All technical processes are subject to dysfunctions during their lifespan, and large solar thermal systems (LSTS) are no exception to this rule. In order to deal with them and minimize their impact, a good knowledge of dysfunctions affecting LSTS is a major issue. In this way, the return on investment can be increased and the competitiveness of solar thermal energy could be also improved. This paper presents a study of the dysfunctions which can affect LSTS. We first conducted a literature review and found out that more studies are necessary to obtain some up-to-date reliability data on the dysfunctions. To complete the available information, our methodology combines a top-down approach based on a Failure Modes, Effects and Criticality Analysis (FMECA) with a bottom-up approach based on a survey for domain experts. Thanks to the merging of various sources, we propose a ranking of sub-systems reliability, showing in particular that the less reliable solar sub-systems are the controller (control and sensors) and the primary transport (hydraulic components of the primary loop). Other sub-systems are less prone to failure, but the status of solar collection is particularly interesting. While previous studies often point it out as a critical sub-system, our results tend to show that it is more reliable in recent LSTS.
