Advances in the linear Fresnel single-tube receivers: Hybrid loops with non-evacuated and evacuated receivers

In the first place, this work performs a comparative analysis of the heat loss associated to the three single-tube receiver designs proposed: evacuated, non-evacuated and non-evacuated with a glass plate at the aperture. The heat loss is quantified in each case as a function of three parameters: the temperature difference between the tube wall and the environment, the incident concentrated flux on the tube and the wind velocity. Although the evacuated design has the lowest heat loss, the differences with the other two designs decrease as the working temperature is lower. Thus, a hybrid loop is proposed, which consists of non-evacuated modules at the beginning and evacuated modules at the end. The lower investment of the non-evacuated tubes, as well as their robustness and simplicity, can compensate for the lower energy absorbed by these type of receivers. Next, a study of the annual electricity cost produced by Fresnel plants with hybrid loop is performed. The work concludes that there are specific configurations of hybrid loops that minimize the electricity cost, when the different investment, operation and maintenance costs of the receivers are quantified. The maximum percentage of non-evacuated tubes in the loop will depend on the technology and the working temperature range.