Renewable sources of Power

Wind is generated by pressure differentials in the Oceans and over large landmasses. Air moves from a high-pressure area to a low-pressure area. The Sun heats the air near or in the tropics causing high pressure that then flows towards the colder, low pressure air at the poles. The wind tends to flow in a circular direction around the centre of pressure. The direction is influenced by the rotation of the earth. Due to something called the Coriolis effect, winds in the northern hemisphere rotate clockwise around a centre of high-pressure and anti-clockwise around a centre of low-pressure. In the southern hemisphere this is the opposite way round

Wind turbines have blades that rotate in the wind and drive a generator.

The wind causes waves to form out in the ocean and some waves, as you may have observed on a stormy day, can have a great deal of energy.

The action of the waves can be used in a variety of ways to harness the energy. One method is to use the up and down action to force air through a tube that drives a turbine connected to a generator.

wave power is fairly clean but there are huge debates about whether the wave machines damage the local environment and the wildlife in it.

The action of tides can be used to generate electricity. This would involve creating a barrage across a river estuary where tidal ranges are greatest. Despite being able to produce clean energy, tidal barrages are expensive to produce and can dramatically alter the local eco-systems, causing damage to wildlife populations.

Power from running water has been used for generations. The earliest examples would include corn mills with large wheels turned by water running over them.

Modern methods of extracting energy from running water mainly involve trapping the water using dams. The water is allowed to run out through turbines at the base of the dam where the pressure is highest. These turbines drive generators to produce electricity. These Hydro-electric power stations are very expensive to produce but can generate large amounts of energy fairly cheaply without pollution or contributing to the greenhouse effect.

A hydro-electric power station effectively converts the potential energy of the the stored water, created by gravity, into usable energy. The flow of water can be controlled to limit the production of electricity to the times when it is required.

Hydro-Electric Dams are large scale engineering projects and require suitable locations, of which there aren't many around. They can also cause serious devastating changes to the local environment and wildlife populations due to flooding large areas of land.

The Sun is the source of most of the energy that we use. We normally get this energy indirectly from burning fossil fuels for instance. Fossil fuels are the remains of trees and plants that were alive many millions of years ago, they converted the sun's energy into food by a process called photosynthesis. We simply unlock this energy by burning it.

The Sun's energy however can be tapped directly by using technology.

Solar cells are photovoltaic cells that generate electricity from the light (photons) emitted from the sun as it burns hydrogen. Cells can be combined into panels that can generate significant amounts of power, especially in sunny climates. PV cells were originally designed to provide power to spacecraft but are becoming more and more common in terrestrial (ground) applications.

Solar Water heating is a technique whereby the sun is used to heat water in black tubes behind glass panels. Most of us will have experienced touching a black object left in the summer sun. It will be very hot because black objects absorb more energy than other colours; white tends to reflect more of the suns light.

Convection moves the water around from the storage tank to the panels so that it all gets heated. Sometimes pumps are used to augment this process.

Solar Water Heaters produce clean energy and can reduce the cost of heating at home.

Solar Furnaces use mirrors or lenses to focus the sun's light rays onto one spot. You may have tried the similar trick of lighting a piece of power with a magnifying glass on a hot day. Some of the big commercial furnaces can achieve temperatures of nearly 3,000 degrees Celsius. Smaller versions are used in hot sunny climates for cooking.

The rocks beneath the crust of the Earth are hot. The centre of the Earth is about 6000 degrees Celsius, and nearer the surface they can still be as high as 250 degrees Celsius.

These high temperatures can be utilised to heat up water to produce steam. Water is pumped down through specially drilled holes. When it returns to the surface it turns to steam, which is used to drive a turbine connected to a generator in much the same way as in a fossil fuel or nuclear fuel power station. Sometimes the steam is simply used to supply heat for warming houses and other buildings.

The main advantages of geothermal energy is that it has very little impact on the environment, producing no direct pollution and contributing nothing extra to the greenhouse effect. It is however only practical in certain parts of the world where the crust is thin and the hot rocks are easily accessible, like in Iceland or certain parts of Japan.