Renewables: Sustainable Energy

Transcription

1 Renewables: Sustainable Energy In this part of the unit you will need to consider the potential for sustainable energy supply and consumption. Also you need to consider the appropriate technology in relation to the level of economic development in order to ensure the above. Sustainable Development is meeting the needs of the present without compromising future generations to meet their own needs. Fossil Fuels and Nuclear can never be sustainable! As discussed in the last part of the unit as they are finite, will suffer resource exhaustion and contribute considerably to negative environmental impacts. The CURRENT pattern of supply and consumption are therefore unsustainable in the long term, as there is an over dependence on fossil fuels and nuclear (use of which is only set to increase in medium term). What types of energy resources therefore are available to provide us with a source of sustainable energy? Answer: Renewables as they are flow resources meaning they are infinite and will never run out! E.g: -Solid Biomass (Wood) - Bio-ethanol -Solar - Tidal - Wave - Hydroelectric (HEP) - Geothermal - Wind - Ground-source Heat Pumps This however does not simply mean the above sources are without environmental impact, but their impacts tend to be less as often some renewables can be small scale, but not all. Renewables however don t damage the atmosphere like fossil fuels do and do not cause the problems of disposing waste like nuclear does. Key Concept: Appropriate Technology: is a concept generally applied to the LDW as it means the technology experience and equipment being applied is suited to the level of economic and technological development. E.g. in Chad a Solar Cooker may be the appropriate technology for sustainable energy use and socio-economic development and higher tech solutions less appropriate to power generation and to people s needs. Whereas in the MDW the where levels of wealth are much higher it is the responsibility of governments and corporations (TNC s) to ensure investment of sustainable energy systems for the future. Biomass living plants and matter comprise the bulk of Earth s biomass How it works Wood is the simplest form of biomass and it can be used sustainable as long as the consumption rate does not exceed the NET replacement level. Wood is used in many LDC s unsustainably and these areas are suffering from resource scarcity (see previous case study under environmental impacts). Most wood in LDC s is used as a primary source of energy for cooking and space heating. More efficient wood burners would provide the appropriate technology to ensure more sustainable use of wood, the technology does not have to be complicated as the level of wealth

2 low and the lifestyle of the people simple. Dung and crops are also burned in the LDW, but this is inefficient. Wood, in the more developed world can be burned in wood fired power stations to heat boilers, to produce steam to drive turbines to produce electricity. Or dung and crop waste can be gasified and then burned or even methane from landfill sites! Pros Cons and Pro s Con s Lower pollution than fossil fuels Cheap and sustainable Uses up waste created by agriculture for useful purposed Can be easily applied in the LDW Need gasification to be efficient, therefore inefficient in the LDW If wood used unsustainable causes resource exhaustion. Bioethanol How it Works Sugar cane is harvested and taken to a mill, where it is crushed to extract the juice. The juice is used to make sugar, whilst the left-over pulp, called "bagasse" can be burned in a power station. The station usually provides power for the sugar mill, as well as selling electricity to the surrounding area. 2008: plans have just been announced by the energy company Eon for a biomass-fuelled power station Portbury, near Bristol. The fuel would be wood, brought in by boat, and the station would produce 150MW of electrical power Some counties like Sweden and Japan have begun to import Brazilian ethanol to meet the Kyoto protocol. Source Eon Website ( Bioethanol Eon in Somerset E.ON is planning to develop one of the UK s largest biomass renewable energy plants at the Royal Portbury Dock in North Somerset. We submitted a planning application to the Department of Energy and Climate Change (DECC) in August 2009 to build a 150MW renewable energy plant, which could produce enough renewable energy for more than 200,000 homes by burning sustainably sourced wood materials that would largely be brought to the plant by ship. The proposed renewable energy plant will displace almost 400,000 tonnes of CO2 emissions annually by burning sustainably sourced biomass.

