Wave and Tidal Power Back

Estimates from Long and Whittaker (1988) suggest that wave power could supply thirty percent of the world’s current energy use. Waves are caused by the sun's radiation warming the earth's atmosphere and setting up pressure changes that cause the air to move as wind.    The winds move the surface of the sea to create waves.  The power of the waves is well known and has the potential to cause immense damage. 

 Wave energy technologies can be based either onshore or offshore.  In the early part of this century, navigation buoys were fitted with a vertical open bottomed tube to allow waves to oscillate inside.  This up and down motion forced air through a whistle to act as a signal.  Later, in the 1940s, generators were fitted to replace the whistle with a light.  There are over one thousand such devices currently in operation around the world.  Research and development was advanced during the oil crises of the 1970s and many new wave power installations were developed around the world.  The coasts of the UK were identified as possibly  providing a potentially significant source of renewable energy.  Indeed, the UK was a ‘lead nation’ in the development of wave power up to 1985 (Prins and Stamp 1991).  These schemes, however, looked at large-scale projects, rather than smaller projects suitable for island communities.  The Government decided to cut expenditure on wave power as it was considered to be uneconomic at the time.   However, in reality, this was not the case.  The main device being investigated at the time was the Salter Duck, named after its inventor, Professor Stephen Salter of Edinburgh University. The Salter Duck  was designed for operating in the open sea.   It consists of floats, ‘ducks’, which nod as waves pass.  This oscillating action generates electricity by compressing air to drive turbines.  In 1985, the first full-scale pilot plant was built in Norway and produced electricity at 4p/kWh.  However, in the same year, the UK Government cancelled all research on wave power.  The reason for this action was a secret report, produced by the Advisory Council on Research and Development which recommended saving the £3M being spent on research. At that time £200M was being spent on nuclear research. Indeed, the nuclear lobby and Government, were pushing for  the Sizewell B nuclear power station, and were afraid that cheap wave power would undermine the nuclear programme.  Thus, wave power had to be stopped. Evidence pointing towards deliberate ‘dirty tricks’ came to light in 1990, indicating a clear policy from Government and the nuclear industry to make wave power seem more expensive.  Some of these devices included: deliberately altering the views and conclusions of the consultant engaged to assess the technology;  ‘adjusting’ certain figures to make construction  costs appear fifty times greater and the reliability of the transmission cables seven thousand five hundred times less reliable; postulating  very low resource availability (Prins and Stamp 1991). 

 Despite the withdrawal of government funding,  the Salter Duck is still being investigated along with other plants, such as the Oscillating Water Column (OWC) and   smaller individual ‘duck’ devices have also been researched.  The OWC, operates in a similar way to the wave powered buoy.  A number of different devices have been researched and include  breakwater devices and bottom water structures. The most successful design to date, however, has been the shore mounted OWC system developed by Queen’s University, Belfast.  On Islay in the Inner Hebrides, one such coastal wave energy generator has been in operation since 1991 producing electricity for the national grid at a rate of 60-100KW.  This uses  natural coastal features and is situated in a gully.  All these devices use the Wells generator,  in which the turbine spins in only one direction no matter which way the air is passing over the device.  Plans for a 1MW generator are being drawn up (Long and Whittaker 1988).

Tidal energy can also be utilised. In France at La Rance, near St. Malo, an estuarine tidal scheme has been operating since 1966.  The scheme consists of twenty four 10MW Kaplan turbines with reverse flow and pumping capability.  These turbines are capable of generating or pumping in both directions. The barrage also provides  communications with a dual carriageway running over it linking the two sides of the estuary.   Other sites include: a 400KW site in the north of Russia, operating since 1967; a 20MW barrage at Annapolis in Canada and a 100MW scheme in China (Organisation for Economic Co-operation and Development 1988). 

A number of estuarine sites,  including the Severn and the Mersey have been examined around the UK.  The Severn Estuary proposal consists of a single basin barrage designed to operate on the tide’s ebb.  This system allows for the rising tide to flow in through the sluice gates and turbines.  After high tide, these are closed until the tide has ebbed sufficiently for the difference in water level between the sea  and the barrage basin to drive the turbines.  This continues until the water level is too low for the turbines to operate and  they are then closed down.   If the controversial Severn Barrage scheme were built, it could supply up to six percent of  the UK’s current electricity needs.  The proposed barrage, set to produce 7000MW of electricity, would have significant environmental impacts on the Severn estuary, an internationally important wetland.  The problems associated with the barrage include impacts on the freshwater-seawater interface.  In particular are effects on fish migration and reproduction and the breeding zones of other aquatic organisms both of seawater and freshwater.  Navigation would also be affected and there might be a build up of pollutants and nutrients that could cause eutrophication and toxicity effects.

Solar Power Back

Solar power, even in the UK, is an established technology.  The main product, solar panels, are quite a common feature on houses.  There are  a number of methods of using solar energy.  These include, passive and active heating, photovoltaics and daylighting.

A key development is the use of passive solar design in buildings.  However, building regulations still have to be updated to encourage the design of buildings to maximise solar gain.  The  village of Tir Gaia near Rhayader in Powys is a development of buildings based on solar design principles.  Passive solar heating,  such as at Tir Gaia, traps the energy of the sun to provide heating.  A variety of methods are employed. Direct gain is achieved by having large south facing windows. Conservatories on south facing walls heat the air and also act as an insulating space between the building and the outside environment. Trombe walls consist of a glazed wall with the glass increasing heat gain, the energy being stored in the wall behind. Glazed roof spaces fulfil a similar role to conservatories.  The houses at Tir Gaia have large south facing windows and conservatories on the roof.  The walls are insulated and the houses contain five thousand litres of water to act as a heat reservoir in the ceiling of each storey of the houses.  The water is stored in bottles to reduce the risk of leakage.  Heat is collected through convection of warm air and stored heat is  supplied to rooms through radiation. Daylighting  involves building design to allow extra natural light into a building so as to avoid the use of electric lighting.  This is also achieved by putting windows in roofs and by having larger south facing windows.

