Conventional energy usage has various environmental effects that cause global warming. Renewable energy sources are, thus, more favorable, because they have nearly zero emission. Biogas was merely seen as a sub-product obtained from anaerobic decomposition (without oxygen) of organic residue. One of the key concerns of biogas plants with energy generation is the disposal of comparatively large amounts of digestate in an economically and environmentally sustainable manner. In this article, the economic performance of the given biogas plant has been analyzed based on net present value (NPV) and energetic pay-back time (EPBT) concepts. The case study has produced an electricity yield of 2,223,951 kWh per year of feedstock digested. The hourly producible electricity energy has been 277.99 kWh. The producible heat energy has been 2,566,098 kWh per year and 320.76 kWh per day, respectively. The produced solid fertilizer and liquid fertilizer, respectively, have been 2047 t/a and 26,055 t/a. The plant with dairy cows and stall is a good economic situation under 3.4 years pay-back time, earning profits and showing a positive NPV of (sic)27.74 million. The co-generation system has reduced emissions by 7506 t CO2 per year. (C) 2012 Elsevier Ltd. All rights reserved.