Comparison of Thermal Losses Due to Heating-Up of System Components in Two Solar Process Heat Plants with Parabolic Trough Collectors
Abstract
Two solar process heat plants with liquid heat transfer parabolic trough collectors (PTC, 627 m² and 115 m² aperture) at Swiss dairies have been experimentally investigated in detail. They provide solar thermal heat for a hot water network of 102 °C and a steam network of 135 °C - 150 °C, respectively. Detailed yearly, monthly and daily evaluation with regard to usable solar gains Quse and solar energy necessary for heating–up system components to required temperature Tset is presented. Thermal heat capacities of the primary circuit have been analyzed and the change in inner energy ΔU has been calculated and cumulated for periods with no usable heat output below Tset. Over the year, the ratio of not usable solar energy required to heat-up the system to overall solar gains in the collectors (ΔU /(Quse+ ΔU)) varies between 14-18 % and 20-22 %, respectively. During winter months ΔU can even exceed Quse. These capacitive losses can be reduced by lower heat capacities or an improved thermal insulation. With intermediate storages, inner energy contained in the hot system could be stored for re-heating after an idle period.