In this work, we demonstrate the improvement of thermal performances of a heat pipe parabolic trough solar collector by optimizing the annulus space, between the evaporator and the glass envelope, and using an appropriate filling gas. We compared the system thermal effectiveness for nine filling gases (hydrogen, air, helium, neon, oxygen, nitrogen, argon, krypton, and xenon). The results showed that using xenon or krypton leads to the best thermal yield (70%). While krypton arises to be the most energetically efficient filling gas, argon, with a thermal yield of 62%, presents a best compromise as the cheapest inert gas. In addition, we showed that the annular space size should be less than a critical value to minimize heat losses and to reduce the material cost during manufacturing.