RENEWABLE ENERGY TECHNOLOGIES

 

 

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Energy from Biomass

Another way in which solar energy becomes available for us to use is through green plants.  The sun is the energy source which powers photosynthesis and every year plants are creating new matter - biomass - using energy equivalent to ten times our total human requirements.  Although we might only be able to extract a fraction of this for our own use, plants still represent a major source of energy and biomass currently provides about one seventh of the world's energy.

In developing countries, biomass in the form of wood or dung accounts for over 40% of all fuel burnt, and in some countries it provides over 90%.  It is the main source of fuel for about half the world's population.  4% of the USA's energy also comes from biomass (about the same amount as generated by nuclear or hydro power).  However, it is argued that in many areas, fuel wood cannot be considered a "renewable" energy source because supplies are not being sustained.

Improvements can also be made in the ways that wood is used.  Open fires burn at 20% efficiency whilst a well designed woodstove can raise this to as much as 80%.  Large scale wood combustion plants can also be used to provide both heat and electricity.  Wood, and other plant materials, can also be processed to widen their use as fuels or to make them more economic to transport.

Charcoal is made by burning wood slowly in limited oxygen.  The process is inefficient and wasteful but the end product is much lighter than wood, burns easily at a higher temperature and produces less ash.  This has made charcoal an extremely important fuel in developing countries, especially in the urban areas.

The sun's power can also be used to convert plant crops into transport fuels.  In Brazil, no fewer than two million vehicles run on alcohol produced by fermenting sugar cane.  A further eight million cars run on a mixture of alcohol and unleaded petrol.  Brazil hopes to become self-sufficient in automobile fuels by using just 4% of its land area to grow energy crops.

Other plants, such as sunflowers and Soya, produce natural oils which are extracted and used as cooking oil and in human and animal foodstuffs.  Perhaps more surprising is that diesel engines can be made to run on vegetable oils, and that the sunflower crops from one field can produce enough fuel for a tractor ploughing ten fields the same size.  Perhaps sunflowers and other oil producing plants will become the "oil fields" of the future ....?

Until recently, plumes of smoke rising above newly harvested fields were a familiar sight as cereal farmers disposed of some 6 million tons of unwanted straw every year by the most cost effective means ... putting a match to it.  This practice has now been stopped and new uses are having to be developed.  It's ironic that commercially generated electricity is supplied to a farm to power crop driers while back in the field, a primary energy source is going up in smoke!

One alternative is small scale straw-burning furnaces which can use about 20 tons of straw each year and produce heat for space heating or crop drying.

Methane is also produced by decomposing material on landfill sites and this can also be tapped and used as an energy source.

 

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