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The Twenty Percent Estimate

“At least 20% of the country’s electricity needs could be generated by land-based turbines”

(Page 1 Source 1)

This, the first section, is an evaluation of the validity of this statement through analysing the viability of generating 20% of the UK’s energy from wind energy.

It is worth noticing that the above quote, from the source that I am analysing, gives no reference to the time by which 20% could be achieved.


To make easier reading I have used the same conventions throughout this document

The various pieces of information (Sources) that I used in this analysis (●) and their analysis (Þ) are bulleted, so that they are easily picked out. The source analyses are placed at the end of the paragraph or calculation string, separately from the use of the source, in so that they don’t interfere with the flow of the text. The details of each source are given in the Bibliography section of this document under the corresponding source number. Calculations are highlighted in green, results underlined and equations used are in equation font . Numbers used in calculations are matched to their source, using colour coding between the two.

My data and calculations for wind turbines will only consider Horizontal Axis Wind Turbines. This is because they are the type which is widely used- this is even the case for old-fashioned wind-powered mills. Vertical Axis Wind Turbines (VAWTs) are awkward, as they need a motor to start moving. VAWTs do not need the angle of the nacelle altering according to wind direction (they don’t have one), but this is very easily done with modern technology anyway. They are almost never used.


Þ    P1 Source 1: (see page 3 of this document for a fuller analysis of BWEA) The British Wind Energy Association (BWEA) is the national organisation representing the interests of the UK wind industry and its associates. It should therefore be knowledgeable on the issue, and the booklet (used in many parts of this document) should be accurate, scientific information. As it represents the interests of the industry, however, is possible that it is biased into promoting the development of it.

Calculate UK’s electricity needs:

·        The energy requirements of the country are now about 315 to 320 thousand Gigawatt hours per year.

(Source 2)

Energy demand (GW)=annual requirement (GWh)

                                    annual hours (365*24)

Therefore 20% of the UK’s electricity needs are:

320*103GWh/(365*24hrs)*0.2= 7.3 Gigawatts (2SF)

Þ    Source 2: This source should be reliable and accurate as the Electricity Association represents the UK electricity industry. Also, it costs £50 and is used by many electricity boards suppliers, shareholders, etc. The same source also gives many other statistics, like supply of electricity, sales of electricity, number of customers, average cost of electricity, number of employees, average/max demand, max capacity, etc. for 1995/96, 96/97, 97/98. The Electricity Association represents all forms of electricity production in the UK so, if it were biased towards one, the others would not support it, but this does not guarantee neutrality. I therefore assume that the source is reliable, scientific information and will use it thus.

Add energy demand increase:

In this part, I plan to estimate a value for the energy usage in the year that 20% electricity production by onshore wind energy would be attainable.

It relies on my estimation that establishing this resource would take at least about 80 years. This is based on the following facts and calculations:

·        The government’s plans to produce 10% of the UK’s energy using renewable resources was summarised by:

“if present trends continue, 10% will not be achieved” (by the year 2010)

(Letter 2 Source 6)

Therefore, a change of trends would be necessary to obtain even 10% generated by renewables as a whole.

·        Around 20% of this will come from onshore wind.

(P20 Source 3)

That means that the BWEA thinks that producing

20%*10% = 2% of the UK’s electricity by wind energy by the year 2010 will not be possible.


·        “The cost effective level of renewables generation in 2010 lies in the range 16.0 TWh to 41.2 TWh, which represents between 4.2% and 11.0% of total electricity generation”

(P16 Source 3).

Electricity needs (TWh) =(100/(% of total))*(power value of % of total (TWh))

Therefore, electricity needs in year 2010 (TWh) are estimated to be:

(100/11.0)*41.2=375 TWh (3SF)

This is a (375-320) =55 TWh increase in ten years. (320 in first step of calculation from Source 2)

If 10% (P1 (Forward) Source 4) of the 375 TWh comes from renewable energy, and 20% of that came from new onshore wind (P20 Source 3), this would mean an increase of 375*0.1*0.2=7.5 TWh (2SF) installation in 10 years. As

Energy demand (GW)=annual requirement (GWh)

                                    annual hours (365*24)

, this equates to 7.5*103GWh/(365*24)=0.86 GW installation of onshore wind capacity in ten years, or a rate of installation of  0.086 GW/yr.

            Using the equation

Years taken (yrs)=necessary installation (GW)

   rate of installation (GW/yr.)

            , the time taken (using necessary installation for 20% of present energy needs of 7.3 GW) will be

7.3GW/0.086GW/yr.=85 years without taking into account the energy demand increase of 55 TWh every ten years, 5.5TWh every year.

