Green Renewable energy uses natural resources such as sunlight, wind, water, biomass and geothermal heat - all of which are naturally replenished.
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There are three main ways of capturing energy from sunlight
- Solar Thermal - Solar Water Heating Collectors
Solar water heating systems are the most popular form of solar energy used in the UK. These systems are connected to the hot water system of your house. Solar water heating systems can provide over half of a household's hot water requirements over the year. There are 2 types of solar water heating collector: flat plate collectors and evacuated tubes.
- Flat Plate Collectors
Solar water heating panels in their simplest form are made from a sheet of metal painted black which absorbs the suns energy. Water is fed through the panel in pipes attached to the metal sheet and picks up the heat from the metal. For the UK climate the pipe work contains non-toxic anti-freeze to prevent freezing in cold wheather. The pipes are often made of copper for better conduction. The metal sheet and pipes are embedded in an insulated box and covered with glass or clear plastic on the front. The system is usually installed on the roof of your house.
- Evacuated Tubes
Vacuum or Evacuated Tubes are made from glass - typically ultra-strong and heat resistant Pyrex with a double wall construction. The glass on the inner tube is coated on its outer surface with an absorbant coating, and on its inner surface with a reflective coating. Inside each tube all air is removed, making a vacuum, and a copper heat pipe is located through the centre of the tubes. Most of the infra-red radiation (i.e heat) from the sun is absorbed by this sealed heat pipe which contains an anti-freeze type liquid.
As heat rises, hot vapours from the antifreeze rise up to the top of the heat pipe where its copper tip connects with a header pipe through which more antifreeze flows. This hot antifreeze is then pumped through pipes inside the hot water tank with the end result that the water gets hotter and the antifreeze cooler. The antifreeze then continues its journey around the system and back out to the solar water heater to be reheated.
The copper at the tip of the heat tube can reach well over 200 degrees celcius easily heating water to 90 degrees celcius on hot days and to 60 degrees celcius even in the winter. This simple system is completely sealed and needs minimal maintenance over its 20+ years life.
The advantage of using evacuated tubes is that they will work even during the coldest winter months unlike old style Flat Plate Solar Collectors. The vacuum helps prevent the heat tube from being cooled by the ambient temperature. This can be well below freezing and so winter sun can easily heat water to 50+ degrees celcius. Even in the depths of the coldest season. Even if it is very cloudy and very cold, enough sunlight gets through to keep the tubes well above freezing and so they will be still be pre-heating the water which can then be heated further by a standard heating system.
The cost of installing a solar hot water system ranges from approximately £500-£1500 for a DIY system, to £2000-£5000 for a commercially installed system. These prices however, are dependent on the size of the system. A typical installation in the UK has a panel of 3m2 to 4m2 (2m2 for evacuated tubes) with a storage tank of 150- 200L .
- Solar Electricity - Photovoltaic (PV) Panels
Photovoltaic (PV) or solar electric panels transform sunlight directly into electricity using semi-conductor technology. PV or solar electric offer the ability to generate electricity in a clean, quiet and renewable way and the variety of applications for solar electric are numerous. Photovoltaic (PV) cells can be used in simple applications such as calculators and wrist watches but may also be used for domestic and larger applications. Large PV systems can be integrated into buildings to generate electricity for the building itself or even for export to the national grid. Photovoltaic cells can be expensive and the cost of equipment may take many years before receiving any payback. However, in remote areas where grid connection is expensive, PV is often the most cost effective power source.
- Solar Passive
The use of passive solar design is possibly the simplest form of solar energy. Many buildings today are designed to utilise the energy of the sun as efficiently as possible. The location and orientation of the building are all key factors in optimising passive solar design.
Passive solar design can be best applied in new buildings, where the orientation of the building, the size and position of the glazed areas, the density of buildings within an area, and materials used for the remainder of the structure are designed to maximise free solar gains. Designing a property to maximise free solar gain need not add to the price of construction.
Studies have shown that low cost passive solar design features, draughtproofing and insulating measures can reduced heating bills by up to 40%. The money saved can pay back the investment costs within two years.
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This technology relies on wind to rotate blades which drive turbines to generate electricity. Wind energy applications range from small battery charging units, producing useful electricity when remote from the electricity distribution network, to large wind farms producing electricity in competition with the conventional power stations. Wind power is one of the cleanest and safest of all the renewable methods of generating electricity and has great potential in both onshore and offshore wind farms. In the UK we currently get less than 1% of electricity from wind yet the UK has the largest wind resource in the whole of Europe. There is the potential for wind to provide 10% or more of our power requirements over the next twenty years.
It is possible to produce electricity from wind for as little as 2 pence per kWh. This compares favourably with the cost of electricity from conventional sources. However low cost generation is only possible on the windiest sites. Typically, electricity from wind will cost between 2p/kWh and 10p/kWh depending on scale and location. Overall wind energy projects are simple, clean and cheap to maintain. The land can still be part of the agricultural system and jobs are often created both in the short and long term in the building and maintenance of the turbines.
Wind power produces no pollutants or emissions during operation. A typical wind turbine for electrical generation will repay the energy used in its manufacture in the first 6-9 months of its operation. The main area in which wind power impacts upon the environment is in its visual impact which is one of the most contentious issues when siting wind farms.
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The kinetic energy potential of moving water is used to turn water wheels or turbines to produce electricity. Hydropower currently produces 2% of the UK electricity needs. Whilst most of this comes from large dam projects installed many years ago, it is estimated that there is still an untapped potential of about 200 MW using small-scale hydropower schemes.
