Electrical Efficiency Increase in CPVT Collectors by Spectral Splitting

Abstract

Concentrating photovoltaic-thermal (CPVT) collectors have to face the challenge of contrary temperature requirements in the single receiver parts. The PV cells require low temperatures to achieve high efficiency, whereas the thermal part should generate high temperatures for providing industrial heat. The approach of “Spectral Splitting” can offer a solution for compact CPVT receivers; however, a clear quantification of the expected conversion efficiency is difficult. Therefore, this paper describes a modelling methodology for obtaining electrical and thermal performance parameters for a Spectral Splitting configuration using semiconductor-doped glass combined with appropriate heat transfer fluid. The PV technologies c-Si, CIGS and CdTe are considered. The presented model yields distinct results for maximising the electrical efficiency, calculates the reduction in waste heat dissipation within the cells and assesses the impacts of concentration factor and cell temperature. An optimised configuration could be found with CIGS cells, impinged by a selected wavelength spectrum between 868 nm and 1100 nm, where the theoretical efficiency reaches 42.9%. The waste heat dissipation within the cells is reduced by 84.9%, compared to a full-spectrum operation. The depicted CPVT receiver design using bendable thin-film PV cells will be realised as a prototype in a subsequent project phase.

State-of-the-Art of Concentrating Photovoltaic Thermal Technology

“…In this way, the entire filter characteristic can be adjusted to different PV technologies to support varying spectral requirements. On the other hand, this adjustability provides the option to choose the fractioning between electrical and thermal output of the CPVT system, which can make it possible to configure the CPVT collector according to the customers' needs [12].…”

“…As realizing this filter width in one piece is hardly feasible, the illustrated approach of four adjacent glass tubes with implemented SDG filters was chosen. By contrast, technical feasibility was a major aspect during the developing phase of a novel CPVT receiver design proposed by Resch and Höller [12]. Figure 8 provides the cross-section of the proposed concept, whereas Figure 9 presents the rendering of a 3D visualization of the receiver.…”

“…According to the opinion of the authors, the constructive design of a spectral splitting CPVT receiver should not be too complex, because if this technology shall overcome its niche status on the long-term perspective, it must also be economically viable in the future. Therefore, the research work of the authors focusses on spectral splitting by selective absorption, because this approach appears to be promising for developing compact CPVT receivers with a high probability of being experimentally feasible [12,[16][17][18][19][20][21].…”

Optical Modelling of a Linear Fresnel Concentrator for the Development of a Spectral Splitting Concentrating Photovoltaic Thermal Receiver

“…A detailed description of the completed receiver design process can be found in [15]. One of the novelties of their construction is the utilisation of bendable CIGS PV modules representing the electrical receiver part [16]. Secondly, triethylene glycol was successfully tested for its implementation in the CPVT receiver, both as a heat transfer fluid and as the liquid part of the required optical filter [17].…”

“…The receiver input plane is supposed to be planar for the current version of the optical model. However, as the currently available design concepts of the authors include a circular cross section of the CPVT receiver [15,16], this simplification needs to be revised in an ensuing version, in case the proposed receiver designs are implemented into a prototype.…”