Biomass is the name given to any material which is recently derived from plants that use sunlight to grow, such as wood from forests, material left over from agricultural and forestry processes, and organic industrial, human and animal material. It is sometimes classified as ‘combustible renewables and waste’.
The energy contained in biomass originally came from the sun. Through photosynthesis carbon dioxide in the air is transformed into other carbon containing molecules (e.g. sugars, starches and cellulose) in plants. The chemical energy that is stored in plants and animals (animals eat plants or other animals) or in their waste is called bio-energy.
When biomass is burned it releases its energy, generally in the form of heat. The biomass carbon reacts with oxygen in the air to form carbon dioxide. If fully combusted the amount of carbon dioxide produced is equal to the amount which was absorbed from the air while the plant was growing.
In nature, if biomass is left lying around on the ground it will break down over a long period of time, releasing carbon dioxide and its store of energy slowly. By burning biomass its store of energy is released quickly and often in a useful way. So converting biomass into useful energy imitates the natural processes but at a faster rate.
Provided biomass is not used faster than it can be produced, the energy obtained from biomass is considered a form of renewable energy. Using biomass energy means that the total amount of carbon dioxide in the environment stays reasonably constant, unlike burning fossil fuels which increases the amount of carbon dioxide in the air. Of all the existing renewable energy sources, biomass is the only one that stores solar energy as a convenient solid, liquid or gaseous fuel.
Many crops that are grown for food can also be used to make biofuels. Corn, sugar cane and sugar beet are used to make ethanol because of their high sucrose content. Tiny organisms feed off the sucrose and convert it to a form of alcohol called ethanol. Ethanol is a flammable liquid that can be used to run cars or be added to petrol.
Other crops are processed for their oils, to be used as a fuel. This includes a wide variety of seed crops like linseed, rapeseed, soy bean and jojoba. These oils are used as biodiesel in engines.
Another way of getting energy from plants is by capturing the gases produced as the plant matter decomposes. As plants decay, microbes that live on the decomposing material give off methane gas. If this gas can be collected it can be used as a fuel.
Rubbish dumps, containing such things as household waste or kitchen scraps, produce methane gas. Some local councils collect this gas and burn it to generate electricity that is fed back into the grid. One council uses the gas from an old tip to help heat the local swimming pool.
Capturing methane gas is also very important as it is very a potent greenhouse gas. When methane gas is burned for energy, the CO2 created has less greenhouse impact plus we get to use the power created. Methane is 21 times worse than CO2 for its greenhouse gases content, so converting methane into CO2 is a good thing.