We evaluated the economic feasibility of small CHP (combined heat and power) and CC (combined cycle) systems using a 5 MW-class gas turbine fueled with biogas. The significance of this study is that we used practical hourly and seasonal variations of the CHP and CC performance based on detailed performance analysis. Using the investment and running costs of the entire facilities and the prices of electricity and heat, economic indices such as the annual gross margin, the net present value of the cash flow and the payback period were estimated. Two kinds of heat demand patterns were compared in the CHP system. Major findings are as follows. A strong dependence of the project economics on heat sales was observed. Both of the CHP cases showed an economic benefit over both the CC system and the gas turbine-only system. Another important finding is that the CHP system would be more beneficial than the CC system in terms of the total net present value after twenty years as long as the annual heat demand is over thirty percent of the annual electricity supply. The effect of increasing prices and costs was also simulated, and improvements in project economics were estimated. (C) 2014 Elsevier Ltd. All rights reserved.