This would amount to

85*5.5=460 TWh (2SF) increase over 85 years, and increase the electricity requirements by about two and a half times (it is currently about 320TWh, so energy requirement would be 320+460 = 780, 780/320 = 2.4)

If wind turbines get bigger and better, and the pace of installation is stepped up from current plans (the only way to enable 20% generation by wind energy!), we can assume that this would catch up with the electricity demand increase, and settle for about 60 or 70 years before 20% of the UK’s electricity demands could be met. This would only be possible if a large amount of resources were spent on the project. By this time, the requirements would have doubled. I will therefore assume that 2*7.3GW = 15GW would be 20% of the electricity requirement.

This calculation relied on the assumption that 20% would be achieved eventually.

Þ    Source 6: The chief executive of the British Wind Energy Association writes in the same source that the “BWEA represents the interests of over one hundred companies and several hundred individuals active in, or seeking to become active in, wind energy in the UK”. I therefore assume that the organisation is knowledgeable on the issue. If the part of the source that I used were positive about wind energy, I would suspect bias. Since this is saying that 10% of Britain’s energy supplied by renewable resources by the year 2010 may not be achievable, I will take this into consideration with my use of the government's estimates. These include the one discredited above. It must therefore be recognised that calculations using these estimates should be seen as optimistic. It could, however be biased if the motive behind saying this is to gain more government support (the document is a letter to Neil Hornsby (responsible for Source 4), in response to Source 4), as it representing the interests of the above companies/people, as he himself says in the quote.

Þ    Source 3: This paper is the supporting analysis for the document analysed below, published by the government and therefore too should be reliable, scientific information. It contains precise analysis of the various renewable energy resources, both technical and economical, and is much researched. A very valuable resource, but to be carefully used. Not all the exact details of the theoretical conditions on which they tested their “scenario models” are given, therefore any political motives existing which could bias the estimates that they used cannot be identified.

Þ    Source 4: This paper is published by the government and therefore is reliable as scientific information. The Minister for energy and Industry (the author) is himself partly responsible for this government commitment, and therefore can be trusted on this issue! I will not assume that there is no bias in the form of political motivation here, but I will use it as scientific and accurate data, in the case of Source 3 and Source 4.

Calculate the number of turbines required for this:

·        The average rating of the more recently installed turbines is about 550kW.

(P171 Source 3)

Þ    Source 3: (more fully analysed above) This paper is published by the government I therefore will take it as reliable scientific information, but the estimate only holds true for the rating of the more recently installed capacity, and political motivation cannot be ignored. Newly installed turbines’ ratings increase as technology advances. It is therefore only accurate to two significant figures, but at this accuracy, bias should not be a consideration. Compare this to my calculations below.

Mathematical estimation of the power output of a wind turbine to compare to the above (using Betz’s Law- see Appendix 3):

·        Over the course of a year, wind turbines will normally produce around 30% of their theoretical capacity. This is the average load factor, due to the intermittent nature of wind.

(Argument 2 Source 7)

·        The density of air (Temperature = 273.15K, Pressure = 100 kPa) is 1.247 kgm-3

(P579 Source10)

·        The most economical places to place turbines in the UK is on open plains, on the coast or on the hills. Using this as a guide, wind speeds would be between seven and eleven metres per second. I will use a working estimate of 9m/s a low speed for hills.

(P8 Source 1)

·        The normal length for a modern wind turbine blade is currently around 45m, with an optimum wind speed of 16m/s (average of several).

(Source 5)

Area = p r2

The area that the blades cut through is therefore

p * (45/2)2 = 1500m2 (2SF)

·        Text Box:   
Source 9


A wind turbine obtains its power input by converting the energy in the wind into torque acting on the rotor blades. The amount of energy that the wind transfers to the rotor depends on the density of the air, the rotor area, the blade design and the wind speed. When the energy is taken from the wind, the latter obviously slows down. It is also deflected, as it changes direction as it passes the wind turbine (the lower pressure makes the air go faster over the top than the bottom, and therefore the direction of the final air stream is tended downwards on the diagram (right)).

Text Box:  

The interactions of the air stream cause the wind around the turbine to spread out, as shown below (Source 8). V1 and V2 (the velocities of the air before and after the turbine, respectively) can then be used, together with other factors, to calculate the theoretical maximum output of the turbine.

·        Using the equation derived by Betz (Appendix 3), we can plot the ratio of power taken out of the wind to that in undisturbed wind going through the same area, P/P0, as a function of v2/v1, as shown below. We can see that the function reaches its maximum for v2/v1 at 1/3 (optimum blades slow the wind down by 2/3 of the original speed), and that the maximum value for the power extracted from the wind is 0,59 or 16/27 of the total power in the wind.

