Biomass Fuel

Biomass is organic material derived from living, or recently living things but with regard to domestic biomass fuel it normally refers to plant-based material which can be burned to release heat energy. Biomass is carbon-based just like any other type of fuel used in central heating boilers such as gas, oil, LPG and coal.  Through the process of photosynthesis, living plants grow by using energy from the sun to absorb carbon dioxide from the atmosphere. The process of burning biomass material results in carbon dioxide emissions back into the atmosphere and produces heat energy as a by-product.  This renewable heat energy is the release of previously absorbed solar energy.

Heat energy created by burning biomass fuel is referred to as renewable, because it releases no more carbon dioxide back into the atmosphere than was absorbed by the tree or plant whilst it was alive.  Biomass energy is considered sustainable as long as new trees are planted to absorb more carbon dioxide from the atmosphere and continue the ‘biomass carbon cycle’.

Biomass fuel - biomass carbon cycle

It is important to note that if a tree was allowed to die naturally and rot away into the ground, the organic material would break down and eventually, any carbon dioxide previously absorbed whilst it was alive would be released back into the atmosphere. Converting a tree into biomass wood pellet fuel and burning it in a biomass boiler simply speeds up this natural process. The same amount of carbon dioxide is released whether the tree is converted to biomass fuel and burned, as would be if nature was allowed to take its course.

Biomass fuel – compacted wood pellets

Fuel for biomass boilers and biomass stoves can include logs, wood chips & briquettes, food & industrial waste and high energy crops such as miscanthus, willow, rape & maize but modern domestic biomass boilers are predominantly designed to use compacted wood pellets. Wood pellets used as biomass fuel for biomass boilers and stoves are generally made from 100% untreated sawdust and wood shavings which are compressed under high pressure into fairly uniformly sized small cylindrical shapes. This provides a very convenient fuel with a high calorific value and very little ash residue when burnt.

The biomass wood pellets are held together by lignin, a polymer which occurs naturally in wood and they are often a by-product of saw milling, furniture manufacture or tree surgery. Logs and wood chips retain moisture which means that they absorb more energy before combustion can take place but wood pellets have the moisture removed to allow combustion to start much faster, maximising the amount of energy released to heat your home. Because biomass wood pellets are much denser than natural wood and have a low moisture content they are a rich and compact source of combustible energy with a higher calorific value than logs, wood chips or coal.

Biomass fuel - biomass wood pellets

Accepted standard for biomass fuel

As part of Domestic RHI criteria, wood pellets biomass fuel for biomass boilers and biomass stoves must be sourced from a supplier who is on the RHI Biomass Suppliers List to ensure compliance with sustainability requirements. Random checks will be carried out to ensure compliance with RHI regulations so it is important that householders claiming RHI tariffs keep a log of fuel deliveries and copies of invoices.  This is so that Ofgem can verify that 100% biomass fuel  is being used, with no fossil fuel contamination.

The accepted standard for the quality of biomass wood pellets in the UK is known as ‘DINplus’ and has the following specification:

• It must be 100% untreated wood, with no additives
• Have a maximum length of 30 mm and be between 5 mm and 8 mm in diameter.
• Have a calorific value of at least 4.9 kilowatts per kilogram
• Have water content no greater than 10% of weight
• Create ash waste up to a maximum of 0.5% of its original weight

There is also a European standard for wood pellets used as biomass fuel: EN 14961-2, which has been agreed upon by the European Pellet Council and approved products display the following sign:

European standard for biomass fuel, wood pellets

Cost of biomass fuel

Wood pellet biomass fuel costs approximately £200 per tonne including VAT and delivery (at December 2013 prices) which equates to just over 4 pence per kilowatt hour of renewable heat energy produced.  Like all types of domestic fuel though, wood pellets for biomass boilers have been increasing in price year on year.  It is anticipated however, that as biomass boilers become more popular, especially through schemes such as the Domestic RHI, more suppliers will enter the market and economies of scale in the production of pellets should prevent vast prices increases.

The cost of heating your home with biomass fuel is comparable to using mains gas, which is much cheaper than using oil, LPG, electricity or coal. The added advantage of biomass fuel is that historically there has been no discernable increase in its cost during the colder months. Users of oil and LPG will be well aware that the price of these fossil fuels seems to rise dramatically as the temperature drops.

