This work concerns the production of electricity from renewable sources produced from biomass (wood waste) in cogeneration plants. Two facilities are compared: a 2 MW electricity power plant and a 10 MW one. They are also compared to electricity production in a diesel engine cogeneration. The objective is to compare the environmental impact of various power plants, using two different fuels and/or of different power. A detailed LCA methodology is therefore presented. The results - in favor of the 2 MW wood plant but sensitive to assumptions - are then discussed.