The paper discusses alternative designs of receivers for parabolic trough collectors with smaller rim angles. The Half Insulation Filled Receiver (HIFR) and Linear Cavity Receiver (LCR) designs have been studied and optimized for minimum heat loss. Different combinations of insulations and annulus gasses have been evaluated. From this study, the best combination of insulation material and annulus gas and its pressure has been obtained for geometry optimization of the receiver. Configuration of SCHOTT PTR 70 receiver has been considered as the base case for this study. Heat losses from the HIFR and LCR for the microtherm - air (at 0.1 atm pressure) combination are the least being 255 W/m and 246 W/m respectively. The radius ratio (RR = D-G/D-p) value of HIFR for this is 2.5 and insulation thickness for LCR receiver is 20 mm. HIFR and LCR show maximum optical efficiency at rim angle psi = 45 degrees whereas, for a conventional cylindrical receiver the same is true at rim angle psi = 90 degrees. Therefore, both the proposed receiver designs are expected to be suitable alternatives of evacuated receivers for parabolic trough collectors with smaller rim angle (around 45 degrees). (C) 2018 Elsevier Ltd. All rights reserved.