BIOMASS

 

 

 

HOME PAGE

A brief introduction to microgeneration, what it is and what it can do for you and the planet

MICROGENERATION TECHNOLOGIES

An overview of different electricity and heat producing microgeneration technologies with links to further details on each

ENERGY EFFICIENCY

Before you look for ways to produce your own energy, it makes sense to minimise your energy needs.  An outline of some energy efficiency measures you can take.

Custom Search

MICRO CHP • MINI CHP • BIOMASS • HEAT PUMPS • SOLAR HOT WATER • SOLAR PHOTOVOLTAICS (PV) • MICRO WIND • MINI WIND • MICRO HYDRO

Biomass boilers burn wood pellets, chips or logs to produce heat in a central heating system.  Biomass is effectively zero carbon over its life cycle, and a typical system in a larger family home can save around 6 tonnes of CO2 annually.

Pro

Virtually zero carbon heat

Cost-effective in operation compared with gas

Cheaper to operate than other fuels in off-gas applications

Less volatile fuel prices than oil and LPG

Con

Expensive to install

Substantial space for fuel storage required

Fuel availability may be an issue in some areas

Difficult to control for smaller, lower thermal demand homes

Verdict

Ideal product for larger homes, particularly in off-gas areas

Biomass boilers burn wood-derived fuel to produce heat for a central heating system in much the same way as a gas boiler.  However, it is difficult to accurately regulate heat output and biomass boiler systems cannot be turned on and off at will, so tend to incorporate a large thermal storage tank (hot water cylinder) to act as a buffer storing heat when demand is low and providing additional capacity when demand is highest.  Efficient modern biomass boilers do not directly burn the fuel, but heat it to release combustion gas which is then burned in a second stage of the boiler.  This results in much cleaner and more effective combustion so that boilers can be installed in locations where the Clean Air Act would otherwise prohibit their use.

In all cases, there is a need for dry storage of substantial volumes of fuel which can add significantly to the cost and size of an installation.  A typical family home (20,000kWh per year heat demand) would, for example, require a total of 27m3 for a year's fuel.  The fuel can be produced from purpose grown crops, waste timber or forestry by-products and can be supplied as chips, pellets or logs:

Wood pellet boilers

Wood pellets are manufactured from wood products and as such is a consistent, high calorific (heating) value, dry fuel.  It is easier to handle and requires less storage space than other biomass fuels.  However, it is also more expensive at around 2.5p/kWh and may be difficult to obtain locally.

Wood chip boilers

Wood chip fuel is somewhat inconsistent in its calorific and moisture content and can cause severe sooting of the heat exchangers, so boilers require constant maintenance.  It tends to be used for larger installations where the lower cost (as little as 1-1.5p/kWh for bulk orders) offsets the higher maintenance costs.

Log boilers

Dry logs can have a consistently high calorific content, but require manual handling including at least daily fuelling of the boiler.  Depending on location, fuel can be relatively inexpensive.

Carbon emissions from biomass

Although biomass boilers emit CO2 when burning the fuel, it is the same amount as the original wood has absorbed during its lifetime.  Biomass can thus be considered effectively carbon neutral, the only net emissions being those resulting from the processing and transport of the fuel.  There is a widely held, but incorrect, view that if biomass fuel is transported for significant distances, it quickly becomes unviable in CO2 terms; the rule of thumb generally quoted is 25 miles for break-even.  In fact, even transporting a truckload of woodchips (22 tonnes-enough for 5 homes for a year) would only produce 400kgCO2 for a trip of 250 miles; even shipping woodchips from the other side of the planet works out at no more than 120kgCO2 per tonne of woodchip transported.  When compared with the annual CO2 savings for a biomass heating system of 4 tonnes against gas, 6 tonnes against oil and 10 tonnes against electric heating, it should be clear that the CO2 economics are not substantially reduced by transport of fuel, regardless of its source.

 

To advertise on or to sponsor this site, please email info@microchap.info

Jeremy Harrison 2008  Last update 20th November 2008