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Renewable Energy

Renewable energy uses resources that are naturally replenished unlike fossil fuels which are non-renewable and once used cannot be replaced. The five most commonly used renewable sources are hydro (water), solar, wind, geothermal and biofuels. Renewable energy sources represent about 15% of global energy use with hydro-power accounting for 97% of this figure.

Apart from continual replenishment, the main strengths of renewable energy are that it can be easily utilised anywhere in the world and it does not result in the production of polluting gases that lead to global warming and climate change.

Hydro Power

The basic of hydro-electric power is that energy in moving water is converted to electricity by turning a turbine which is connected to an electrical generator. Large scale hydro-electric power plants involve the construction of dams or weirs. The biggest plants use dams and produce the most electricity. The dams store rain and river water in huge reservoirs. When electricity is required, the water is released through the turbine.

Currently the largest hydro power operation in the world is at Itaipu in Brazil which generates the same amount of electricity as 12 nuclear power stations. On an even large scale is the Three Gorges Dam in China which when completed will provide over 10% of the country’s energy needs and save 45 million tons of coal a year.

Hydro Power in the UK is on a much smaller scale with most operations in Scotland and Wales. It only provides 2% of the country’s energy needs but there is scope to improve this figure. Hydro Power systems range from the size of a small conventional power station to micro systems in rivers and streams.

The water in the oceans can also be used to generate electricity by harnessing the movement of waves and tides. Waves rise and fall and it is this up and down motion that can be converted into electricity. Tides move huge amounts of water each day, but the rise and fall of tides needs to range at least 5 metres to make electricity generation viable. There are eight sites around the coast of the UK, where this is possible, such as the river estuaries of the Severn and the Mersey. Tidal barrages could be built across these estuaries with a series of turbines at the bottom which are turned as the water flows through. But these would be expensive to construct and there are concerns about their effect on bird and sea life.

Solar Power

The sun radiates 174,423,000,000,000 kilowatt hours of energy to the earth every hour in the form of light and heat. This is more than enough to serve the entire global population’s energy demands, as well as providing light and heat energy for plants and animals to live and grow. We can use solar energy to heat water and space for our buildings. We can also generate electricity from the sun through solar electric cells, known as photo-voltaic or PV cells.

One of the simplest ways in which we can harness the energy of the Sun directly is by using it to heat water. This is known as Solar Thermal. There are many different types of solar thermal systems ranging from those that help provide domestic hot water to systems that can heat water to over 150oC for industrial purposes. The most common systems are solar panels or solar collectors. Water circulating through the units is heated and stored in a large tank.

There are millions of domestic solar thermal systems in use around the world. When visiting Mediterranean countries you will often see solar panels and tanks on the roofs of houses. Even with our climate in the UK solar panels are efficient enough to provide hot water. The temperature of the water obviously depends on the amount of sunshine but even in cloudy conditions water can be warmed. The warmer the water the less fossil fuel or electricity is required to provide the optimum temperature for hot water.

Photovoltaic or PV cells convert light energy directly into electricity. A PV cell contains thin layers of silicon. When light hits the cell electrons move between the layers of silicon and this produces electricity. A PV panel is made up of many PV cells laid side by side. If several PV panels are connected together, then enough electricity can be generated to put to use powering lights, equipment or charging up storage batteries.

PV panels require little maintenance and running costs are very small. They are ideal for use in remote and underdeveloped parts of the world, often providing electricity for the very first time to power water pumps, lighting and refrigerators for storing food and medicines.

Recent years have seen an increase in use of solar PV in the UK as the efficiency of their use in cloudier conditions has improved. Large arrays can now supply a significant proportion of the electricity used by office blocks. A good example of this is the CIS tower in Manchester where solar panels generate an amazing 180,000 units of electricity each year - enough energy to make 9,000,000 cups of tea. In some places, the energy is stored in accumulator batteries during the day for use at night. Solar panels are now frequently fitted to road signs, to power lighting, particularly in rural locations and when it would be expensive to lay cables to provide electricity from the main supply.

Passive Solar Heating

Buildings are naturally warmed by sunlight. Windows and skylights allow sunlight to penetrate into rooms to provide warmth. The shape of buildings and the materials from which they are constructed will affect the amount of heat provided by the sun. Buildings such as office and schools with large arrays of south-facing windows can collect the heat and circulate it to other parts of the buildings.

The use of sunlight in this way is known as passive solar design. Carefully positioned windows can significantly cut energy costs in homes and other buildings. Architects are now being encouraged to design buildings that make best use of passive solar design to reduce the energy consumption of the occupiers. Providing opportunities for increased sunlight in buildings also has the added value of reducing the need for artificial lighting.

