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 datacorresponding 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.
A facility for testing different components for HCPV application has been developed in the framework of\ud
“Fotovoltaico ad Alta Efficienza” (FAE) project funded by the Sicilian Regional Authority (PO FESR Sicilia 2007/2013\ud
4.1.1.1). The testing facility is equipped with an heliostat providing a wide solar beam inside the lab, an optical bench\ud
for mounting and aligning the HCPV components, electronic equipments to characterize the I-V curves of multijunction\ud
cells operated up to 2000 suns, a system to circulate a fluid in the heat sink at controlled temperature and flow-rate, a\ud
data logging system with sensors to measure temperatures in several locations and fluid pressures at the inlet and outlet\ud
of the heat sink, and a climatic chamber with large test volume to test assembled HCPV modules
In geographical areas where direct solar irradiation levels are relatively high, concentrated solar energy systems are one of the most promising green energy technologies. Dish-Stirling systems are those that achieve the highest levels of solar-to-electric conversion efficiency, and yet they are still among the least common commercially available technologies. This paper focuses on a strategy aimed at promoting greater diffusion of dish-Stirling systems, which involves optimizing the size of the collector aperture area based on the hourly frequency distributions of beam irradiance and defining a new incentive scheme with a feed-in tariff that is variable with the installed costs of the technology. To this purpose, a new numerical model was defined and calibrated on the experimental data collected for an existing dish-Stirling plant located in Palermo (Italy). Hourly-based simulations were carried out to assess the energy performance of 6 different system configurations located on 7 sites in the central Mediterranean area using two different solar databases: Meteonorm and PVGIS.A new simplified calculation approach was also developed to simulate the dish-Stirling energy production from the hourly frequency histograms of the beam irradiance. The results reveal that an optimised dish-Stirling system can produce 70-87 MWhe/year in locations with direct irradiation varying between 2000-2500 kWh/(m 2 •year). The proposed incentive scheme would guarantee a payback time for investment in this technology of about ten years and the effect of economies of scale could lead, over the years, to a levelized cost of energy similar to that of other concentrating power systems.
HIGHLIGHTS• DNI hourly frequency distribution is analysed in 7 Mediterranean locations.• Influence of DNI peak values on electricity production are investigated.• Effects of redesigned and optimised aperture area of the collector are analysed.• A new procedure using DNI frequency histograms to forecast energy production is presented.
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