3 If the project gets the green light, construction could begin in 2012 and be fully operational as early as It s expected that the site would create 35 full-time jobs within the local area once completed. Angus Grahamslaw, Project Developer for E.ON Climate & Renewables, said: We believe that this is a great location for the plant and underlines the south west region s reputation as one of the country s leading green areas. We re hopeful that the Local Planning Authority and DECC will see the benefits of the scheme, both to local stakeholders and also to the environment. Our planning application follows three public exhibitions we held across the region in June 2009, which gave residents and stakeholders the opportunity to learn more about our proposals for the site and meet the project team. The Portbury Dock scheme is the latest addition to our biomass portfolio. Our first biomass renewable energy plant, Steven's Croft near Lockerbie in Scotland, produces enough electricity for 70,000 homes and prevents emissions of around 140,000 tonnes of CO2 annually. And we have received planning permission to build a new biomass plant at Blackburn Meadows in Sheffield, which we hope to begin constructing in Tidal The tide moves a huge amount of water twice each day, and harnessing it could provide a great deal of energy - around 20% of Britain's needs. Although the energy supply is reliable and plentiful, converting it into useful electrical power is not easy. There are eight main sites around Britain where tidal power stations could usefully be built, including the Severn, Dee, Solway and Humber estuaries. Only around 20 sites in the world have been identified as possible tidal power stations. However in 2011 the government have scrapped the Severn Tidal barrage scheme. A few years ago, "tidal power" meant "tidal barrage", but these days there are other options as well. How it works These work rather like a hydro-electric scheme, except that the dam is much bigger. A huge dam (called a "barrage") is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam. The ebb and flow of the tides can be used to turn a turbine, or it can be used to push air through a pipe, which then turns a turbine. Large lock gates, like the ones used on canals, allow ships to pass.

4 If one was built across the Severn Estuary, the tides at Weston-super-Mare would not go out nearly as far - there'd be water to play in for most of the time. But the Severn Estuary carries sewage and other wastes from many places (e.g. Bristol & Gloucester) out to sea. A tidal barrage would mean that this stuff would hang around Westonsuper-Mare an awful lot longer! Also, if you're one of the 80,000+ birds that feeds on the exposed mud flats when the tide goes out, then you have a problem, because the tide won't be going out properly any more. The largest tidal power station in the world (and the only one in Europe) is in the Rance estuary in northern France, near St. Malo. It was built in A major drawback of tidal power stations is that they can only generate when the tide is flowing in or out - in other words, only for 10 hours each day. However, tides are totally predictable, so we can plan to have other power stations generating at those times when the tidal station is out of action There have been plans for a "Severn Barrage" from Brean Down in Somerset to Lavernock Point in Wales. Every now and again the idea gets proposed, but nothing has been built yet. It would cost at least 15 billion to build, but other figures about the project seem to vary depending on where you look. For example, one source says the Severn Barrage would provide over 8,000 Megawatts of power (that's over 12 nuclear power station's worth), another says it would be equivalent to 3 nuclear power stations. The variation in the numbers is because there are several different Severn Barrage projects being proposed, However, in 2011 the Severn Estuary project has been declined so it now seems unlikely that it will ever happen! There would be a number of benefits, including protecting a large stretch of coastline against damage from high storm tides, and providing a ready-made road bridge. However, the drastic changes to the currents in the estuary could have huge effects on the ecosystem, and huge numbers of birds that feed on the mud flats in the estuary when the tide goes out would have nowhere to feed. Another option is to use offshore turbines, rather like an underwater wind farm. This has the advantage of being much cheaper to build, and does not have the environmental problems that a tidal barrage would bring. There are also many more suitable sites. Find out more (marineturbines.com)

5 The University of Wales Swansea and partners are also researching techniques to extract electrical energy from flowing water. The "Swanturbines" design is different to other devices in a number of ways. The most significant is that it is direct drive, where the blades are connected directly to the electrical generator without a gearbox between. This is more efficient and there is no gearbox to go wrong. Another difference is that it uses a "gravity base", a large concrete block to hold it to the seabed, rather than drilling into the seabed. Finally, the blades are fixed pitch, rather than actively controlled, this is again to design out components that could be unreliable Find out more (swanturbines.co.uk) December 2008, a "Tidal Reef" across the Severn Estuary was proposed, but it has now been declined as on option (2011). At first glance this looks like a tidal barrage, but this design does not block the water movement as much, so it wouldn't affect the tides as severely and the environmental consequences would be much less. It could be built in sections, so power could start being generated sooner. Migratory fish could get through, mud flats could still be exposed at low tide, and it would be able to generate power for more hours in the tidal cycle. Sections of it would open to allow shipping through, and it could be used to control tidal levels further upstream, for example preventing storm surges from flooding low-lying land. Tidal barrages have been built before, whereas this idea is untested - so it'll be interesting to see if it gets approved. Another option could be vertical axis turbines e.g. the Orkneys. Source BBC website Aug Huge tidal turbine arrives in Orkney ahead of testing A device thought to be the largest tidal turbine of its type to be built in the world has arrived in Orkney for testing. Atlantis Resources unveiled its AK1000 at Invergordon last week ahead of it being shipped to Kirkwall. Trials on the device will be run at a European Marine Energy Centre test site off Eday.

