Geothermal Power

Introduction

The centre of the Earth is around 6000 degrees Celsius - hot enough to melt rock. Even a few kilometres down, the temperature can be over 250 degrees Celsius. In general, the temperature rises one degree Celsius for every 36 metres you go down. In volcanic areas, molten rock can be very close to the surface. 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 Town Hall in Southampton, England, is partly heated this way.

More details

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.

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.

See Also:

Find out more from Mighty River Power, New Zealand

A geothermal project in Hawaii http://www.geothermalhawaii.com/

A diagram showing a geothermal project http://www.geothermal.marin.org/GEOpresentation/sld037.htm

Advantages

• 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.
  
  
• 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.

Disadvantages

• 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.
  
  
• 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.

Is it renewable?

Geothermal energy is renewable.
The energy keeps on coming, as long as we don't pump too much cold water down and cool the rocks too much.

hydro-electic power

ntroduction

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 1878. 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. 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. There's a good explanation of how hydro power works at www.fwee.org. 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.

More details

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, hydro-electric 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. See also: www.fuelfromthewater.com

Advantages

Once the dam is built, the energy is virtually free. No waste or pollution produced. 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.

Disadvantages

The dams are very expensive to build. However, many dams are also used for flood control or irrigation, so building costs can be shared. 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.

Is it renewable?

Hydro-electric power is renewable.
The Sun provides the water by evaporation from the sea, and will keep on doing so.

wave power

Ocean waves are caused by the wind as it blows across the sea. Waves are a powerful source of energy. The problem is that it's not easy to harness this energy and convert it into electricity in large amounts. Thus, wave power stations are rare.

How it works

There are several methods of getting energy from waves, but one of the most effective works like a swimming pool wave machine in reverse. At a swimming pool, air is blown in and out of a chamber beside the pool, which makes the water outside bob up and down, causing waves. At a wave power station, the waves arriving cause the water in the chamber to rise and fall, which means that air is forced in and out of the hole in the top of the chamber.

We place a turbine in this hole, which is turned by the air rushing in and out. The turbine turns a generator.

A problem with this design is that the rushing air can be very noisy, unless a silencer is fitted to the turbine. The noise is not a huge problem anyway, as the waves make quite a bit of noise themselves.

More details

Once you've built it, the energy is free, needs no fuel and produces no waste or pollution.

One big problem is that of building and anchoring something that can withstand the roughest conditions at sea, yet can generate a reasonable amount of power from small waves. It's not much use if it only works during storms!

Example: A company called Wavegen now operate a commercial wave power station called "Limpet" on the Scottish island of Islay, Find out more at www.wavegen.co.uk...
>>View a simulation from the Greenpeace website, with a good animation of how "Limpet" works.

Example: A company called Ocean Power Delivery are developing a method of offshore wave energy collection, using a floating tube called "Pelamis". This long, hinged tube (about the size of 5 railway carriages) bobs up and down in the waves, as the hinges bend they pump hydraulic fluid which drives generators. Find out more, including an interactive model, videos and technical details at www.oceanpd.com...

Example: Another company is called Renewable Energy Holdings. Their idea for generating wave power (called "CETO") uses underwater equipment on the sea bed near the coast. Waves passing across the top of the unit make a piston move, which pumps seawater to drive generators on land. They're also involved with wind power and biofuel. Find out more at www.reh-plc.com...

Advantages

The energy is free - no fuel needed, no waste produced. Not expensive to operate and maintain. Can produce a great deal of energy.

Disadvantages

• Depends on the waves - sometimes you'll get loads of energy, sometimes nothing.
  
  
• Needs a suitable site, where waves are consistently strong.
  
  
• Some designs are noisy.
  
  
• Must be able to withstand very rough weather.

tidal power

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.

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.
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 Weston-super-Mare an awful lot longer! Also, if you're a wading bird 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. It was built in 1966.
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 may have over 200 large turbines, and provide over 8,000 Megawatts of power (that's over 12 nuclear power station's worth). It would take 7 years to build, and could provide 7% of the energy needs for England and Wales.
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.

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 about the world's first offshore tidal power station at .

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.


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.
Offshore turbines and vertical-axis turbines are not ruinously expensive to build and do not have a large environmental impact.

Disadvantages
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. There are few suitable sites for tidal barrages.
Only provides power for around 10 hours each day, when the tide is actually moving in or out.

nuclear power

Nuclear power is generated using Uranium, which is a metal mined in various parts of the world.
The first large-scale nuclear power station opened at Calder Hall in Cumbria, England, in 1956.
Some military ships and submarines have nuclear power plants for engines.

Nuclear power produces around 11% of the world's energy needs, and produces huge amounts of energy from small amounts of fuel, without the pollution that you'd get from burning fossil fuels.


Nuclear power stations work in pretty much the same way as fossil fuel-burning stations, except that a "chain reaction" inside a nuclear reactor makes the heat instead.
The reactor uses Uranium rods as fuel, and the heat is generated by nuclear fission. Neutrons smash into the nucleus of the uranium atoms, which split roughly in half and release energy in the form of heat.
Carbon dioxide gas is pumped through the reactor to take the heat away, and the hot gas then heats water to make steam.
The steam drives turbines which drive generators. Modern nuclear power stations use the same type of turbines and generators as conventional power stations.
In Britain, nuclear power stations are built on the coast, and use sea water for cooling the steam ready to be pumped round again. This means that they don't have the huge "cooling towers" seen at other power stations.
The reactor is controlled with "control rods", made of boron, which absorb neutrons. When the rods are lowered into the reactor, they absorb more neutrons and the fission process slows down. To generate more power, the rods are raised and more neutrons can crash into uranium atoms.


