Thermal and optical characterization of parabolic trough receivers at DLR's QUARZ Center - Recent advances

Kurzfassung

The performance of a parabolic trough receiver can be described by two parameters, the specific heat loss at operating temperature and the optical efficiency. DLR operates two test benches for the measurement of these parameters with high accuracy in its QUARZ Center. In the heat loss test bench THERMOREC the receiver is electrically heated to operating temperatures. In a steady state of constant heating power and absorber temperature an energy balance equation yields the thermal losses. Recent work was dedicated to the introduction of end heaters which lead to a significantly more even absorber temperature profile. Furthermore brass is now used for the homogenization tube with far reduced oxidation at the tube surface compared to the formerly used copper. In the ELLIREC, the linear focus test bench for the measurement of optical efficiency, the receiver is irradiated with solar simulator lamps. The enthalpy increase of cooling water flowing through the receiver at ambient temperature indicates the optical efficiency. The test bench has been characterized for reproducibility to 1 σ = 0.25% and homogeneity of the incident radiation in the linear focus to ± 5 % of the average. By comparison of the enthalpy increase to that of the defined reference receiver DLR 70-1 the relative optical efficiency is determined.