6 The device stands 22.5m (73ft) tall, weighs 1,300 tonnes and has two sets of blades on a single unit. It has been designed to harness ebb and flood tides and could generate one megawatt of power - enough electricity for about 1,000 homes. Atlantis said it was the largest bladed turbine of its type because of its rotor diameter of 18m (59ft). The AK1000's two sets of blades have also been designed to move slowly underwater and Atlantis said they would not pose a threat to sea life. Tests on the AK1000 will be run at a site off Eday Pros and Cons Pro s Once you've built it, tidal power is free. It produces no greenhouse gases or other waste. It needs no fuel. It produces electricity reliably. Not expensive to maintain. Tides are totally predictable. Con s A barrage across an estuary is very expensive to build, and affects a very wide area - the environment is changed for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed. Fish can't migrate, unless "fish ladders" are installed. Only provides power for around 10 hours each day, when the tide is actually moving in or out. Offshore turbines and vertical-axis turbines are not ruinously expensive to build and do not have a large environmental impact. There are few suitable sites for tidal barrages It is renewable as tides continue to ebb and flow so it is there for the taking Wave It is possible to harness the power of waves as well as tides. Waves are caused by the wind blowing over the surface of the ocean. In many areas of the world, the wind blows with enough consistency and force to provide continuous waves. There is tremendous energy in the ocean waves. Wave power devices extract energy directly from the surface motion of ocean waves or from pressure fluctuations below the surface.

7 Wave power varies considerably in different parts of the world, and wave energy can't be harnessed effectively everywhere. Wave-power rich areas of the world include the western coasts of Scotland, northern Canada, southern Africa, Australia, and the north-western coasts of the United States. How it works A variety of technologies have been proposed to capture the energy from waves. Some of the more promising designs are undergoing demonstration testing at commercial scales. Wave technologies have been designed to be installed in nearshore, offshore, and far offshore locations. The OCS Alternative Energy Programmatic EIS is concerned primarily with offshore and far offshore wave technologies. Offshore systems are situated in deep water, typically of more than 40 meters (131 feet). While all wave energy technologies are intended to be installed at or near the water's surface, they differ in their orientation to the waves with which they are interacting and in the manner in which they convert the energy of the waves into other energy forms, usually electricity. The following wave technologies have been the target of recent development. Terminator devices extend perpendicular to the direction of wave travel and capture or reflect the power of the wave. These devices are typically onshore or nearshore; however, floating versions have been designed for offshore applications. The oscillating water column is a form of terminator in which water enters through a subsurface opening into a chamber with air trapped above it. The wave action causes the captured water column to move up and down like a piston to force the air though an opening connected to a turbine. A point absorber is a floating structure with components that move relative to each other due to wave action (e.g., a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical or hydraulic energy converters. Rendition of a Wave Farm Made Up of Permanent Magnet Linear Generator Buoys Point Absorber Wave Energy Farm

8 Attenuators are long multisegment floating structures oriented parallel to the direction of the waves. The differing heights of waves along the length of the device causes flexing where the segments connect, and this flexing is connected to hydraulic pumps or other converters. Attenuator Wave Energy Device Overtopping devices have reservoirs that are filled by incoming waves to levels above the average surrounding ocean. The water is then released, and gravity causes it to fall back toward the ocean surface. The energy of the falling water is used to turn hydro turbines. Specially built seagoing vessels can also capture the energy of offshore waves. These floating platforms create electricity by funnelling waves through internal turbines and then back into the sea. Environmental Considerations "Wave Dragon" Prototype Overtopping Device Potential environmental considerations for the development of wave energy include the following: Positive or negative impacts on marine habitat (depending on the nature of additional submerged surfaces, above-water platforms, and changes in the seafloor); Toxic releases from leaks or accidental spills of liquids used in those systems with working hydraulic fluids; Visual and noise impacts (device-specific, with considerable variability in visible freeboard height and noise generation above and below the water surface); Conflict with other sea space users, such as commercial shipping and recreational boating Hydroelectric (HEP) We have used running water as an energy source for thousands of years, mainly to grind corn. The first house in the world to be lit by hydroelectricity was Cragside House, in Northumberland, England, in In 1882 on the Fox river, in the USA, hydroelectricity produced enough power to light two paper mills and a house. Nowadays there are many hydro-electric power stations, providing around 20% of the world's electricity.

