Researchers at the National Renewable Energy Laboratory completed heat-loss testing on two of Solel’s UVAC3 parabolic trough receivers. The receivers showed identical heat losses within experimental uncertainty. Normalized per meter of receiver length, heat losses are 130, 200, 310, and 460 W/m at average absorber temperatures of 300°, 350°, 400°, and 450°C, respectively. Experimental uncertainty is about ±10 W/m. A correlation was developed to predict receiver heat loss as a function of the difference in °C between the average absorber temperature and ambient temperature. This correlation is:
UVAC3 heat loss (W/m) = 0.26 * ΔT + 1.05 * 10e-8 * ΔTe4
Care must be taken to apply this correlation within context. The correlation was derived with ambient temperatures of about 23°C, and it should not be used to predict heat losses at ambient temperatures more or less than 10°C from this value. This limitation is explained further in the report.
UVAC3 heat losses were compared to heat losses from UVAC2, the previous generation of receiver. The UVAC3 receiver shows significantly lower heat loss: 310 vs. 380 W/m at 400°C, which is a 20% reduction in heat loss.
It is important to note that receiver performance depends on more than just heat losses. Optical efficiency testing is required to create a collector/receiver efficiency curve that estimates the heat gain to the heat-transfer fluid flowing within the receiver. Heat losses, as tested in this report, serve to reduce the heat gain to the heat-transfer fluid and therefore reduce the collector/receiver efficiency.