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Biomass Energy Conversion Factors

This list of conversion factors and data was developed by Dr. Jonathan Scurlock of North East Community Forests, originally for the United States Department of Energy Bioenergy Feedstock Development Program at Oak Ridge National Laboratory (ORNL). It was compiled from a wide range of sources, and was designed to be concise and convenient rather than all-inclusive. Most conversion factors and data are given to 3 significant figures or less. Users are encouraged to consult other original sources for independent verification of these numbers. See also the following links to other measurement conversion Web sites (many universities worldwide maintain good guides and conversion calculator pages):

Energy contents are expressed here as Lower Heating Value (LHV - also known as "net CV" or net calorific value) unless otherwise stated (this is closest to the actual energy yield in most cases). Higher Heating Value (HHV, including condensation of combustion products - also known as "gross CV" or gross calorific value) is greater by between 5% (in the case of coal) and 10% (for natural gas), depending mainly on the hydrogen content of the fuel. For most biomass feedstocks this difference appears to be 6-7%. The appropriateness of using LHV or HHV when comparing fuels, calculating thermal efficiencies, etc. really depends upon the application. For stationary combustion where exhaust gases are cooled before discharging (e.g. certain power stations using condensed gases for pre-heat), HHV may be more appropriate. Where little or no attempt is made to extract useful work from hot exhaust gases (e.g. motor vehicles, small heating boilers), LHV is more suitable. In practice, many European publications report LHV, whereas North American publications use HHV.

  "Frequently Asked" biomass energy statistics and equivalents

  • Metric tonne wood fuel (bone dry) = 18 GJ (gigajoules) = 5 MWh (megawatt-hours of heat) = 500 litres heating oil or >500 m3 natural gas
  • Tonne wood fuel (air-dry, 35% moisture) = 3 MWh (about 11 GJ)
  • Tonne wood chip (from bone dry to 50% moisture) = about 3 to 4 m3 (this ratio does not vary much with moisture) - therefore 1.0 cubic metre of almost any wood chip = about 1.0 MWh (3.6 GJ)
  • Energy content of a barrel of oil = approx. 6.1 GJ or 1.7 MWh, equivalent to 1.7 m3 wood chip or 0.5 m3 (0.34 tonnes) solid bone-dry wood
  • Typical UK household energy use = 25 MWh/year, of which electricity = 5 MWh/year, lighting = 1 MWh/year
  • UK household heating and hot water use = 20 MWh/year (72 GJ) = 2000 litres/year heating oil (releasing 1.5 tonnes carbon to the atmosphere) = 4 tonnes bone-dry wood (around 7 tonnes air-dry, or 12-16 m3 wood chip), roughly the content of 10 large spruce trees (releasing no carbon to the atmosphere after re-growth)

  Energy units

Quantities

  • 1.0 joule (J) = one Newton applied over a distance of one meter (= 1 kg m2/s2).
  • 1.0 joule = 0.239 calories (cal)
  • 1.0 calorie = 4.187 J
  • 1.0 gigajoule (GJ) = 109 joules = 0.948 million Btu = 239 million calories = 278 kWh
  • 1.0 kilowatt-hour (kWh) = 3.6 megajoules (MJ) = 3413 Btu
  • 1.0 British thermal unit (Btu) = 1055 joules (1.055 kJ)
  • Therm (of natural gas, methane) = 100,000 Btu (= 105.5 MJ)

Power Output

  • 1.0 watt = 1.0 joule/second = 3.413 Btu/hr
  • 1.0 kilowatt (kW) = 3413 Btu/hr = 1.341 horsepower
    • for example, a 60,000 Btu/hr heating boiler = 17.6 kW
    • a 30 kW boiler is equivalent to 102,000 Btu/hr

Energy Costs

  • £1.00/GJ = 0.36p/kWh = £1.06 per million Btu (10.6 p/therm)
  • 1.0 p/kWh = £2.77/GJ = £2.93/million Btu (29.3 p/therm)
    • thus heating oil @ 30p/litre and 36 MJ/l = £8.33/GJ or 3p/kWh
    • wood fuel @ £50/tonne and 11 GJ/t = £4.55/GJ or 1.6p/kWh

  Other common units of measure

  • Metric tonne (tonne) = 1000 kilograms = 2205 pounds
  • Imperial ton (long ton or shipping ton) = 2240 pounds
  • United States ton (US ton or short ton) = 2000 pounds
  • Imperial gallon = 4.55 litre = 1.20 US gallon
  • US gallon = 3.79 litre = 0.833 Imperial gallon
  • Litre = 0.264 US gallon = 0.220 Imperial gallon

  Areas and crop/forestry yields

  • Hectare = 10,000 m2 (an area 100 m x 100 m, or 328 x 328 ft) = 2.47 acres
  • km2 = 100 hectares = 247 acres
  • Acre = 0.405 hectares
  • Imperial ton/acre = 2.51 tonne/ha
  • Metric tonne/hectare = 100 g/m2 = 0.4 Imperial ton/acre
    • for example, a crop yield of 4 tons/acre = 10 tonnes/hectare (1000 g/m2)

