  Solar systems based on the coupling of parabolic concentrating collectors and
thermal engines (i.e. dish-Stirling systems) are among the most efficient
generators of solar power currently available. This study focuses on the
modelling of functioning data from a 32 kWe dish-Stirling solar plant installed
at a facility test site on the University of Palermo campus, in Southern Italy.
The proposed model, based on real monitored data, the energy balance of the
collector and the partial load efficiency of the Stirling engine, can be used
easily to simulate the annual energy production of such systems, making use of
the solar radiation database, with the aim of encouraging a greater
commercialisation of this technology. Introducing further simplifying
assumptions based on our experimental data, the model can be linearised
providing a new analytical expression of the parameters that characterise the
widely used Stine empirical model. The model was calibrated against data
corresponding to the collector with clean mirrors and used to predict the net
electric production of the dish-Stirling accurately. A numerical method for
assessing the daily level of mirror soiling without the use of direct
reflectivity measures was also defined. The proposed methodology was used to
evaluate the history of mirror soiling for the observation period, which shows
a strong correlation with the recorded sequence of rains and dust depositions.
The results of this study emphasise how desert dust transport events, frequent
occurrences in parts of the Mediterranean, can have a dramatic impact on the
electric power generation of dish-Stirling plants.
