bio-energy what is bio-energy? · bedzed housing development near london uses passive solar design....

Information card level 1Information card level 1

Bio-energywhat is bio-energy?

Biomass is plant and animal matter, such as wood,straw, sewage and waste food.

We can burn these natural materials to produce heatand electricity. The Earth’s biomass is a huge store ofenergy, which is continually renewed by the sun throughphotosynthesis.

The power we produce from biomass is called bio-energy. People all around the world use wood, ricehusks and other plant and animal material (biomass) asfuel to create heat (bio-energy) for use on a small scale.

How does bio-energy work? There are two main large-scale ways of generating bio-energy.

Oil from oilseed rape can beused as fuel.Photo courtesy of DEFRA. Crowncopyright.

A farmer harvests trees for fuel. Photo courtesy of NRE Slide Library/DTI

n Energy crops such as wood, oilseed rape and sugarbeet are specially grown for fuel. A form of bio-dieselcan be produced from vegetable oils. Other cropscan be fermented to produce ethanol, a high-energysubstance similar to petrol.

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To find out more about bio-energy, visit www.dti.gov.uk/renewables/schools

n Waste is an important source of bio-energy. Landfill sites, animaldroppings and sewage all give off methane gas as they rot.Methane can be burnt to produce electricity and heat.

Advantages

n The fuel is cheap.

n It helps get rid of waste, which can cause smells and pollution.

n It is not using up limited resources like coal: biomass cannot runout.

Disadvantages

n Burning the fuel creates carbon dioxide, a greenhouse gas.However, if you grow crops that absorb the same amount ofcarbon dioxide from the air that is created by burning them, theeffect on the environment is less harmful.

n Collecting waste in big enough amounts to generate energy canbe difficult.

n If trees aren’t grown especially for fuel, and re-planted, the resultis deforestation.

household wastedecays and producesmethane gas

steam turnsturbines turbines rotate

the generator tomake electricity

water is turned intosteam by burning

methane gas

electric cables

to the National Grid

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gas wells collect methane

Using landfill gas to generate electricity


Geothermal energywhat is geothermal energy?

Old Faithful in Wyoming, USA,which erupts hot steam from farbelow the Earth’s surface every45 minutes. Photo courtesy of www.pdphoto.org

Geothermal power plant

Coal miners know that the deeper you dig, thehotter it gets. This is because of the natural heatthat exists deep within the Earth. We call thisnatural heat, geothermal energy.

There are two main ways to make use of geothermalenergy.

n Use the water from naturally occurring undergroundreservoirs.

n Inject cold water into hot dry rocks.

How does geothermal energywork? n In some areas of the Earth, geothermally heated

underground water rises to the surface as steam orhot springs. If the hot water or steam doesn’t riseto the surface on its own, we can drill boreholes toaccess it.

n Alternatively, cold water is pumped underground,where it is heated by hot dry rocks, and thenreturned to the surface. The hot water is then usedin a steam turbine, or for direct heating.

power station

cool water ispumped down the

injection well

hot water returns upthe recovery well

hot rocks (or geothermal hot water reservoir)

cooling towers


Southampton Civic Centre uses heat from ageothermal well. Photo by kind permission of Southampton City Council

Where are geothermalpower stations sited? Places that are near a tectonic plateboundary (i.e. are volcanic), such asIceland and Japan, have many placeswhere boreholes can reach reservoirs ofwater at high enough temperatures andpressures to produce electricity.

The UK doesn’t have any geothermalpower stations that produce electricity,but lower-temperature reservoirs (faraway from plate boundaries) are used fordirect heating.

An example is the SouthamptonGeothermal District Heating Scheme,where water at 70°C is pumped up froma depth of 1800m, and provides heat to anumber of buildings within 2km of theborehole.

Advantages

n Geothermal energy doesn’t produce any pollution.

n Running costs for a geothermal power station are very low.

