Parabolic trough collectors have become some of the important elements of solar power plants in recent years. These devices are usually located in dry deserts, however their widespread use leads us to expect such facilities of trough collectors in wetlands. In fact, the idea was to study a possible installation in Casablanca in the town of Morocco which is humid. As a result, heat transfers could be affected in the presence of water vapor when the annulus is air-filled at atmospheric pressure, thus it is interesting to design the PTC as a function of the effect of moisture. In this paper, a detailed numerical study is presented. First, the mathematical model is validated by the experimental results of Sandia laboratories in the USA. Then, an evaluation of the effect of humidity on thermos-physical properties of humid air is carried out to assess convective heat transfers. Later, we have calculated the optical properties of water vapor in order to take into consideration the participation of humid air in radiative heat transfers. Thereby, a numerical simulation has been performed in order to compare the performances of trough collectors between humid and dry areas.