Coupled thermal and optical analysis of a planar waveguide concentrator-receiver

Harvesting solar energy using optical concentrators such as parabolic troughs or heliostats involve active tracking that requires costly drives and sizable support structures. This study explores the use of optical waveguides based on total internal reflection for concentrating sunlight onto thermal receivers, with the goal of minimizing or eliminating moving parts, tracking structures and cost. To this end, the paper presents an analytical closed-form solution for the coupled optical and thermal transport of solar irradiation through an ideal planar waveguide concentrator integrated with linear receiver at both ends. The effects of various design and operating parameters are systematically investigated on the system performance, which is quantified in terms of net thermal power delivered, aperture area required and collection efficiency. Design envelopes that identify feasible waveguide configurations based on thermal stress, maximum continuous operation temperature and structural constraints are illustrated. The study provides an upper bound for the maximum performance achievable with planar waveguide concentrator-receiver configuration that can be used asa benchmark to compare different practical designs. Further, a cost analysis is presented to determine the preferred design configurations that minimize the cost per unit area of the planar waveguide concentrator coupled to the receiver. Considering applications to thermal desalination and concentrated solar thermal power generation, optimal design configuration of waveguide concentrator-receiver system is identified that results in the least levelized cost of power (LCOP). Sensitivity analysis of the total cost per unit area and LCOP to waveguide material parameters and cost is used to derive improvements needed to meet the U.S. Department of Energy (DOE) SunShot’s solar field cost target of $75/m2.