Green Energy > Biomass

Burning wood for energy is carbon-friendly and efficient.

Biomass refers to non-fossil organic matter that can be used to produce energy. Wood, crops and grasses, as well as animal and food waste are prime examples. Biomass can be converted to different forms of energy – including heat, power,combined heat and power (CHP) or liquid biofuels – through processes such as direct combustion, anaerobic digestion and fermentation.
On a domestic level, biomass refers primarily to wood fuel. Wood is a great natural source of energy that can be managed sustainably and has served humans well for thousands of years. Modern wood burning technology is much more efficient than the days of open fires and hearths, and is able to convert up to 90% of the energy in wood into heat. Open fires only manage to use around 20% of this energy.

Large-scale facilities, such as apartment blocks or factories, use large wood-fired boilers to produce heat on a grand scale. For example, a medium density fibreboard (MDF) plant in County Tipperary uses a 19 megawatt wood-burning furnace to burn its waste wood and supply heat to the facility. In a domestic setting, smaller-scale wood-burning stoves are more common.

Wood fuel on a domestic level is available as wood pellets or logs. Most modern equipment is designed to burn pellets, which is derived from wood waste, such as sawdust and small timber pieces, left over from industrial processes. Pellets are easier to transport and handle than logs, take up less storage space, and can be fed automatically into the boiler or stove.

Pellet stoves generally achieve efficiencies of around 80%. They work as standalone systems or can be fitted with back boilers to provide hot water and heating. Pellet boilers can also be fed automatically and are plumbed into the LPHW (Low Pressure Hot Water) circuit of a house to provide heat to radiators and the hot water cylinder. Pellet boilers can be up to 90% efficient.

Logs can be sourced sustainably from properly managed forests and short rotation coppice (e.g. willow). They demand a lot of storage space and are more readily available in rural locations than in the midst of towns and cities. Log stoves rely on manual feeding, which can be more troublesome and messy.

Like pellet stoves, log stoves can produce standalone heat or be fitted with a back boiler to provide hot water and heating. Modern log stoves are clean burning, producing less smoke than in days gone by. They’re not quite as efficient as pellet stoves, achieving efficiencies in the region of 70%. Log boilers work like pellet boilers to produce hot water and radiator heating.

The cost of a log or pellet boiler depends upon the size and type of system. A  typical biomass pellet stove will cost around £4,300 including installation. Installing a new log stove will usually cost less than half this, including a new flue or chimney lining. For boilers, an automatically fed pellet boiler for an average home costs between £14,000 and £19,000, including installation, flue, fuel store and VAT at 5%. Manually fed log boiler systems can be slightly cheaper.

There’s also the associated cost of the fuel. If the energy being replaced is LPG (Liquefied Petroleum Gas) or electricity then there are definite savings to be made. The economic benefit is diluted when comparing wood to gas.

However, wood fuel is kinder to the environment. It’s classed as carbon neutral because the CO2 that’s released when the wood is burned is equal to the CO2 that the wood absorbed during its lifetime. The transporting of the wood fuel ups the emission count somewhat, but there are beneficial knock-on effects elsewhere.

Demand for wood fuel stimulates jobs in the countryside. The use of farmland for fuel cultivation is less intensive than other crops, and helps natural habitats to thrive. People become more aware of how much energy they are using when they have to buy and take delivery of their fuel source, which can lead to them reducing their energy use. Burning wood can also help to divert waste from landfill.

A report from Sustainable Energy Ireland pointed out that the potential annual yield of wood in Ireland is almost three times that of Finland, where the energy use from biomass is 18%. In fact, wood supplies could be sufficient to meet 14% of the country’s total primary energy supply by 2010. Wood fuelled boilers might be expensive to buy and install right now, but if that situation changes the outlook for biomass on a domestic scale is healthy.