Assuming electricity bill is £1 000 (10 000kWh) Electricity purchased from grid at 10 p/kWh Electricity sale price 4p/kWh ROC price 4 p/kWh

Small Scale Wind

Introduction