Renewable Energy Information

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Renewable Energy Explained

With world wide fossil fuel resources becoming increasingly depleted, fuel prices rising year on year and the need to commit to reducing carbon dioxide emissions to combat global warming renewable energy has become an important field within the construction industry.

A renewable energy resource is a naturally occurring energy resource that will replenish itself if used to produce energy. Key renewable energy resources include solar, water, wind, geothermal and biomass. These renewable energy resources can be harnessed by a range of different renewable energy systems governed by factors such as climate and location.

The most commonly used renewable energy resource for domestic applications within the UK is solar. Solar heating systems utilise the sun's power either directly or indirectly. Direct usage of solar power involves heating water directly with radiation from the sun, where as indirect heating utilises antifreeze type substances to transfer heat gained from the sun to the water. Flat plate solar collectors commonly provide a means of direct water heating, where as evacuated solar collectors are an example of indirect water heating. Traditionally flat plate solar collectors were commonly used, however with developments in manufacturing and materials evacuated tube solar collectors have become a more efficient alternative and are now widely specified. Evacuated tube collectors can be used effectively within countries prone to overcast weather conditions for solar heating applications as they utilise a vacuum to cut heat loss.

Flat plate solar collectors generally house pipes containing water positioned under a transparent surface often with a selective surface (a coating to limit heat loss). The water is heated by radiation from the sun and either naturally siphons (known as thermo siphoning) into a water header tank or is circulated by a small electric pump. Other variations may also utilise circulation pipes filled with an antifreeze type substance to transfer heat to water within the water tank. Flat plate collectors are generally considered to be more susceptible to heat loss especially in areas where sun intensity is low, however this depends on the site and location. Evacuated tube solar collectors comprise a series of vacuum sealed toughened glass tubes, known as evacuated tubes, connected to a header manifold positioned at the top of the unit. A copper heat pipe filled with a non toxic antifreeze type liquid passes through the centre of each evacuated tube and is connected to a copper pipe within the header manifold by its cooper tip. Radiation from the sun heats up the antifreeze type liquid within the heat pipes which rises to transmit heat to the header manifold via its copper tip. The antifreeze type liquid contained within the header manifold is then pumped through copper pipes within the water tank to heat the water. Where solar collectors can not provide all hot water heating requirements they can be used in conjunction with conventional hot water heating methods to meet any short fallings.

Solar energy can also be harnessed to produce electricity, known as photovoltaics, the process is referred to as photovoltaic electricity production. The technology requires photovoltaic panels, commonly referred to as PV panels, to convert solar radiation from the sun in to electrical current. The electrical current can then be consumed by an electrical appliance, fed in to the national grid or battery stored for later use. Photovoltaic panels can are manufactured from silicon based semi conductors which produce a flow of electrons under sun light. PV panels are generally used to supplement electricity supplies within the domestic environment to cut the usage of fossil fuels. They are ideal for off grid electrical appliances like lighting or the operation of small appliances such as electric water pumps. The electrical output of PV panels is usually in DC (direct current format) and will have to be passed through an inverter to convert it to AC format for use within existing appliances. Photovoltaic panels may be generically referred to as solar panels, which is a term sometimes used to describe solar collector panels.

The burning of biomass materials is provide a renewable energy resource. Biomass consists of natural materials which can be harvested and burnt to produce heat or used to generate electricity indirectly. Although biomass materials produce carbon dioxide when burnt they capture and store carbon from the atmosphere during their life cycle. Examples of biomass materials include wood, straw, saw dust and waste paper. Waste materials such as saw dust and fine wood chippings are compressed to form biomass pellets for combustion. The pellets have a high volume energy density and are easier to store and dispense within a residential environment. In order to burn biomass pellet products specially designed biomass boilers are required. The boilers can be purchased to undertake both hot water and space heating, or as stand alone units for single room heating. Other forms of biomass include the combustion of methane gas produced from the anaerobic digestion of animal, plant and human wastes. An example of a biomass fuel is ethanol derived from sugar cane and commonly used as an alternative to petrol in Brazil.

Wind energy is a key renewable energy resource within the rest of Europe and is currently undergoing rapid expansion with the UK. Wind energy can be harnessed on a large or small scale depending on the desired application. Wind turbines are used to convert motion resulting from wind speed in to electricity, which can be consumed directly or feed in to a battery for storage. A number of small scale wind turbines have been developed for the domestic market and are now readily available in kit form. These tend to produce power out puts of between 1 kW and 6 kW dependant on wind speed. There are also many larger heavy duty wind turbines on the market for industrial and commercial power generation, often used to export electricity to the national grid. The efficiency and the amount of electricity that can be generated from wind turbines depend hugely on their location and it is best to undertake a wind survey prior to installation.

A renewable energy resource often overlooked by many is that of water. Tidal forces can be harnessed to produce electricity on a commercial scale. Tidal installations are costly and only applicable to coastal locations. Inland locations where a stream or larger water course runs down a gradient may be suitable for the installation of a small scale hydro energy project to generate electricity. Small scale hydro electric installations utilise the force of the water to turn rotors within a generator as it flows downhill from a higher gradient.

A heat pump can be used to produce heat by taking advantage of naturally occurring temperature gradients relative to the temperatures of water, air or the ground. Heat pumps transfer natural heat contained within water, air or the ground to a heat exchanger which extracts the heat and uses it to heat air or water for home central heating. Heat pumps require electricity to drive the pump which circulates an antifreeze type liquid used to absorb the heat from the ground, water or air. For a heat pump system to be considered renewable the energy to run the circulatory pump must come from a renewable source. The efficiency of heat pumps are measured by their CoP (coefficient of productivity) with typical heat pumps having a CoP of 4, which indicates the system uses 1kW electricity for every 4kW of renewable energy heat produced. In order to make the most of heat energy produced it is vital that the house is fitted with good thermal insulation. Water source heat pumps, typically positioned in streams and water courses generally represent the most efficient form of heat pump system. Ground source heat pumps extract stored heat within the subsurface where temperatures may typically be 10 degrees hotter than the air at depths below 1m. High operational efficiencies can be achieved if heat pump systems are used in conjunction with underfloor heating systems.

A key area within the domestic environment where both environmental and monetary savings can be made is in water usage. Water efficient sanitary ware should be considered such as low flush volume toilet cisterns and water conserving baths to cut water consumption. Even bigger savings can be made where water is reused. A number of systems are on the market, known as greywater systems which collect and filter spent shower and bath water. This 'grey water' can then be used around the home for non potable applications, such as flushing toilets, washing cloths or to water plants. A grey water recycling system will help to reduce water bills. Alternatively natural rain water can be collected, stored and filtered for use within washing machines and toilet cisterns, this system is known as a rain water harvesting systems. A water butt, typically used for garden irrigation, represents a classic example of rain water recycling.