In this paper, an attempt has been made to btain an analytical expression for the instantaneous thermal efficiency of a greenhouse integrated biogas system and the instantaneous thermal loss efficiency factor from the system for a given capacity. It has been shown that the use of solar energy (greenhouse effect) reduces the period to achieve the optimum temperature for biogas production. The proposed mathematical expression can be used to test any greenhouse integrated biogas system. The results of the
parametric studies have been analytically and numerically determined.