Wood Pellets
Pellets consist of 100% dry (typically less than 10%) natural wood residues which are finely divided, force dried and compressed into small cylinders which easily disintegrate. These cylinders are around 10mm in diameter. They have an extremely high energy density and have better energy efficiency levels than any other fuel.
Fuel pellets also offer distinct advantages:
- Pellets are one of the cheapest fuels on the market.
- Pellets mean that you no longer have to rely on unstable fuel prices which are linked to global markets.
- Pellets offer a safe fuel supply, as they are produced using local wood residues.
- Pellets offer a consistent calorific value.
- Pellets are efficient from a storage and transportation perspective being a high bulk density per m3 than wood chip. Good quality wood pellets have a bulk density of about 600-700kg/m3 as opposed to wood chip (assuming 25% moisture content) which will have a bulk density of about 200-350kg/m3 depending on wood type.
The downside is the cost of this additional processing reflected in the wood pellet price. Check our cost comparison chart for typical current prices.
Wood Chip 
Wood harvested from many sources can be chipped to provide fuel for biomass boilers. Wood chips must be no larger than 16mm. When using wood chip, consideration must be given to moisture content, wood type, chip size as well as transport, storage and feeding systems. The efficiency of the wood is linked closely to the moisture content of the wood when it is burnt in the boiler. See our table which shows the impact of fuel moisture on thermal rating power.
The storage system for chipped wood fuel being fed into the boiler for smaller systems is known as a hopper or silo. For a larger system a fuel store room separated from the boiler room by a partition is used.
The bulk density of wood chip is about 200-350kg/m3 (assuming 25% moisture content and depending on species). Check our cost comparison chart for typical current prices.
