What is wood energy?
Energy from wood can come in several forms. In the UK there are three options currently available for producing heat from wood: logs, woodchips and reconstituted fuels such as pellets and briquettes. Other options which are at the research stage include liquid fuels produced from wood and bales of compressed forest residues.
Logs and wood chips can come from forest thinnings, coppicing, tree-surgery and pruning operations - even whole trees can be chipped to provide fuel. Woodchips can also be produced from fast-growing varieties of willow and poplar which are cultivated by Short Rotation Coppicing specifically to produce energy. Wood pellets are made from highly compressed dry wood shavings and sawdust, usually from sawmilling and joinery operations.
Logs
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Log-fired heating conjures up images of open fires and logstoves for many people, but there are also sophisticated, controllable, Log Boilers available which can provide central heating and hot water. Logs are readily available in many areas where there are existing markets for domestic fuelwood. Log suppliers can be found in our suppliers list, by looking under "Firewood" in the Yellow pages or by looking up the Logpile website. Logs should be well seasoned before burning to ensure the most efficient combustion, and should ideally be stored under cover in a well ventilated logstore for a year or more.
Logs are ideal for providing heat for domestic buildings and are suitable for heating loads of up to around 50kW. Log heating systems do require manual stoking once a day, which makes logs less convenient than more automated heating systems such as woodchips and pellets. Log-fired systems are available with outputs greater than 50Kw to heat larger building such as village halls; however these larger systems will require more frequent fuelling. Further details on log heating systems and storing and seasoning logs can be found in other pages on this site.
Woodchips
The potential for woodchip heating in Scotland is enormous. The use of Scotland’s large timber resource for local woodchip heating would provide a valuable economic return and stimulate the rural economy.
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Wood chips are made from whole trees, branchwood or coppice products which have been mechanically shredded by a chipping machine. For some types of boilers, the wood needs to have been air-dried before chipping, or the chips dried before burning. Wood chips are a bulky fuel and sufficient storage and delivery access needs to be considered when designing a heating system. Transport costs can be high, but if wood chip is sourced within 20 miles it can be a very cost-effective fuel.
Woodchip systems can provide automated, clean and convenient heating for larger domestic properties with outputs of 20-30kW, up to large scale systems for hospitals, factories, schools and district heating schemes with heating loads in the megawatt range. Woodchips can also be used to fuel Combined Heat and Power Plants (CHP) in which the heat produced during electricity generation is used to provide hot water, and is not lost as in conventional power stations.
Further details on woodchips and equipment can be found in other pages on this website.
Pellets
Pellets made of compressed sawdust or woodshavings are a relative newcomer to the UK, though they have been available in much of Continental Europe for more than a decade. Because they are compressed, pellets offer a more concentrated form of fuel than wood chips. Consequently they need less storage space and are easier to handle. Their manufacture requires more energy than woodchips and the capital cost for production plant is high; pellets are therefore more expensive than chips. Scottish wood pellets are now being produced, with the first plant due to be up and running in December 2007 with others to follow.
Pellets can be used to fuel a variety of appliances and heating systems. The smallest are pellet stoves with outputs of up to around 9kW which are suitable for heating individual rooms. These stoves are electronically controlled and can deliver regulated heat output and only need fuelling once every few days. Pellet boilers are available in a wide range of outputs from small domestic scale to large industrial scale to heat schools or hospitals.
For the domestic user, pellets offer the most user-friendly form of wood heating. In Scandinavia, wood pellets are delivered by tanker and are pumped into storage silos, which feed, automatically into the boiler. This is also available from some suppliers in Scotland, although here pellets are usually supplied in plastic sacks on pallets, see our Current Woodfuel Suppliers for details.
Biofuels
Wood can be used to make both liquid and gaseous fuels. When wood is heated in the absence of air, or with a reduced air supply it is possible to produce a liquid fuel which can be used in a similar way to conventional oil fuels. It can be used to run internal combustion engines in vehicles or generators. The gas produced from wood is a mixture of hydrogen and carbon monoxide which is similar to the coal gas which was made before the arrival of natural gas from the North Sea. This wood gas can be used in internal combustion engines or in gas turbines which can be used to power generators. Although the liquid fuels are rarely produced from wood at present, wood gas is important in other countries for producing electricity in more remote areas.
Costs of woodfuel
Suppliers of woodfuel