Biofuel isn't the only renewable energy option as you'll see below. It is one in a mix of solutions that may help us to stop damage to our environment through our energy use.
The information below is courtesty of The Rewewable Energy Association. The Renewable Energy Association was established in 2001 to represent British renewable energy producers and promote the use of sustainable energy in the UK. Your own country should have its own equivalent - check the internet or local library for more information.
biogas
Biogas is a mixture comprising mainly methane and carbon dioxide. It is produced when organic matter decomposes in the abscence of oxygen. This can take place in a landfill site to give landfill gas or in an anaerobic digester to give biogas. Sewage gas is biogas produced by the digestion of sewage sludge.
landfill gas
Landfill gas is a mixture comprising mainly methane and carbon dioxide, formed when biodegradable wastes break down within a landfill as a result of anaerobic microbiological action. The biogas can be collected by drilling wells into the waste and extracting it as it is formed. It can then be used in an engine or turbine for power generation, or used to provide heat for industrial processes situated near the landfill site, such as in a brickworks. Landfill sites can generate commercial quantities of landfill gas for up to 30 years after wastes have been deposited. Recovering this gas and using it as a fuel not only ensures the continued safety of the site after landfilling has finished, but also provides a significant long term income from power and/or heat sales.
anaerobic digestion
The biological processes that take place in a landfill site can be harnessed in a specially designed vessel known as an anaerobic digester to accelerate the decomposition of wastes. Anaerobic digestion is typically used on wet wastes, such as sewage sludge or animal slurries but the biodegradable fraction of municipal wastes can be added to wetter wastes to increase the biogas output.
energy from waste
Wastes represent an increasingly important fuel source. Using wastes as fuel can have important environmental benefits. It can provide a safe and cost-effective disposal options for wastes that could otherwise present significant disposal problems. It can help reduce CO2 emissions, through displacement of fossil fuels. Methane is 23 times more damaging than CO2 for global warming. If biodegradable waste is diverted from landfill methane emissions can be avoided.
Any energy that is recovered from biological wastes can be regarded as renewable energy. It comes from plant material (either directly, or in the case of animal wastes, paper or card, indirectly). As plants grow they absorb carbon dioxide from the atmosphere. When this biomass material is used as a fuel, the carbon dioxide is returned to the atmosphere in a "carbon neutral" cycle. If biomass is used to displace fossil fuels instead of being left to decompose naturally, it will actually help to limit the emission of carbon dioxide and methane into the air.
There are many ways of combining waste disposal with energy recovery. A number of well established technologies are available for generating heat or power from wastes. There are also new technological developments, especially in power generation, which have the potential to increase the efficiency of energy recovery.
Recovering energy from wastes from municipal or industrial sources can turn the problem of waste disposal into an opportunity for generating income from heat or power sales. The safe and cost-effective disposal of these wastes is becoming increasingly important worldwide, especially with the demand for higher environmental standards of waste disposal and the pressure on municipalities to minimise the quantities of waste generated and disposed to land.
The technology
A very wide range of municipal or industrial wastes may be used as fuel. The nature of the waste and the waste disposal method will determine the way that energy can be recovered. Dry household, commercial or industrial wastes can either be burned (combusted) as raw waste, or they may first undergo some sorting or processing to remove waste components that can be recycled separately.
fuel cell, hydrogen, batteries
With Fossil Fuels projected to run out within the next century, the world is in need of a permanent replacement fuel. In addition, pollution is becoming an ever-increasing problem. What the world needs is a non-polluting inexhaustible fuel supply. Hydrogen encompasses approximately 70 % of the mass of the universe. When burned in air, or used within a Fuel Cell, water is the only waste product.
solar energy
Photovoltaics
The suns energy can be converted directly into electricity using photovoltaic cells. PV cells can be used for applications as small as watches and calculators, to large grid-connected arrays of panels. The great attraction of PV technology is that it delivers electricity at the point of use, for example panels can be integrated into buildings to supply the buildings themselves.
In areas where grid connection or other forms of generation are too expensive or not feasible, PV can be very cost-effective. This may be in remote locations, but could also be in a city centre where grid connection may be impractical. For example it can be cheaper to power parking meters with solar energy than with power from the grid.
PV materials are usually solid-state semiconductors. various forms are used:-
mono-crystalline silicon (crystalline)
Poly-crystalline silicon (crystalline)
amorphous silicon (thin film)
cadmium telluride (thin film).
Active solar thermal
Active solar heating systems convert solar radiation into heat which can be used directly. In the UK uses are primarily domestic water heating and other low temperature heating applications such as swimming pools. In hotter climates a wider range of applications is possible, including electricity generation.
Domestic water heating schemes consist of solar collectors, (usually) a preheat tank, pump, control unit, connecting pipes, the normal hot water tank, and backup heat source such as gas or electric immersion heater. The collectors are mounted on the roof and heat the water tank via a fluid circulated between the collectors and the tank. The overall area of the panels is typically 3-4 square metres.
hydro power
Hydro power is produced when the kinetic energy of flowing water, is converted into electricity by a turbine connected to an electricity generator.
