Introduction

Energy from biomass is produced from organic matter of recent origin. It does not include fossil fuels, which have taken millions of years to evolve. The CO2 released during the generation of energy from biomass is balanced by that absorbed during the fuel's production. This is called a carbon neutral process.

People have been producing energy from biomass for centuries, and in many parts of the world it is still the principle source of heat. However, modern technologies are far more efficient than open fires and an increasing number of fuels are now being utilised.

Biomass is often called 'bio-energy' or 'bio-fuels'. These bio-fuels are produced from organic materials, either directly from plants or indirectly from industrial, commercial, domestic or agricultural products. Bio-fuels fall into two main categories:

• Woody biomass includes forest products, untreated wood products,energy crops and short rotation coppice.
• Non-woody biomass includes animal wastes, industrial and biodegradable municipal products from food processing and high energy crops.

Fuel

For small scale domestic applications of biomass the fuel usually takes the form of wood pellets, wood chips and wood logs. We are generally familiar with wood chips and logs. Wood pellets are a compact form of wood, which have a low moisture content and a high density. Although, they are currently more expensive than logs and wood chip, they are easier to handle and ideal for automated systems.

The energy content of the fuel is related to its moisture content. High moisture will slow the combustion process, as the moisture must first boil off before the fuel can burn. The efficiency of combustion relies on as much of the carbon and hydrogen being oxidised as possible. Full combustion is also the cleanest process, leaving no partial combustion products like carbon monoxide, particulates or un-burnt volatile hydrocarbons.

Highly efficient pellet burning stoves, like the one opposite, fall into this category. Leaving very little ash.

Applications - Individual Dwellings

There are four main methods of using biomass to heat a domestic property:

• Stand alone stoves - providing space heating for a room.
• Stoves with back boilers - supplying domestic hot water and central heating.
• Ranges - used for cooking as well.
• Boilers - connected to central heating and hot water systems.