A comparison of biomass energy with other renewables Patrick Moriarty & Damon Honnery Laboratory for Turbulence Research in Aerospace and Combustion Monash University

Global Primary Energy Global primary energy use in 2003 around 430 EJ Biomass primary energy use 30-50 EJ Net primary production of biomass by photosynthesis (land) around 120G T/yr equal to around 1900 EJ Global renewable resource base and terrestrial resource base

Biomass Energy Inputs Renewable energy sources must provide a net source of energy after conversion Primary sources like solar and geothermal are all converted to secondary energy in the form of electricity Electricity is the assumed secondary energy produced from the primary biomass feedstock Excluding irrigation and drying, primary energy inputs for a range of biomass feedstocks vary from 0.5-1.0 GJ per above-ground dry tonne (odt) If irrigation is needed, additional energy inputs are required Mechanical energy cost of irrigation (pressure, run and depth) Efficiency of mechanical system (pump and drive) Efficiency of electrical power generation system (and transmission) Energy Transpiration efficiency Water application efficiency Water Use

Plantation Net Energy: Effects of Irrigation Irrigation energy per odt biomass vs total annual cultivated biomass (in odt) A: Non-irrigated agriculture: typical net output 17-17.5 GJ/odt B: Present irrigated agriculture has increased energy inputs: net output <17-17.5GJ/odt C: Could be irrigated for energy plantations but at even higher input energy: net output <<17-17.5GJ/odt and possibly negative net energy output.

Bioenergy Plant Costs Electricity cost for biomass vs plant capacity (Bridgwater, 2005) For biomass electricity production, costs decrease with plant size.

Energy ratios for 0.5 MW and 1.5 MW wind turbines vs wind speed Wind Power Energy Ratios 1990 installed capacity 1.9 GW (3 TWh) 2005 installed capacity 50 GW (100 TWh) Energy ratios for 0.5 MW and 1.5 MW wind turbines vs wind speed Energy inputs predominantly arise from manufacturing, so scale with size For wind, energy ratio (output/input) is very sensitive to wind speed.

Conclusions Wind energy is presently favoured for RE electricity production because good windy sites are available and grid integration problems are minor at low wind penetration. The technology is proven, and construction lead times are short. Because energy costs for irrigation water will continue to rise, biomass plantations for electricity production are not a long-term solution. However, where biomass is available at low energy and economic cost, electricity production may be competitive with wind,particularly if energy storage is required.