Novel solar cogeneration trough system based on stretched microstructured mylar film

Abstract

Hybrid CSP / CPV (Concentrating Solar Power / Concentration Photovoltaic) systems provide a good alternative to traditional CPV systems or CSP trough architectures. Such systems are often described as solar cogeneration systems. Trough systems use mainly the IR portion of the spectrum in order to heat up a pipe in which water is circulating. CPV systems use only the visible portion of the spectrum to produce the photo-voltaic conversion. Due to the achromatic nature of traditional thermal trough CSP systems, it is very unlikely that a CPV system can be integrated with a CSP system, even a low concentration CPV system (LCPV). We propose a novel technique to implement a low concentration CSP/LCPV system which relies on commercially available solar trough concentrators / trackers that use reflective stretched Mylar membranes. However, here the Mylar is embossed with microstructures that act only on the visible portion of the spectrum, leaving the infrared part of the solar spectrum unperturbed. This architecture has many advantages, such as: the existing Mylar-based thermal trough architecture is left unperturbed for optimal thermal conversion, with linear strips of PV cells located a few inches away from the central water pipe; the infrared radiation is focused on the central pipe, away from the PV cells, which remain relatively cool compared to conventional LCPV designs (only visible light (the PV convertible part of the solar spectrum) is diffracted onto the PV cell strips); and the Mylar sheets can be embossed by conventional roll-to-roll processes, with a one-dimensional symmetric micro-structured pattern. We show how the positive master elements are designed and fabricated over a small area (using traditional IC wafer fabrication techniques), and how the Mylar sheets are embossed by a recombined negative nickel shim. We also show that such a system can efficiently filter the visible spectrum and divert it onto the linear strips of PV cells, while leaving the infrared part of the spectrum un-perturbed, heating up the water pipe.