A technoeconomic analysis has been undertaken considering the optimum number of energy producing generators using biogas coming from anaerobic digestion. Inputs for this analysis originate from available data on the first generator for energy production from biogas, installed in Greece at the wastewater treatment facility of Iraklio city. The data spans a period of 5.5 years of operation. It is concluded that the cost per kWh produced is 0.0876 is an element of/k Wh if one generator is used covering 15.9% of the facility's needs. If two generators are used, more biogas is utilized contributing 32.6%, of the facility's needs at a marginal production cost of 0.0886 is an element of/k Wh. Similar estimations have been made for scenarios involving up to six generators. In contrast, the marginal cost of conventionally produced energy is 0.1383-0.2483 is an element of/kWh. (c) 2007 Elsevier Ltd. All rights reserved.