An On-site Test Method for Optical Efficiency of Large-size Parabolic trough Collectors

An on-site test method for optical efficiency of large-size parabolic trough collectors (PTCs) is proposed. This method is based on energy balance of incident solar radiation, heat gain, cosine loss, end loss, optical loss and heat loss. The heat loss is calculated based on the correlation between the cooling power and absorber-ambient temperature difference obtained by fourth-order polynomial data-fitting. The incident solar radiation and heat gain are calculated based on the experimental data. The cosine and end losses are calculated based on local time and astronomical conditions. Therefore, the optical loss is achievable based on the energy balance and so is the optical efficiency. This method was implemented on the 300kWt PTC experimental rig located in Langfang, Hebei, China. The optical efficiency is evaluated to be (76.15 ± 1.7) %, which agrees well with that of the LS-3 collector (77%). On the other hand, a thermohydraulic model for PTC using heat transfer fluid (HTF) developed before is incorporated with the optical efficiency obtained on the 300kWt PTC experimental rig. The good agreement between the simulation results and experiment data verifies the on-site test method and the thermohydraulic model.