Wind Power

The use of wind power has significantly increased in the UK in recent years. For many years windmills have been used to work machinery such as in flour mills, but today’s windmills, known as wind turbines, range from1 kilowatt systems used on small buildings to collections of very large turbines in wind farms both on land and out at sea.

There are over 140 onshore wind farms spread across the UK generating nearly 2,000 megawatts of electricity. They have all required planning permission and there have often been strong objections to their position because of the way they look and the perception of the noise they make. However research has shown that many people believe the advantages of wind farms far outweigh any disadvantages and that people grow to like them once they have been installed.

The greatest potential for wind power in the UK is offshore where huge arrays of large turbines can be grouped together. There are 5 offshore wind farms currently operating round our coastline producing over 300 megawatts of electricity. However, plans are in place for more and larger farms to be built in the future. Although construction costs are greater than those of onshore wind farms they produce more electricity and usually have fewer objections from the public.

Geothermal Energy

Geothermal energy uses the heat from inside the earth’s core for heating. The energy can be exploited safely and reliably when water flows through hot rocks inside the earth creating hot water and steam, which reaches the earth’s surface as hot springs and geysers. The steam that escapes the earth is captured and used to turn turbines to make electricity, in the same way that steam is used in a coal fired power station.

‘Hot rocks’ is another technique for collecting geothermal energy where water is actually pumped into hot rocks several kilometres below the surface of the ground. The water turns to steam and it flows back to the surface under high pressure to drive a turbine and generator. It is almost the same process as natural geysers but uses engineering to pump the water in.

Geothermal energy can also be used for heating. One of the best UK examples is in Southampton, where geothermal energy, combined with a gas turbine Combined Heat and Power system, supports a district heating scheme which supplies the Civic Centre, hotels, shops, commercial operations and homes.

Ground Source Heat Pumps use escaping geothermal energy and/or solar heat absorbed by the soil under car-parks and similar large dark surfaces. Water flows in pipes just a few metres below the ground surface. The warmed water is passed through a heat pump. This extracts the heat from a large volume of warm water and concentrates the energy in a smaller volume of water that therefore becomes much hotter than the source water. Electricity is required to drive the water and heat pumps, but typically it is only a quarter of the amount that would be required to obtain the same volume of hot water using a conventional electrical heating element. Ground source heat pumps raise the temperature to about 40˚C and so are best used for under-floor heating systems or to pre-heat water.

The heat pump is not a new technology. In fact it is heat pumps that are used in refrigerators and air-conditioning units. Therefore it is not surprising that heat pumps can also be used for cooling as well as heating. In the winter months the ground is warmer than the air so heat can be pumped into buildings. In the summer the ground is cooler than the air and the process can be reversed to pump heat out of buildings into the ground to cool rooms down. This type of renewable energy is becoming increasingly popular in the U.K.

Air Source Heat Pumps can be used in much the same way, to heat space in winter and cool space in summer.

Biomass

Biomass is a collective term for all biofuels derived from plant and animal material. Biofuels come from many different sources, including wood, straw, energy crops such as miscanthus grass, willow and sugar beet and even from cow dung! The energy released when biofuels are burnt can be used for cooking, space heating, hot water and making steam to generate electricity.

Wood is still the primary source of energy in the developing world and is increasingly being used as a fuel for boilers in the UK. Wood chips or pellets made from waste wood are being used to provide hot water and heating in a range of public and private sector buildings such as schools and offices. The attractiveness of using wood stems from the fact that burning wood is carbon neutral. This is because when wood is burnt the same amount of carbon dioxide is released as the trees absorbed when they were growing. The same applies to other energy crops.

Animal waste can be treated to produce a gas rich in the fuel methane. The waste is put in tanks where it rots, producing the biogas, which can then be used for heating and generating electricity. Methane can also be extracted from the treatment of sewage and from landfill sites. There is pressure to reduce the amount of waste going to landfill in the UK as the availability of appropriate sites is declining. One answer is to use waste in a refuse-burning power station to generate electricity.

Liquid biofuels such as biodiesel can be used to power transport vehicles. Biodiesel is made from oily plants, animal fat, or used vegetable oil. When burnt it produces less emissions than petroleum-based diesel and can be used in existing diesel engines without any modifications. Ethanol (a type of alcohol) is another alternative fuel for vehicles. It is produced from sugar-rich crops such as maize and sugar beet. The sugar is extracted from the plants and allowed to ferment, producing ethanol. Ethanol is used widely in Brazil where it is mixed with petrol – 80-90 per cent petrol and 10-20 percent ethanol. Such mixes are also used in the USA, especially in cities that suffer from air pollution such as Los Angeles. The presence of just a small amount of ethanol makes the fuel burn more cleanly. The availability of biodiesel and ethanol-petrol mixes is increasing in the UK.