Study Of Dynamic Thermal Performance Of Two Kinds Of Linear Concentrating Solar Collectors

Linear concentrating solar collectors have higher operating temperature and can provide energy of higher grade than ordinary solar collectors. They have an excellent application prospect in concentrated solar power and central solar heating or cooling systems. At present, most investigations of linear concentrating solar collector's thermal performance are still using steady-state method. However, this kind of solar collector's thermal performance is affected by direct normal incidence solar radiation resource and other factors' dynamic variation. It's inaccurate when we only use steady-state method to investigate linear concentrating solar collector's real operating performance. Therefore, it's necessary to conduct dynamic-state experimental and simulation studies for linear concentrating solar collector's thermal performances on the basis of an analysis of direct normal incidence solar radiation resource.This paper investigated parabolic trough solar collector's(PTC) and Linear Fresnel reflector's(LFR) dynamic thermal performances along with an observation of the direct normal incidence solar radiation resource in Tianjin area. Tests and analysis of the long-term dynamic thermal performance variation of the two kinds of solar collectors under different weather, season and operating conditions were carried out. Then, a simulation for long-term heat collecting capacity according to the predictive model for concentrating solar collectors from British Standard EN 12975(2006) was conducted. In the last, a preliminary analysis of PTC and LFR's applicability in Tianjin area will be given.In terms of solar energy resources base, the total direct normal incidence solar radiation level in Tianjin area from November 2013 to October 2014 was 3838.88MJ/m2, while the usable direct normal incidence solar radiation was 2987.98 MJ/m2. The effective sunshine duration was 1633.3h which account for 71.6% of the total sunshine duration. Through a long-term dynamic-state test experiment, the investigation found that direct normal incidence insolation was the main influence factor to PTC's and LFR's dynamic thermal performance variation besides the collector designs. When direct normal incidence insolation decreased from 900W/m2 to 300W/m2, PTC's and LFR's instantaneous thermal efficiency both decreased 10% to 20%. Secondly, PTC's and LFR's dynamic thermal efficiency increased with a higher system flow rate. Under same working conditions, LFR's total collected heat per unit collecting area account for 71.7% of PTC's. Moreover, LFR's monthly thermal efficiency was lower than PTC's by 10%~18%. PTC's overall thermal performance was better than LFR's under the working conditions in this paper. In terms of simulation study, the selected predictive model showed a good accuracy when predicting the long-term heat collecting capacity of PTC and LFR compared to the experimental data. The total prediction error for PTC was only-1.0%, while the LFR's was 3.7%. But, the model was still not very precise for hourly prediction.The investigation results showed that the solar energy resource in Tianjin area was satisfactory and the tested PTC and LFR showed a good energy saving potential under restricted operating condition. Considering the background of related policies and industrial developments, linear concentrating solar collectors are applicable in Tianjin area.