Steady state criteria for parabolic trough receiver heat loss measurements

Heat loss of parabolic trough receivers is measured in the laboratory at Steady State. Criteria for the Steady State shall ensure sufficient stabilization of the measurands without being excessive. The IEC TS 62862-3-3:2020 provides such criteria. This paper presents a model for the assessment of Steady State criteria in heat loss tests. Assuming constant heating power, lumped heat capacity and linearized heat loss, the model shows, that the IEC TS 62862-3-3 allows for significant deviations at low temperatures and large heat capacity. For the investigated configuration of low heat loss and large heat capacity, the model shows allowed deviations of 12.6 K at 100 degrees C, 5.5 K at 200 degrees C and 2.5 K at 300 degrees C. The paper discusses the weaknesses of Steady State criteria in the IEC TS 62862-3-3 and proposes to clarify the meaning oft 0.5 K and +/- 1% and, to expand the stabilization period to 60 minutes for measurements below 300 degrees C and to limit the scope of the standard to measurements > 240 degrees C.