An Introduction to Biomass

After a brief sidestep into the realm of policy with last week’s Green Deal post, we turn our focus back to renewable technology. This week we are looking at biomass.


Biomass is biological matter composed of living, or recently living organisms, which can be burned or broken down by anaerobic digestion to produce energy. Examples of biomass include wood, straw, animal waste, agricultural by-products and energy crops like oilseed rape. Domestic biomass boilers usually burn logs or wood pellets, so this post will be focusing mainly on wood biomass.

Historically, heating homes with wood was the norm. Today, the practice is popular in mainland Europe and the USA. Many houses in the UK have a fireplace, although heating an entire house using biomass is less common. With the introduction of the Renewable Heat Incentive (see the policy section below) the popularity of biomass as a potentially cheap and sustainable way of heating the home is expected to increase.

So how sustainable is biomass? Burning wood or straw releases carbon stored in the plant matter over the course of its lifetime. When fossil fuels are burned, they release carbon absorbed over millions of years. The carbon released by burning biomass is converted into new plant material by photosynthesis, negating the release of the stored carbon. However, it is important to note that wood biomass is only sustainable if the forests it comes from are properly managed. There is a limit on the land area available to grow these fuels, meaning that in the future biomass will be one of several renewable energy sources used to heat our homes.


The Upside

• Biomass is much more environmentally friendly than using coal, oil or gas. Heating the average home using a wood pellet boiler rather than oil would release 10 times less carbon dioxide (CO2) every year.

• Burning logs or wood pellets is generally cheaper than using oil or electricity. If you can harvest your own wood then it will be even more cost efficient. The Energy Saving Trust estimates that replacing an electric heating system with a biomass one can save roughly £630 per year, with a CO2 saving of 7.5 tonnes per year.

• Biomass energy sources are renewable, but we must make sure that they are sustainably managed.

• There are several different types of biomass, so you can choose which one best suits your situation.

• It is possible to use biomass from local sources. This minimises carbon emissions from transportation, and also supports the local economy. Search for local wood fuel suppliers using Log Pile.

• It is easy to store wood pellets in your home, even if you live in a small house. To see an example of a wood pellet stove being used to heat a home, watch this video.

CAT's wood pellet boiler with automated feeder. To the right are our two log boilers.

The Downside

• Installing a biomass system can mean high initial costs. A simple log stove can cost around £500, with an automated wood pellet boiler costing up to £15,000.

• Biomass is a low-carbon technology, but it is not carbon neutral. The harvesting, processing and transportation of materials all contributes to CO2 emissions. Wood pellets require more processing than logs, but they have a lower moisture content so they burn more efficiently.

• It is cheaper to order fuel in bulk, but storing large amounts of  logs can be difficult in smaller homes.


The 2008 Climate Change Act is a legally binding agreement that the UK will reduce its net carbon emissions by 80% by 2050, compared to emissions in 1990. Government policies like the Green Deal and the Energy Company Obligation are all aimed at reducing the UK’s carbon output and encouraging people to embrace less carbon-positive fuel sources.

The Government’s latest scheme is the Renewable Heat Incentive. This will operate on a system similar to the Feed-in Tariffs for wind and solar energy, with householders who take up the scheme being paid for heating their homes using renewable energy. The domestic RHI has yet to be launched in the UK, although the non-domestic scheme has been in place since November 2011. The domestic RHI is expected to be launched this summer. More information can be found on the Government website.

Preceding the launch of the RHI is the RHIPP scheme (Renewable Heat Incentive Premium Payments), giving householders money towards upgrading their heating systems.

A look inside one of CAT's log burners

And did you know…

Over the past year CAT has been building a biomass teaching facility, which has just opened. Approved by HETAS – the regulatory body for biomass installers – CAT now offers Biomass for Installers (HETAS H005). Intended for experienced plumbers and engineers who want to expand into the renewable heating market, Biomass for Installers will enable those in the plumbing and heating sector to move in to the renewable energy field.

In Ofgem’s last quarterly report of 2012 it was noted that 90% of installations done as part of the non-domestic RHI were for biomass boilers. With the imminent roll-out of the domestic RHI, the number of skilled biomass installers required can only increase.


More information on biomass can be found on CAT’s info page.

  • Dear Freya,

    Even allowing for the presentation as an Introduction, this
    article does not present a balanced and comprehensive picture of the
    environmental effects of burning biomass. You simplify the issue of the biomass
    carbon balance and you credit biomass energy with completely unrealistic carbon
    savings; you don’t mention that UK demand for woody biomass is driving huge
    increases in imports and impacting on land-use in other countries; and you fail
    to mention local air pollution from biomass burning.