  Wood and other biomass fuels

Definitions

  • Roundwood: any section of the stem or the thicker branches of a tree of commercial value that has been felled or cut but has not been processed beyond removing the limbs or bark
  • Small Roundwood: roundwood about 7 to 14 cm (3 to 5.5 inches) in diameter, too small for sawmill processing, and therefore available for wood fuel, paper pulping or chipboard manufacture
  • Cordwood: an American term for roundwood, generally after harvested timber has been stacked in a cord (see below)
  • Cord (US terminology): a stack of wood comprising 128 cubic feet (3.62 m3); standard dimensions are 4 x 4 x 8 feet, including air space and bark. One cord contains roughly 1.1 oven-dry tonnes (2400 pounds) of timber

Solid fuels

  • Metric tonne wood = 1.4 cubic meters (solid wood, not stacked)
  • Energy content of wood fuel (HHV, bone dry) = 18-22 GJ/t (7,600-9,600 Btu/lb)
  • Energy content of wood fuel (LHV, air-dry @ 35% moisture) = about 11 GJ/t (4,800 Btu/lb)
  • Energy content of agricultural residues (range due to moisture content) = 10-17 GJ/t (4,300-7,300 Btu/lb)
  • Metric tonne charcoal = 30 GJ (= 12,800 Btu/lb) (but usually derived from 6-12 t air-dry wood, i.e. 66-132 GJ original energy content)

Liquid fuels

  • Metric tonne ethanol = 7.94 petroleum barrels = 1262 litres
  • ethanol energy content (LHV) = 26.7 GJ/t = 21.1 MJ/litre = 11,500 Btu/lb = 75,700 Btu/US gallon. HHV for ethanol = 23.4 MJ/litre = 84,000 Btu/US gallon
  • ethanol density (average) = 0.79 g/ml (= tonnes/m3)
  • Metric tonne biodiesel = 37.8 GJ (33.3 - 35.7 MJ/litre)
  • biodiesel density (average) = 0.88 g/ml (= tonnes/m3)

  Fossil fuels

  • Barrel of oil equivalent (boe) = approx. 6.1 GJ (5.8 million Btu), equivalent to 1,700 kWh. "Petroleum barrel" is a liquid measure equal to 42 U.S. gallons (35 Imperial gallons or 159 litres); about 7.2 barrels oil are equivalent to one metric tonne of oil = 42-45 GJ.
    • N.B. the energy content (heating value) of petroleum products per unit mass is fairly constant, but their density differs significantly – hence the energy content of a litre, gallon, etc. varies between gasoline, diesel, kerosene.
  • Gasoline (Petrol): US gallon = 115,000 Btu = 121 MJ = 32 MJ/litre (LHV). HHV = 125,000 Btu/gallon = 132 MJ/gallon = 35 MJ/litre
    • Metric tonne gasoline = 8.53 barrels = 1356 litre = 43.5 GJ/t (LHV); 47.3 GJ/t (HHV)
    • gasoline density (average) = 0.73 g/ml (= metric tonnes/m3)
  • Petroleum diesel = 130,500 Btu/US gallon (36.4 MJ/litre or 42.8 GJ/t)
    • diesel density (average) = 0.84 g/ml (= metric tonnes/m3)
  • Metric tonne coal = 27-30 GJ (bituminous/anthracite); 15-19 GJ (lignite/sub-bituminous) (the above ranges are equivalent to 11,500-13,000 Btu/lb and 6,500-8,200 Btu/lb).
    • N.B. the energy content (heating value) per unit mass varies greatly between different "ranks" of coal. "Typical" coal (rank not specified) usually means bituminous coal, the most common fuel for power plants (27 GJ/t)
  • Natural gas: HHV = 1027 Btu/ft3 = 38.3 MJ/m3; LHV = 930 Btu/ft3 = 34.6 MJ/m3

  Carbon content of fossil fuels and bioenergy feedstocks

  • coal (average) = 25.4 tonnes carbon per terajoule (TJ)
    • 1.0 metric tonne coal = 746 kg carbon
  • oil (average) = 19.9 tonnes carbon / TJ
    • carbon emissions from gasoline (petrol) = 2.9 kg carbon / UK gallon
    • carbon emissions from diesel or fuel oil = 3.3 kg carbon / UK gallon
    • another way of expressing this = roughly 2.5 kg CO2 per litre of fuel used
    • N.B. LPG (liquefied petroleum gas) has about 10% less carbon content than petrol and diesel
  • natural gas (methane) = 14.4 tonnes carbon / TJ
    • 1.0 cubic meter natural gas (methane) = 0.49 kg carbon
  • carbon content of bioenergy feedstocks: approx. 50% (about 28 tonnes carbon / TJ) for all forms of wood and woody crops; approx. 45% (26 tonnes / TJ) for grassy crops and agricultural residues
    • N.B. there are no NET carbon emissions from the use of bioenergy fuels, assuming that the fuel is harvested on a sustainable basis with regrowth

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