Assessment of three types of heat pipe solar collectors

New comparative tests on three different types of heat pipe solar collectors are presented in this paper. These three collectors are installed in parallel and tested at the same working conditions.Results are also presented in terms of efficiency plotted against temperature of the heat transfer fluid entering the collector minus the ambient air divided by the global solar irradiance upon the aperture plane of the collector. This allows representing the comparative characteristics of the three collectors when operating under variable conditions, especially with wide range of incidence solar radiation.