Italian Feed-In Tariff Mechanism Applied to a Cogenerative Plant Fuelled by Solid Biomass: A Technical-Economic Comparison between Microturbine and Stirling Engine

The paper presents part of the results of two researches focused on an area situated in Central Italy: the European Project “Radar” (Raising Awareness on renewable energy Developing Agro-eneRgetic chain models) and the “energy and environmental plan for the consortium of the Commons in the mountain area of Esino-Frasassi”. This area is characterized by a huge availability of forestry biomass and, in a lower measure, of agricultural discards. This work presents a technical-economic study for a cogenerative plant applied to a public building with a small thermal demand. The choice of the best energy conversion system mainly depends on two factors: the availability of biomass and the user demand. Microturbine and Stirling engine are the technologies which better matches both with the size of the final user and with the availability of solid biomass. The biomass used comes from residual of olive tree pruning. The technical analysis is then followed by an economic one which shows how fundamental are the economic incentives for renewable sources (provided by Italian legislation, in this case) in order to make the technology appealing for energy investors; in particular the feed-in tariff mechanism is studied. The energy and economic analysis are carried out, both for microturbine and Stirling engine, considering different working hours over the years, different operating modes (with or without cogeneration) and three different costs of the solid biomass. Furthermore, the economic analysis points out that, beside the crucial role of incentive, the economic feasibility of solid biomass plant depends on the cost of biomass, the annual operating hours and the opportunity of recovery discharged heat in cogenerative application. In particular, the cost of biomass is, before everything else, the result of an agreement between the manager of the energy conversion plant and the suppliers.
Proceedings of the 18th European Biomass Conference and Exhibition, 3-7 May 2010, Lyon, France, pp. 2340-2346