9 The name comes from "hydro", the Greek word for water How it works A dam is built to trap water, usually in a valley where there is an existing lake. Water is allowed to flow through tunnels in the dam, to turn turbines and thus drive generators. Notice that the dam is much thicker at the bottom than at the top, because the pressure of the water increases with depth. Hydro-electric power stations can produce a great deal of power very cheaply When it was first built, the huge "Hoover Dam", on the Colorado river, supplied much of the electricity for the city of Las Vegas; however now Las Vegas has grown so much, the city gets most of its energy from other sources. The World s largest HEP scheme is the Three Gorges Project, Yangtze River, China. There's a good explanation of how hydro power works at Although there are many suitable sites around the world, hydro-electric dams are very expensive to build. However, once the station is built, the water comes free of charge, and there is no waste or pollution. The Sun evaporates water from the sea and lakes, which forms clouds and falls as rain in the mountains, keeping the dam supplied with water for free.

10 Gravitational potential energy is stored in the water above the dam. Because of the great height of the water, it will arrive at the turbines at high pressure, which means that we can extract a great deal of energy from it. The water then flows away downriver as normal. In mountainous countries such as Switzerland and New Zealand, hydroelectric power provides more than half of the country's energy needs. An alternative is to build the station next to a fast-flowing river. However with this arrangement the flow of the water cannot be controlled, and water cannot be stored for later use. Pros and Cons Pro s Con s Once the dam is built, the energy is virtually free. No waste or pollution produced. The dams are very expensive to build. However, many dams are also used for flood control or irrigation, so building costs can be shared. Much more reliable than wind, solar or wave power. Water can be stored above the dam ready to cope with peaks in demand. Hydro-electric power stations can increase to full power very quickly, unlike other power stations. Electricity can be generated constantly Building a large dam will flood a very large area upstream, causing problems for animals that used to live there. Finding a suitable site can be difficult - the impact on residents and the environment may be unacceptable. Water quality and quantity downstream can be affected, which can have an impact on plant life

11 Geothermal The centre of the Earth is around 6000 degrees Celsius - easily hot enough to melt rock. Even a few kilometres down, the temperature can be over 250 degrees Celsius if the Earth's crust is thin. In general, the temperature rises one degree Celsius for every metres you go down, but this does vary depending on location In volcanic areas, molten rock can be very close to the surface. Sometimes we can use that heat. Geothermal energy has been used for thousands of years in some countries for cooking and heating. The name "geothermal" comes from two Greek words: "geo" means "Earth" and "thermal" means "heat". How it Works Hot rocks underground heat water to produce steam. We drill holes down to the hot region, steam comes up, is purified and used to drive turbines, which drive electric generators. There may be natural "groundwater" in the hot rocks anyway, or we may need to drill more holes and pump water down to them. The first geothermal power station was built at Landrello, in Italy, and the second was at Wairekei in New Zealand. Others are in Iceland, Japan, the Philippines and the United States. In Iceland, geothermal heat is used to heat houses as well as for generating electricity. If the rocks aren't hot enough to produce steam we can sometimes still use the energy - the Civic Centre in Southampton, England, is partly heated this way as part of a district heating scheme with thousands of customers Geothermal energy is an important resource in volcanically active places such as Iceland and New Zealand. How useful it is depends on how hot the water gets. This depends on how hot the rocks were to start with, and how much water we pump down to them. Water is pumped down an "injection well", filters through the cracks in the rocks in the hot region, and comes back up the "recovery well" under pressure. It "flashes" into steam when it reaches the surface.

