Present paper reports the comprehensive study of evacuated tubular collector (ETC) for a fixed outlet temperature from the collector. The detailed numerical modeling has been done in terms of energetic and exergetic gains under constant collection temperature mode of operation. For getting higher outlet temperature, one have to decrease the rate of flow of water in the U-shaped copper tube inserted in the glass tube of the collector, but it has been noticed that mass flow rate gets saturated after a certain value of collection temperature, and there is no meaning of decreasing the mass flow rate after the saturated value for further increase of the outlet temperature. The characteristic equations similar to Hottel–Whiller–Bliss (HWB) have been developed for ETC with U-shaped copper pipe for getting constant outlet temperature. Values of gain and loss terms for constant collection temperatures are found to be 0.69 and 17.42, respectively.