Natural uranium is only 0.7% "uranium-235", which is the type of uranium that undergoes fission in this type of reactor. The rest is U-238, which just sits there getting in the way. Modern reactors use "enriched" uranium fuel, which has a higher proportion of U-235.
The fuel arrives encased in metal tubes, which are lowered into the reactor whilst it's running, using a special crane sealed onto the top of the reactor.

Carbon dioxide gas is blown through the reactor to carry the heat away. Carbon dioxide is chosen because it is a very good coolant, able to carry a great deal of heat energy. It also helps to reduce any fire risk in the reactor (it's around 600 degrees Celsius in there) and it doesn't turn into anything nasty (well, nothing long-lived and nasty) when it's bombarded with neutrons.
You have to be very careful about the materials you use to build reactors - some materials will turn into horrible things in that environment. If a piece of metal in the reactor pressure vessel turns brittle and snaps, you're probably in trouble.
Uranium itself isn't particularly radioactive, so when the fuel rods arrive at the power station they can be handled using thin plastic gloves. A rod can last for several years before it needs replacing. It's when the "spent" fuel rods are taken out of the reactor that you need the full remote-control robot arms and Homer Simpson equipment.
Nuclear power stations are not atomic bombs waiting to go off, and are not prone to "meltdowns". There is a lot of U-238 in there slowing things down - you need a high concentration of U-235 to make a bomb. If the reactor gets too hot, the control rods are lowered in and it cools down.If that doesn't work, there are sets of emergency control rods that automatically drop in and shut the reactor down completely.
With reactors in this country, the computers will shut the reactor down automatically if things get out of hand (unless engineers intervene within a set time). At Chernobyl, in Ukraine, they did not have such a sophisticated system, indeed they over-rode the automatic systems they did have. When they got it wrong, the reactor overheated, melted and the excessive pressure blew out the containment system before they could stop it. Then, with the coolant gone, there was a serious fire. Many people lost their lives trying to sort out the mess.
If something does go wrong in a really big way, much of the world could be affected - some radioactive dust (called "fallout") from the Chernobyl accident landed in the UK.
With AGR reactors (the most common type in Britain) there are additional safety systems, such as flooding the reactor with nitrogen and/or water to absorb all the neutrons - although the water option means that reactor can never be restarted.
Nuclear power stations in England are open to the public. Visit www.bnfl.com to find out more about how nuclear power stations work - choose a "Brief Overview" or "In depth" from their menu


Nuclear power costs about the same as coal, so it's not expensive to make.
Does not produce smoke or carbon dioxide, so it does not contribute to the greenhouse effect.
Produces huge amounts of energy from small amounts of fuel.
Produces small amounts of waste.
Nuclear power is reliable.

Nuclear power costs about the same as coal, so it's not expensive to make.
Does not produce smoke or carbon dioxide, so it does not contribute to the greenhouse effect.
Produces huge amounts of energy from small amounts of fuel.
Produces small amounts of waste.
Nuclear power is reliable.

Actually, it's not that simple - we can use "fast breeder" reactors to convert uranium into other nuclear fuels whilst also getting the energy from it. There are two types of breeder reactors - ones that make weapons-grade plutonium and ones that are for energy production.

wind power

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.
To be worthwhile, you need an average wind speed of around 25 km/h. Most wind farms in the UK are in Cornwall or Wales.

Isolated 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 land beneath can still be used for farming.


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 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.



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.

solar power

Now those behind the Welsh operation think they may have made a crucial breakthrough. Their solar cell works in a different way from most, and is not based on silicon - the expensive raw material for conventional solar cells. G24 Innovations (G24i), the company making the new cells, says it can produce and sell them for about a fifth of the price of silicon-based versions. At present, it makes only small-scale chargers for equipment such as mobile phones and MP3 players. But it says larger panels could follow - large enough to replace polluting fossil fuels by generating electricity for large buildings.



"This has been at the laboratory stage for 18 years and now we are ready to take it into a huge amount of applications," says Clemens Betzel, president of G24i.





G24i's technology is based on a coloured dye and tiny crystals of titanium oxide - a common pigment in white paint. It exploits a discovery made in 1991 by a Swiss chemist called Michael Graetzel, who found that the combination could be used to copy photosynthesis. When struck by sunlight, the dye spits out an electron, which is immediately captured by the specks of titanium oxide. By collecting the electrons at one side of his new solar cell, and replacing them at the other with an iodide electrolyte solution, Graetzel produced an electric current.



The new so-called Graetzel cells offered a simpler and potentially cheaper way to generate solar power. (Traditional silicon cells are more complicated because they require the generation of an electric field within the silicon to carry away the liberated electrons.) And because they work in a different way, Betzel says the new cells offer other advantages too. They work better in low light levels, including indoors, he says, and they are lighter and less fragile than silicon cells, which are usually mounted on glass or rigid plastic.





At least one big hitter in the renewable energy industry agrees with him: Bob Hertzberg, founder of venture capital firm Renewable Capital, a backer of the G-Wiz electric car, has invested in G24i and talks of it making annual profits of £130m within five years. The company has not yet found a major buyer for its technology, but Betzel says there are some in the wings.







Design students have also been involved with the development process. Earlier this year, the company ran a competition with 45 product design students at St Martin's college of art and design in London, who were asked to think up new uses for the Cardiff solar cells. The winning entries include portable safety lights mounted on life buoys, and lamps to mark scaffolding and hoardings around roadworks and on building sites. They also featured solar-powered security lights, fire exit signs, and window blinds, which could cut electricity use.