In this article the validity of the utilisability method for evacuated heat pipe solar panels was tested, through a comparison of expected useful energy and that measured in an experimental plant. The panels used are distinctive for the working of the heat pipes, which for collection, require a threshold irradiance value higher than the critical, used in quantification of heat losses. Working limits were identified and the basal utilisability calculation hypotheses tested by using a calculation code that simulates heat pipe behaviour. Dynamic phenomena linked to inertia during collection were studied with a mathematical model constructed from results provided by the collector＇s held at stepped variation to solar irradiance. The numerical and experimental results enable a critical comparison between calculated and measured energy.