Claimed and Realistic Carbon Dioxide Emissions Savings

Prof Michael Jefferson is Chairman of the Policies Committee for the World Renewable Energy Network and Congresses and Associate Editor of RENEWABLE ENERGY, a journal published by Elsevier.

He has been appointed an Expert Reviewer by the Intergovernmental Panel on Climate Change (IPPC), Working Group III with special reference to energy supply and use matters.

CLOWD asked Prof Jefferson to prepare an independent evaluation on the claimed and realistic carbon dioxide emmissions savings and electricity generation from the proposed Airfield Farm wind farm.

It makes fascinating and essential reading for anyone concerned with the truth about the potential (or lack of it) for wind energy in North Bedfordshire.

The paper is available by following the link : - clowdCarbonSavings

Efficiency of large scale wind generation in a low ground inland environment

If we take for example a site in the middle of Great Britain, Airfield Farm, the wind speeds have been assessed nationally (the data is available on BWEA's and DTI's websites) at an average of about 6.5 metres per second. This is on the edge of viability even with the benefits of the ROC system subsidy. Wind speeds at this level compare with continental Europe.

The inefficiency of the inland sites has meant that bigger and bigger turbines have been put forward. Many of this type of turbine were designed for use at sea and have found no useful purpose following the clampdown on new development on the continent. In an offshore situation, much less attention has been given to noise levels, flicker and glint and they have not been given the same weight as is required for an inland site.

The data for a Nordex N90 /2,300kW, which is currently Nuon's turbine of choice for Airfield Farm, has an overall height of 125 metres, a height to the hub of 80 metres and a rotor diameter of 90 metres. The advertised power output is in the order of 390kW at a given speed of 6.5 m/s. This represents under 17% of the design capacity. This figure must be reduced still further to take into account stoppages for repair and maintenance. Together with the stopping of some turbines to prevent flicker and glint, and the practice of slowing turbines in optimum winds to attenuate noise nuisance, particularly at night. Also the slowing of blades where turbines are close to rights of way used by horses and riders.

A realistic figure for the production of electricity on an annual basis must therefore be significantly under 15% of the installed capacity of a wind farm. This corresponds with the Continental experience.

This demonstrates the hollowness of many of the statistics banded about by wind energy companies: for instance, with regard to the number of houses that can be supplied by a given windfarm. The normal figure quoted should be halved as it is common practise to use the spurious factor, in a Midlands context, of 30% of design capacity for operating efficiency. The house supply figure is based on the total housing stock in a given area (possibly all England and Wales) and averaging consumption over a whole year, summer and winter, day and night. It would be more interesting to calculate how many houses could be supplied in mid-winter in a house heated purely by electricity, during peak demand such as commercial breaks during popular TV soaps or 12 o'clock in the morning on Christmas Day when the turkey is in the oven. The answer lies between very few and nil. The latter would be the case if a high pressure system affected the whole of the UK. With the prospect of climate change and the increasing occurrence of extreme weather conditions, low wind speeds and high speeds in which wind turbines will not be in use, must be increasingly expected.

Even though National Government is far too prone to rely on information fed to it by the very effective PR campaign undertaken by those funded by wind energy companies, the DTI figures on efficiency make interest reading. In the year 2004, the DTI did a survey of all windfarms in the UK, based on figures produced by OfGEM, and found that the average percentage of possible output in a year was 26.6% for on-shore wind turbines (24.2% for off-shore wind turbines). This is necessarily based on sites in remote coastal areas and other prime sites which were the first to be cherry picked for development.

More information is required on the effect on performance of turbines when the wind is second hand having been used by turbines on their windward side. The Airfield Farm has several placed line astern in the direction of the prevailing wind. This is clearly another factor which will further reduce efficiency.

It should also be noted that the current cropof very large turbines require larger spacing between each turbine and a windfarm will therefore cover a much larger area of land than hither to and will fill a larger proportion of the skyline if placed in a prominent position.

