Reciprocating steam engines can be employed successfully in small size power plants (under 500 kWe) fed by facilitated renewable energy sources like Wood Waste. Reciprocating Steam Engines, until now employed only in energy short Third World Countries, has become attractive to developed countries because of growing environmental sensitivity. Application to a real case shows conditions for the economic feasibility of Reciprocating Steam Engine in comparison with the heat based or other cogeneration techniques. An economic analysis is performed by the Annual Equivalent Method and the Internal Rate of Return Method.