Title: Optimization of concentrator photovoltaic solar cell performance through photonic engineering

Abstract

The goal of this program was to incorporate two new and innovative design concepts into the design and production of CPV cells that have near zero added cost, yet significantly increase the operational efficiency of CPV modules. The program focused developing luminescent coupling effects and radiative cooling layers to increase efficiency and suppress CPV module power losses due to spectral variations and heating. The major results of the program were: 1) The optics of three commercial refractive (Fresnel) concentrators were characterized and prevent application of radiative cooling concepts due to strong mid-IR absorption (4-12µm) required to effectively radiate blackbody radiation from the cells and provide cooling. Investigation of alternative materials for the concentrator lenses produced only undesirable options—materials with reasonable mid-IR transmission for cooling only had about 30-40 visible transmission, thus reducing incident sunlight by >50%. While our investigation was somewhat limited, our work suggests that the only viable concentrator system that can incorporate radiative cooling utilizes reflective optics. 2) With limited ability to test high concentration CPV cells (requires outdoor testing), we acquired both semi-crystalline and crystalline Si cells and tested them in our outdoor facility and demonstrated 4°C cooling using a simple silica layer coating on the cells.more » 3) Characterizing Si cells in the IR associated with radiative cooling, we observed very significant near-IR absorption that increases the cell operating temperature by a similar amount, 4-5°C. By appropriate surface layer design, one can produce a layer that is highly reflective in the near-IR (1.5-4µm) and highly emissive in the mid-IR (5-15µm), thus reducing cell operational temperature by 10°C and increasing efficiency by ~1% absolute. The radiative cooling effect in c-Si solar cells might be further improved by providing a higher thermal conductive elastomer for securing the cover glass on top of the AR-coating. Since it was never imagined that the front surface would provide any cooling for solar cells, thermal conductivity of this elastomer was never a design consideration, but, improving the conductivity could decrease cell temperature by another 3-4°C. The combined effect could be an ~1.5% absolute increase in cell and module efficiency, a very significant improvement. 4) Developed a numerical model to explore dependence of luminescent coupling efficiency over a broad range of operating conditions. We developed a novel method and facility to experimentally measure the luminescent coupling that can be used to confirm the dependence of luminescent coupling on multi-junction cell design parameters.« less

Authors:

Harris, James ^[1]

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+ Show Author Affiliations

1. Stanford Univ., Stanford, CA (United States)

Publication Date:

Wed Apr 04 00:00:00 EDT 2018

Research Org.:

Stanford Univ., CA (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office

OSTI Identifier:

1431038

Report Number(s):

DE-EE0007544

DOE Contract Number:  

EE0007544

Resource Type:

Technical Report

Country of Publication:

United States

Language:

English

Subject:

14 SOLAR ENERGY; 36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; concentrator photovoltaic cells; CPV; multi-junction; radiative cooling; luminescent coupling; high efficiency; solar cell; photovoltaic; photon management