    You only address one of the biomass energy sectors, i.e.
    heat. The major use for biomass in this country over the next few years and
    decades is in electricity generation. Large, centralised, inefficient thermal
    power stations are planning to burn several times the UK’s harvest of wood –
    and several times the current world production of wood pellets every year. More
    on this later.


    Regarding the local air pollution impacts of burning biomass
    – there is no doubt that biomass smoke is dirty: The US EPA for example says


    “Fine particles from combustion are easily inhaled deep
    into the lungs… Scientific studies have linked particle pollution, especially
    fine particles, with …significant health problems, including: premature death
    in people with heart or lung disease; nonfatal heart attacks; irregular
    heartbeat; aggravated asthma; decreased lung function, and increased
    respiratory symptoms…. Particle pollution can cause coughing, wheezing, and
    decreased lung function even in otherwise healthy children and adults.”




    DEFRA minister Richard Benyon recently
    gave an estimate of the human health impacts of additional biomass burning
    stimulated by the Renewable Heat Incentive, i.e. for heat only, not power. He
    said, “The health impacts of particulate matter PM2.5 emissions from biomass
    combustion are expected to cost the UK £215 million in 2020”. And an
    estimate from the previous government (Jim Fitzpatrick at DEFRA) was that in
    2020 up to 1.75 million life-years could be lost as a result of increased
    particulates from biomass burning in the UK.


    And this is based on the biomass burning that would be
    eligible for the RHI – so the impacts of smoke from open wood fires and single
    room wood-burning stoves, and from power stations will be in addition.


    Returning to what’s in the article. Your viewpoint on the
    bioenergy carbon cycle is naïve: “Burning wood or straw releases carbon
    stored in the plant matter over the course of its lifetime. When fossil fuels
    are burned, they release carbon absorbed over millions of years. The carbon
    released by burning biomass is converted into new plant material by
    photosynthesis, negating the release of the stored carbon.”


    Forget where the carbon came from and look at it another
    way. Whatever you burn as fuel – fossil or bio- creates carbon dioxide
    emissions, adding to atmospheric concentrations and driving global warming. In
    this respect CO2 from wood and from coal are indistinguishable. Then the
    argument goes – biomass CO2 in the atmosphere is taken up by new plant growth.
    That argument only holds water if the new growth is additional to what would
    have happened anyway. If this sequestration does actually happen – and this
    cannot be guaranteed – it will inevitably take time. In the case of whole tree
    logging of old-growth temperate and boreal forests, it could take decades.


    The long delay before new growth sequestering enough carbon,
    and the immediate  reduction in growth when trees are felled and
    replaced with seedlings, means that a large and long-lasting pulse of CO2 is
    emitted for each kWh of biomass heat produced.


    DECC themselves have admitted that because of this, using
    whole trees to fuel production of heat or electricity is a higher carbon
    option than leaving the trees to grow in the forest, and producing the energy
    by burning fossil fuels. This is true for at least 100 years after the energy
    is produced, and DECC concludes: “The use of harvested wood from UK managed
    forests exclusively for bioenergy (replacing fossil fuels) has higher relative
    GHG emissions than leaving the trees unharvested in the forest. This means that
    on the basis of GHG emissions, there is not a strong case to produce bioenergy
    in this way.”



    In September 2011, the European Environment Agency’s
    Scientific Committee gave an important opinion
    on bioenergy on Greenhouse Gas Accounting in Relation to Bioenergy – saying


    “Several European Union energy directives encourage a
    switch from fossil fuels to renewable energy derived from plant biomass based
    on the premise that biomass combustion, regardless of the source of the
    biomass, would not result in carbon accumulation in the atmosphere. This
    mistaken assumption results in a serious accounting error. …The potential
    consequences of this bioenergy accounting error are immense. Based on the
    assumption that all burning of biomass would not add carbon to the air, several
    reports have suggested that bioenergy could or should provide 20% to 50% of the
    world’s energy needs in coming decades. Doing so would require doubling or
    tripling the total amount of plant material currently harvested from the
    planet’s land. Such an increase in harvested material would compete with other
    needs, such as providing food for a growing population, and would place
    enormous pressures on the Earth’s land-based ecosystems.”


    Unmoved by these rational and scientifically based carbon
    balance arguments, the UK Govt is pressing ahead with large-scale bioenergy in
    order to meet the EU 2020 target for renewable energy as cheaply as possible.
    Under EU legislation, bioenergy is currently classified as renewable energy,
    even though the combustion emissions are not accounted for.  Member states are therefore allowed under
    the EU Renewable Energy Directive to give subsidies for biomass burning for
    heat (UK’s RHI), and for power (UK’s Renewable Obligation).


