This section contains general background information about biomass and woodfuel.
When we talk about biomass for energy, what exactly are we talking about?
What is the point of using biomass for energy, rather than other fuels and energy sources? And how can we be sure we do it in a way that is sustainable and actually gives saving in greenhouse gases compared to the alternatives?
What is biomass
Biomass is biological material derived from living, or recently living organisms. In the context of biomass for energy this is often used to mean plant based material, but biomass can equally apply to both animal and vegetable derived material.
Chemical composition
Biomass is carbon based and is composed of a mixture of organic molecules containing hydrogen, usually including atoms of oxygen, often nitrogen and also small quantities of other atoms, including alkali, alkaline earth and heavy metals. These metals are often found in functional molecules such as the porphyrins which include chlorophyll which contains magnesium.
Plant material
The carbon used to construct biomass is absorbed from the atmosphere as carbon dioxide (CO2) by plant life, using energy from the sun.
Plants may subsequently be eaten by animals and thus converted into animal biomass. However the primary absorption is performed by plants.
If plant material is not eaten it is generally either broken down by micro-organisms or burned:
- If broken down it releases the carbon back to the atmosphere, mainly as either carbon dioxide (CO2) or methane (CH4), depending upon the conditions and processes involved.
- If burned the carbon is returned to the atmosphere as CO2.
These processes have happened for as long as there have been plants on Earth and is part of what is known as the carbon cycle.
Fossil fuels
Fossil fuels such as coal, oil and gas are also derived from biological material, however material that absorbed CO2 from the atmosphere many millions of years ago.
As fuels they offer high energy density, but making use of that energy involves burning the fuel, with the oxidation of the carbon to carbon dioxide and the hydrogen to water (vapour). Unless they are captured and stored, these combustion products are usually released to the atmosphere, returning carbon sequestered millions of years ago and thus contributing to increased atmospheric concentrations.
The difference between biomass and fossil fuels
The vital difference between biomass and fossil fuels is one of time scale.
Biomass takes carbon out of the atmosphere while it is growing, and returns it as it is burned. If it is managed on a sustainable basis, biomass is harvested as part of a constantly replenished crop. This is either during woodland or arboricultural management or coppicing or as part of a continuous programme of replanting with the new growth taking up CO2 from the atmosphere at the same time as it is released by combustion of the previous harvest.
This maintains a closed carbon cycle with no net increase in atmospheric CO2 levels.
Categories of biomass materials
Within this definition, biomass for energy can include a wide range of materials.
The realities of the economics mean that high value material for which there is an alternative market, such as good quality, large timber, are very unlikely to become available for energy applications. However there are huge resources of residues, co-products and waste that exist in the UK which could potentially become available, in quantity, at relatively low cost, or even negative cost where there is currently a requirement to pay for disposal.
There are five basic categories of material:
- Virgin wood, from forestry, arboricultural activities or from wood processing
- Energy crops: high yield crops grown specifically for energy applications
- Agricultural residues: residues from agriculture harvesting or processing
- Food waste, from food and drink manufacture, preparation and processing, and post-consumer waste
- Industrial waste and co-products from manufacturing and industrial processes.
Why use biomass?
Biomass is a renewable, low carbon fuel that is already widely available throughout the UK. Its production and use also brings additional environmental and social benefits. Correctly managed, biomass is a sustainable fuel that can deliver a significant reduction in net carbon emissions when compared with fossil fuels.
Benefits of using biomass as a sustainable fuel
Correctly managed, biomass is a sustainable fuel that can offer a wide range of benefits:
- Biomass is a “carbon lean” fuel producing a fraction of the Carbon emissions of fossil fuels. Click here for more details
- Biomass can be sourced locally, from within the UK, on an indefinite basis, contributing to security of supply.
- UK sourced biomass can offer local business opportunities and support the rural economy.
- The establishment of local networks of production and usage, allows financial and environmental costs of transport to be minimized. There is no region in the UK that cannot be a producer of biomass.
- The use of biomass fuel provides an economic incentive to manage woodland which improves biodiversity. click here for more details (PDF -117 kB)
- Many biomass fuels generate lower levels of such atmospheric pollutants as sulphur dioxide, that contributes to ‘acid rain’. Modern biomass combustion systems are highly sophisticated, offering combustion efficiency and emission levels comparable with the best fossil fuel boilers. See our facts and figures section for more information.
- Biomass residues, arisings, co-products and waste not used for energy, or some other application will usually rot. This will generate CO2 in any case, and may also produce methane (CH4), a greenhouse gas 21 times more potent that CO2.
More about fossil fuels and climate change
