Technical-economical comparison between cogeneration, pellet production and thermal uses of biomass

The logistics for the collection of energy biomasses is a major constraint in areas with severe orography, lack of transportation infrastructures and dispersed land ownership. The use of small size units eases this process for it reduces the extension of the gathering area. Nevertheless, small size means low electrical efficiency and high specific costs. Many yearly operating hours are required for making a small plant become a cost effective solution. A difficult compromise must be settled, between the proximity of the plant to the woodland and the presence of a local heat demand, for a full exploitation of the power output. This paper discusses the idea of using the heat surplus of a biomass-fired cogeneration unit to treat a share of the biomass and produce fuel like pellet, to be stored and distributed for heating purposes. This form of thermal energy storage makes time and geographical shift of heat utilization possible, also in small-scale applications. A technical-economical comparison is carried out and discussed between the above mentioned system and a district heating supplied by a traditional biomass boiler, or a conventional chip-fired cogeneration plant without pellets production. The economic profitability of different plant solutions is investigated in some case-studies.