Biomass Fuels

Biomass, a renewable energy source, is biological material from living, or recently living organisms, such as wood, waste, (hydrogen) gas, and alcohol fuels. Biomass is commonly plant matter grown to generate electricity or produce heat.

The most conventional way in which biomass is used is by direct incineration. Forest residues, for example (such as dead trees, branches and tree stumps), yard clippings, wood chips are often used for this. However, biomass also includes plant or animal matter used for production of fibers or chemicals.

Biomass may also include biodegradable wastes that can be burnt as fuel. It excludes such organic materials as fossil fuels, which have been transformed by geological processes into substances such as coal or petroleum.

Biomass Fuel Types


Wood pellets are produced out of waste products from the timber industry. Wood shavings and sawdust pressed together to form pellets. 2.2Kg of wood pellets replaces 1 litre of fuel oil.	Grain and similar fuel crops may also be used as fuel, stored in a silo. Grain tends to clinker, however this may be reduced by adding lime to the silo. 2.5Kg of grain replaces 1 litre of fuel oil.


Wood Chip size varies from 5 to 50mm. The water contents of the woodchip should not exceed 20-25% by volume. About 15m³ of chipped conifer wood is needed to replace 1,000 litres of fuel oil, and about 11m³ if chipped hard wood.	Rapeseed cake is produced as a by-product of rapeseed oil production. Produced by cold pressing rapeseed, the cake can be either in the form of a meal or actual pellets (as shown). 1kg of cake (about 11% oil content) has an energy value of approximately 5.4 kWh/kg.

Biomass Fuel Sources

Energy Crops – robinia, willow, poplar, eucalyptus, miscanthus, sweet sorghum etc.
Clean Residues from Industry – furniture manufacturers, sawmills, timber processors, recycled timber.
Wood Wastes & Forest Residues – forest residues, primary wood processing, straw, secondary wood and textile wastes.

Biomass & Fossil Fuel Relative Costs

Fuel Comparison Table
Fuel	Fuel Price (p per unit)	Unit	Pence per kWh (after boiler efficiency)	Energy Content (kWh per unit)	CO² Emissions per kWh^*
Electricity Standard Rate	13.01	kWh	13.01 (100%)	1.00	0.617
Electricity Online Rate	10.76	kWh	10.76 (100%)	1.00	0.617
Mains Gas Standard Rate	3.89	kWh	4.32 (90%)	1.00	0.226
Mains Gas Online Rate	3.74	kWh	4.16 (90%)	1.00	0.226
Kerosene	58.41	Litre	6.62 (90%)	9.80	0.308
Gas Oil	73.58	Litre	7.86 (90%)	10.40	0.344
LPG	47.82	Litre	7.98 (90%)	6.66	0.256
Butane	102.28	Litre	14.23 (90%)	7.97	0.256
Propane	70.17	Litre	11.03 (90%)	7.07	0.256
Smokeless Fuel	40.81	Kg	8.12 (75%)	6.70	0.413
Coal	32.16	Kg	6.27 (75%)	6.85	0.413

Woodchip (30% MC)	8.0	Kg	2.5 (90%)	3.50	0.025
Wood Pellets	24.8	Kg	5.7 (90%)	4.80	0.039

Information accurate as of 26 January, 2011

^* CO² emissions (kg of CO² per kWh) - These factors are based on DEFRA's 2010 GHG
fuel conversion factors

Useful Conversion Factors

The SI unit for heat energy ( in fact all forms of energy ) is the Joule (J).

1 thermal calorie (cal) = 4.184 J
1 British thermal unit (Btu) = 1055.056 J
1 therm = 100 000 Btu = 105.5 MJ

Heat flowrate is also defined as power, with the SI unit of Watts (W)

1 W = 3.41214 Btu/h = 0.238846 cal/s
1 kWh = 3412.14 Btu/h
1,000,000 Btu/h = 293 kWh

Fuel	kWh	MJ
1 kg Wood pellets (8%)	4.80	17.00
1 l fuel oil	10.0	36.00

Fuel oil <===> Bio fuels (calculated from thermal values)

1 kg wood pellets (8%)	0.47 litre oil	1.37 kg wood chips (30%)	1.13 kg straw (15%)
1 litre fuel oil	2.91 kg wood chips (30%)	2.12 kg wood pellets (8%)	2.4 kg straw (15%)