Text Box:  Using Appendix 3:

Theoretical power (Pt) = air density * area blades sweep through * (v2+v1)*(v2-v1)2

Pt= (1.247 kgm-3/4) * 1500m2 * (9m/s+3m/s) * (9–3)2

Pt= 800 kW theoretical power

with the turbine taking 2/3 of the energy from the wind (see Appendix 3) and 100% efficiency. We also know that:

Average power output(Pa)= Pt * turbine availability(percent)

Pa = 800kW*(30/100)

Pa = 240 kW

            for an annual turbine availability (also called load factor, the time when the turbines are producing) of 30%. This is much lower than the rated capacity of such a turbine, because wind speed rarely reaches it's optimum of 16, at which the NEG Micon turbines are rated, and where the turbine draws most power from the wind. There is also energy loss (discussed in the next section) resulting in lower efficiency. Also because of few wind turbines attaining exactly 2/3 reduction in wind speed due to fluctuations in the wind speed, imperfections in yaw, etc.

The calculation at the 55kW turbine's optimum wind speed would be:

Pt= (1.247 kgm-3/4) * 1500m2 * (16m/s+5.333m/s) * (16–5.333)2

Pt= 4.54 MW theoretical power

with the turbine taking 2/3 of the energy from the wind (above) and 100% efficiency. We also know that:

Average power(Pa)= theoretical power(Pt) * availability (percent)

Pa = 4.54 MW*(30/100)

Pa = 1.36 MW

Even the yearly average power output by my calculation is about double than the 550kW nominal rating, with 100% availability it is 4.54MW! This suggests that wind turbines use nowhere near their theoretical available energy. Where this energy is lost is discussed in the next section (The Environmental Effects of Using Wind Energy). The efficiency of the wind turbine (often called its Cp value- but this is not expressed as a percentage) must therefore be much lower than the theoretical maximum of 59% (explained above).

·        Page 16, Source 1 (see page 1 for analysis) says that the Cp value varies between 0 and 50%. If we say that:

Power output = (Efficiency/0.59) * Pt

Power output = (0.50/0.59) * 4.54MW = 3.85 MW

Using the maximum value of 50%. This is obviously still much greater than the nominal rating.

Calculate actual efficiency:

Pt/Nominal Rating = 0.59/Efficiency

So, to obtain the nominal rating of 550kW, the efficiency would need to be:

Text Box:  0.59 * (550kW/4.54MW) = 7.15% efficiency- and that’s at optimum wind speed!

Possibilities to account for the difference between my estimate of maximum efficiency and that of the BWEA could be:

·        The difference suggests that the BWEA’s estimate could be biased, incorrect or for a different type of turbine (although the source doesn’t specify a type with an efficiency of 50%, and 7.15 is between 0 and 50.)

·        My estimations result in only a very approximate value.

·        The BWEA are considering a different class of turbines

It should be noted that the diagram on the left is from the same source, but shows a maximum Cp value of 30%, explained by the second diagram showing that conditions differ from the ideal. Perhaps this booklet is just badly researched.

This mathematical study has shown that the actual power is much lower than the theoretical. As my calculations involve so many estimates, I will continue to use the company’s specifications for the remainder of this analysis.

As this is the rated capacity, and not the output, this must first be converted to the power output at a wind speed of 9m/s- about half the optimal.

            In the NEG Micon Specifications (Source 5- see next page for analysis, Appendix 1 Figure 2 for an example), most turbines' power curves were such that a halving of wind speed from the optimal caused a halving of power output. This is due to the fact that, at lower wind speeds, it is much harder to reduce the speed by 1/3, the optimal. The power output of the recently installed turbines would therefore be about 550/2=280kW (2SF).


Number of turbines =         power requirement(W)__

                             power output of each turbine(W)

The generation of 15 Gigawatts would require

(15*109W)/(280*103W)= 54,000 turbines (2SF)

Þ    Source 7: (see page 3 for more detailed analysis) The British Wind Energy Association should be providing reliable, scientific information, although the estimate may be a bit high. Bias may be introduced by the fact that, in this document, the 30% quote is used to argue the case against wind farms being called inefficient. This is, of course in the interests of the BWEA, as it represents the interests of the industry.

Þ    Source 10: This is an accurate value recorded in the data section of a scientific book and is therefore reliable. Field conditions, however, vary slightly.

Þ    Source 1: See Appendix 1, Diagram 1

This iso-vent (equal wind speed region) chart is of most of Europe, and, together with its key is very detailed, although the regions are not so well defined. It's representation may be biased to show high wind speeds than exist. See top of page 1 for full analysis of Source 1.

Þ    Source 5: NEG Micon is a large merger of a few wind companies (see Appendix 2, Correspondence 2). Company specifications (up to date) should be reliable sources of accurate information. The leaflets are, however advertising leaflets as part of a package for prospective customers and will therefore be made to look good wherever possible. They cannot lie, however, as they would be breaching statutory rights, and I will use the information as accurate. The weak point of this information is that it is only from one company.