In a 2003 Report to the Bedfordshire County Council it is stated that in the short to medium term Bedfordshire was an unlikely candidate for wind energy development due to high population and to wind speed less than 7 m/s.

Wind Resource

There are few independent persons who genuinely believe that wind turbines add an element of beauty to a rural landscape. Many of those that do, believe that wind power will save the planet. The reality is that carbon emissions will be barely reduced.

It is therefore surprising, in the face of mass disruption of landscapes, that more attention has not been given to the size of the benefit, if any, to society as a whole. Much of the work carried out to date has been based on dubious science. What little information that has been passed down to the public has been spun or coloured by politicians or those in pursuit of profit at all costs.

The main element to be evaluated is clearly wind speed in the context of location. The wind factory developers have been very secretive about data coming from their anemometers, which prevents due consideration of public benefit in a political and planning environment.

The NOABL wind speed figures, used by the DTI and the British Wind Energy Association in a wind speed calculator, exaggerate significantly expected wind speeds. This is in part due to a proven dropin average wind speeds that has taken place over the last five years. The NOABL statistics are based on data more than twenty years old.

The Review Paper is based upon current Met Office data and clearly demonstrates that wind speeds, particularly in a Midlands setting, are much lower than previously forecast by wind energy developers and others. This fact is being confirmed by evidence from operating wind factories that is now becoming available from OFGEM who publish the Renewable Obligation Certificate (ROCs) statistics for each individual installation.

The wind energy industry has been claiming an average Capacity Factor figure of 30% or more. This is the percentage of the theoretical total potential output. This is not happening and is nearly double the 17% Capacity Factor that could be expected at an inland site in the Midlands.

The fact that turbines are being planned for this area is due to the overgenerous and too closely focused ROC payments system.

The Review Paper and its charts demonstrate dramatically the yoyo nature (spikeness) of production at a local and national level. The uncertain level of production makes the electricity produced virtually useless in the context of grid management and the need to meet consumer demand consistently.

Offshore wind generation

It is often claimed that offshore wind farms are more expensive to developand this will be true as far as easy access to consumers and the grid is concerned. But there are compensatory factors. The size of the turbines and particularly the rotor diameter can be increased. Safety features can be reduced. Factors such as noise, flicker and glint and so on have much less impact at sea. Most importantly of all the wind speeds at sea will be material higher and will greatly increase operating efficiency.

Technology of large turbines designed for use offshore

Turbines designed for offshore use can be noisier without causing offence to nearby inhabitants. There are also reduced problems with regard to flicker and glint.

There is the suspicion that, following the decision in Denmark and Germany to stopor reduce windfarm development, there are a number of turbines surplus to current requirements in continental Europe. These could be dumped on UK inland sites.

References

The economics of wind energy within the generation mix : Helmut Alt (November 2003)

Unfortunately, this technically exploitable potential is not directly equivalent to what is economically realizable. To be able to use the available wind energy potential, enormous surface areas would have to be set aside for wind power plants to convert flow energy into useful energy. What is more, considerable capital resources would have to be tapped for actual plant construction.

[PDF : 2814kB]

Wind Report 2004 : E.ON Netz GmbH (2004)

Only limited wind power is available. In order to cover electricity demands, traditional power station capacities must be maintained as so-called"shadow power stations" at a total level of more than 80 % of the installed wind energy capacity, so that the electricity consumption is also covered during economically difficult periods. Only limited forecasting is possible for wind power infeed. If the wind power forecast differs from the actual infeed, the transmission system operator must cover the difference by utilising reserve capacity. This requires reserve capacities amounting to 50 – 60 % of the installed wind power capacity.

[PDF : 344kB]

Power To The People - Future-proofing the security of UK power supplies : Professor M.A.Laughton (2003)

The function of this paper is to stress the importance of security of power supplies within national energy policy. It recommends evidence-based actions to address gaps in current practice that would helpto futureproof the UK against the possibility of serious power failures.

Adam Smith Research Trust [PDF: 2074kB]