This is the second essay I have written on energy strategy, and follows on from my energy efficiency essay. I have decided to do an essay on each of the possible renewable sources, and follow these up with essays on energy storage and a general look at renewable potential. Unfortunately this will be a lot of work, so it will be some months before I could finish it all! In fact over the next couple of months I will be busy studying for exams and won't have time for it at all. Thus this essay, and my forthcoming defence of Amory Lovins will be the last major articles from me for the next couple of months at least. I simply do not have the time to spend hours putting together essays with lots of references at the moment. Therefore I will not be ready to post any more of these essays until at least June. In fact it could be longer still especially if I get a job for the summer that isn't in Edinburgh(in which case I'm off the net from July to September inclusive). Anyway for the moment here is my essay in wind energy. If you wish to learn more about renewables I suggest consulting the sources I use here: Energy Strategy and Global Warming ---------------------------------- Part 2: The Potential of Renewable Energy:Windpower --------------------------------------------------- By James A. Hammerton --------------------- Introduction ------------ Many people believe that renewable energy sources are only capable of making a minor contribution to our energy needs. However there is a growing body of evidence which suggests that renewables could actually provide us with considerable amounts of energy, and ultimately it could even supply all our energy needs.These essays will look at each kind of renewable source in turn, and there will be two further essays one on intermittency and energy storage, and one which explores the possibility of a totally renewable based energy supply.This essay will look at one of the more successful renewable sources, namely wind power. The Wind Potential ------------------ Estimates of the total theoretical wind potential vary for the US, but one source puts it at 3,000 Exajoules(EJ)[1], compared to the 89EJ consumed in the USA in 1991. Thus even if only a small fraction of this potential could be tapped, it would supply significant amounts of energy. For example a review of studies conducted in the 1970s concluded that there was a potential for satisfying 10-40% of US electricity demand with wind power[2]. More recently, a highly detailed analysis was published in 1991, by researchers at Pacific Northwest Laboratory. Here the amount of land area in the 48 contiguous states supporting wind speeds in each of seven classes was estimated using a national wind resource database. Then they group areas into five different types of land use, and constructed four scenarios and arrived at a range of estimates for the practical wind resource in each class. Using the median scenario, the estimates found that the windiest areas of the US, could supply 18-53% of the electricity consumed in 1990. The lower figure was attained using severe assumptions of land use exclusion, whilst the higher figure assumed none[3]. If more moderately windy areas were included they found a potential of producing between 1.7 and 6 times the current US electricity demand.These figures show a considerable potential for developing a significant wind energy supply from land based wind power in the US. In the UK, there is a similar potential for wind energy on land and an even greater potential for off-shore wind development( a source of energy that wasn't considered in the sources I have for the US). For example the Central Electricity Generating Board in 1988 indicated that around 17% of the UK's electricity supply could come from on-shore wind power, and that the off-shore potential was comparable to Britain's total electricity supply, and that was just the resource in the shallow waters of East Anglia. Other studies have put the recoverable resource for Britain's wind power to be between 10-40% of the current supply from land based sources, when environmental considerations were taken into account[4]. Off-shore power could produce 60TWh of electricity by the year 2025, according to a study done by Michael Flood[5]. The costs of wind power ----------------------- So we have established that there is a considerable potential for developing wind power, but how much does it all cost? Over the 1980s wind power(like other solar technologies) made a lot of progress, to the extent that wind machines can now be mass produced to a standard reliable design. This has lead to falling costs, which could fall even further if wind power was taken up more vigorously. So what is the cost of electricity from a wind plant today? Well as of 1990, the levelized cost of wind generated by turbines in California was 5-8 cents/kWh, down from 25 cents/kWh in 1981[6]. The cost per installed kilowatt fell from $1,300-$2000 to $950-$1,100 over the same period. Operation and maintenance costs have been brought down to 1.4 cents/kWh. According to one source the cost of electricity generated by one quarter of the current capacity in California is competitive with new nuclear capacity[7]. In the future these costs are likely to fall even further, perhaps to as low as 3-5 cents/kWh[8]. Some of the newer developments in wind technology confirm this; A design slated for production this year is being developed by a consortium including US Windpower, EPRI, and several utilities led by Pacific Gas & Electric, which