Calculate the area covered by these:

·        “The machines are usually spaced five to ten rotor diameters apart to reduce interaction effects, which impair their performance, to an acceptable level.       “ I used an average of 8 diameters

(P171 Source 3)

·        Rotor diameters are around 45 metres on average.

(Source 5)


Area per turbine= p  * (turbine separation (m) / 2)2

Separation(m)=rotor diameter(m)*recommended separation (rotor diameters)

So, each turbine would take up about

p*((45m*8)/2)2=100,000 square metres (1SF), assuming approximate honeycomb spacing (most economical use of area)

Total area = area per turbine * number of turbines

For 54,000 turbines, the area taken up would be

100,000*54,000= 5.4*109 square metres = 5400 square Kilometres, about 73*73 Km (2SF), or four and a half times the size of Bedfordshire!

(Source 13)

Text Box:  This can be compared to a claim by the BWEA that 10% could be generated from 1200km2 (Source 18 see diagram). This could be an example of BWEA's bias. However, this claim is for offshore wind, which enables bigger turbines. The contrast is, however, very large, and the BWEA could be making wind energy sound better than it is. The map on which this is written is shown on the previous page. The fact that it says NOT TO SCALE increases my suspicions!

Þ    Source 3:  (more fully analysed on page 3 of this document) Specification depends on type of turbine, but as accurate as it is given (between 5 and 10), it should be reliable. I used an average of 8m.

Þ    Source 5: (see page 7 for fuller analysis of NEG Micon) I have rounded the average to the nearest five metres. The weak point of this information is that it is only from one company.

Þ    Source 13: This source is generally fairly negative about wind energy, (although the style of it is weighing up the pros and contras) saying that providing 10% of Britain's energy from it would not be feasible. It uses the example of Bedfordshire to show the unfeasibility of wind power generating 10% of Britain’s electricity. It is directly referencing the BWEA’s estimate of 1200km2 (see page 7), and should be biased towards wind by doing so. What it does not point out is that the actual turbines and tracks of a wind farm cover about 1% of the land (Source 19), so 1200 square kilometres seems a lot.

Þ    Source 19: This is again from the BWEA, so it should be accurate, but may be an underestimate (rounded down) or data from a spread-out wind farm.

Divide this into a number of farms:

Number of farms = total number of turbines

                                 turbines per farm

·        Text Box:  “A purely arbitrary separation distance between wind farms is assumed for the purposes of estimating the national resource. The specifications used are:

§         Minimum wind farm size 20 turbines

§         Maximum wind farms size 50 turbines

§         Maximum sparseness 0.2

§         Maximum turbine density 15 per km2

§         Minimum centroid separation 7km”     

(P180 Source 3)

Number of farms = number of turbines / turbines per farm

Therefore taking an average of 35 turbines per site, the turbines would be split up into:

54000/35 = 1500 farms (2SF)


Size = area covered by all wind farms

            number of wind farms

then these- with added separation of the farm from people, trees, and roads- would all be about

5400/1500 = 3.6 square kilometres ≈ 4Km2 (1SF) (as accurate as this estimate can be, when all the estimations used to derive it are considered)

Þ    Source 3: (more fully analysed on page 3 of this document) As clearly stated, these are purely arbitrary numbers, but were similar to my estimates from other sources. It should be safe to take these numbers to be correct, if they are used as rough estimates, as they are only given as estimates.

20% Estimate Conclusion

One thousand five hundred is sounds like a large number of substantially sized (4km2) obtrusive features (wind farms) to fit in a small country, and an even smaller countryside. To put it into perspective, 54,000 turbines is over two and a half times the number of the number of electricity pylons currently in the UK! (54,000 is my estimate of the number of turbines required, 54,000/21,000 electricity pylons (P25 Source 1) = 2.57). Even with the 773 turbines so far installed (Source 15) there have been numerous complaints (see next section), and the government realises that future planning will have to be more carefully thought out. 54000 is about seventy times as many. However, the theoretical resource is huge- generating 20% of the UK’s electricity would cover only a very small fraction of the countryside if one considers that most of the ground o which the farm is situated can still be used. If landowners are not happy, 20% is a bit optimistic, although if public opinion changed and turbines got quieter, there is easily enough land for this, and an on-shore wind initiative could be very successful.

Offshore wind, however, has larger promises, as here the turbines cause less of a disturbance (see next section) and can be bigger (as well as getting more energy and less wear due to the smoothness of the water reducing turbulence), but the technology is still under development. In Denmark, this has been very successful.

Þ    Source 1: BWEA Booklet, more fully analysed on Page 1. In Source 1 the number is being used to say the following: “The visual prominence of the turbines would be equivalent to replacing every grey transmission pylon with an aesthetically designed wind turbine”. This is two and a half times more optimistic than my estimate, and could show BWEA bias, or inaccuracies in my working, or both.

