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Glossary

The following is a short explanation of terms that are used within the bioenergy industry.  If you have any additional questions, please feel free to contact us.
 
 

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Bioenergy / biorenewable energy

A generic term covering electricity and/or heat and transport fuels derived from biomass i.e. plant material and animal residues/wastes. A wide range of biomass can be used for energy production including crops grown specifically for energy production e.g. willow, Miscanthus, oil seed rape; agricultural wastes such as straw and other crop residues; forestry residues and wastes from a range of sources including food production.

Bioethanol

A petrol substitute produced by the fermentation of organic materials (carbohydrates) such as sugar (beet) and starch (cereal crops). The current European specification for petrol (EN228) can contain up to 5% ethanol without any need to declare it.

Biodiesel

A diesel substitute or extender produced from vegetable oils or animal fats used in either unprocessed form or converted to biodiesel. The vegetable oils can come from crops such as oil seed rape or sunflowers. Diesel is sold as EN 590 which can contain a blend of 5% biodiesel. Using 100% biodiesel can cause problems with engine performance unless the vehicle has been modified for its use.

Biofuels

These are potential replacements or extenders for transport fuels such as diesel or petrol derived from petroleum-based fossils fuels. Biofuels (bioethanol and biodiesel) are produced from crops such as sugar beet, cereals, oil seed rape or re-processed vegetable oils.

Biomass

Biomass, in biological terms, is the total dry weight of all living organisms within a biological community. Biomass can be used as fuel directly by burning to generate heat and power or for the production of liquid transport fuels.

Biomass energy

Heat and/or power produced using biomass as the fuel source. Biomass fuels include fast growing energy crops such as short rotation coppice and Miscanthus; agricultural residues such as wheat straw; forestry residues; poultry litter; livestock and sewage slurry and organic municipal waste.

Bioremediation

Any process that uses plants to return a contaminated environment to its original condition.

Calorific value

The amount of heat generated by a given mass of fuel when it is completely burned. Measured in joules per kilogram or gigajoules per tonne e.g.:

Poultry litter oven dry 9Gj/t

Straw oven dry 15Gj/t

Miscanthus oven dry 16.2Gj/t

SRC oven dry 18.6Gj/t

Coal 24-28Gj/t

Carbon dioxide

(CO2) An odourless greenhouse gas produced through respiration and the decomposition of organic substances which is harmful to the environment. It contributes approximately 60% of the potential global warming effect of man made emissions of greenhouse gases world-wide. The burning of fossil fuels releases CO2 fixed by plants millions of years ago and therefore increases its concentration in the atmosphere today.

Climate Change Levy

The Climate Change Levy is a tax on energy use in industry, commerce, agriculture and the public sector – not on domestic energy use - aiming to encourage these sectors to improve energy efficiency.

Co-firing

The burning of biomass fuels with coal to reduce C02 emissions from coal-fired power stations. Biomass can be blended in differing proportions, ranging from 2% to more than 25%. The most critical factors are fuel costs and the capital cost of the modifications to the power plant to allow co-firing. Even so co-firing in existing power boilers could be one of the most economical ways to use biomass for energy on a large scale. There are also other environmental benefits such as lower sulphur emissions and around a 30% reduction in nitrous oxides.

Combined heat and power

A power station where the waste heat from electricity generation is utilised to heat buildings therefore improving the overall efficiency of the power station.

Embedded generation

Electricity generation, usually on a relatively small scale, connected to the distribution network rather than to the high voltage national grid.

Energy Crops

Crops grown specifically for use as fuel. They generally produce high yields i.e. large volumes of biomass and also have high energy potential. Energy crops are carbon neutral as the CO2 released at fuel use is equal to that taken from the atmosphere by the plants during photosynthesis. However, energy used in planting, harvesting and processing the crops must be taken into account.

Energy ratios

The units of energy used in production compared to the units of energy generated:

Willow SRC 1:30

Miscanthus 1:33

Poplar (single stem) 1:37

Wheat 1:9

OSR 1:4

Biodiesel 1:3.2

Bioethanol 1:1.3

Coal 2.8:1 (2.8 primary units of energy are used to deliver 1 unit of electricity)

Forest residues

These become available during first and intermediate thinnings and at final harvest in forestry operations and are also produced as waste during woodland management. Residues include the tops, branches and foliage which are unsuitable for most current uses but can be chipped for use as biomass fuel.

Fossil Fuels

Coal, oil and natural gas are naturally occurring fuels rich in carbon and hydrogen formed by the decomposition of prehistoric organisms. They currently provide around 66% of the world's electrical power and 95% of the world's total energy demands.

Gasification

Oxygen in the form of air, steam or pure oxygen is reacted at high temperature with biomass fuel to produce a combustible syngas, ash and tar product. Syngas can be more efficiently converted to energy such as electricity than would be possible by direct combustion of the original fuel.

Greenhouse gases

Those gases present in the atmosphere that trap heat from the sun and warm the earth. They include carbon dioxide, methane, water vapour, nitrous oxide, ozone and halocarbons.

Hectare

One hectare (ha) is equivalent to 10,000 square metres or 2.471 acres, approximately the size of a football pitch.

kWh

Kilowatt hour - a unit of energy. The energy of a 1kW device running for 1 hour or a 100W device running for 10 hour.

kWth

1000 watts of thermal power i.e. heat.

Methane

(CH4) A colourless, odourless gas formed when organic matter decomposes anaerobically. Methane is approximately 20 times more effective than carbon dioxide as a greenhouse gas. Major sources include fermentation in ruminant animals, decay of organic material in rice paddies and landfill.

Miscanthus

A perennial, high yielding C4 grass propagated by rhizomes. The rhizomes are planted in spring at densities of between 10-20,000/ha. Harvest yields will be low for the first 2 or 3 years depending on ground conditions. The stems produced (3-4m in height) during each summer are harvested the following March/April. Plantations should remain viable for at least 15 years.

MSW (Municipal Solid Waste)

The waste collected from households and other places by Local Authorities. Potentially a major source of energy.

MW ( MWe)

Megawatt - 1000kW or 1,000,000 watts of electrical power.

MWh

Megawatt hour - A 1MWe power station running for one hour will produce one MWh of electrical energy.

ODT

Oven dry tonnes i.e. the dry weight of fuel.

Pyrolysis

The thermal degradation of biomass in the absence of oxygen to produce a mixture of gaseous and liquid fuels and a solid inert residue (mainly carbon).

Renewable energy

Heat and power produced from wind, wave, tide, solar, water, geothermal and biomass sources.

Renewable Obligation Certificates

Renewable Obligation Certificates or ROCs for short is the name given to the digital certificates which hold details of exactly how a unit of electricity was made, by whom and who bought and used it. ROCs are traded separately to the actual electricity itself and work as a bonus premium on top of the price paid for the unit.

Short rotation coppice

Densely planted (15,000/ha), high yielding, specifically-bred varieties of shrub willow harvested on a 2 to 4 year cycle. SRC is a woody, perennial crop with the rootstock or stool remaining in the ground after harvest after which new shoots emerge. An SRC plantation should remain viable for 30 years.

Short rotation forestry

Fast growing trees harvested between eight and 20 years after planting. Poplar and Eucalyptus are two tree species currently being grown or trialled in the UK as SRF.

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