  Active solar heating involves heating water in solar panels.  Water from the panel is pumped to a heat-exchanger to heat water in a hot water tank for domestic use or for radiators.  Photovoltaics is the process of converting the sun's energy directly into electricity.  It uses the capacity of some minerals to transform sunlight into electricity,  including crystalline silicon and gallium arsenide.  Such solar cells have been used in watches and calculators for many years, but have also been developed for larger equipment, such as solar powered fridges in remote areas of Africa.  In the UK, they have been used in a variety of isolated situations, for example, on boats, navigation aids and remote telephone boxes. Photovoltaics can also be linked into the electricity grid. In California, for example, there is a 10MW photovoltaic power plant which provides peak demand electricity for air conditioning systems in phase with the sun.  Switzerland has a national target of 200MW from this source by the turn of the century. 

Biofuels Back   

Organic matter, comprising carbohydrates, compounds of carbon, hydrogen and oxygen, has the potential to be used as a fuel.  This is termed biomass energy. Photosynthesis forms the basic carbohydrate molecules which are converted into plant  materials and structures.  They are also assimilated into animals through the food chain.  Biomass energy, therefore, occurs in many forms and from many sources such as specially grown fuel crops, natural vegetation, surplus crops, dry crop residues, municipal or industrial waste and sewage, both animal and human.  Man has used biomass energy since the utilisation of fire.  Wood and dry leaf litter have been used for heating and cooking.  Wood has also been used in the recent past in industrial processes directly or as charcoal.  Current use of biomass depends on extracting the energy through  conversion processes, such as digestion, fermentation, direct combustion, or by thermally producing a gas, alcohol or pyrolytic oil.

Although biomass production by plants uses the sun's ‘free’ energy, the photosynthetic processes involved to convert sunlight into biomass is very inefficient.  In temperate crops, the conversion rate of sunlight to biomass is at best one percent and, more realistically, averages nought point four (Schneider 1973).  In the UK according to 1978 figures, twenty three percent of energy requirements could be obtained in this way.  However, this rate would be dependant on utilising two hundred and thirty thousand square kilometres of the country,  clearly impracticable.  Indeed, even large-scale energy schemes would only have a limited contribution to the energy needs of the developed world.

Tissue production in plants depends on the solar input  and the nature of the storage of carbohydrates.  Solar inputs are lost as light travels through the atmosphere and by reflection off clouds and other surfaces.  Consequently, position on the globe is of great importance - the lower the latitude, the greater the solar intensity.  The energy received by a plant is a function of day length, season, latitude, local conditions and the efficiency of the plant.  Plants can only use a portion of the energy input, as photosynthetically active radiation is confined to the wavelength range 400-700nano metres. Furthermore, not all the photosynthetic production is stored, some is used to meet the plant's own energy requirements.  Thus, only net primary production is available for use.  Photosynthesis is also the basis of most food chains, so a variable proportion of the fixed energy will be removed from a system by herbivores.

Production also varies with the different types of photosynthetic pathway.  Temperate plant species have a different system to tropical and sub-tropical species.  Temperate plants have a C₃ process so-called because the compound first formed, 3-phosphoglyceric acid (PGA), has three carbon atoms.  In tropical species, the compounds produced, malic or aspartic acid, have four carbon atoms.  These C₄ plants can operate at higher light intensities than C₃ plants.  The C₄ process is not more efficient, but production is greater because C₄ plants are able to operate in high light levels not utilisable by C₃ species.  For example, C₃ temperate grassland produces 23 t/ha/yr, whilst C₄ sugar cane produces 64 t/ha/yr (Cooper 1975).

The actual energy that can be harvested will vary with the plant material.  A typical yield from air-dry plant at fifteen percent moisture is 16-18 megajoules/kg.  Energy is lost in the conversion into a useable energy form, leaving thirty five percent available.  In Europe, dry biomass yields over a season can reach a maximum 20-30t/ha (Long 1977).  Yields will often be greater in experimental conditions than would be expected in practice.  Optimum yields equate to intensive agricultural production.

The economic considerations of biomass energy will have to be weighted against the costs of conventional fossil fuels.  Realistically, biomass may be competitive only when it becomes cheaper than fossil fuels.  Account will also have to be taken of the present use of biomass products, such as straw for animal bedding.  In addition, attention will have to focus on the environmental impacts of land-use change.  Forestry, based on the use of technical equipment, new cultivation techniques and larger schemes, is likely to be the preferred option in the UK because of economies of scale.  The uses of biomass energy as a fuel, however,  all involve the conversion of the material to a useable energy form, each of which has some environmental impact.  The various methods currently used are shown in table 1.

Biofuels are organically derived and include wood, straw, farm wastes and municipal wastes.  The  nature of the raw material will determine, to a large extent, the method for energy recovery that would be most appropriate.  For dry materials, such as wood and straw, burning in a controlled manner allows water to be heated and turned into steam to power a generator to provide space heating.  For farm and municipal wastes, the gas methane, produced during decomposition, is collected and burnt, again, to provide electricity or heat.

Table 1 Energy conversion methods for biomass resources.

Thermal processing.

                        a) carbonisation or pyrolysis.

                        b) air or oxygen gasification.*

                        c) gasification with water or steam.*

                        d) added hydrogen.*

Biological conversion.

                        a) anaerobic digestion.**

                        b) fermentation.**

                        c) others - bacterial and algal production of hydrogen.