Þ    Source 15:  This up-to-date leaflet  (updated July 1999)

Conclusion Evaluation

Comparison with the BWEA’s figures shows that they are consistently more optimistic estimates than those that I deduced are, e.g. pages 7&9. This could show the uncertainty of any calculations, the inaccuracy of my results or the BWEA’s bias. There have, naturally, been many estimations and assumptions involved in this analysis, but the evidence for the conclusion is nonetheless strong and I think that the conclusion is a valid one.

The Environmental Effects of Using Wind Energy

"Using wind energy is very environmentally friendly, producing no gases, chemicals, ash or radioactivity"

(P1 Source1)

In this section I will evaluate the environmental effects of wind energy, and compare my conclusion to the above quote.

Þ    Source 1 is analysed on Page 1


Text Box:  
Source 11 (adapted)
As discussed in Section 1, wind turbines slow the wind down, using it to turn their blades, and thus extracting power. To extract the power from the torque of the shaft they use a turbine generator in a rotating nacelle. The key to the parts of the turbine labelled on the right is below.

1)     Hub

2)     Rotor Blades- see diagram below

3)     Low speed shaft (19-30 rpm)

4)     Gear box (1:50 ratio)

5)     High-speed shaft (~1500rpm)

6)     Text Box:  
P17 Source 1
The value of Cp varies with the ratio of the blade tip speed to the wind speed, and with blade pitch angle. Thus, in order to get the best performance of the blade as a whole, the pitch angle has to be set to different values down its length, and changed for different wind speeds.

Electrical Generator

7)     Electric controller- controls:

·        Yaw (motor changing the way the turbine faces to maximise wind usage from any direction- and prevent twisting of cables!)

·        Blade pitch angle à

(used to vary the Cp-

discussed in the previous section)

·        Cut-out (blades disconnecting from generator at too high/low wind speeds)

·        Stall (adjustment of the blade pitch to an angle where it no longer slows the wind down- used to stop high wind speeds making the turbine spin out of control)

·        Connections to computers by modem link

8)     Cooling unit: electric fan, oil cooling, some have water cooling

9)     Anemometer and wind vane

10) Tower (40-60m)

11) Hydraulics system to reset aerodynamic brakes

Þ    Source 11: This is a large Danish web site containing lots of scientific and accurate information about wind energy. I do not, however, know it’s political motivation or industrial relations, so neutrality cannot be assumed.

Sound Pollution

With all these mechanics, it is only to be expected that there would be a fair amount of friction. This would imply heat and sound loss. Imagine having lots of these, the sound could get to quite high levels.

·        Text Box: Source 12
Below there is a chart for the sound produced by a farm. It appears to suggest that the level of noise generated by a wind farm is little more than what people in a rural area hear at night.

Þ    Text Box:  
Source 5

Source 12: The BWEA (see page 3 for fuller analysis of BWEA), although knowledgeable on the issue, have manipulated data on this diagram, so that the sound from a wind farm looks almost negligible. The maximum distance that turbines are situated from a house is actually about 10 metres, and not 350m, for which the value on the diagram is. This was adapted from a by friends of the earth, London. They too are very supportive of wind energy, as is shown from the extract below by Gordon James, Friends of the Earth Cymru: "wind is better than the alternatives" (Source 13- see below for analysis).

·        The diagrams (e.g. on previous page, from Source 5, in Appendix 1) on the NEG Micon specification sheets show the noise levels generated by a SINGLE modern wind turbine to be about 37.5 decibels at 350m. This is not much less than that claimed by Source 1 to be the noise produced by a whole wind farm at this distance (previous page). The claim by the BWEA could therefore only be made using very few turbines, for example the minimum that could be called a wind farm!

This could be an example of BWEA bias, or bias in the measuring techniques of NEG Micon.

Þ    Source 5: (see page 7 for fuller analysis of NEG Micon) Although it is unlikely, bias THis may be incurred in the sound measurement methods, to make them look quieter e.g. in the choice of the testing wind speed.

·        "Perhaps the biggest surprise has been the protests over noise. Before their wind farms were generating power, some developers predicted that they would be inaudible. Although they knew that turbine noise would increase as the wind blew harder, they assumed that the increase in background noise from wind blowing in the trees would mask the sound. Unfortunately, it doesn't always work out like that. The sheltered valley in Powys where Chris Lord-Smith lives, for example, lies in a 'wind shadow'. When the wind picks up, the background noise rises hardly at all. As a result, he says he can clearly hear the 'mechanical droning' from Europe's biggest wind farm at Llandinam about 1.5 kilometres away. Lord-Smith complained to Tim Kirby, the head of Ecogen, the company that developed the site, and to the local council."

(Source 13)

Þ    Source 13: This non-scientific part of the source is generally fairly negative about wind energy, (although the style of it is weighing up the pros and contras) saying that providing 10% of Britain's energy from it would not be feasible. One must consider that this is the biggest wind farm in Europe (shown on the next page), and that "Environmental health officers have visited his house 17 times and say the turbines do not constitute a noise nuisance" (same source).