Disadvantages

n It is difficult to find suitable sites for geothermal power stations.The hot rocks have to be of a suitable type and depth, and therocks above them have to be soft enough to drill through. Thereare hardly any sites in the UK.

n If not carefully managed, a borehole can ‘run out of steam’ andmay not be useable again for several decades.

n Occasionally, dangerous gases and minerals can come out of aborehole, and it may be difficult to dispose of them.

To find out more about geothermal energy, visitwww.dti.gov.uk/renewables/schools


Hydroelectricitywhat is hydroelectricity?

This picture shows water being releasedunder pressure, after it has turned theturbines inside the dam to generateelectricity (Laggan Dam). Photo courtesy of Roy Dyckhoff

When we use the energy in flowing waterto produce electricity, we call ithydroelectricity.

The name comes from the Greek word forwater, ‘hydro’. Hydroelectricity makes a majorcontribution to the world’s energy supplies –more than any other kind of renewable energyresource.

How does hydroelectricitywork? There are two main ways of using the energyin flowing water to produce electricity.

n Hydroelectric dams trap flowing water,then release it again under greaterpressure.

<< A river flowing through a valley isblocked by building a large concretedam.

<< The valley is flooded by the river,creating a reservoir of water, like a man-made lake.

<< The water trapped in the reservoir isallowed to flow out through pipes, inthe dam wall, under great pressure.

<< The flowing water turns a turbine,which then turns a generator. Agenerator is a machine that containscoils of wire and powerful magnets.When the wire coils are spun quicklyinside the magnets, they produceelectricity.

<< For example, in the Elan Valley inWales, four dams hold 199 milliontonnes of water. Not only is it the mainwater supply for Birmingham: theturbines also produce enough electricityto power nearly 11,000 homes.

generator

water turnsturbine

tosubstation

dam

reservoir

sluice gate isopened to allowwater into intake

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Hydroelectric dam


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Dams depend on kinetic energy, which is the energysomething possesses when it is moving. The bigger theheight difference between the upstream and downstreamwater level (the ‘head’), and the bigger the water flowthrough the turbines, the more electricity is generated.

n Pumped storage is not really a renewable energysource but a way of storing energy.

<< This system uses two reservoirs: one is muchhigher than the turbine and one is below it.

<< When electricity is needed, water is released fromthe top reservoir. It flows through pipes and turnsthe turbines to produce electricity.

<< When demand for electricity is low (e.g. at night),an electric pump is used to pump water back up to the top reservoir to be used again.

<< An example is the Dinorwig Power station inWales, where water from a mountain lake is used to generate 288MW (megawatt).

Dworshak Dam, USA Photo courtesy of US Army Corps of

Engineers

To find out more about hydroelectricity, visit www.dti.gov.uk/renewables/schools

Pumped storage

Advantages

n Once construction is completed, operating costs arevery low.

n No waste or pollution is produced.

n Electricity can be generated constantly, because watercan be stored and used as needed.

Disadvantages

n Dams are very expensive to build.

n Hydroelectricity sites are often remote, which leads tohigher distribution costs.

n Suitable sites for large-scale projects are hard to find.

reservoir

power plant andgenerator

sluice gate isopened toallow waterinto intake

lower reservoir

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Hydrogen fuel cellswhat is a hydrogen fuel cell?

A hydrogen fuel cells works like a battery,but it uses hydrogen to make electricity. Inother words, it converts hydrogen toelectrical power.

Until recently, fuel cells were difficult andexpensive to build, and were only used in veryspecialised areas such as on spacecraft andsatellites.

Today we have the technology to producecheaper and more efficient fuel cells thanbefore, and many countries are testing themto see how well they work – for example, topower buses and cars, to heat water, supplyelectricity, even to provide clean water. But ifwe were to use them to replace other kindsof energy, fuel cells would need to be evencheaper and more efficient.

