Executive Summary

Two Schott 2008 model year PTR70 receivers were tested on the National Renewable Energy Laboratory’s parabolic trough receiver heat loss test stand from 100°C – 500°C in 50°C increments. Heat loss in the laboratory, normalized per meter receiver length, is summarized by the following correlation:

The absorber temperature in the above correlation is in °C, and the calculated heat loss is in watts per meter (W/m) receiver length. There is ± 10 W/m uncertainty associated with the results.

The emittance of the receiver absorber was calculated from the laboratory heat loss test results. The following correlation fits the calculated emittance to the absorber temperature.

The emittance is a non-dimensional quantity and the absorber temperature in the correlation is in °C. Emittance uncertainty depends on the testing temperature and is described further in the report. At an absorber temperature of 400°C the emittance uncertainty is ± 0.005.

A multi-step process was used to estimate solar field heat losses from the laboratory results. A parabolic trough collector/receiver model calculated solar field heat loss using the emittance curve correlation presented above and reasonable collector and solar field assumptions. Solar Advisor Model (SAM) and Excelergy heat loss correlation coefficients were generated from the heat loss outputs of the model. These coefficients are presented in Table 8 of this report.

The 2008 Schott PTR70 heat loss correlation coefficients were used in an annual SAM simulation for a 100 MWe parabolic trough power plant with 6 hours of thermal energy storage. SAM shows that the heat loss associated with the Schott 2008 PTR70 will decrease the levelized cost of energy (LCOE) from the power plant by about 0.5 ¢/kWh and increase annual electricity production by 5% relative to previous published PTR70 heat loss results. This analysis assumes that the 2008 PTR70 is priced similar to the previous model and that they share similar optical characteristics.

This report presents the thermal performance of the 2008 PTR70 parabolic trough receiver. We did not perform receiver optical, durability, nor structural tests. These factors also affect the solar plant performance of parabolic trough receivers and will be the subject of future testing.