  N.B.  * produce methane/methanol, hydrogen, CO₂ and water.

The process of turning wood into energy is now greatly more efficient than simply putting logs on to a fire.  The process is known as energy forestry. There are two main types of energy forestry, short rotation forestry or coppice (SRF) and long rotation plantation (LRP).  SRF is described in detail below.  LRP is similar to conventional forestry and would be sited in the same geographic areas. The difference is that the coniferous trees are harvested after ten to fifteen years. SRF, first examined in the 1970s as a response to the oil crisis (Szego and Kemp 1973),  is a means of using quick growing tree species, generally of the genera Salix and Alnus, for energy production instead of timber.  The system involves a rapid three to four year cycle.  After one year's growth, the trees are coppiced and the resulting shoots are grown for two or three years before being harvested.  Thereafter, the trees are harvested every three to four years.  The crop is air dried and pelleted before being burnt as a fuel for a steam turbine.  This process is CO₂ neutral, as the CO₂ released on burning was taken up from the atmosphere during the tree's growth.    In the Scottish Borders there are plans for a 5MW power station utilising energy forestry (Seed 1993).  Although the technology is available, advances are needed to encourage farmers to take up energy forestry.  Alternatively, instead of being used in a burner, the chipped material could be briquetted and sold for domestic or community use. SRF has a number of advantages.  These are shown in table 2.

Table 2 Characteristics of SRF.

Renewable.

Production of raw material will not be disturbed.

Production and use will not affect CO2 balance.

Non-polluting.

Residues are recyclable.

High yields per unit of land.

Quick return on investment.

Improved harvesting efficiency through mechanisation.

Higher labour productivity through mechanisation.

Source, White and Plaskett (1981).

SRF does have negative features and these include the high establishment costs in the first year and additional management costs.  Also, the monoculture stands are prone to disease or infection, large areas of land are needed and mechanisation means plantations defined by economies of scale.

High production yields will be required if SRF is to be economic.  Frissel et al. (1978) obtained yields of 15-18 t/drywt/ha/yr for poplars.  This SRF system yielded 16 GJ/t for air dried or 20GJ/t for oven dried fuel.  However, the large areas of land needed for SRF to be put on an industrial scale can be gauged from the sixty five thousand hectares required to power a 150MW power station.  This estimate is based on an efficiency of conversion of potential energy in the wood to electrical energy of about thirty five percent.  In the United States, it is estimated that eight hundred square kilometres  of forest with nought point four percent solar conversion and  thirty five percent energy conversion rates, could supply a 400MW power station (White and Plaskett 1981)

In practice, space availability will also have to take environmental factors into account.  SRF needs a minimum rainfall of 500-600m and the land will have to be suitable for growing trees.  This suggests that areas within MAFF land classification category II would be required, especially as sites would also have to be suitable for machinery to operate.  On an industrial scale, the energy budget of SRF would also have to be considered.  Swedish work indicates that a return of three or four times the amount of energy put into a project can be expected.  For example, in one study, an input of 24KW per hour per hectare or 4.8t/drywt/ha/yr yielded  15-18t/drywt/ha/yr (Frissel et al. 1978).

For SRF to become viable, the internal economic parameters would have to be favourable.  In practice, this would mean a number of conditions being met.  Cheap land would have to be readily available and cost-effective methods of propagation, mass planting, cultivation, crop treatment and harvesting would be required.  The costs of additives, fertilisers and pesticides would have to be taken into account.  Technical innovation, for example in fuel processing techniques, would be required.  Competition from other land-uses and alternative uses of the coppiced wood would also have to be assessed. Technical matters, however, are only one type of issue that must be addressed because, finally, the policies within a country have to be favourable.  In this respect, the prognosis is good.  At present, the EU agricultural sector is addressing ways of reducing agricultural production and investigating the diversification of  land-use, including energy production.      

Trees are not the only option, as other crops can be grown as specific energy sources.  Natural stands can also be utilised.  Several species, bracken, (Pteridium) the common reed (Phragmites) and the elephant grass (Miscanthus) have been investigated.  Each of these species dries out naturally towards the end of the growing season and could be harvested with existing technologies.  It is estimated that a stand of Phragmites could produce 11 t/ha/yr of dry matter (Palz and Chartier 1980).  Recent Miscanthus estimates have been higher.  This species is of interest as it  has a C4 tropical photosynthetic pathway. Research in Wales has investigated the potential of Miscanthus and  there have already been field trials in Germany (Dunn and Clery 1992).

Other ways of using timber have also been investigated.  Wood, the traditional biofuel,  is used in many other commercial processes such as construction, fabrication and paper.  As a consequence, commercial value of timber mitigates the use of wood as a fuel.  In terms of the proportion of the tree biomass harvested, forty percent is usually left in the forest as waste.  This includes the tops, leaves and branches, stump and the roots. ‘Cull trees’, those of odd shape, rotten or dead also add to the waste.  Only the economically important trunk is used.  Processing also leads to waste.  This includes the trimmings, sawdust and bark.  Much of the waste, however, is used as a by product, for example chipboard, in the chemical industry and  as fuel in timber processing plant.  Wood, however, does have a significant energy potential, as it is mainly cellulose and lignin.  In the UK, one third of wood residues are used as fuel. Green wood, with a moisture level of fifty percent yields 10.5 GJ/t, air dried wood with twenty percent moisture yields 16.3 GJ/t and oven dried wood yields 19.8 GJ/t at only eight percent moisture content. Thus, if traditional forestry were modified, this waste could be utilised for energy production (White and Plaskett 1981).