Small-scale hydropower has been used in this country and abroad from the earliest times of electricity generation. Sluices and dams of old mills were used to generate a few thousand watts locally,however most of these systems died out with the introduction of large national distribution schemes. Now, small-scale(micro hydro) electricity generation is being looked at seriously again. With improvements in small generator technology, it is now quite feasible to produce a few tens of kilowatts of electricity from water heads as low as 2 to 3 metres.
Turbines either use water "dropped" from behind a dam or from a natural "run of the river" with no water storage reservoir. The requirements of micro hydropower schemes are:
- Good rainfall
- Adequate volumetric flow of water and a pressure head of at least 2 meters (These two factors determine the amount of power attainable)
- A water intake above a weir or behind a dam
- A water transport system, which will channel the water
- A flow control system
- A turbine and generator
- An outflow
As with any small renewable energy scheme, micro hydro does not benefit from the economies of scale of a larger scheme. Also, as a general rule of thumb, capital costs rise as available head decreases.
One can estimate the capital cost of a micro hydro installation at between £200 and £3000 per kW capacity. This is a very rough figure and is highly dependent upon:
- Degree of existing infrastructure, disused mill/weir etc.
- Willingness to assist manufacturer/installer
- Type of hydro resource available
- Type of hydropower system used
Any system below 10kW is probably not worth connecting to the grid unless an existing grid connection is already present. Systems of this size would be better suited to battery charging or use as a backup for a critical load (in place of a diesel generator, for example). Hydro projects require various consents and licences which are generally dealt with by the Environment Agency and Local Planning Authorities.
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Biomass is a collective term for all plant and animal material. A number of different forms of biomass can be burned or digested to produce energy. Biomass is a very versatile material and can be used to produce heat (for space and water heating), electricity or a combination of both. The UK has some of the largest examples of Biomass electricity generation in Europe.
Examples of biomass fuels include wood, straw, poultry litter and energy crops such as willow and poplar.
- Energy from Wood
In order not to increase the amount of carbon dioxide in the atmosphere it is important that the wood burned as a fuel comes from sustainable sources. This means that as trees are felled to be use as a fuel, more trees should be planted. That way, the carbon released during the combustion of the wood is reabsorded by the new trees growing and the process is carbon neutral. Other examples of sustainable sources of wood include forest residues (what is left over after timber has been extracted), tree surgery waste and other wood residue.
Wood can then be made into logs, wood chip and wood pellets and burnt in wood/pellet burning stoves or wood chip/pellet boilers for space and water heating.
On a larger scale wood can also be used for the production of electricity. The main method of producing electricity from wood is a combustion plant where the material is burned to produce steam. Other methods include gasification (where the material is heated in such a way that gases are given off) and pyrolysis (where the wood is heated in the absence of oxygen to produce a bio-oil liquid with some charcoal and gas).
- Energy Crops
Today trees like willow and poplar are being grown on Short Rotation Coppice(SRC) systems because they are fast growing they can be coppiced every 3-4 years. The perennial grasses Miscanthus and Switch-grass are other examples of energy crops as they produce high yield of dry matter.
Some agricultural crops are grown specifically with energy use in mind. Crops such as wheat and oil seed rape are being processed to produce liquid transport fuels such as ethanol and biodiesel.
Biodiesel can fuel most cars without any modification to the engine and most car manufacturers are happy for a blend of 5% Biodiesel and 95% fossil diesel to be used. Petrol stations selling biodiesel mostly use this ratio in their blends.
Biodeiesel production costs are higher than for fossil diesel however a combination of new tax breaks and the current high price of fossil diesel are starting to make biodiesel a viable alternative.
Clean vegetable oil can also be used as an effective fuel for diesel engines. As opposed to biodiesel, where the oil is modified, some modifications to the engine are required. There are modification kits available and the changes to the engine still allow the car to run on fossil diesel if needed. Many people are now producing their own diesel with oil obtained from their local restaurant.
- Agricultural Waste
Other forms of biomass produced by farmers are by-products of conventional agricultural activity. They include 'dry' agricultural wastes such as straw that can be combusted (burned) to produce energy.
'Wet' wastes such as green matter or slurry can be 'digested' to produce methane in a process known as anaerobic digestion. This can then be used to fuel a gas engine to produce electricity and heat.
There are already examples of chicken litter combustion, animal slurry digestion and 'straw combined heat and power' projects working well in this country. In many cases however, these projects are only economically viable if a sales outlet can be found for the heat produced (such as nearby factories) and the by products (eg. fertilisers for farms).
- Municipal and Industrial Waste
Even after the recycling of municipal waste there will always be some waste left over for disposal. Some of this, such as waste food, wood and paper can be utilised as biomass. This can be used to generate electricity and/or heat and also reduces the demand for landfill space. However care has to be taken with emissions and residues as they can cause further environmental problems.
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When the sun shines on the ground its heat energy is absorbed and ground Source heat pumps are able to extract this energy for use in space heating. So, strictly speaking, the energy source that is used for Ground Source heat pumps comes from the sun and not from the earth.
In the UK the constant ground source heat temperature is around 12ºC and this can be utilised to heat and cool buildings. Pipes are buried underground in trenches or in vertical wells and water is pumped through to extract the heat energy from the ground. A heat pump can extract the ground’s heat and transfer it into a building for space and water heating, or it can remove heat from a building and deposit it into the ground to cool the building during hot weather.
Heat Pumps do need some power to operate; however for 1 unit of energy they use they can generate up to 4 units of power. The energy generated by a ground source heat pump can be considered 100% renewable if the power to operate the pump comes from solar electric panels or from a wind turbine.
For further information please phone Dr Richard Owen on 01485 544637 or email .