The CO2 that is released when wood fuel is burnt is equivalent to that taken from the atmosphere through photosynthesis during tree growth. Even allowing for CO2 generated during planting, harvesting, processing and transport of the wood, replacement of fossil fuel with wood fuel will typically reduce net CO2 emissions by over 98%, assuming that the wood is managed sustainably. Whilst wood fuel has been utilised for centuries, technological applications for its use have progressed rapidly in recent years, with Austria and the Scandinavian countries leading the way.
Wood fuel can be split into three categories; wood chips, wood pellets and logs. Woodchips arise mainly from woodland management or dedicated wood-fuel crops, such as short rotation coppice willow. They are best suited to a building or buildings with a consistent ‘24/7’ heat requirement throughout the heating season, such as schools, halls of residence, old peoples’ homes, hospitals, prisons etc., or for district heating/CHP schemes.
Wood pellets are mainly produced from untreated wood waste, such as sawdust, pulverised pallets or reclaimed timber. They are more expensive then wood chips, however, they are easier to store and handle, require less storage space and have a higher calorific value. Pellets are typically used in smaller systems, down to the domestic level, but can also be the fuel of choice in larger systems if storage or handling issues are a problem. Pellet fuelled systems are also quicker to respond than wood chip systems.
Logs are a well known fuel and tend to be used in smaller community and domestic systems. They normally require a higher manual input that pellets and chips, so are not under consideration for this site.