    To that end, DECC recently confirmed that higher levels of
    subsidies will be granted for biomass conversion of existing coal-fired power
    stations with Gigawatts of capacity, as well as continuing to subsidise biomass
    electricity from new dedicated biomass power stations. These will consume many
    millions of tonnes of imported biomass every year: estimates put the figures as
    high as 30 million tonnes of wood pellets just for the big coal power stations
    that are converting: Drax, Eggborough, Ironbridge, Lynemouth and Tilbury. As
    context – total UK ‘green’ wood production for all purposes is around ten
    million tonnes per year, and total global wood pellet production was just 14
    million tonnes in 2010.


    The power station operators who burn wood will be heavily
    subsidised from consumers’ electricity bills. Drax will get an estimated
    minimum of £600 million per year from Renewable Obligation Certificates, and
    will avoid the need to invest in expensive sulphur dioxide abatement systems
    needed to meet tightening EU pollution limits.


    The government has developed a series of “sustainability
    standards” which are supposedly will ensure that subsidised biomass can be
    sourced sustainably. The standards themselves are sorely inadequate in that
    they fail to account for greenhouse gas emissions properly and lack any credible
    auditing or verification – but most importantly, the key reason why big biomass
    will be unsustainable is that it is being deployed on a completely
    unsustainable scale. The sustainability standards only really serve to
    legitimise the expansion of the industry.


    The UK expects to have to import at least 80% of the biomass
    burned in UK power stations, and although the biomass industry is still in the
    infancy, the pressure of demand for wood is already being felt across the


    Global forest cover is already in dramatic decline – a
    decline masked by statistics which falsely classify monoculture tree
    plantations as forests.  The excessive
    demand for wood and wood products, especially for paper, in the global North
    has been the major underlying cause of forest destruction; large-scale biomass
    developments will aggravate the problem.


    In Canada, new demand for biomass is going hand in hand with
    greatly increased logging quota and licenses, leading to biodiverse old-growth
    forests being destroyed at an ever faster rate and threatening the overall
    well-being of forest ecosystems, with exports to Europe having risen by 700% in
    8 years.


    The Southern US which contains some of the most rich and
    biodiverse temperate forests in the world is already the world’s leading
    exporter of wood pellets to Europe. New demand for biomass for European
    markets, coupled with existing pressures on those forests from the paper
    industry and the US’ own biomass targets, spells disaster for the forests of
    the region as industries compete for the woody resource.


    In the longer term, energy companies expect to rely on new
    plantations of fast-growing trees in tropical regions such as Brazil.  One of the first such investments is by pulp
    and paper company  Suzano Papel which is
    developing new large scale eucalyptus monocultures specifically for use as
    biomass , having entered into a supply agreement with UK energy firm MGT
    Power.  Such plantations are heavily
    dependent on the use of chemical fertilisers and pesticides and they are being
    established at the expense of local communities who lose their land,
    livelihoods and access to fresh water as a result.





    Tackling climate change effectively is becoming increasingly
    urgent. Energy consumption and production are key areas to address. But we are
    deluding ourselves if we think that burning ever more carbon-based bio material
    will help drive down emissions in the short term. When you add in the local
    human health impacts from more air pollution, and the unwarranted extra
    pressure on lands and people in overseas countries, industrial scale bioenergy
    is a dangerous distraction


    We simply can’t maintain business as usual by simply
    converting from fossil to biological carbon – running cars on biofuels,
    packaging stuff in bioplastics, dousing ourselves and the planet with
    biochemicals, treating subsequent illnesses with bio-pharmaceuticals. That will
    require several planet’s worth of land, water, soil and nutrients.


    campaigns to raise awareness of the issues posed by industrial bioenergy and to
    reverse the policies which promote it. We believe “that bioenergy is a
    false solution to climate change – it adds to the debt that we today are
    leaving future generations by supporting the idea that current consumption
    levels of energy and material can continue while ever-more techo fixes are


    See also:






  • Thanks for this very thorough analysis, Robert. Could the Zero Carbon Britain energy researchers please comment and say how in the light of this they are modifying the dangerous over reliance on biomass of previous ZCBs. An analysis of how wood wastes could be used in insulation to remove the need to burn them for heat would be a really useful contribution to the debate. I would be keen to help on this having insulated the outside of my house with 180mm of ‘biomass’ to avoid needing to burn the stuff inside.


  • Frankie Thomas

    there are a lot of benefits from biomass heating, you can save a lot of money by making the change.