will use a variable speed generator to produce electricity over a wider range of wind speeds. As of 1991, a prototype of this turbine (which will be rated at 300 or 400 kW), was installed in Altamont Pass. Once in full production this design is expected to cost $735/kW(at the 400KW rating) and generate electricity at a levelized price of under 5 cents/kWh in a 7m/s (16 mph) average wind[9]. In the UK, the costs are also fairly low, one source gave figures as follows[10]: Discount Rate 5% 8% 10% 12% Wind speed=9.8 m/s 1.79 1.93 2.43 2.71 Wind speed=7.6 m/s 2.45 3.04 3.46 3.91 Sizewell B 3.15 4.26 5.18 6.25 Estimates of the wind sites with wind speeds of 7.6 m/s vary, but included the majority of the sites which produced the 10-40% electricity contributions mentioned above. Here it seems obvious that wind power would have provided cheaper electricity than one of the UK's nuclear power stations. Reliability and Intermittency ----------------------------- There are some concerns about wind power as an electricity source that have to be addressed before the go ahead is given to use a large amount of it. Basically it concerns the reliability of a supply, given that it is an intermittent source(the wind does not always blow...). Many would cite this as a reason for expecting wind power to contribute only a minor amount of electricity, unless a good storage system could be invented. However on two counts, the situation isn't so pessimistic. Firstly the amount of supply which a grid can take from an intermittent source is considerably higher than most believe. Secondly, storage is done more easily if one does not insist on storing electricity, but instead considers storing the energy in a different form. Evidence for the first point is given below: * Some utilities in the US, and elsewhere have estimated that their systems could accept wind energy for 5-20% of their power, without significant adjustments for the intermittent nature of the energy source[11]. * In the UK, estimates of the possible contribution for wind, without using storage have been put at 1/3 of the total energy supply[12]. Further by using two intermittent sources the joint contribution could rise to over 50% without major penalty. * Back in the US, a study showed that upto 1/2 of a hypothetical Californian utility's peak load, and 1/3 of it's annual generation could be supplied by a combination of solar and wind power with no additional need for storage[13]. I'll briefly give some of the evidence for the second point, evidence that is directly applicable to wind power, but I will leave a more detailed discussion to a separate essay: * A technique known as Compressed Air Energy Storage is already in use, for example a plant in Huntorf, Germany can produce 290 MW for 4 hours, which allows off peak electricity to be stored ready to backup peak power production. Also the Alabama Electric Corporation has a facility completed in 1991 which uses off peak power to compress the air, which then uses gas to heat it up and the air is passed through an expansion turbine. For each kWh of electricity produced, 0.82 kWh electricity are used and 3.9 MJ gas. Emissions are around times lower than comparable combustion turbines.[14] Thus we can see the possibility for storing wind/solar generated electricity from day to day in this method. * More generally for renewable energy, the possibility of generating hydrogen electrolytically could both supply a potential fuel for vehicles and get round the intermittency problem at the same time. Although this is still to be confirmed one study suggests that within ten years, mass produced amorphous silicon cells could cost around 16 cents per peak watt and achieve 18% efficiency, implying a delivered hydrogen cost of $8.40 per GJ roughly the current cost of gasoline at the pump. If one were to use wind power instead of solar, this implies even cheaper hydrogen. However this is an area which will require considerable development. [15] * The above evidence suggests that wind power could be stored more easily than some suggest, but do not give a particularly optimistic picture, however storage of heat is a viable possibility for solar power and could also help with wind power; By converting wind electricity to heat one could use off peak electricity to build up heat reservoirs to use in winter. Alternatively some buildings use off-peak electricity over night to create ice which provides cooling during the day.[16] These possibilities allow the intermittent renewable technologies that produce electricity to be used much more effectively. Admittedly the above evidence is sketchy though this is mainly because I have concentrated only on what is applicable to wind power. For renewable energy in general the situation is much better, but a detailed discussion of this would require another essay. In the meantime a look at the energy storage chapter in Michael Brower's book 'Cool Energy' will provide much of the evidence. The Environmental Impact of Wind Power -------------------------------------- Wind power is one of the most environmentally benign energy sources, but it is not completely without it's impact. There are several points to consider. Firstly, there is the nature of land use required for wind power. One study done in 1977, concluded that to supply 20% of American electricity would require the use of 18,000 square miles(7% of the size of Texas)[17]. However, this ignored the fact that the turbines would occupy only a small fraction of that area. In fact the rest of the land can