12 The steam may be used to drive a turbogenerator, or passed through a heat exchanger to heat water to warm houses. A town in Iceland is heated this way. The steam must be purified before it is used to drive a turbine, or the turbine blades will get "furred up" like your kettle and be ruined Pros and Cons Pro s Con s Geothermal energy does not produce any pollution, and does not contribute to the greenhouse effect. The power stations do not take up much room, so there is not much impact on the environment. No fuel is needed. The big problem is that there are not many places where you can build a geothermal power station. You need hot rocks of a suitable type, at a depth where we can drill down to them. The type of rock above is also important, it must be of a type that we can easily drill through. Once you've built a geothermal power station, the energy is almost free. It may need a little energy to run a pump, but this can be taken from the energy being generated It is renewable as long as long as we don t pump too much water down and cool the rocks too much Sometimes a geothermal site may "run out of steam", perhaps for decades. Hazardous gases and minerals may come up from underground, and can be difficult to safely dispose of. Ground-source heat pumps How it works Source (energysavingtrust.org/generate-your-own-energy/ground-source-heat-pumps) Ground source heat pump circulates a mixture of water and antifreeze around a loop of pipe - called a ground loop - which is buried in the garden. Heat from the ground is absorbed into this fluid and is pumped through a heat exchanger in the heat pump. Low grade heat passes through the heat pump compressor and is concentrated into a higher temperature useful heat capable of heating water for the heating and hot water circuits of the house. Ground loop fluid, now cooler, passes back into the ground where it absorbs further energy from the ground in a continuous process while heating is required. The length of the ground loop depends on the size of your home and the amount of heat you need - longer loops can draw more heat from the ground, but need more space to be buried in. Normally the loop is laid flat, or coiled in trenches about two metres deep, but if there is not enough space in your garden you can install a vertical loop down into the ground to a depth of up to 100 metres for a typical domestic home.

13 Heat pumps have some impact on the environment as they need electricity to run, but the heat they extract from the ground, air, or water is constantly being renewed naturally. Unlike gas or oil boilers, heat pumps deliver heat at lower temperatures over much longer periods. This means that during the winter they may need to be left on 24/7 to heat your home efficiently. It also means that radiators should never feel as hot to the touch as they would do when using a gas or oil boiler. Pros and Cons Pro s Con s Can reduce your carbon footprint: heat pumps can lower your home s carbon emissions, depending on which fuel you are replacing. No fuel deliveries required. Can provide space heating and hot water. Can lower fuel bills, especially if you are currently using conventional electric heating. It's often classed as a fit and forget technology because it needs little maintenance Does not provide much energy Can t be used everywhere Initial outlay expensive High tech not good in LDW The Hot Dry Rock Method Cornwall (Source: It is estimated that geothermal power from the south west of England alone could meet 2% of the UK s annual electricity demand. Two companies are gearing up to tap Cornwall s extensive potential resources of deep geothermal energy and look set to convert the English county into a hot spot for enhanced geothermal systems. Traditional geothermal energy is derived by pumping naturally occurring hot water from underground to the surface. Enhanced geothermal systems (EGS) manufacture geothermal resources by creating similar conditions to traditional geothermal energy in hot dry rocks. This is achieved by pumping high pressure cold water down into rocks at depths of around three miles (five kilometres). The rock then fractures, allowing the water to circulate and heat up and subsequently re-emerge from a second borehole as very hot water to be converted into electricity.

14 Cornwall was the location for Europe s first deep geothermal R&D initiative, the Hot Dry Rock (HDR) project, which took place in Rosemanowes. Triggered by the 1973 Middle East oil crisis and subsequent search for alternative energy sources, Cornwall was identified because its geothermal resources are large: the geothermal gradient (i.e. the temperature increase with depth) is higher than elsewhere in the UK (see chart). Knowledge gained from the Rosemanowes project, on the behaviour of rocks at significant depths, has been applied by geothermal experts across the globe ever since. After the project was disbanded in 1991, its scientists and engineers took off to apply their technical and geological knowledge to the European Enhanced Geothermal Systems Project which integrated all European EGS research activity and established a pilot EGS plant at Soultz-sur-Forêts, France. Soultz-sur-Forêts was the springboard for Europe s first commercial EGS plant, in Landau, Germany. Although the UK geothermal story seemed to end with the disbanding of Rosemanowes, the UK is still perceived as a pioneer. Ryan Law, Managing Director of Geothermal Energy Ltd (GEL) believes that: The UK is still seen as a groundbreaker because of that project. People have a lot of faith in it. According to Law: Geothermal is coming back home to the UK. GEL has received planning permission to mine for hot rock energy in Cornwall and create the UK s first commercial-scale plant to generate some 55MW of heat for local use and 10MW of electricity for the grid. Heat will initially be drawn from a J-shaped well up to five kilometres deep, the deepest geothermal well in the UK. If successful, two more wells will be built, pumping water down to rocks that are naturally at 200 C, where most of the water turns to steam. This will then be pumped back to the surface and converted into electricity using a steam turbine. When cool, the water can be reused to produce further geothermal energy. The stress regime the nature of the pressure on the rock at those depths is key to making the system work well, Law explains. The plant is expected to be operational in 2013 and will cost 40 million, financed potentially by a mix of Department of Energy and Climate Change (DECC) funding, private investment and the European Regional Development Fund.