London is one of several European citiestesting how well electric buses powered byfuel cells work.Photo courtesy of Matthew Wooll

How does a hydrogen fuel cell work? Water is a compound made from hydrogen and oxygen. If an electric current is passed through water, the watermolecules split into separate hydrogen and oxygenmolecules. The oxygen and hydrogen arereleased as gas and can be collected in separatecontainers. This process is known aselectrolysis.

A fuel cell uses electrolysis in reverse. Itconverts hydrogen and oxygen into water,and produces electricity and heat in theprocess. This is all done without burningthe hydrogen.

Fuel cells need hydrogen to work, and weneed electricity to create hydrogen, so they arenot a renewable energy resource. But it should be possible to use renewable resources to produce thehydrogen fuel. In Iceland there are plans to producehydrogen using geothermal and hydroelectric power, whichare both renewable sources of energy. The hydrogen willbe used to power fuel cells to drive the country’s cars.

oxygen from air

hydrogen

heat

water

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Woking Park leisure centreis the first leisure centre inthe UK to use hydrogenfuel cells for its energyneeds. The fuel cells heatthe swimming pool,provide clean water, andsupply all of the centre’selectricity. The systemeven makes chilled waterfor the building’s airconditioning. Photo courtesy of Woking BoroughCouncil

Advantages

n There’s no pollution: the only waste product iswater and some heat, which can also bereclaimed.

n There’s no noise.

n Fuel cells can be built in a huge range of sizes tosuit almost any use.

Disadvantages

n Fuel cells rely on hydrogen, which has to be made.Most of the methods we use to produce hydrogentoday use a lot of non-renewable energy, but thiscould change.

n It will be some time before hydrogen is as freelyavailable as petrol is now.

n Hydrogen, like petrol, is flammable, but there aresystems we can use to allow safe use.

To find out more about hydrogen fuel cells, visitwww.dti.gov.uk/renewables/schools


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Solar energywhat is solar energy?

Solar energy is energyfrom the sun. The sun isincredibly powerful. Eachminute of the day, itdelivers enough energy tothe earth to meet globaldemand for a whole year.

BedZED housing development near London uses passivesolar design. Photo courtesy of Bill Dunster Architects

How does solar energy work? Solar energy can be captured and used in three mainways.

n Passive solar design involves designing buildings tomake the most of the sun’s natural heat, so that lesselectricity is needed to provide additional heat. Forexample, lots of glass is used to allow the sun’s heatto warm rooms directly, and thick insulation holds inthat heat.

n Active solar heating is a simple way of using thesun’s heat to provide hot water for homes. Water ispumped through pipes into solar panels (calledcollectors) on the roof, and heated by the sun.

The black, insulated base of the panels helps to trapheat. The heated water is then circulated through aheat exchanger to heat water for use in the home.It’s surprisingly efficient, even in the chilly UK.

n Photovoltaic cells (PV cells) contain silicon, whichconvert energy from the sun into electricity. PV cellscan be arranged in panels and can be fitted to almostanything, from your roof to your backpack.Experimental cars have been built where the body ofthe car is covered in PV cells, which generateelectricity to power the vehicle.

Passive solar design

Active solar heating –solar collector

sunlight

largearea ofglass

air warmedby sunlight

very thickinsulation toprevent heat

escaping

house

sunlight

glass cover

black surface

cold waterhot water


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Direct and indirect solar energy The sun actually gives us almost all the energy we use.It provides energy in two ways. We use the sun’senergy directly to heat air and water for use in thehome. We use it indirectly by burning fossil fuels.Millions of years ago, the coal, oil and gas that we burntoday were plants and trees. They stored the sun’senergy using a process called photosynthesis. When weburn these fossil fuels for fuel, the sun’s energy istransformed into other kinds of energy that we can use.Even wind energy and tidal energy depend on the heatfrom the sun.

Advantages

n Once the solar power plant is constructed, runningcosts are very low.

n Solar energy can be used to generate electricity inremote places.


n Energy is usually generated at or near where it willbe used, keeping transmission and distributioncosts to a minimum.