Farm crop wastes can also be used for energy production. Crops are only usually grown for the part of the plant that has a marketable value.  However, this constitutes only a fraction of the total plant biomass.  In temperate conditions, for example, the total dry weight of wheat or barley produced is between 11-14.5 t/ha/yr.  This can be divided up as: grain 4-5 t/ha/yr; straw 2.5-5 t/ha/yr; stubble 2.5 t/ha/yr, roots 2.0 t/ha/yr. Furthermore, only thirty five percent of the plant, the grain, is harvested with the rest left as waste.  Whilst straw can be harvested readily, there is no easy way of harvesting the stubble and root components. Indeed, these should be left  as cereal land needs a minimum organic content in order to remain fertile (Palz and Chartier 1980).  Straw from cereals and the stem waste of other crops constitute the largest source of plant matter arising in agriculture.  The material has a low moisture content, about fifteen percent, and can readily be burnt or thermally processed.  Vegetable wastes have high moisture contents, around eighty percent, and would require drying prior to combustion.  They are more suited to  biological processing by anaerobic digestion to produce methane.

Other dry stems could be used in combustion or thermal processing and include rye and oat straw, rice straw, maize stover and dry residues from rape, peas and beans.  Suitable tropical crops include sugar cane, cassava and waste from jute and hemp manufacture.  Indeed, sugar cane bagasse is used to fire the boilers of sugar cane processing plants.  Nut shells, such as almonds, in the Mediterranean and coconut shells over a wide geographical area, are also used.  However, most crop residues are not used, for a variety of reasons including: the convenience of other fuels; the labour involved in handling bulky materials; storage requirements and the technical problems involved in feeding the crop wastes into the energy converting appliances such as boilers and heaters.

Wastes are available ‘free’ as part of the crop production.  Economic demands and technical processes will give rise to economic opportunities for people to use them.  However, cereal straw is currently in demand for livestock bedding and other applications.  In parts of France, straw is traditionally ploughed into the ground to maintain humus levels, moisture and crumb structure (Palz and Chartier 1980).

The utility of a crop residue will depend, in part, on its availability.  The yield of straw, for example, will vary not only according to the environment in which the grain is grown, but also with  the cultivar.  Clearly, longer stemmed grain varieties will produce more straw than the shorter varieties. The logistics of collection and storage of the material are important economic considerations. The material is located on an expanse of fields with harvesting being additional to gathering the main crop.  This puts pressure on labour, equipment and  costs and will increase soil compaction. As materials cannot be used immediately, there will be additional costs associated with handling in and out of store and for storage services.  Similarly, costs will also be involved in transporting waste to the energy plant.  Off site utilisation must be profitable.  The type, amount and density of residue per hectare will also influence costs and benefits.  Work  on different harvesting methods, bale sizes and transport distances has been undertaken in the UK, France and Denmark (Palz and Chartier 1980).   

Straw burning in Denmark has been used for farm domestic heating and crop drying for a number of years.  At larger scales, it has been used in process heating, to provide space heating, steam raising in industry, in district heating schemes and to provide electricity. Using residues as fuel, however, precludes other competitive uses, for example crop wastes are useful fertilisers.  In Europe, sixty percent of straw is utilised as animal bedding and feed.  Non-agricultural industries, such as the mushroom industry, thatching, particle board manufacture, paper production, biochemical and chemical industries, also use straw.  Wet crop residues, such as beet tops, often go to animal feed.

Farm slurry, human sewage and refuse can be utilised to produce biogas energy.  Under anaerobic conditions, bacteria decompose organic material to form methane.  The gas can be collected and burnt to provide energy.  The CO₂ released on burning is a less damaging greenhouse gas than methane and the whole system is CO₂ neutral as the gas was originally taken from the atmosphere by green plants.  Methane, from farm slurry and human sewage, is obtained from anaerobic digesters, whereas methane from refuse comes from land fill sites.  Dairy herds and intensive pig rearing or chicken  farms are ideally suited to anaerobic digestion.  It also has the environmental benefit of turning the final solid residue into a saleable compost with  reduced risk of pollution and little odour.

In Dorset, a seven hundred and fifty cubic metre digester using piggery waste was built in 1984. The slurry is pumped into the digester and is kept there for between seven and ten days at around 37^oC, the optimal temperature for microbial activity.  After this time, the material is separated into a solid compost, which is sold, and a liquid effluent is spread back on the fields.  The effluent has less odour and  is sixty percent less polluting of water than untreated slurry.

In the UK, sewage gas operations are being set up. Indeed, some are already operating  at sewage works (STW), using schemes developed by Water Authorities. The process is similar to farm slurry digestion.  At Beckton STW, the waste from over 2.5 million people is treated by Thames Water.  This is treated in thirty two digesters which fuel two gas turbines.  The waste heat from these turbines also powers a steam turbine and provides heat for the digesters.  The scheme is rated at 7.8 MW of electricity and is the largest in the UK (Anon 1993a).

Landfill gas, as the name suggests, is based on the gases given off from landfill refuse sites as a result of the decomposition of any putrescible material  It is an unavoidable and hazardous consequence of the process and control of the gas is a priority at any landfill site.  When the landfill site is being filled, pipes are incorporated into the site to collect the gas.  Finally, it is capped with impermeable material, usually clay, to trap the gas being produced.  The gas collected in the pipeline network is pumped to gas turbines (Anon 1993b). For example, domestic waste from Manchester tipped at Appley Bridge Quarry, near Wigan, Lancashire, since 1981 now generates sufficient gas to be sold to a neighbouring factory to heat a bitumen boiler.  Five 1MW gas turbines have been installed and heat from the exhaust gases is used to warm the water of a koi carp fish farm installed on the site in an efficient combined heat and power scheme.  About eighty percent of the total energy is used and both the fish farm and the factory enjoy lower fuel bills (Anon 1993b).

