One of the major advantages of biomass installations is
that they can achieve significant reductions in emissions of carbon
dioxide (CO2).
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