Using wind power
Wind power has normally been regarded as a technology primarily for rural areas but technological and design advances increasingly mean that it can also be integrated into urban fringe locations.
Wind turbines capture wind energy and convert it to usable electricity. Turbines can be large, medium, small, or micro scale depending on the situation and electrical requirement.
By utilising easily available GIS information, data on mean wind speeds at 10 metres height are easily available. By assuming that economic wind generation is only possible at mean wind speeds of about 6 metres per second, this GIS information can be used to plot where wind power can be generated.
As a ‘rule of thumb’, if one then takes out areas in proximity to forests, tall buildings and other obstacles and establishes a 350 metre exclusion zone from housing (because of the noise effects of larger turbines) then it becomes possible to refine projections of where wind-derived energy can be usefully captured across regions and districts. The actual siting of wind turbines should only be decided following tests in situ.
Wind power can be strategically considered at the regional scale. Regional energy strategies can provide a useful assessment of the technology’s potential, and a steer towards the areas that could best accommodate wind farms at the sub-regional scale. The UK Renewable Energy Strategy places greater emphasis on this scale by suggesting energy targets could be addressed through the regional planning system in a similar way to housing targets.
The South West Renewable Energy Strategy is an example of an energy strategy that has been informed by a landscape character assessment and has established wind power delivery targets in line with this.
At the city and neighbourhood scale ground-mounted medium or large scale turbines constructed in groups or individually may be appropriate. For a given investment, a larger turbine will produce a higher yearly output of electricity than a number of smaller ones. However, urban environments typically have low wind speeds and inconsistent wind direction, which significantly reduces the potential for electricity generation and can make urban turbines economically and environmentally unattractive.
Micro scale turbines
Micro scale turbines are currently commercially available as conventional propeller blade horizontal axis turbines (HAWT) and a vertical axis turbines (VAWT). Both can be mounted on buildings and some models have been developed specifically to work in low wind speed environments.
Vertical access turbines are easier to accommodate as they require less space and are quiet in operation. One design type, the Savonius rotor, (similar in concept to the signs outside shops that spin in the wind) provides considerably less energy than HAWTs, being less efficient as one blade is always being returned against the wind . Another VAWT design, the Darrieus rotor, overcomes this issue and when positioned in an inherently poor, vortex laden, urban wind position can be even more efficient than an equivalent micro HAWT. But the differences in capital costs may more than outweigh this increase in efficiency.
Each potential type of turbine in each specific urban wind condition must be rigorously checked to consider lifetime carbon balance and cost benefit against larger scale alternatives in a better wind environment (which are nearly always better). It should however always be borne in mind that some microturbines can be beautiful, have educational benefit and add architectural excitement. There is also emerging evidence that iconic renewables installations such as microturbines can cause people to constantly question the carbon consequences of other, unrelated lifestyle choices which really can produce carbon savings.
Other factors to consider before making a decision include:
- meteorological investigations and site tests to establish local wind conditions need to be carried out before the final economic case for turbines in any particular location can be made
- planning constraints can limit the generation potential by restricting the turbine size
- a bat and bird survey may also be required as part of the planning process
- turbine noise levels should be kept to within 5 dB(A) of the average existing evening or night-time background noise level, according to the Government's wind turbine noise working group
- many larger turbines also require a planning stage radiological survey to check that there is no local interference to TV, radar or microwave signals (mobile phones) and a study to reduce nuisance from 'sun-flicker' shadows from the moving blades.
Wind turbines by their nature generate an unpredictable quantity of electricity. The level of production rarely matches demand on a small scale approach and this means energy is either being drawn in parallel from the grid or is being exported back to the grid. Low export tariffs mean that for smaller turbines the additional investment in grid export capability has generally not been cost effective.
However, export tariffs are set to become more in line with or higher than standard grid electricity charges with the introduction of incentivisation income streams from Renewable Obligation Certificates/ Kwh for electricity from microgeneration (from April 2009) and feed-in tariffs.
In general, the amount of energy generated is directly related to the swept area and the cube of the wind speed. Therefore for best value, the bigger the better and the taller the better.
Medium to large scale free standing wind turbines of between 100kW and 2 MW are most appropriate at the neighbourhood scale, particularly in relation to industrial sites of urban extensions. Smaller scale free standing turbines (of between 6kW and 100kW) can provide energy for block scale developments. Both scales require open space and uninterrupted wind flow as basic conditions for feasibility.
Small scale, building-mounted turbines can be considered at the individual building scale, but are rarely applicable in urban situations due to their need for uninterrupted airflow. Caution should be exercised in considering wind at this micro-generation scale. Research by the Building Research Establishment on urban micro turbine installations did not find a single instance given normal low urban wind speeds where the renewable energy production in the lifetime of the micro turbine ‘paid back’ the embodied energy of its construction. They therefore caused carbon emissions rather than offering savings.
The capital costs of wind power benefit from economies of scale. The costs identified in the 2008 Communities and Local Government research are now much lower than current calculations. The figures in this research include the displaced carbon calculation factor that will soon be removed and this will add around a third to the costs quoted. In addition, following this research, global increases in steel prices and global supply chain issues with regard to wind turbine equipment have resulted in increased costs. At the moment (February 2009), large scale wind power is projected to cost around £2,500 per kilowatt.
Turbines in areas with lower wind speeds can be economical in a situation where a user can take all the energy generated and therefore avoid selling energy to the grid at wholesale rates.
The CLG research included an economic cost and benefit analysis of each technology. This found that the operating and maintenance costs for wind generated electricity were more expensive on a cost only basis than for electricity taken from the grid, but when considered on the basis of whole life cost the net present value of ongoing costs and benefits was between £1,100 and £2,675 net benefit per tonne of CO2 saved.
Ladygrove Primary School
The attraction of larger scale wind schemes, can be illustrated through the high costs and long payback periods experienced by small scale initiatives.
For example,a small turbine has been installed at Ladygrove Primary School in Telford that meets 15 per cent of the total school’s electrical needs. Installation cost around £10,000 and has resulted in a virtual income for the school of some £400 per annum in avoided electricity costs.
CABE and Urban Practitioners
with the cities of Birmingham, Bristol, Leeds, Liverpool, Manchester, Newcastle, Nottingham and Sheffield