15 So what has sparked this renewed interest in geothermal power? As an industry we ve become more coherent in the UK, says Law. There s the Renewable Energy Association s Deep Geothermal Sector group. Instead of individually lobbying, it helps us get to the right ears. And the UK Government does not want to appear to be late to the party. At the moment we are lagging behind, says Law. In particular, Germany and the US where the Government recently made $330 million available for the exploration of geothermal are years ahead of the UK. But momentum is gathering. In 2009, the DECC made 6 million of funding available over two years for geothermal plants generating between 5-10MW. The first round of funding, some 4 million, focused on deep geothermal and supported two Cornwall-based projects, of which GEL was one. The other Cornish company to receive funding from the UK Government was EGS Energy, which is hatching plans for a 4MW plant at the Eden Project. EGS Energy aims to drill two wells up to 4.5 kilometres deep (almost 3 miles) and use hot rock mass to produce heat and electricity at the surface to power the famous conservation centre. Water will be pumped down into one well and returned through the other, heated up by contact with the hot rock. The excess electricity will be supplied to the grid and possibly also to businesses and homes. We re bringing geothermal back to Cornwall. Private investors and people in the DECC that had to be won over are really persuaded, especially when they look at the area s geology, says Guy Grant-Macpherson, EGS Energy s Managing Director. According to Grant-Macpherson, the company s strength is in the combined experience of its team, which includes Roy Baria who helped set up the Rosemanowes HDR project and led the European EGS Project for 15 years. Roy was a man with a plan. I was looking for a plan. We started lobbying government and put together a company with private funding. The idea of a journey to the centre of the earth, [the title of the Jules Verne novel] captured people s imaginations, he says. Support from individual politicians has been encouraging, but a huge question mark hangs over public sector spending. Add to this the fact that geothermal is one of the lesser known renewable energies and funding begins to look precarious. Finance is going to be difficult it s a costly project, says Macpherson-Grant. EGS Energy received 2 million of the DECC s

16 geothermal fund and is seeking private financing from utility and oil companies to find the 24.5 million necessary. The Eden Project geothermal project received planning permission in December Drilling is scheduled to start in summer 2011 and electricity should be produced from the second half of It is expected to produce up to 4MW of energy for use by Eden with the surplus to be sold to the National Grid. Geothermal technology falls into the UK Government s innovative technology band, which means it is eligible for support in the form of Renewable Obligation Certificates (ROCs) at a rate of two ROCs per MWh generated. Heat produced from geothermal sources is also likely to be eligible for subsidies under the yet-to-be-published Renewable Heat Incentive. Wind We've used the wind as an energy source for a long time. The Babylonians and Chinese were using wind power to pump water for irrigating crops 4,000 years ago, and sailing boats were around long before that. Wind power was used in the Middle Ages, in Europe, to grind corn, which is where the term "windmill" comes from. How it Works The Sun heats our atmosphere unevenly, so some patches become warmer than others. These warm patches of air rise, other air blows in to replace them - and we feel a wind blowing. We can use the energy in the wind by building a tall tower, with a large propellor on the top.

