Fuel

What is biomass?

Biomass is biological material derived from living or recently living organisms. In the context of biomass for energy, this is often means plant-based material, but biomass can also be animal-derived.

Biomass is carbon based. If it is biologically broken down, it releases the carbon back into the atmosphere, mainly as either carbon dioxide or methane. If it is burned, the carbon is returned to the atmosphere as carbon dioxide.

These processes have been happening for as long as there have been plants on Earth and are part of what is known as the carbon cycle.

Biomass is classed as a renewable energy source and it is considered to be carbon neutral, as the carbon dioxide released during combustion is balanced by that absorbed as the plants grow.

What is wood fuel?

Wood fuel falls into four different categories:

• Woodchips
• Pellets
• Logs
• Briquettes.

Woodchips
Woodchips are sourced from a wide range of sources, including forestry timber, arboricultural thinnings, coppicing waste, reclaimed timber and sawmill residue. They can be significantly cheaper than fossil fuels and are more economical if sourced locally.

Wood chips are generally 20–50 mm long and are suited to automatically fed boilers rated at 30 kWh or more. As long as they are stored dry, woodchips can be kept for several years without any deterioration in quality or loss of energy value.

Pellets
Wood pellets are mainly produced from untreated wood waste such as sawdust, pulverised pallets or reclaimed timber.

The pellets range in size from 5–40 mm in length and 5–12mm in diameter. In comparison to other wood fuels, pellets are more expensive to buy and are currently less readily available. They are, however, easy to store and handle, and they have a higher calorific value than woodchips.

Logs
Logs are the most well known and historically most used wood fuel. They are most efficiently used in closed boiler systems, which tend to be smaller-scale domestic-type systems.

Briquettes
Wood briquettes are the least common wood fuel alternative and can be used in place of logs in traditional manual feed stoves and log boilers. Briquettes are produced from clean waste wood.