Reducing greenhouse gas emissions

All energy generation emits some CO2. This includes renewable and non-renewable energy sources. For example, conventional heating systems which consume heating oil emit greenhouse gases directly as a consequence of the combustion of the oil. Additionally, indirect greenhouse emissions arise for all other aspects of the complete life cycle of any oil heating system, mainly as a result of fossil fuels being used in fuel extraction, processing and transportation, as well as the manufacture, installation and eventual decommissioning of equipment, plant and machinery.

Wood fuel is low carbon

These considerations also apply to biomass installations. Direct emissions, in the form of CH4 and N2O, arise from the combustion of wood fuel. However, whilst CO2 emissions also occur, an equal amount of this particular greenhouse gas will have been absorbed during the growth of the trees that provide the wood fuel. Hence, in this regard, wood biomass heating systems are often referred to as being 'carbon neutral', although technically this should really be 'low carbon'.

The Supergen 'Bioenergy: a graphic novel' has a very useful explanation of whether bioenergy helps us avoid climate change and what is really meant by 'carbon neutral'.

There are numerous studies on the levels of carbon savings that can be achieved by biomass heating projects.  The graph featured below is typical and illustrates the grammes of CO2 emitted per kWh of energy supplied from a variety of sources.

Levels of CO2 emitted from a variety of sources

Whilst wood fuels can deliver carbon savings compared to fossil fuels it is equally important to note they usually deliver better carbon savings compared to other forms of renewable energy as well. Here are some figures for commonly used renewable energy technologies:

• Ground Source Heat Pumps - 123g/kWh
• Wind -  48g/kWh
• Solar PV - 105g/kWh to 190g/kWh

This compares to wood fuels - 25g/kWh to 97g/kWh