An irreversible hybrid solid oxide fuel cell (SOFC)-Brayton heat engine system is taken into account in this study. Ecological based thermoenvironmental function is considered to assess the performance of the system as well as the power, exergy destruction, energy and exergy efficiencies. This function enables someone to determine environmental impact of any thermal cycle. Optimum operating conditions for all investigated parameters are obtained. Results are presented numerically and discussed. Some important results are; maximum power density of the hybrid system is 15260.9 (W m(-2)) at i = 17,000 (A m(-2)), maximum energy efficiency of the hybrid system is 0.841 at i = 7200 (A m(-2)), exergy efficiency of the hybrid system is 0.676 at i = 5200 (A m(-2)) and ecological based thermoenvironmental function density of the hybrid system reaches maximum value at i = 5800 (A m(-2)) and it is equal to 0.00603 (W m pts(-1) m(2)). Finally, environmental friendly and efficient operation conditions, i(f) <= i <= i(p), is suggested for the hybrid system. (C) 2017 Elsevier Ltd. All rights reserved.