The software THD for thermal hydraulic dimensioning of solar thermal plants was validated against experimental data. Analytical models were replaced by new models which are solved numerically. These models take into account the two major simultaneous processes that dominate the steam range: Displacement of liquid by the growing steam volume and evaporation of residual liquid. The validated version of THD will be published, again, as an open source software. A new parser was implemented, which enables import of XML-files from Polysun simulations. Validation of THD fulfils the precondition for the acceptance by the solar industry. Design errors, unnecessary costs and malfunctions can be avoided by application of THD. In this sense, THD contributes to cost reduction of solar thermal plants.