A final type of system, based on farm waste, is represented by the power plant installed at Eye in Suffolk.  The 12.5MW plant runs entirely on chicken litter which is a mix of droppings, wood shavings and straw. The material is transported from up to thirty kilometres away and is fed into a furnace to heat water for a steam turbine.  One advantage of this process is that it reduces the risk of pollution. Chicken litter has been traditionally used as a fertiliser because it is high in nitrogen and phosphates.  The EU Nitrogen Directive is seeking to limit  fertiliser applications in some areas and in some parts of the UK there is a surplus of chicken litter that has to be disposed of.  Nearly 1.5 million tonnes of chicken litter are produced annually in the UK.  The ash from the chicken litter power plant is virtually free from any nitrogen and can be used as a fertiliser (Anon 1993c).

Hydro-electric Power Back

Hydro-electric power (HEP) is already an established technology with about two percent of  the UK's electricity generated from HEP. The largest conventional HEP station is at Sloy on the shores of Loch Lomond.  This has a capacity of 130MW and started generating electricity in 1950.  HEP tends to be used at peak demands, because full electricity capacity can be reached within five minutes.  There are unlikely to be major developments with HEP in the future, because of  a lack of suitable sites in the UK.  However, it would be technically possible to build generating equipment into existing reservoir schemes.  Kielder is one example where creation of the HEP station was an additional operational development. Wales already has a number of large-scale HEP schemes such as on the Afon Rheidol (56MW), but it will be small-scale HEP, that is generators below 5MW, that will be of value to electricity production in Wales.

HEP relies on utilising the energy generated as water in the higher reaches flows down to the lower part of a river.  The difference in height is known as the head, the greater the head the bigger the potential resource.  However, even rivers with low heads, that is below three metres, have HEP potential if there is a large water resource.  Modern HEP generators are highly efficient and a number of individual schemes already operate.  Wales has the necessary resource, although not as great as Scotland, of high rainfall and a hilly landscape with many rivers.  In Dyfed alone, an estimated 72MW of hydro-electric resource is available (Assistant County Planning Officer, Dyfed County Council 1982).  This  estimate is based on the capacity of the main river channels.  It did not consider in any detail the tributaries or head waters.  Even a small catchment of four or five square kilometres could maintain a 10KW turbine.  On this basis, there could be potentially hundreds of such small-scale schemes throughout Wales capable of meeting typical needs of domestic and farm requirements.   

Large schemes exemplify the impacts of HEP. The dams and reservoir are visually intrusive, they flood land and habitats and sometimes require the relocation of villages.  The advantage of small schemes is that they can be fostered on a scale compatible with the environment and small communities. Sites where there is a sudden change in river level offer opportunities for HEP and will be the easiest to identify.  These include weirs which often have historical uses, for example associated with mills.  Producing electricity locally also reduces losses on transmission.  There are a number of such schemes already being developed such as at Aberdulais near Neath where a 200KW generator has been installed.   At East Mill in Belper the River Derwent falls over the Horseshoe Weir giving a head of four metres.  Two 200KW generators with Glikes Francis turbines have been fitted to provide power at this industrial site.

Wind Energy Back

As with most renewable energy resources, the sun is the ultimate driving force behind wind energy.  Heating of the earth's surface creates different pressure zones, causing movement, hence winds.  The transfer of heat energy from the equator, where there is an excess, to the poles, where there is a deficit, is the simplified process for generating wind.  The process is in fact much more complex, as only eighty percent of the energy is transferred by the atmosphere, the rest of the energy is moved by the oceans.  Warm equatorial air rises and flows to the poles with cold polar air sinking and spreading towards the equator to replace the displaced warm air.  The earth's rotation also complicates the situation. In the Northern Hemisphere, for example, equatorial air flows north and eastwards and polar air flows south and westwards, creating westerlies and trade winds, the converse occurs in the southern hemisphere.  In addition to the general circulation, local wind patterns evolve including valley winds and sea breezes. The geographical factors that affect the wind at a particular location include latitude, distance from coast, topography, elevation and surface texture.  It is believed that about one percent of the sun’s energy is converted to wind energy.  To put this into context on a world-wide scale, the total energy used by humans, currently, amounts to only five hundredths of a percent of the energy contained in the wind flowing around the planet.  This wind energy is kinetic, that is a movement, and it is this movement that is utilised.  The stronger the wind blows the more energy that is being moved and the more that can be used.  The relationship between wind speed and energy of the wind is cubed, thus, increasing the wind speed by one unit raises its energy by a factor of three.

Wind has been used as a source of energy for  about four thousand years. The earliest evidence for wind power comes from China and Japan, in 2000 B.C., soon followed by developments in Babylon and the Middle East (Flettner 1926).  However, it was not until the 12th century that Europe saw the first windmills (Skilton 1947). In the past, it has been used for irrigation, grinding corn and powering sailing ships. 

This century has seen the development of wind energy for producing electricity.  Following World War I, individual multi-bladed turbines were developed for use in outlying rural areas of the United States to provide electricity.  Use of this technology then lapsed with the development of cheap fossil fuels and electricity networks.  Despite this setback, research has continued, especially in the last twenty years as a result of increases in the price of fossil fuels.  Wind energy is now being seen as an economically commercial option.  Its price compares favourably with other forms of electricity generation and is seen to be an environmentally friendly form of energy production.

Recent developments have aimed at harnessing the wind for electricity on a large strategic scale, rather than just for remote locations.  A great deal of research and development continues.  In the early 1980s, a number of trial sites were developed in the UK, with individual wind turbine generators (WTGs).  Table 3 shows some of these early locations.