17 The wind blows the propellor round, which turns a generator to produce electricity. We tend to build many of these towers together, to make a "wind farm" and produce more electricity. The more towers, the more wind, and the larger the propellors, the more electricity we can make. It's only worth building wind farms in places that have strong, steady winds, although boats and caravans increasingly have small wind generators to help keep their batteries charged. The best places for wind farms are in coastal areas, at the tops of rounded hills, open plains and gaps in mountains - places where the wind is strong and reliable. Some are offshore. To be worthwhile, you need an average wind speed of around 25 km/h. Most wind farms in the UK are in Cornwall or WalesIsolated places such as farms may have their own wind generators. In California, several "wind farms" supply electricity to homes around Los Angeles. The propellors are large, to extract energy from the largest possible volume of air. The blades can be angled to "fine" or "coarse" pitch, to cope with varying wind speeds, and the generator and propellor can turn to face the wind wherever it comes from. Some designs use vertical turbines, which don't need to be turned to face the wind. The towers are tall, to get the propellors as high as possible, up to where the wind is stronger. This means that the Pros land and Cons: beneath can still be used for farming. Pro s Con s Wind is free, wind farms need no fuel. Produces no waste or greenhouse gases. The wind is not always predictable - some days have no wind. Suitable areas for wind farms are often near the coast, where land is expensive. Some people feel that covering the landscape with these towers is unsightly. The land beneath can usually still be used for farming. Wind farms can be tourist attractions. A good method of Can kill birds - migrating flocks tend to like strong winds. However, this is rare, and we tend not to build wind farms on migratory routes anyway. Can affect television reception if you live nearby. Can be noisy. Wind generators have a reputation for making a constant, low, "swooshing" noise day and night, which can drive you nuts. Having said that, as aerodynamic designs have improved

18 supplying energy to remote areas modern wind farms are much quieter. A lot quieter than, say, a fossil fuel power station; and wind farms tend not to be close to residential areas anyway. Off shore wind farm UK map (2009)

19 Solar How it works We've used the Sun for drying clothes and food for thousands of years, but only recently have we been able to use it for generating power. The Sun is 150 million kilometres away, and amazingly powerful. Just the tiny fraction of the Sun's energy that hits the Earth (around a hundredth of a millionth of a percent) is enough to meet all our power needs many times over. In fact, every minute, enough energy arrives at the Earth to meet our demands for a whole year - if only we could harness it properly. Currently in the UK there are grants available to help you install solar power in your home. There are three main ways that we use the Sun's energy: 1 Solar Cells (really called "photovoltaic", "PV" or "photoelectric" cells) that convert light directly into electricity. In a sunny climate, you can get enough power to run a 100W light bulb from just one square metre of solar panel. This was originally developed in order to provide electricity for satellites, but these days many of us

20 own calculators powered by solar cells. 2 Solar water heating, where heat from the Sun is used to heat water in glass panels on your roof. This means you don't need to use so much gas or electricity to heat your water at home. Water is pumped through pipes in the panel. The pipes are painted black, so they get hotter when the Sun shines on them. The water is pumped in at the bottom so that convection helps the flow of hot water out of the top. This helps out your central heating system, and cuts your fuel bills. However, with the basic type of panel shown in the diagram you must drain the water out to stop the panels freezing in the winter. Some manufacturers have systems that do this automatically. Solar water heating is easily worthwhile in places like California and Australia, where you get lots of sunshine. Mind you, as technology improves it's becoming worthwhile in the UK. There is a more advanced type of solar water heating panel. The suppliers claim that in the UK it can supply 90% of a typical home's hot water needs from April to November. This "Thermomax" panel is made of a set of glass tubes. Each contains a metal plate with a blue-ish coating to help it absorb solar energy from IR to UV, so that even in diffuse sunlight you get a decent output. The air has been removed from the glass tubes to reduce heat loss, rather like a thermos flask. Up the back of the metal plate is a "heat pipe", which looks like a copper rod but contains a liquid that transfers heat very quickly to the top of the glass tube. A water pipe runs across the top of the whole thing and picks up the heat from the tubes. Find out more at

21 3 Solar Furnaces use a huge array of mirrors to concentrate the Sun's energy into a small space and produce very high temperatures. There's one at Odeillo, in France, used for scientific experiments. It can achieve temperatures up to 3,000 degrees Celsius. Solar furnaces are basically huge "solar cookers". A solar cooker can be used in hot countries to cook food. This one is in the UK, making tea and coffee, although it does take a long time! Pros and Cons Pro s Con s Solar energy is free - it needs no fuel and produces no waste or pollution. In sunny countries, solar power can be used where there is no easy way to get electricity to a remote place. Handy for low-power uses such as solar powered garden lights and battery chargers, or for helping your home energy bills. Doesn't work at night. Very expensive to build solar power stations, although the cost is coming down as technology improves. In the meantime, solar cells cost a great deal compared to the amount of electricity they'll produce in their lifetime. Can be unreliable unless you're in a very sunny climate. In the United Kingdom, solar power isn't much use for high-power applications, as you need a large area of solar panels to get a decent amount of power. However, technology has now reached the point where it can make a big difference to your home fuel bills