The level of sound pollution may be exaggerated in source 13, but this section shows that noise could definitely be a big consideration in some cases.


Effects on Wildlife

·        The text surrounding Source 12 (page 11) says: "There have been very few reported cases of ill effects or injury to birds, livestock or wildlife as a result of wind turbines"

Þ    They do not specify what these very few cases are. Otherwise analysed on page 11 of this document.

·        "In California, between 1989 and 1991, researchers funded by the California Energy Commission searched for bird carcasses at sites on the 7000-turbine wind farm at Altamont Pass. Of the 182 they found, most had collided with turbines, and had suffered amputations. Others had been electrocuted or collided with wires. Almost 120 were birds of prey, including red-tailed hawks, kestrels and protected golden eagles."

(Source 13)

7000 is a large number of turbines for a relatively small number of casualties.

Annual casualties = casualties / years

Casualties per turbine = casualties / turbines

Casualties per TWh = casualties per turbine*turbine rating*3600*24*365

Annually = 182/2 = 91

Per turbine = 91/7000 = 1/77

This is about one casualty per 80 turbines per year.

Per TWh = 1/77*500kW*3600*24*365= 2*108 casualties per kWh (1SF)

Makes approximately one per 5TWh generated, estimating an output of 500kW pert turbine.

Þ    Source 13: This source is generally fairly negative about wind energy, (although the style of it is weighing up the pros and contras) saying that providing 10% of Britain's energy from it would not be feasible.

Environmental Effects Conclusion

As can be seen, in some situations, the development of wind turbines could have effects on the surrounding flora, fauna, and human populations. Siting of future wind farm sites and wind turbines must consider these factors. The effects, however, are overhyped, and are not really that serious. The calculations above show this. The wind farm in the example above was sited near a major colony, and more careful placing would avoid even these many.

The main limiting factor on the growth of the wind industry in this respect is the complaints of humans- wind farms are the most effective in exposed places like ridges, and are seen as spoiling the view by many, and the sound can travel quite far.

Other than this, wind energy is very unpolluting, having no long-distance effects. Wind could be a concern to some species apart from humans, but I have no evidence of this. Wind farms could therefore be sited in many places that are remote enough to avoid sound pollution to humans, and the visual prominence will have to be tolerated.

Conclusion Evaluation

Despite the possible bias of some sources, I have conflicting sides of the argument and they can therefore be compared. I think that this is a valid conclusion, although the range of sources was limiting, as even the possibly anti-wind sources turned out to demonstrate the effects as minimal.

Comparison Between Wind and Other Renewable Energy Resources

“With recent changes in the law and technological developments [wind] is now a viable commercial option”

(Source 1)

This section is an analysis of the forms of energy for use in the United Kingdom, now and in the future. The future prospects for particular renewable technologies in the UK will be determined by the commercial availability of that technology, the presence of an exploitable resource, the economic competitiveness of the technology compared to other available options, and the overall demand for energy.

The renewable energy types currently available include the following. The classification of them in Energy Paper 62 (published by the government) is given on the right (see Key).


Type:                                                                                                   Classification:

1.      Direct From the Sun:

active solar;                                                                                 2

passive solar design;                                                                 1

photovoltaics;                                                                              2

2.      Combustion:

agricultural and forestry residues;                                             1

energy crops;                                                                               1

landfill gas;                                                                                   1

municipal solid waste combustion;                                           1

3.      Water:

tidal stream;                                                                                 3

wave power;                                                                                3

small-scale hydro power;                                                           1

large-scale hydro power;                                                            3

4.      Advanced Fuel Cells;                                                                 2

5.      Wind Power:

onshore;                                                                                       1

offshore; and                                                                                3

6.      Other/New Technologies (i.e. those technologies                  

which are unlikely to be deployed at a significant scale

within the UK without significant fundamental research

and/or fundamental changes in approach that radically

alter the economic case in support of commercial

deployment).                                                                                      3


1= Market enablement via NFFO and/or RDD&D

2= Assessment, RDD&D

3= Watching Brief

(P21 Source 3)

Source 3:       (more fully analysed on page 3 of this document) This classification of the various technologies is what the government uses to decide on its spending on Research and Analysis of the technology, and which gain support via the NFFO. This should be reliable information, but political motivation cannot be ruled out, as this involves donating money to companies for them to carry out research. See below for evaluation of an example of the government’s classification.

