A procedure for estimating the value of forest fuels

The gross calorific value (or 'higher heating value') of fuelwood is typically 18·6 MJ kg^-1 of dry wood. But the heat energy actually available from combustion of freshly-harvested fuelwood may be as low as 5·9 MJ kg^-1. For this reason, there is a tendency to overestimate the true energy and economic values of forest biomass with respect to commercial energy sources. This paper interprets the main conventions used in quoting fuel values, and derives simple formulae (and graphs) for estimating energy contents of fuelwood at any given moisture level. The 'usable heat content' approach is developed as an equitable basis for comparing fuel values, and here provides energy and economic equivalents for wood, oil, coal, natural gas and peat.