"Alternative energy sources, such as solar power, tidal power and wind power, are often derided by critics as expensive, impractical or even (in the case of wind turbines) damaging to the environment. But there is another little-discussed alternative which can be used both as a fuel and to provide electricity.
It is widely available, easily renewable and carbon-neutral. And unlike wind and solar power, it provides energy on demand rather than intermittent energy dependent on the weather.
This revolutionary material is wood. Banish from your mind the thought of a homely log fire. Often referred to as biomass - because it is a combustible product of biological origin - wood fuel these days comes in the form of dried pellets, 15mm long and 6mm in diameter.
Pellets provide twice as much energy as wet wood - 1kg of wood pellets provides as much heat as a 1 kilowatt electric fire running for five hours. They are burned in specially adapted boilers that can be used both in ordinary homes and in large buildings to fuel central heating systems.
Widely used in Germany, Austria and Scandinavia, wood pellets have been slow to find a market in the UK. But what exactly is so good about wood? "It's a renewable fuel, because obviously you can plant more trees," says Laura Yates, a climate campaigner at Greenpeace. "And it's effectively carbon-neutral, because trees and plants suck up carbon dioxide when they grow and then emit that same amount of carbon dioxide when they're burnt."
Helped by funding from the Regional Development Agency, Nottinghamshire County Council has over the past three years replaced coal-fired boilers in 15 of its schools with wood pellet boilers. There are now plans to install them in 27 more schools, which will result in an additional reduction of carbon dioxide emissions of 3,000 tonnes a year.
Having achieved its aim, agreed with government, of reducing carbon emissions by 27% by 2006, the authority's long-term aim is to become carbon-neutral in terms of the energy it uses in buildings. It uses other renewable sources, such as wind turbines and hydro-electricity but, says energy manager Alan Allsop, "the best carbon savings per money spent come from the biomass boilers".
The amount the council spends on wood fuel has now grown so much that it has had to put the supply of wood pellets out to tender. This was won last year by the Energy Crops Company, a Surrey-based business founded in 2005. Energy crops is partnering with Biojoule, which is building a new pellet mill in Nottinghamshire that will produce 10,000 tonnes of pellets a year.
Biojoule is sourcing most of its wood from local farmers, who are growing willow, a short-rotation coppice that takes three years to grow and can then be harvested yearly. About 30% of each tree goes to make pellets; the rest is bark or made into planks. Each tree will produce about three tonnes of pellets - enough to keep 200 homes warm for a week.
The wood is broken down into sawdust and then dried, before being forced through a die to make it into pellets and then cooled and stored. A particle of wood takes about two hours to go through the whole process.
New trees will be planted to replace the ones burned, making the wood pellets a carbon-neutral source of energy. What of the cost to users? Compared with oil boilers, which cost between £1,000 and £2,000, wood pellet boilers are expensive, costing between £4,000 and £9,000. They are still cheaper than wind turbines, however - which, per unit of capacity, cost roughly 100 times as much as wood pellet boilers.
Per unit of delivered energy, wood pellets start to look more attractive. At 2.5p per kilowatt hour (kWh), wood pellets are more expensive than coal (2p per kWh) and gas (2.2p kWh) but cheaper than oil (3.5p per kWh) and electricity (6.5p per kWh). People who had previously used oil boilers can expect payback on their investment within about five years, says Graham Hilton, chief executive of Energy Crops.
Cassop School in Durham replaced its old oil boiler with a wood pellet boiler from 3GEnergi three years ago, and head teacher Jim McManners says the school has saved £2,000 a year. Apart from initial teething troubles, he says, the practicalities of using a wood pellet boiler have been no different from those involved in using an oil boiler.
There are downsides. Wood's energy density is about two-thirds that of coal, and half that of oil; you need more wood to get the same amount of energy. Regulations on oil storage, however, require that oil containers are held within a secondary containment system, such as a bund, that will hold any oil that has escaped from its container. This bund must be able to hold at least 110% of the volume of any single container in the storage area, so the storage area used to keep the wood is the same as for oil, says Hilton.
Wood pellets are often imported from Scandinavia, adding to the environmental cost, but this will be reduced as more pellets are produced in this country. Another potential drawback is that land used for growing trees could otherwise be used for crops - although, as Hilton points out, willow tends to grow on land that is unsuitable for crop growing.
Yates believes we can reduce the environmental impact further by burning wood that would otherwise end up in landfill: "We should be making sure that all forestry waste is put to use, not just left to rot because then it produces methane, which is a very potent greenhouse gas." She also advocates maximising efficiency by using wood, not only for fuel, but electricity.
Wood supplier Balcas, another Energy Crops partner, is doing just that. Based in Fermanagh, Balcas uses virgin sawdust and wood chips from its own timber processing activities to produce pellets. The pellets will be used in an onsite plant, now under construction, that will provide all its own heating and electricity needs, as well as supplying 10,000 homes in Northern Ireland.
Sourced locally or from waste timber, the case for wood as a carbon-neutral replacement for fossil fuels is compelling - and very simple. As Hilton says: "If you're not burning oil, you're not polluting the environment.""
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