Table 3 Early wind power developments in the UK.  

Wind energy research has looked at WTG  designs from 50 Watts to many mega-watts of electricity generation, from multi-bladed to single-bladed, horizontal and vertical axis types.  The designs most favoured appear to be two or three bladed horizontal axis machines rated at 600KW to 2MW.   The structure consists of the blades, with the rotor hub, blade pitch mechanism, a braking system, gearbox, generator and electrical switching system located in a nacelle housing.  These components are mounted on a yaw system which turns the rotor blades into the wind. The WTG is mounted on a thirty metre hollow tower  made of steel.  The blades of a  turbine are made of steel, wood epoxy or glass reinforced plastic and are thirty to forty metres in diameter.

The relationship between the amount of wind energy that a wind turbine can convert into electricity depends on the square of the blade diameter and the operational characteristics of the wind turbine.  It can be expressed as:-

 P = Cp¹/₂ p AV³

where:

P= power in Watts, Cp= machine efficiency, p= density of air, A= area swept by blades, V= wind speed if wind turbine was absent.

 The speed of rotation of the wind turbine blades varies with wind speed, but can be up to forty-five revolutions per minute.  However, the gearbox increases this and the generator  produces between four and seven hundred volts of electricity, dependant on turbine design, which passes to a transformer with an output of eleven thousand volts. This can further be increased to thirty three thousand volts at a sub station for grid distribution.

Wind turbines can be sited individually or in clusters known as wind farms.  In the UK, numerous individual machines were built in the 1980s as table 3 shows.  The first wind farm in the UK was developed in Cornwall at Delabole where a ten turbine site was developed to produce 4 MW of electricity.  This became operational in December 1991.  The first wind farm in Wales came on line in November 1992 at Mynydd-y-Cemmaes with 24 turbines and a capacity of 7.2 MW.  It is likely that future provision will exploit a combination of individual turbines and wind farms  depending on resource availability, site size and electricity requirements. The potential for offshore wind energy developments is being realized.  At Blyth, Northumbria two turbines have been built offshore and there are plans for a large wind cluster on the Gun Fleet Sands off the Essex coast.

Along with the expansion of wind farm projects, there has been a growing realisation that their development is not without environmental impact.  These effects can occur at a strategic level and have implications for the environment or for particular environmental policies.  Alternatively, they can affect particular components of the environment.  In the following sections, the environmental impacts of wind energy projects are discussed in detail.

 Wind Energy and the Environment Back

Despite being an environmentally benign form of electricity production, there are environmental implications in the development and use of wind power.  PPG 22 on renewable energy contains specific reference to wind energy.  Environmental Impact Assessment is a feature of the PPG.  The European Communities Council Directive 85/337/EEC of 27 June 1985 on the assessment of the effects of certain public and private projects on the environment was implemented in the UK Town and Country Planning (Assessment of Environmental Effects) Regulations 1988 (SI No 1199).  Two categories of projects are involved in the EA process, Schedule 1 projects are subject to mandatory EA and include thermal power stations over 300MW.   Schedule 2 lists projects requiring EA if the development is likely to have a significant effect on the environment by reason of its nature, size or location.

 Initially, the Department of the Environment initially concluded that WTG developments were not covered by the 1988 EA regulation and so did not require the production of an Environmental Statement. Given the nature of the wind resource, however, the most suitable sites for such developments are on exposed locations such as hills, ridges or the coasts.  Thus, WTGs may have significant local environmental effects for such sites are often within designated areas such as National Parks or Areas of Outstanding Natural Beauty (AONBs). As a consequence, the Department of the Environment, after a consultation exercise, included wind turbines as Schedule 2  category projects (Department of the Environment 1994).  Thus, wind turbine proposals must now be accompanied by an Environmental Statement when the development is likely to have significant environmental effects. 

Guidance suggests that EA would normally be required for particular projects sited within National Parks, AONBs, heritage coasts and Sites of Special Scientific Interest (SSSI) or within two kilometres of any of these areas.  It is suggested that a threshold of total installed capacity greater than 5MW or more than ten turbines should be applied (Department of the Environment 1994).

The Countryside Council for Wales (CCW) policy on wind turbine power stations  goes further than the Government's EA measures by opposing wind farms in designated areas (Countryside Council for Wales 1992).  However, CCW, in policy 10, ...‘support the development of wind turbine power stations which are well-designed and well-landscaped’...  CCW will not oppose ...‘individual non-commercial, domestic-supply wind turbines for individual homes or farms’... which are not detrimental to countryside needs or to wildlife.  Clearly wind farms cannot be located on prime conservation sites in an ad-hoc manner.  What is needed is a planning policy for wind farms developed as part of an overall energy strategy.  Indeed, many district and county councils in Wales are starting to prepare guidelines for wind farms within their local plans, for example Powys County Council (1992), Montgomeryshire District Council (1993) and Rhymney Valley District Council (1993).  However, there is clearly a need for these plans to be co-ordinated. 

Planning issues would be simplified if wind farms were not allowed on designated sites. This would not mean that wind farms elsewhere would get automatic planning approval.  As with any development requiring planning permission, each proposal would have to be judged on its merits.  This would eliminate much of the controversy surrounding landscape issues, yet still allow for the development of a strategic energy supply.  Indeed,  the response of LPAs to wind farms through their structure plans has been to identify areas of landscape importance, either national or local, and to stress that wind farms would not be permitted in these areas.  Indeed, some district councils, such as Preseli Pembrokeshire, have carried out ‘search’ exercises to identify specific areas where they would allow wind farms.  Preseli Pembrokeshire identify five major areas that they consider would meet the planning requirements for wind power (Preseli Pembrokeshire DC 1993).  However, this does not necessarily mean that an individual proposal would get planning permission, it would still have to be evaluated like any other development proposal. 