The following graph illustrates the cost of biomass fuel per kilowatt hour of energy produced compared to other fuels:


Biomass Suppliers List

Domestic RHI tariffs are only payable to eligible participants of the scheme who use biomass only boilers or biomass pellet stoves with integrated boilers and who source their biomass fuel from accredited suppliers from the RHI Biomass Suppliers List. This ensures that there is no fossil fuel contamination in the biomass fuel used by householders taking advantage of the scheme and rules will be introduced to ensure that all biomass fuel used can be proven to be obtained from sustainable sources.

To this effect, the Department of Energy and Climate Control (DECC) has announced that in order to ensure that recipients of RHI tariff payments comply with sustainability requirements for biomass wood pellet use, a list of accredited suppliers will be drawn up, from whom domestic participants in the scheme must source their biomass fuel. The list will be referred to as the RHI Biomass Suppliers List and it will come into force after 1st October 2014. This delay from the introduction of the Domestic RHI scheme on 9th April 2014 is to allow suppliers to monitor their processes with regard to sustainability criteria and introduce the necessary systems to demonstrate compliance. It is also to provide time for domestic installers of biomass boilers and stoves to source appropriate suppliers of biomass fuel. Participants in the Domestic RHI scheme are advised to keep a log of biomass fuel deliveries and to keep copies of invoices as Ofgem has indicated that random checks will be carried out to ensure compliance with the sustainability requirements of the RHI scheme.

Once a biomass fuel supplier has successfully registered on the RHI Biomass Suppliers List they will be permitted to label their products with a statement illustrating that their biomass fuel complies with relevant Renewable Heat Incentive sustainability criteria, of which there are two main requirements:

  1. Greenhouse gas emissions criteria (planned for Autumn 2014) – that biomass fuel used by RHI participants results in at least a 60% reduction of greenhouse gas emissions compared to the EU fossil fuel average. This equates to an emissions target of 34.8 g of carbon dioxide per megajoule (MG) of heat.
  2. Land criteria (planned for Spring 2015) – this is based on criteria about the land used to grow biomass as outlined in the UK Timber Standard for Heat and Electricity.

This means that for domestic consumers receiving RHI payments, they will need to comply with sustainability criteria and to achieve this all biomass fuel will need to be purchased from a supplier listed on the RHI Biomass Suppliers List, the only exception being where a participant in the RHI scheme produces their own biomass fuel.

Self-supply of biomass fuel

You can register on the RHI Biomass Suppliers List with Ofgem as a ‘self-supplier’ of biomass fuel if you use your own fuel from the same estate as your boiler or source fuel from your local area.  You are strongly recommended to provide evidence of your ability to self-supply biomass fuel, such as a Forestry Commission approved management plan. If you do this, and as long as your boiler is under 1 megawatt (MW) in capacity, you will not need to undertake an assessment against the sustainability criteria that commercial biomass suppliers are obliged to do. Self-suppliers of biomass fuel have to make a declaration to Ofgem that they are registered as a self-supplier as per the RHI Biomass Suppliers List compliance method and they may be audited by Ofgem.  Any self-supplier of biomass fuel who fails to stick to the criteria required by the Domestic RHI scheme may have their RHI tariff payments suspended or withdrawn altogether.

Delivery and storage of biomass fuel

Domestic deliveries of biomass wood pellet fuel are normally made by a lorry with a tail lift and the pellets are generally supplied in 10kg or 15kg bags on pallets carrying up to a tonne of fuel. For larger bulk deliveries of several tonnes, the wood pellets can be supplied loose and blown through a pipe into a fuel storage silo but this would apply more to customers such as farmers and commercial organisations with larger biomass heating systems than most domestic users would require.

Biomass wood pellet fuel to be used on a domestic scale would normally be stored in a dry shed or outbuilding which should be near enough to the road for the supplier to make a delivery but not too far from the boiler.  Otherwise you will soon tire of carrying 10kg or 15kg bags of pellets to feed your boiler.  Biomass wood pellets have a bulk density of 650 kg per cubic metre, so if you were to order a tonne of wood pellets it would take up around 1.5 cubic metres on a pallet, more space would be needed if the bags are removed and stacked separately in a shed.

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