often be used for other purpose or left in it's natural state. For example wind power can be safely combined with farming and provide a significant addition to a farmer's income. Secondly there's the question of it's visual impact, which is comparable to that which we already have with electricity pylons. The main point here is to keep the windmills away from areas of scenic beauty, and to reduce the impact with careful siting. As mentioned above, the evidence suggests that these requirements do not greatly affect the potential for wind power to provide say 20% of our energy requirements(more if we use storage, but then the impacts of storage have to be considered). Thirdly there's the aural impact.It is grossly overstated by many people, according to one source modern turbines cause little more noise than the rush of the wind[18]. At a distance of 300 yards the noise level is negligible. Finally there is the environmental impacts of any storage used by wind power. This could be significant, but a lot depends on the storage methods, and in any case this would not become a problem whilst wind power is contributing the 5-20% possible before the reliability of the total electricity supply is threatened. Currently in the US wind power produces less than 1% of electricity and elsewhere it has hardly been looked at, so a five fold increase in the use of wind power is almost certainly possible without storage being required. Conclusions ----------- With careful siting then, it would seem that wind power can provide a significant clean contribution to our energy supplies and at a reasonable financial cost, and this is before storage becomes a necessity. At that point cost would no doubt rise, and the environmental impact with them, but the latter is still likely to be lower than other sources of power whilst costs potentially could be quite low especially if hydrogen technology achieves it's promise. In short there is no reason why we can't put greater reliance on wind power at least upto the 5% minimum estimates for the amount that can reliably be used without storage. Bibliography ------------ The main source for this essay is 'Cool Energy' by Michael Brower published by MIT press. This provides a good case for renewable energy in the US and has a chapter for each of the sources of renewable energy, for storage and for policy recommendations. 'Energy for Planet Earth:Readings from the Scientific American' has a chapter devoted to renewable sources which also covers wind power, whilst 'Global Warming: The Greenpeace Report' has a chapter which concentrates on the commercial performance of renewables in the US(with a lot of attention to the Californian wind rush). For the UK, 'Green Energy' by David Toke is the source of data used, another source(though not used in this essay) on renewables is 'The Energy Alternative' by Walter C Patterson. Notes ----- [1] This appears in 'Cool Energy' by Michael Brower, page 72(this source will be referred to as Brower from now on). The reference given is National Science Foundation 'An Assessment of Solar Energy as a National Resource,1972. [2] Brower P.74, reference given as "Energy Strategies:Toward a Solar Future" H.W. Kendall, S.J. Nadis, 1980. [3] Brower P. 74, reference: "An Assessment of the Available Windy Land Area and Wind Energy Potential in the Contiguous United States", D. L. Elliot, L.L. Wendell and G.L. Gower, 1991. [4] This appears in "Green Energy" by David Toke(from now on referred to as Toke) page 82. [5] See Toke page 88. Pages 85-88 discuss off-shore windpower. The reference given for this is "Energy Without End" M. Flood, London, Friends of the Earth. [6] Brower P.78, reference: "Wind Energy Comes of Age" Energy Policy October 1991,P. A. Gipe, 756-758. [7] "Global Warming: The Greenpeace Report" (from now on Greenpeace) page 236, same source as Brower used in above note. [8] Brower, P. 80, reference: S.M Hock, R. W. Thresher, J.M. Cohen "Performance and Cost Projections for Advanced Wind Turbines", 1990. "Energy For Planet Earth:Readings from the Scientific American" Chapter 10, "Energy From The Sun", Page 108 cites the US Dept of Energy as suggesting the costs falling to 3.5 cents/kWh over the next 20 years, but without giving a reference for this. [9] See Brower Page 78. [10] Toke Page 84. [11] Greenpeace Page 236. "PG&E's Evaluation of Wind Energy" D.R. Smith 1989. Brower Page 82. References: As for note 2, and M. Grubb "A Wind of Change" New Scientist, March 17, 1988. [12] Toke Page 88. Reference: "The Integrated Analysis of New Energy Sources on the British Supply System: Methods and Application" Paper presented to the IEE Energy Option Conference, Reading, April 1987. London Imperial College of Science and Technology, 1987 p. 3. [13] Brower Page 84. "Energy from the Sun" Scientific American Sept. 1990 Carl Weinberg, Robert Williams. This is reproduced in "Energy for Planet Earth:Readings from the Scientific American". [14] Brower Page 167. [15] The possibilities for using hydrogen are given in Brower Page 169-172 and are also discussed in "Energy for Planet Earth, Energy from the Sun" [16] Again I refer you to Brower's chapter on energy storage. Page 158 has the specific example given. [17] Brower Page 84. A discussion of this issue is presented on pages 84-85 of Brower, it is also covered in Toke, pages 83-85. [18] "Energy for Planet Earth", Page 109. Toke also mentions this on Page 84, which is where the 300 yard figure comes from. James Hammerton AICS3 University of Edinburgh, Email jamesh@aisb.ed.ac.uk