Renewable energy refers to power generated by a renewable source. When the energy is generated , the resource is not depleted or used up They are naturally replenished and can either be managed so they last forever or their supply is so enormous humans can never meaningfiully deplete them. Unlike fossil fuels renewable energy sources do not release C02 as a by-product into the atmosphere. As the amount of fossil fuel resources on Earth decreases it is becoming increasingly important to find and utilise alternative fuels. Examples are.-
WIND POWER.
Air moves around the Earth because of the differences in temperature and atmospheric pressure Wind turbines harness the movement of air to produce energy. The wind turns the blades which turn a rotor shaft; the resultant mechanical power is used to drive an electricity generator. Wind turbines are often grouped together in wind farms. Wind power has very promising potential in the UK as we live in the path of Atlantic depressions (low- pressure systems) which bring windy weather. The UK currently has over 20 wind farms that could be supplying 10% of the UK's electricity by 2025. Wind farms provide a clean source of energy, but some people do not like their visual impact and the fact that they can be noisy in windy conditions. Suitable locations are often in areas of scenic beauty and so careful consideration needs to be given before they can be built. It is estimated that the UK has a very large offshore wind resource but it is not thought to be financially viable at present.
SOLAR POWER.
Solar power is the term used to describe energy derived directly from the Sun. The Sun provides the basis of energy for all living things. Sunlight has been utilised by humans for drying crops and heating water and buildings for millions of years. Solar energy is free and will never run out. We can use solar panels to turn the Sun's energy into useful energy. There are a number of ways to do this.
Passive Solar Heating.
Houses can be designed with large windows in the south and small windows in the north facing walls. This would allow natural light and heat from the Sun to be used to its full potential and reduce the need for electricity.
Active Solar Heating.
Solar power can be used to heat large bodies of water mainly for domestic hot water systems but also swimming pools.
Photovoltaics.
Photovoltaics allow the direct conversion of solar radiation into an electric current by the interaction of light with the electrons in a semiconductor cell. As development in solar technology has increased it has become much cheaper and the UK is starting to invest in the technology
BIOFUELS.
This is the term used to describe plant material and animal waste which can be burnt to produce energy. It is the oldest source of renewable energy known to humans. Unlike other renewables biomass energy does release C02 but only as much as was removed through photosynthesis during the plant's lifetime. Burning fossil fuels, by contrast, returns C02 to the atmosphere that has been locked away in the Earth's crust for millions of years. Crops can be grown with the purpose of being burnt to produce energy, e.g willow and oil seed We can also extract methane from waste landfill sites and burn it to produce energy. Methane is a powerful greenhouse gas and burning it would reduce the amount in the atmosphere.
HYDRO ELECTRIC POWER (HEP).
On the Earth water is neither created or destroyed but is constantly moved around. Water evaporates from the oceans, forming clouds, falls out as rain and snow, collects into streams and rivers, and flows back to the sea. This is known as the Water Cycle. All this movement provides an enormous opportunity to create useful energy. HEP uses the force of moving water to create electricity. However HEP stations often require large dams, which can disrupt ecosystems and displace people. There are a number of large scale HEP stations in Britain. In Scotland they provide a considerable amount of energy. Unfortunately there is little room for further development of large scale HEP stations and the potential of small scale ones is being investigated.
GEOTHERMAL ENERGY.
Rocks under the Earth's crust contain naturally decaying radioactive materials like uranium and plutonium producing a continuous supply of heat. The amount of heat within 10,000 metres of the Earth's surface contains 50,000 times more energy than all the oil and gas resources in the world. Geothermal energy is power generated by harnessing this heat. Wells are used to pipe steam and hot water from deep within the Earth, up to the surface. The hot water is then used to drive turbines and generate electricity. The regions with highest underground temperatures are in areas with active or geologically young volcanoes. These "hot spots often occur around the Pacific Rim. In the UK at a depth of 1500-3000 metres below the surface there are some aquifers that contain water at very high temperatures which can be pumped to the surface and used in heating schemes.
TIDAL POWER.
The idea is very similar to HEP. A dam-like structure is constructed across an estuary to trap a high tide of water and then let it pass through turbines to generate electricity The water flow can generate electricity on the falling tide only, or on the falling and rising tide. The Rance Estuary in France is an example of a successful plant. The UK has potential to widely use tidal power with the Severn and Mersey estuaries being possible sites.
WAVE POWER.
Ocean waves are a concentrated form of wind energy. Friction develops between air and water as wind blows across the water, and waves are produced as energy is transferred between these elements. Taking the motion of the waves, and translating it into mechanical or electrical energy, generates energy from waves. The UK has the potential to exploit a great deal of energy from wave power. There are 2 types of instruments that can generate electricity from wave energy: floaters and sitters. Salter's Duck and Cockerell's Raft are floaters and Vicker's "Duct is a sitter.
Salter's Duck.
This design can extract approximately 90% of the energy from a wave It is made up of a chain of about 25 floats. As they bob up and down on the water a pump is driven and electricity is generated.
Cockerell's Raft.
Lines of rafts are placed at right angles to the wave front. Between the rafts are hydraulic motors or pumps, which convert the energy to high pressure that then drives the turbines.
Vicker's Duct.
Water goes up and down a submerged tube and as the pressure changes water is squirted out and electricity generated.