Comparison of my analysis of a technology (Active Solar Heating Technology) to its government classification in Energy Paper 62

Text Box:  Active Solar

This is the use of black, heat-absorbing plates (or evacuated tubes as in industry) to heat water or oil and using heat exchangers to convert use the heat either to heat domestic hot water (DHW) systems and central heating, as shown on the diagram, or to generate steam to turn turbines (on an industrial scale). Hot water can also be stored in an insulated tank for later use. Evacuated tube collectors are basically the same, but the tubes and the plates are in a vacuum surrounded in glass, which eliminates heat loss by conduction and convection. The plates are black because black is a good absorber of light: it looks black as it absorbs (nearly) all the light falling on it, and little is reflected to enter our eyes.

"The UK climate has a high fraction of diffuse solar radiation and long periods of low radiation levels. Consequently, solar heating in the UK is best suited to low-temperature heating applications, which do not require direct sunlight. The most common application is the provision of heat for domestic hot water (DHW) systems."                                          

(Source 3)

"The overall area of the collector array is typically 3-4m2, although a wide range of sizes is possible." I will use an optimistic 4 as a working estimate.

(Source 3)

Þ    Source 3: (more fully analysed on page 3 of this document) This is merely to be taken as an arbitrary unit, as, although the source is unlikely to be able to lie outright, there may be political motives and it states that a wide range of sizes is possible, so it just chose this number for convenience.

·        (See diagram above.) The intensity of solar flux falling on the United Kingdom (average over a year) is between 100 and 150 watts per square metre. I will use 100 as a working estimate.

(P115 Source 14)

Þ    Source 14: This is a scientific textbook, and should be accurate, scientific information. Although there should be no reason for bias (multiple authors, multiple subjects), the source of the diagram, if not original, or the data from which it was constructed, could be biased. I very much doubt it, however and cannot predict which way any bias would be (positive/negative), so I will use it as a working figure.

Using this information;

Watt- hours per year = watts per m2 (average) * area (m2) * seconds per hour

hours per year


Watt-hours per year = 100Wm-2*4m2*(3600seconds/(365.25 days*24 hours))

Watts per m2 per year = 200 Wh/yr

I am assuming average household consumption of 4,200kWh/year

(Source 15)

Þ    Source 15: This is the estimate used by the BWEA to calculate the amount of homes the installed capacity of wind farms could supply in the UK. Seeing as they represent the interests of the industry, it is possible that they promote wind energy. This may therefore be a low estimate, as this would make it look like they could supply more homes. I will, however, use it as a working estimate, as I have no conflicting evidence.


% of annual use (for a household) = 200/total annual use *100

Then a 4m2 solar panel would provide

200/4,200*103*100= 0.005% of annual electricity usage of a household

With this being an optimistic estimation (due to possible bias in Source 15 and rounding up), it is hardly likely that DHW systems contribute a great deal to solving the UK's energy problems.


The government's classification is therefore justified, and their other classifications should be equally reliable, although this cannot be guaranteed. I will therefore evaluate those in class 1 as competing with onshore wind energy.


Text Box: P17 Source 16
Onshore Wind is therefore competing with passive solar design, agricultural and forestry residues and energy crops, landfill gas, municipal solid waste combustion, and small-scale hydropower. I will evaluate these briefly in the next section.

Passive solar design

This is simply the design of houses so that they absorb a maximum of sunlight from the sun, and re-emit a minimum, as shown on the previous page and below.

Conclusion: This only cuts people’s electricity bills and the annual usage, instead of supplying electricity, so I cannot properly compare it to my analysis of wind.

Text Box: P17 Source 16

Agricultural and forestry residues and energy crops (see Appendix 1 no. 3)

·        “The DTI set the price of electricity from the wood-burning plants at 8.6 pence per kilowatt-hour. This is double the prices it announced for energy from new wind and landfill gas projects and nearly three times the 3.2 p/kWh paid for energy from coal.”Text Box:   “Researchers at ETSU calculate that by 2005 provided costs do come down, energy crops will have a greater potential for producing electricity than all other renewable sources put together (see graph)”

(Source 17)

The use of resources depends on their commercial viability. With such a high price, it is not commercially viable. In the same article, the author says that the price is expected to fall with new technology, which would explain their classification of it, but the government is “ready to drop their plans” (Source 17) if this doesn’t turn out to be the case.

·        “The development of energy crops has been slow. This reflects the complexity of creating a fuel supply of a novel crop and then using it in conversion plant that have not been proven commercially. Despite these problems, the future prospects for energy crops are encouraging.”

·        “Forestry residues will be used as the main fuel for the NFFO wood-fired projects currently under development. Projects are not ‘bankable’ without a well quantified fuel supply and wood residues from existing forests are the only source available at present.…The rate at which this development takes place depends mainly on political decisions to ‘level the playing field’ so that energy crops can compete for land on an equal basis with conventional agricultural crops. If this is done, forest residues will act as a precursor to the development of energy crops. The long-term development of wood as a fuel for power generation depends on the development of energy crops since the small area of forest in the UK can sustain little development beyond the power stations currently being planned and built.”