Disadvantages

n It doesn’t work at night.

n Photovoltaic (PV) cells are very expensive (but theyare getting cheaper).

Sainsbury’s is testing two solar-powered refrigerated trailers.The PV cells on the roof chargea battery, which powers therefrigeration system. Photo courtesy of DTI

To find out more about solar energy, visit www.dti.gov.uk/renewables/schools


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Wind energywhat is wind energy?

Wind is created because some partsof the earth get more heat thanothers.

The warmer air rises and cooler airmoves in to replace it. This movementof air is the wind.

People have been using wind forthousands of years to pump water, millgrain and power sailing boats, amongstother things.

In the future we may develop evencheaper technologies, but today windenergy is one of the cheapest ways toproduce electricity. There are over 1000wind turbines at 89 sites in Britain.There are offshore wind farms at Blythe,North Hoyle and Scroby Sands. Mostwind farms are located in the west ofBritain, with the exception of ScrobySands, off the east coast near GreatYarmouth.

Thanks to its position on the edge of thecontinent, Britain is the windiest place inEurope.

How does wind energywork? The force of the wind turns the rotor(which is like a huge propeller). The rotoris connected to a generator; this is amachine that contains coils of wire andpowerful magnets. When the coils arespun quickly inside the magnets, theyproduce electricity.

Out Newton Wind Farm, England Photo courtesy of E.ON UK

Inside a wind turbine

shaft gear

generator

rotor

tower


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This offshore wind farm is at Blythe,England. Photo © E.ON UK

Novar Wind Farm, Ross-shire, Scotland Photo © npower renewables 2005

To produce power, you need a windspeed of at least four metres per second(around 14KPH). Wind speed increasesas you go higher above ground level, sowind turbines are usually mounted on talltowers. Wind speed also increases ifthere are no hills or buildings to slow itdown. It is normally windier at sea thanon land.

For commercial wind power stations,large numbers of turbines may begrouped together in wind farms.

Advantages

n Once the wind turbine is built, runningcosts are very low.


n The land occupied by a wind farm canstill be used for farming.

n Wind farms can become touristattractions.

Disadvantages

n No wind, no power.

n Some people object because they feelwind farms spoil the view.

n Wind farms create a constant low-levelnoise.

n They can interfere with televisionreception and radar.

To find out more about wind energy, visit www.dti.gov.uk/renewables/schools

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Wave energywhat is wave energy?

LIMPET at Islay, Scotland Photo courtesy of Wavegen

If you have seen the sea on a rough day, you willknow that waves contain a lot of energy.

We can use this energy to produce electricity. Specialmachines have been designed to harness the power ofthe waves

Because of our position on the edge of the Atlantic, theUK has some of the best wave-power sites in the world.

How does wave energy work? There are two main types of wave-energy generator.

n Fixed devices are fixed to the sea bed or theseashore, for example the LIMPET (Land InstalledMarine Powered Energy Transformer) on the Scottishisland of Islay. The strong concrete walls set half inand half out of the water trap a column of air insidethe machine. As the waves rush in, the air is forcedupwards and spins the turbine. As the wave retreats,air is sucked back through the turbine, causing it tospin again. The turbine is connected to a generator,which produces electricity.

The LIMPET was the world’s first large wave powermachine. It can supply electricity to about 350homes. Inside the LIMPET is a Wells Turbine: thisspecial turbine turns in the same direction regardlessof which way the air moves, allowing the generatorto be turned by both incoming and retreating waves.