These assessments for individual projects, would have to take cognisance of site specific effects.  All forms of energy production cause environmental effects or impacts.  The effects of renewable energy operations tend to be more benign than those associated with fossil fuel or nuclear generation.  These latter have both physical and chemical effects which, in turn, can lead to biological impacts.  Renewables tend to have only physical impacts.  In the case of wind turbines the most obvious impact is visual,  but other impacts include noise, shadow flicker, wildlife, electromagnetic interference and safety.  These impacts are discussed in detail below.

Visual impacts

Wind turbines are between thirty and fifty metres tall with two or three blades thirty to forty metres in diameter occupying a circular sweep of nearly one thousand square metres.  The nature of the wind resource means that WTGs are best located at exposed, high-wind resource sites.  Suitable locations for wind turbines must have high average yearly wind speeds and include hills, ridges, plateaux, mountains and coasts.  Siting a wind turbine or wind farm at any location will cause a visual impact on the landscape.  It is very difficult to judge the effect of wind turbines on the landscape, however, as this assessment is subjective. 

 Perception of the character of a landscape is governed by the extent of views in conjunction with the scale and frequency of land cover features such as waterbodies, woods, roads and buildings.  The  nine basic elements that determine perception of a landscape are shown in table 4.

 Table 4 Elements in  landscape perception (Wathern pers. comm.).  

Water bodies, to break up the image.

Pattern, form, size and location of elements in the landscape.

Perspective, opportunity to see long distances.

Texture, vegetation such as trees.

Nature of edges, soft grading perceived better than hard sharp edges.

Contrast, colours.

Positive human features, small scale traditional features.

There is evidence of both cultural and genetic responses to landscapes and visual impacts.  Idealised landscapes were created by the rural elite during the 18th and 19th centuries.  Cultural exposure to these tamed parkland perceptions has passed through to all levels of society creating a concept of an idealised rural scene.  Such cultural exposure is very important in the appreciation of a landscape.  Rural dwellers will view a city differently to those living in the city and vice versa.  Recent changes in lifestyle are again changing the perception of rural regions with an increasing number of people having access to remote highly prized landscapes.

It is possible  to follow an iterative process in order to arrive at an assessment of visual impact of wind turbines (Chris Blandford Associates 1992).  The first stage would be to review planning policies concerned with the conservation and protection of the landscape within the general location of the development.  A zone of visual influence should then be determined.  This zone defines those areas within the surrounding area from which the development can be seen.  The character of the landscape within the zone should then be determined, if necessary by breaking it down into smaller sub units.  An estimation of  landscapes quality can be made by reference to designations and to documents referring to the development site.  By recording landscape quality before the wind turbine development and predicting how it will look after development, it should be possible to judge the extent to which the project will detract from the character of the landscape.

Siting location is a very important aspect of visual impact.  For wind farms, the actual site chosen within an area will  affect visual impact.   Spacing the cluster of turbines at a project site will also  affect the degree of visual intrusion. 

 Noise Impacts

What is termed  ‘noise’ is merely unwanted sound. Sound is any variation in pressure that the human ear can detect.  This audible sound occurs in the frequency range of 20Hz-20KHz.  Loudness is associated with the sound pressure level exerted on the ear drum.  Not only does the human ear detect various frequencies, it also responds over a wide range of sound pressure levels with a 10¹⁴ fold difference between the quietest sound that can be detected and the loudest that can be tolerated. Noise is measured in decibels (dB), but because of the range in pressure level that an ear can register a logarithmic scale is used.  This starts at 0dB for the threshold of hearing up to 140 dB which is the threshold of pain. Furthermore, human hearing does not respond equally to all frequencies, but discriminates, enhancing certain frequencies and reducing others.  Noise measurements can be taken to mimic human hearing by using a so-called ‘A weighted scale’.  Consequently, noise levels corrected for human perception are expressed in special units, dB(A). Table 5 shows some example noise levels.

Table 5 Typical levels of noise from example activities

Source, British Wind Energy Association (1992).

All machines produce some form of noise and wind turbines are no exception.  Two different noise types are produced by wind turbines, mechanical and aerodynamic.  Mechanical noise is generated by the gearbox and drive mechanisms with aerodynamic noise coming from the rotating blades.  Mechanical noise has distinct tonalities and there are numerous ways that these can be mitigated at source.  Sound proofing is an easy operation as the mechanisms are enclosed in a nacelle.  Anti-vibration mountings and dampeners can be used as can gearboxes designed to produce only low levels of noise.

Aerodynamic noise is produced by air passing over the surfaces of the turbine blades.  A much greater range of frequencies is produced.  However the 'swishing' sound is more akin to natural noises such as the wind blowing through trees.  Tip shape and  trailing edge thickness will affect blade noise and modern designs have reduced noise significantly.

Various legislation and regulations apply to noise produced from industrial or mechanical sources.    BS4142:1990 sets out a system to rate industrial noise affecting mixed industrial and residential areas (British Standards Institute 1990).  This is the most relevant standard to apply to wind turbines.  However, it does have some limitations.  Areas of background noise below 30dB(A) are excluded and the standard specifies that noise should be measured at wind speeds below five metres per second.  Rural areas may have background noise levels below 20dB(A) and wind speeds below five metres per second are typically below wind turbine start up speeds.  Manufacturers are setting a target of limiting wind turbine noise to be below 45dB(A) outside the nearest residence assuming that it is at least three hundred and fifty metres from the nearest turbine.  From Table 5 it can be seen that this level is just above typical rural noise levels.