(P62&77 Source 3- analysed on page 3)

Þ    Source 17:           This source, in a scientific magazine, should be reliable, but the authors of the individual articles may be biased. As I do not know where Fred Pearce works, his political orientation etc, I cannot make this judgement. The article is, however, well argued, with statistics providing both sides, and leaves the reader to come to their own conclusion. I will therefore use it as reliable, scientific information, but cannot be sure.

Conclusion: Agricultural and forestry residues and energy crops are not yet a threat to wind and may, or may not, be a competitor with wind in the future, depending on whether the government’s plans change or the price comes down. Energy crops will become more important in the future, and residues will probably not be developed any further beyond that already planned, and so will only be a minor contributer.

Landfill gas (see Appendix 1 no. 3)

Text Box: Source 16
”The number of schemes using landfill gas in the UK is also expected to rise as EU directives to control methane emissions to the atmosphere are implemented.

Beyond 2025, the number of new landfill gas energy recovery schemes is expected to decline as the implementation of the EU landfill directive will divert organic wastes away from landfill and will thus reduce the potential for methane generation. However, there will still be some landfill gas available as gas generation generally occurs over 15 to 30 years.

(P109 Source 3- analysed on page 3)

·        Text Box: Source 16
The graph on page 19 of this document also shows an optimistic outlook for landfill gas- but only up to 2025 and at prices that aren’t commercially viable.

            Conclusion: This is only set to be a player in the field in the short-term. It was classified as market enablement because anybody can do it with current technology. In the future, however, wind will be much bigger and cheaper.

Municipal solid waste combustion

·        “By the end of 1998 the combustion capacity was about 2.3 million tonnes, with all wastes being combusted in plant with energy recovery.”

·         It is estimated that by the year 2000, waste treated by combustion will total about 2.6 million tonnes.

·        The value of waste is about 500 kWh/Tonne

Resource = tonnes of waste * energy value of waste

Resource = 2.6*106 * 500*103 = 1.3 TWh

·        The annual requirement of the UK in the year 2000 will be about 330 TWh (numbers given at the beginning of this document- presently about 320 with an annual increase of 5.5 TWh)

% of requirement = resource/annual requirement*100

% of requirement = 1.3/330*100 = 0.4% of annual requirement

(P118&120 Source 3- analysed on page 3)

With recycling on the increase, the scope for expansion for this technology is not great. The amount burned will only rise by 0.3 million tonnes between 1998 and 2000 according to the estimate given on the previous page. Much of the unrecyclable matter is toxic, or creates toxic gases. However, as better technology for combustion and pollution control emerges, it could become the end of a recycling chain.

Conclusion: I think that municipal solid waste combustion is not really of significance now, but in the future it could become a medium-sized supplier of the country’s electricity.

Small scale hydropower

·        [Between now and 2010] “The UK is expected to increase its small hydro capacity by only a small amount, from the current 95MW to around 120MW”

(P92 Source 3- analysed on page 3)

·        It is, however, very cheap (see graph page 19) and could compete with wind as a cheaper resource.

Conclusion: Hydropower is about as commercially viable as non-renewable energy resources. This means it could be a direct competitor in the renewables market. However, in the future, it will not affect the growth of wind, as the resource, or the use of the resource, is limited. In the further future, however, a large tidal barrier could be put into place, which could provide a large amount of the UK’s electricity.

Comparison to Other Resources Conclusion

Of those of the other renewable energy resources that I have evaluated, none appear to be infringing on the market of wind energy, presuming little expansion of the latter beyond 20% of the UK’s electricity. Some technologies like landfill gas and hydropower, however, may compete with wind in the near future to limit the rate of expansion of wind. Others, such as agricultural and forestry residues and energy crops may become more important in the future. Onshore wind energy looks set to be biggest player in the growing renewables market.

Conclusion Evaluation

This section relies quite heavily on source 3, the supporting analysis for the government paper “NEW & RENEWABLE ENERGY- Prospects for the 21st Century”. Wind does, however, appear to come out strongly, and my comprehensive analysis of active solar technology did not point to bias of the source, nor did other uses of the paper throughout this document. The degree of competition could be reduced, however, if passive solar energy became a reality for most housing in the United Kingdom- the electricity demand would decrease. Also, I cannot be sure that other technologies classed as research would not have caught up with onshore wind and become real competitors by, for example, 2025, when the potential of onshore will still not be realised. For example, “Photo-voltaic cells have the technical potential to supply about 12% of the UK’s electricity needs by 2025” and “over the next 10 years offshore wind will start coming into it’s own”. The source for this quote, however (Source 21), is an advertisement by a renewable energy company, and only says that the technical potential of PV is this big, and that offshore will start being important. The potential for onshore wind, and therefore the validity of this conclusion, is dependable on future fluctuations in the renewable market due to new technologies, but for now it will be a leader.