Evaluation of Measurements on Parabolic Trough Collector Fields for Process Heat Integration in Swiss Dairies

摘要

Measurements from two solar process heat plants in Switzerland have been evaluated, both equipped with similar types of parabolic trough collectors. The analysis focusses on the description of the plants and the presentation of the performance of the collector fields. For this, both a daily evaluation of selected days is presented as well as a monthly evaluation is introduced where the energy delivery of the collector field is cumulated for each day and plotted against the cumulated direct irradiation on the one-axis tracked collector field aperture area. Both plants have been integrated on the heat supply level aiming at solar fractions of about 7 % and 12 %, respectively. In the first plant (115 m~2 aperture area at an altitude of 1700 m), the collector field performance (the fraction of daily solar gains from total direct irradiation) reaches values in the range of 45 % already in April (spring time) providing outlet temperatures of about 190 °C. Due to high specific direct irradiation at this site, solar energy delivery higher than 500 kWh/d is reached (up to 4.8 kWh per m2 aperture area have been measured). In the second plant (630 m~2 at an altitude of 1000 m), the DNI is much lower (1183 kWh/m~2.a instead of 1881 kWh/m~2.a as in Bever). Although the design temperature of this plant is significantly lower, collector field performances did not yet reach higher values than the Bever plant. However, both the daily and the monthly evaluation presented in this paper show that the collector field performance can be high but the integration and control concept of the Saignelegier plant needs to be improved.