Energy resources, alternative energy

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The alternative energy resources are called that because they offer a different way to generate our energy to the three fossil fuels, coal, oil and gas as well as nuclear energy.  These 4 energy resources are often called 'non-renewable' resources as eventually the supply  of them will run out.  The alternative energy resources are renewable.  That is to say they are renewed in a much shorter timescale.
We are going to cover the following alternative energy resources in this post:  Biomass, Wind, Tidal and Hydroelectric in mountains, Wave, Solar and Geothermal.
All of these have the same advantages over fossil fuels.  They do not cause the pollution that brings climate change or acid rain and they will not run out.  They do come with their own problems however.
Biomass:  in biomass a crop or waste is burnt to heat water into steam, replacing the coal, oil or gas in a traditional fossil fuelled power station.  The steam is then used to spin the turbine which is connected to the generator. However, collecting enough fuel is difficult.  Wood, which can be grown for this has a sixth of the chemical energy in it that coal does.  It also takes away land from agriculture and other uses (some companies are developing a seaweed they hope to farm, dry and burn)

Wind: The wind spins the turbine (the big propeller) and  the turbine spins the generator, which produces the electrical energy.  This is very easy.  However, you need a great many of them to replace one fossil fueled power station, its not always windy and they can be considered ugly.

Tidal: There are several ways we might be able to use tidal power.  At the moment we build a dam across a river estuary.  In the walls of the dam there are tunnels which have the turbines in them.  As the water flows through the tunnels it spins the turbines which are connected to the generators, producing electricity.
Putting turbines and generators very like wind turbines on the bottom of river estuaries is being talked about.  I don't know that this is actually in use anywhere.
The problems are that building the dams is difficult and expensive.  Also the tide only flows hard at certain times of day (but we can at least predict these due to the orbit of the moon).  In between these peaks much less energy is generated.  Damming a river also affects the wetland habitats around it and the migration of some fish.

Hydroelectric in the mountains:  This can be done at any section of a river, not just in mountains.  There has to be a strong flow of water though so having a lake dammed up at the top of a mountain provides a good flow.  The water is allowed to flow down the mountain spinning turbines as it does so.  A small plant has also been build on the River Thames in Abingdon, no mountains there but a strong flow of water through the weir.  Again problems include damming the river and changing the water flow, which can also vary due to rain and bad weather.

Wave:  Wave power has had many different approaches to make it work.  Some of these involve having a floating container on the sea (in the shape of a duck or a snake! Search Salter ducks and wave power snakes to see more).  These contain oil which, as the waves rock the container, flows through a turbine, spinning it.  These have proved to be difficult to get to work well.  There is also the idea of building a chamber on the seashore.  This has no bottom to it so the waves can rise up into the chamber.  In one wall there is a hole and in the hole is a turbine connected to.... yup a generator.  As the wave rises into the chamber the air is forced out through the hole spinning the turbine.  As the wave sinks back out of the chamber the air is drawn back in through the whole spinning the generator again.  This is apparently rather noisy!  Also if there is no wind there will not be waves to make this work.

Geothermal power: This is great for geologically active areas with hot rock close to the surface of the earth.  Water is pipped down to these hot rocks and is heated into steam.  The steam is squired at the a turbine just like in a fossil fuelled power station.
Its not much use in the UK as there are not many areas with these hot rocks.

Solar I have left solar to the end as there is no turbine and no generator involved.  All the other alternatives mentioned here change kinetic energy into electrical energy with a generator.  Solar does not.  It changes the light from the sun directly to electricity. (Exactly how we wont go into here!)  It is getting cheaper to do this all the time but it is still expensive and of course night time presents a real problem particularly during the winter in the UK.