A review of flattened linear Fresnel micro-concentrator on building façade: demands, theories and perspectives

Flattened linear Fresnel micro-concentrators represent a novel type of solar energy device. Their compact design and minimal wind loading make them highly suitable for solar energy collection on building facades. Additionally, their flexible deployment strategies further enhance their adaptability. As a result, they significantly expand the application scope of linear Fresnel reflector (LFR) technology. Mainstream research on linear Fresnel reflectors may not currently focus specifically on micro-concentrators. However, the underlying theories, methods, and techniques can be readily applied to the field of flattened linear Fresnel micro-concentrators. This paper provides a comprehensive review of the relevant literature, including theoretical foundations, methodological approaches, and technological advancements. The paper starts by explaining the principles of non-imaging optics, emphasizing their crucial role in the design of micro-concentrators. Next, the paper provides an overview of popular methods and techniques in LFR research from the perspective of non-imaging optics theory, and their implications for flattened LFRs. The paper also evaluates the applicability and potential limitations of these methods and techniques when applied to the study of flattened micro-concentrators. Moreover, this paper summarizes some innovative LFR concentrator designs, including Elevated LFR, Bi-focal LFR, and Off-axis LFR. These designs make appropriate sacrifices in terms of complexity but achieve higher efficiency compared to conventional LFR designs. These design concepts contribute to the development of flattened micro-concentrators, with some Bi-focal designs already achieving initial low profile and Off-axis LFR achieving initial flattened profile. Additionally, the paper highlights several receiver designs that are particularly well-suited for application in flattened LFR micro-concentrators. In summary, this paper systematically introduces the theories and technologies related to the development of flattened LFR micro-concentrators. The goal is to highlight the non-imaging optical principles behind these theories and technologies and their role in inspiring the development of flattened LFR devices.