The original source of waveenergy is the sun. Waves arecaused by wind, and the wind iscaused by the uneven heatingof the Earth’s atmosphere. Photo courtesy of NRE Slide Library/DTI

trappedcolumn of air

sea wall

generator

turbine

The LIMPET

wave direction

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Pelamis near Orkney, Scotland Photo courtesy of Ocean Power Delivery

Pelamis

n Floating devices or barrages are generallyfound offshore. A good example isPelamis, a wave-power project off theScottish coast. It is a series of giant metaltubes joined together with flexible hinges.The movement of the waves causessections of the snake to move up anddown. Each hinge is connected to a pump,which pumps oil through a hydraulic motoras it moves. The motor generateselectricity as it spins.

Pelamis first began generating electricity in2004. Its location was chosen for idealwaves, the depth of sea, and to avoidpassing ships. It is fixed to the sea bed bystrong cables. Pelamis is Greek for ‘seasnake’.

Advantages

n Once constructed, running costs are very low.


n Wave-energy generators are capable of producinglarge amounts of energy.

Disadvantages

n Wave-energy generators are only effective wherethey are exposed to strong waves.

n They can be noisy.

n Wave-energy generators may be a hazard to shipsand leisure craft.

To find out more about wave energy, visit www.dti.gov.uk/renewables/schools

mooring cable

generators areinside the body wave

wave direction

sea bed


Tidal energywhat is tidal energy?

Tidal barrage at La Rance, France Photo courtesy of EDF Médiathèque / G. Halary

Around the coast of the UK, the sealevel rises and falls twice daily. Thisrising and falling of the sea is causedby the pull of the moon.

If we place barrages or dams in placeswhere the tide moves in and out, andthe difference between high and lowtides is at least 5 metres, we can usethis powerful movement of water tomake electricity.

Today there is only one major tidal powerstation in operation in Europe. This is the240MW (megawatt) barrage on La Ranceriver in France.

In Britain, the high tidal ranges near theSevern estuary could be used for abarrage. A barrage across the Severncould supply as much as 5 per cent ofthe UK’s electricity needs, but it wouldbe very expensive. There are currentlyno plans for a Severn barrage. How does tidal energy

work? Tidal energy relies on the flow and ebb of thetide, caused by the gravitational pull of themoon. There are two main ways to harnesstidal power.

n A tidal barrage is a giant wall (dam) that isbuilt across a river estuary or a bay on thecoast. Gates and turbines are built in alongthe dam wall. The gates are opened toallow the tide to flow in, and turn theturbines, which turn the generators toproduce electricity. At high tide, the gatesare closed and the water is held until thetide level outside the gates has dropped.Then the water is released to run throughthe turbines and turn the generators as itescapes. So electricity is generated bywater flowing both in and out of the dam.

Tidal barrage

tide coming in

tide going out

sea estuary

sea estuary

turbine andgenerator

turbine andgenerator

road

road


Marine turbineImage courtesy of Marine Current Turbines

Advantages

n Running costs are very low.


n The technology is very reliable.

n No fuel is required.

n The amount of electricity and the time when it is produced istotally predictable.

Disadvantages

n There are only a few suitable places for tidal energy projects.

n Tidal stream technology is at a very early stage of development.

n Tidal schemes are expensive to install compared with otherrenewable energies.

n Damming bays or inlets can affect the environment over a largearea.

n Barrage schemes will only provide energy for about 10 hours eachday, as the tide moves in and out.

n A tidal stream generator (alsoknown as a marine turbine) works likean underwater wind turbine. Insteadof using the rising and fallingmovement of the tides, tidal streamgenerators make use of the fast seacurrents that flow as tides move inand out. Sea currents turn turbines,which turn the generators thatgenerate electricity. These can beused in tide races: places where thetide speeds up to 4–6 knots as itpasses through a narrow gap.

Marine turbines avoid the damage tothe environment that barrageschemes can cause. The turbines turnquite slowly, so they do not affect sealife. Tidal barrages can affect sea life,such as fish that migrate up riversfrom the sea.

To find out more about tidal energy, visit www.dti.gov.uk/renewables/schools

bio-energy what is bio-energy? · bedzed housing development near london uses passive solar design....

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