Although wind turbines generally produce only low levels of noise, it is possible for there to be a significant impact  as a result of individual responses to noise, especially the  reaction to a new sound relative to the general background noise.  Where farm machinery is operating or there is traffic, new noise sources may be “masked” until they are several decibels louder than the background noise.  At night in quiet rural areas, an additional noise will be more noticeable.  However, this is dependant not only on the nature of the noise, but also the individual's activity, perception and tolerance of noise.  While it is  possible to record a measurement of decibels coming from a wind turbine objectively, it is completely subjective to assess the human response to that noise.  A noise level deemed significant by one individual may not be noticed by another.  This subjectivity is very difficult to assess.  It may be affected by other factors such as articles on wind turbine noise in newspapers or on TV or interactions with and opinions from other members of a community near a wind turbine or wind farm.

 Shadow flicker

Shadow flicker is the effect caused under certain conditions by the rotation of the turbine blades against the skyline.  If the sun is behind the rotor of a turbine, a shadow may be cast over nearby properties.  As the blades rotate they cast a shadow which flicks on and off.  Poor siting may give potential risk to migraine and epileptic sufferers.

 Wildlife Impact

Impacts on wildlife may occur during the construction and operation of wind turbines.  Noise may cause disturbance during the construction phase.  The hydrology may be affected with additional silt run-off affecting local streams.  Wind turbines are unlikely to be sited near designated sites of wildlife importance which will minimise any conflict with such interests.  Careful planning is imperative to avoid disturbance to wildlife.  Ecological assessment should be carried out to survey the flora and fauna of prospective wind farm sites.  The greatest impact during construction  is building  access roads by stripping vegetation and top soil.  If the terrain is suitable, access roads should, ideally, be dug up and covered with the original top soil and vegetation after the construction of the WTGs.  During operation there are unlikely to be any effects on the wildlife except for birds.  Visitors to a wind farm, however, may cause damage and disturbance.  Therefore, visitors should be encouraged to keep to paths or access tracks. Alternatively, visitor information points should be provided at locations away from sensitive areas to negate the need to wander around the site. 

The noise and general disturbance associated with the construction of a wind farm can have an effect on birds.  This may cause temporary displacement of indigenous birds.  There has also been some concern that birds may be affected during the operational phase   by flying into rotating blades (Crockford 1991).  Thus, the siting of wind farms should avoid known migratory routes and important breeding sites.  There have only been a few studies on the effects of wind turbines on birds.  These include studies on Danish sites by Winkelman (1990), Pedersen and Poulsen (1991), Bell (1990) and Crockford (1991).  It has been shown, by these authors, that the effects of WTGs on birds vary with the parameters of the wind farm, such as number, size and layout, as well as, bird species, presence of other feeding, roosting or breeding birds,  time of day, time of year, weather conditions and visibility (Crockford 1991).  Winkelman's study indicated that weather conditions affected bird flight.  Thus, birds that fly above rotor blade height during favourable conditions, tend to fly lower during strong winds due to the effects of wind shear.  The likelihood of bird strike is minimal, because  birds veer away from the WTGs, although birds have been known to fly into other structures such as electricity transmission lines.  Larger birds, by nature of the area needed to turn, tend to veer away from WTGs at a greater distance than smaller birds.  The response of flocking birds is a shift in flight direction, followed by a return to a similar flight path beyond the WTGs.

Electromagnetic Effects

Wind turbines have two ways of causing electromagnetic effects.  Firstly, they contain equipment for producing electricity and so will produce electromagnetic fields which could interfere with other signals.  However, this is not a phenomena unique to WTGs, so it should not give rise to any unusual problems.

The second effect is interfering with the passage of a signal by acting as a structure to block its path.  Siting away from communication links will mitigate this effect.  Wind turbines may scatter signals such as radio and TV.  This is dependant on the wavelength of the signal and the design, size and material of the turbine.  These problems can be minimised by installing booster stations or modifying the receiving equipment.

 Safety Aspects

There is very little risk to people and property from wind turbines.  Low rural populations and the distance between turbines and residential dwellings minimises contact with the turbines.  The risk of a wind turbine developing a defect is very low, as the system is fully automated.  There have been only rare occasions of wind turbine failure, although this has included blades shearing off.  The maximum predicted theoretical distance a blade or part of a blade could travel is four hundred metres. When a blade, or piece of blade, has failed, the  distance actually travelled has been much smaller.  An assessment of the chance of an individual being struck by a  blade fragment is one hundred times less than being struck by lightning (Dulas Engineering and Powys County Council 1992).  The greatest risk to individuals is to maintenance  staff when climbing up the inside of the towers and while working in the nacelle thirty metres above the ground and appropriate safety guidance notes concerning these activities have been developed (British Wind Energy Association 1996). 

Conclusions

 It can be seen that a range of different technologies are being developed and  researched.  However, the commercial status of the technologies varies.  The reasons for this relate to the support provided in research and development grants.  Different technologies have been funded at different levels or, as in the case of wave power research in the UK, had their funding cut altogether.  Political motivation has been behind such decisions. 

Clearly, some technologies are more advanced in their development than others.  Therefore, the rate at which the different energy resources will enter the market for energy supply will also vary.  However, it may be difficult for those less advanced to find a niche market for energy supply in the future.

However, this is not the case for wind power which has been subject to more detailed scrutiny.  This level of attention, in part, reflects the current proven commercial nature of the technology, and partly its known potential environmental effects.  Indeed, wind energy has become the lead renewable energy system in the UK.  Furthermore, it is also the only alternative energy resource, apart from existing hydro-electric power installations, that has made any impact on the supply of electricity in UK.  The commercialisation of wind energy developments  in terms of electricity supply and economic benefit, along with the implications for land-use are key issues in the sustainable development of energy systems.

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