Renewable Energy Sources

Fast Growing Biomass

This is plant material obtained from fast-growing trees or plants

Willow trees are fast-growing British plants

In warmer countries the giant grass Miscanthus is used

Energy is obtained by harvesting the plants and burning them - either domestically or in power stations

These plants are less polluting than burning fossil fuels because the carbon dioxide released in their combustion is equal to the carbon dioxide they absorbed in their short lifetime. There is therefore no net addition to the pool of carbon dioxide (as there is with fossil fuels)

However these plants contain much less energy per unit mass than does coal so very large areas need to planted

Because there is less energy per unit mass transport costs per unit energy are higher (and transportation does result in an increased release of carbon dioxide) 

Gasohol from sugar

Oil (in the form of petrol) as a fuel source can be replaced by a mixture of oil and ethanol.

Ethanol can be obtained from the fermentation of plants high in sucrose (such as sugar cane) by  anaerobic fermentation by Saccharomyces

Advantages – as for fast growing biomass

Disadvantages – transport costs high, growing and fermenting costs high

Biogas from domestic and agricultural wastes

Biogas is methane produced by the fermentation of domestic and agricultural waste

Aerobic bacteria break down organic materials to simple molecules (monosaccharides, fatty acids etc) and use up the available oxygen

Anaerobic bacteria then convert the fatty acids to methane

 Reactors are usually simple, small scale and sited where the fuel is to be used

 Advantages: cheap because organic waste is in plentiful supply and there are no transport costs

As before there is no net production of carbon dioxide over that absorbed by the plant materials used

Disadvantage: the waste materials are low in energy so to scale up the process to an industrial level would require the transportation of huge quantities of material. This would be prohibitively costly.

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