Wind turbines are becoming a common feature around the world including much of Europe, the USA and China.

Within the wind turbine structure are mechanisms to make it as efficient as possible. Very tall large blades are the most efficient (the wind blows more strongly at greater height).

An anemometer measures the speed and direction of the wind to turn the tower and adjust the pitch of the blades. The rotating blades drive the shaft. The speed in increased by the gearbox to turn the generator at an appropriate speed. The voltage of the electricity generated is increased for transmission into the national grid by a step-up transformer at the base of the tower.

Advantages

• The energy resource is free and non polluting
• There are many windy locations where they work well
• Costs of making the turbines are falling

but

• They are sill quite expensive to build and install
• They can be noisy and some people dislike the appearance
• There are questions over damage to birds
• They don't work if the wind does not blow

Hydroelectric Power

Works by capturing water behind a dam wall fairly high in the hills and then allowing it to run out of a channel through a water turbine driving a generator.

• Totally renewable
• Creates water reserves as well as energy supplies.
• Reliable, easy to control and very low running costs.

But

• Very costly to build.
• Can cause the flooding of surrounding communities and landscapes.
• Dams can have major ecological impacts on local river flow and drainage.

Tidal barriers harness the energy of the sea as the tide flows in and then out twice each day

We can also place turbines on the sea bed in areas of strong tidal flow, for example between islands.

Tidal

• Great potential for an island such as the UK.
• Totally renewable
• Cheap to run.
• Predictable and reliable
• Could generate a lot of energy.
• A tidal barrage can also be used as a bridge and may help prevent flooding.

But

• Construction of a barrage is very costly (running to many billions of pounds).
• Placing turbines in strong tidal currents is difficult and expensive.
• Very few estuaries are suitable.
• May damage the wildlife on the estuary.

Geothermal energy can be exploited where the the earths crust is thin where hot rocks lie close to the surface. The hot water produced can then be used directly to heat homes and commercial premises as is done very extensively in Iceland or it can be used to produce electricity.

In either case cold water is pumped down underground to be heated by fractured rocks.

• Totally renewable
• Potentially infinite energy supply.
• Used successfully in some countries, such as New Zealand and Iceland where the earths crust is thin.

But

• It is likely to be impractical in most areas due to the depth of drilling required.
• Can be expensive to set up.
• Dangerous elements found underground must be disposed of carefully.

There are many ideas for designs to harness wave energy but so far very little practical energy has been produced. The cost of manufacture and of passing cables back to the shore are two expensive problems. In summary:

• Great potential for an island such as the UK.
• Totally renewable.
• Low running costs since energy supply is zero cost (although maintenance may be expensive in inhospitable seas)

But

• More likely to be small local operations, rather than done on a national scale.
• Construction can be costly, there is no large scale production so far.
• May obstruct the view in unspoiled coastline or be a problem for shipping.
• Small output on calm days

In the UK crops such as willow are grown (on a fairly small scale) to burn in a power station much in the same way as coal is burnt. In many countries for example the US, Canada and some Scandinavian countries other soft wood are grown for use and often for export.

Oil from crops such as rape seed (the bright yellow crop seen across the country in late spring) can be used in the production of fuel for diesel cars.

Other sources include sugar grown to produce alcohol for use in vehicles. The composting of plant material or animal manure which decay and produce gas.

• It is can be a cheap and readily available source of energy.
• If replaced, biomass can be a long-term, sustainable energy source.
• If grown locally it is reliable and secure and absorbs carbon dioxide from the atmosphere

BUT

• When burned, it gives off atmospheric pollutants, including greenhouse gases.
• Biomass is only a renewable resource if crops are replanted.
• Using the land to grow fuel reduces the amount available to grow food for the worlds growing population. in particular this may damage food resources in poorer nations.

The use of biomass is regarded as carbon neutral since the carbon dioxide released when it burns is balanced by the carbon dioxide absorbed as it grows.

A PDF copy of all these notes is here:Generation from renewable energy resources