Hydropower can be exploited at various different scales. Large-scale is typically taken to mean more than 20 MW of grid-connected generating capacity and is usually associated with a dam and a storage reservoir. There are many large schemes in Scotland, which were built during the 1950s. The potential for identifying new large-scale schemes is now more limited, not only because there are fewer commercially attractive sites still available, but also because of environmental constraints.
Schemes of less than 20 MW now offer a greater opportunity for providing a reliable, flexible, and cost-competitive power source with minimal environmental impacts. These small-scale schemes are making an increasing contribution towards new renewable energy installations in many regions of the world, especially in rural or remote regions where other conventional sources of power are less readily available. Small scale schemes can be associated with a dam and storage reservoir or can be located in a moving stream ("run of river").
Tidal Power
Tidal power can use either conventional or new technology to extract energy from a tidal stream. It is usually deployed in areas where there is a high tidal range. Typically a barrage with turbines is built across an estuary or a bay. As the tide ebbs and rises, it creates a height differential between the inner and outer walls of the barrage. Water can then flow through the turbines and drive generators. Some tidal barrages operate on both the rising and falling tide, but others, particularly estuarine barrages, are designed to operate purely on the falling tide.
It is also possible to make use of the tidal flow that occurs between headlands and islands or in and out of estuaries. It is this application that is the focus of much research and development, and new products for this purpose are now being commercialised. These “in-flow” tidal turbines can be arranged singly or in arrays, allowing a range of power outputs to be produced.
Wave Power
The power of the waves is readily visible on nearly every ocean shore in the world. There has been much research to harness the power of these waves, and various machines have now been developed. These fall broadly into three categories:
Machines which channel waves into constricted chambers. As the waves flow in and out of the chamber, they force air in and out of the chamber. These airflows are in turn channelled through a specialised turbine, which is used to drive a generator. This type of machine is principally designed for use on or near the shore, or for incorporation into breakwaters. Commercially, this kind of machine is the most advanced and is particularly advantageous when incorporated into coastal protection.
Fixed or semi-fixed machines which utilise the pressure differential in the water that occurs at a submerged point as the wave passes over that point. The pressure differential is used by a variety of means to cause a fluid to flow in a circuit, which is then used to drive a turbine and generator.
Machines which utilise their buoyancy to cause movement in a part of the device as it moves up and down in the wave. The movement is used either directly or indirectly to drive a generator.
wind
Wind energy has been harnessed for over 6000 years, first for powering boats, windmills and wind pumps, and now for generating electricity. Modern wind equipment ranges from small water pumps and chargers (used to charge batteries at remote locations) to large multi-megawatt wind turbines arranged in wind farms that supply power to the electricity grid.
World-wide, there over 25,000MW of installed capacity, mostly in Europe and the USA.
Wind power equipment has been developed to provide a range of power outputs, from under 100W up to 3MW. The overall reliability of wind turbines is high - 97-99% availability is standard for modern turbines - and modern machines are designed to have a useful life of about 25 years. Turbines can have fixed or variable speed rotors, can be pitch or stall regulated, or in the case of small turbines can have furling rotor blades. When used for electricity generation, turbines can generate either direct or alternating current. The flexibility of design of individual turbine components means that machines can be matched to areas with high, medium or low average wind speeds, from the Arctic to the Sahara, and from mountain tops to locations out to sea.
Within the design parameters necessary for conditions at any individual site, the size of turbine required will depend on the type of application:
Large-scale, grid-connected electricity generation
This requires a number of large turbines grouped together on one site to form a wind farm or wind park, either on- or off-shore. The power from the individual turbines is aggregated at a central point before it is fed through a power line to the point where it connects with the national grid. It usually passes through a transformer at the central point to match the voltage to that of the grid. The central point usually doubles as a command point, where computerised equipment can be installed to allow the remote control of the wind farm. This is particularly important for remote and off-shore wind farms, where adverse weather may prevent access for long periods of time.
Small-scale, grid-connected electricity generation
Where electricity grids are unable to accommodate large amounts of generation, typically in remote areas, it is still possible to deploy individual turbines or small clusters of turbines of varying sizes. Frequently the grids in these areas are at relatively low voltage in which case the installations are designed to connect directly into the grid with little or no additional voltage transformation. Where the grid is an isolated grid (not connected to the main national or regional grid), the wind turbines are usually run in conjunction with another form of generation, typically diesel (see hybrid systems below).
Stand-alone generation
Applications for stand alone wind power are more varied. They may be as small as a charger used to charge the batteries on an ocean-going yacht, or megawatt-size turbines used for powering a desalination plant on an arid coastline. The use of solitary wind pumps feeding water tanks has been a familiar sight in much of the world for over 150 years.
Hybrid Systems
Wind power is also very suitable for incorporation into hybrid systems. These offer flexibility, because they can provide power even when the wind is not blowing. Wind-diesel combinations are common, but more recent developments include wind-photovoltaic units, a hybrid option which offers power generation from 100% renewable sources.
Author: ArchitectPage
