The effect of dust accumulation on line-focus parabolic trough solar collector performance

Based on the major Department of Energy Solar Industrial Process Heat Program, it has been determined that the existing techniques for predicting the performance of parabolic trough solar collectors greatly overpredict the thermal output of these systems. The objective of the research reported herein is to improve the predictive capability of existing models by incorporating a factor that accounts for dust and dirt accumulation on the optical surfaces. This has been accomplished by modifying the optical efficiency with a dust factor to account for the reduced reflectivity of the mirror and reduced transmissivity of the cover glass. This technique has been developed independent of the test data used for verification. The dust factors have been developed from exposure tests conducted at six different sites, so that it is also independent of location and collector type. Wash frequency and optical degradation rate are input to the model to compute the time varying dust factors. Recommendations for these parameters are provided based on long-term observations. The complete model is then used to provide realistic predictions of real-world performance of solar IPH systems.