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Research examines some losses in the devices that convert solar energy into useful heat

Elhuyar Fundazioa

This thesis has focused on solar thermal energy, which involves processes to convert solar energy into useful energy. "Today, we know that it can provide a considerable fraction of the current and future world demands for thermal energy, in the industrial as well as in the domestic sector," asserted Fabienne Sallaberry. "This fact is reflected in the growing interest in the new designs of solar collectors, in particular during the last decade, in order to meet the growing heat demands".

According to the new PhD holder, a solar thermal collector is "a box containing various components in which a fluid circulates and is heated thanks to the greenhouse effect. For a broad range of operating temperatures, solar thermal collectors can use optical concentration systems such as parabolic mirrors to optimize their performance", Fabienne Sallaberry pointed out. "Nevertheless, as optical concentration is based on direct radiation which comes directly from the sun, without being dispersed by the atmosphere, it is necessary to use a mechanical device or solar tracker that allows the collector to follow the direction of the sun and thus maximise the amount of solar radiation received by the collector".

Optical losses

In order to achieve optimum performance, it is necessary "to select the appropriate tracking system. Otherwise," added Fabienne Sallaberry, "the collector would sustain significant optical losses due to the inadequate focussing of the solar radiation, irrespective of the quality of the device components and its manufacturing process".

That is why the author of the thesis has focused her research on calculating the errors due to the solar trackers. To do this, initially she conducted some of her own tests to evaluate these mechanical devices. The, she resorted to computer-based simulation techniques and to experimental observations to produce an optical characterisation of various solar collectors that use optical concentration. "It is about determining how far their performance depends on the errors of their solar trackers," she pointed out. "It should be highlighted that a high degree of agreement was observed between the theoretical results provided by the simulation program and the experimental ones".

In a third phase, she calculated the long-term optical losses caused by the solar tracking system. "The impact of the maximum tracking error on the optical performance has been determined for various collectors and different tracking systems," said the PhD holder.

Finally, this thesis indicates the sections included in the international standards (in particular the ISO 9806 standard for testing and certifying solar thermal collectors) that need to be revised in order to determine the influence of solar tracking on the overall performance of the collectors. In this respect, Fabienne Sallaberry has put forward improvements that would need to be included in a future procedure on the standardized testing of solar trackers for solar thermal collectors.


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