8 types of Renewable energy (part 2)

Bio-fuel & Biomass Biogas
Distributed/Embedded Generation Fuel Cell/ Hydrogen / Batteries
Energy from Waste Solar
Water (hydro, Tidal, wave) Wind

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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.

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. These factors combine to present Hydrogen as the ultimate long-term global energy solution...



The sun’s 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.

A plane inclined at about 30 degrees, facing due south ranges from around 900 KWh/m2 per year in the North of Scotland to around 1,250 kWh/m2 in the South West of England.

The optimum angle for a south facing collector is 0.9 multiplied by the latitude + 29°. This maximises winter collection and reduces over-production in the summer. The optimum angle of tilt for the spring and autumn is the latitude minus 2.5°. The optimum angle for summer is 52.5° less than the winter angle.


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.



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