Evidence to the House of Lords Economic Affairs Committee inquiry into ‘The Economics of Renewable Energy’
10 My evidence is mainly concerned with wind power stations for generating electricity. This is because these form the major component of all major country’s future renewable energy policies. …
11 The most important consideration for the future electricity supply has to be security of that supply. …
12 Security of supply implies firm generation capacity with a margin above the peak (winter) demand. The firm generation is supplied by baseload power stations (such as nuclear) and despatchable (controlled by the grid) power (such as coal, gas and certain renewables such as hydro-electric – including pumped-storage schemes such as Dinorwig). Neither on-shore nor off-shore wind power stations contribute significantly to the security of supply because the electricity is intermittent, unpredictable and embedded on the grid (not despatchable). Invariably peak winter demand occurs during extreme cold weather when a high pressure system settles across northern Europe and drags in cold continental air with little wind. Even with wind turbines distributed widely across the UK, under these low wind conditions, little electricity would be generated by wind turbines. …
15 In answer to your second issue, the barriers to greater deployment of wind power stations are suitable on-shore sites, supply of wind turbine components and shortage of equipment needed for off-shore construction. In addition, serious planning issues confront on-shore wind power stations. These include the visual (landscape) and other environmental impacts, military objections (radar interference) and more recently the effect from the current large wind turbines (heights in excess of 100m) of noise and its consequential health impact. …
17 I now turn in greater detail to the technological concerns with wind turbines. As a physicist, it offends my learning, experience and intelligence to attempt to produce electricity on a large scale from wind power. This is for four reasons. Firstly, because of the very low energy density of wind (the energy per volume of moving air): For comparison and in round terms, the energy density of moving water is about 1,000 times as great, that of fossil fuels (coal, oil, liquefied gas) is about 1 billion times as great and that of nuclear is about 1 million billion times as great. Thus wind turbines have to be enormous to capture a useful amount of energy. [emphasis added] Secondly, because the power of the wind is a function of the cube of the wind speed, the electrical output is very sensitive to the wind speed. Thirdly, because of the variability of the wind, wind turbines only produce electricity at about 25% to 30% of their rated output (capacity or load factor). Fourthly, because of the intermittency and unpredictability of wind, the electricity production bears no relation to the demand for electricity. In summary, wind turbines are enormous, produce a pathetically small amount of electricity, intermittently, unpredictably and not when it is most required. [emphasis added]
18 The CO2 emissions saved by wind turbines have been calculated based on the CO2 emissions from displaced plant (coal and gas-fired power stations). A consensus figure of 430 kg/MWh is currently used. However, this figure is only part of the equation needed to calculate the CO2 emissions saved. Also to be included in the equation are the CO2 emissions resulting from the manufacture and construction of the turbine (estimated by various people at the equivalent of between several months to many years of operation – the payback period); the electricity losses down the low voltage distribution line to the consumers (estimated at between 5% and 15% of the electricity generated, due to the long distance as the result of the remoteness of many turbines); and the CO2 emissions produced by conventional power stations operating very inefficiently on standby (and burning fuel) ready as backup to meet the electricity demand when the wind drops. Evidence from Denmark and Germany suggests that CO2 emissions savings from the use of wind turbines are at best small and at worst, they may actually lead to an increase in CO2 emissions. [emphasis added]
19 Although the wind is a renewable source of energy, wind turbines can only operate on the grid in conjunction with backup generation to ensure demand is met when the wind fails. For this reason, it has been claimed that wind-generated electricity cannot be classed as renewable.
20 Because of the intermittency and unpredictability of the wind and thus of the electricity generated by wind turbines, wind turbines cannot replace a significant number of conventional power stations. Thus wind turbines are being constructed as a secondary source of electricity. In essence, the consumer is paying for two sets of electricity generation; the conventional despatchable power stations, necessary to meet demand at all times and wind turbines which operate only when the wind blows and which then displace despatchable power stations.
21 Wind turbines are usually connected to the low voltage distribution grid, rather than the high voltage transmission grid to which conventional power stations are connected. Wind-generated [power] is embedded on the grid as it is not despatchable and cannot be controlled. The national Grid was designed so that electricity flows from the power stations on the efficient high voltage transmission lines and is transformed (stepped) down progressively on the distribution grid to consumers. Thus electricity flows one way and by the most efficient route. However, embedded electricity can flow the wrong way if there is not sufficient downstream demand. This can cause grid problems.
22 Electricity cannot be stored on the grid and grid voltage and frequency are maintained in tight margins to protect sensitive equipment. This is not normally a problem, the grid having operated successfully for over 60 years. This is because demand is accurately predictable and despatchable power sources of various response times are available to match the grid. However, with increasing amounts of intermittent and unpredictable embedded generation on the grid, control becomes increasingly more difficult. This can lead to grid failure and collapse as has happened recently across a large part of Europe and in Texas.
23 In answer to your sixth issue, because of the low energy density of wind and the large separation distance required between individual turbines, the area of land affected by wind power stations is proportionally greater than that of traditional power stations. For example 100m tall wind turbines of 2MW rated power need to be spaced several hundred metres apart and not close to dwellings and roads. Thus except in remote areas, about four wind turbines can be accommodated per square kilometre of land. This is not dissimilar to the figure for nuclear power stations or gas-fired power stations. For comparison purposes, and taking into account capacity (or load factors), the land area covered by a wind power station of the same energy output as a nuclear power station would be about 2000 times as great (or an area of land 20km by 25km would be covered by wind turbines to produce the same electrical output as one nuclear power station occupying an area of land 500m square). Furthermore, the wind turbines are of greater height and rotate so that their visual impact is amplified. A considerable infrastructure in terms of possibly improved roads and access tracks is required for wind turbines. In addition, the wind turbines provide few if any jobs in the district, and possibly destroy employment due to the loss of tourism-related business. …
These external costs in terms of environmental and other impacts should be compared in terms of benefits and disbenefits for each technology on a like-for-like basis … The like-for-like basis must be in terms of energy output (i.e. MWh, GWh or TWh of electricity generated per year) rather than installed capacity (MW). Thus, for example the benefits and disbenefits of a nuclear power station of 1600MW rating with a capacity factor of 90% producing 12.6TWh of electricity per year should be compared with a wind power station consisting of 2880 2MW turbines with a capacity factor of 25% also producing 12.6TWh of electricity per year. …
Dr P A W Bratby
15th May 2008
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