Improved Fresnel Lens Concentrator for Solar Cells

Background

The generation of electricity from sunlight is not cost-effective in many situations because of the inherent limitations of photovoltaic (PV) cells and typical lighting conditions. The production of commonly-used silicon PV cells demands expensive semiconductor fabrication methods and consumption of limited high-grade silicon feedstocks. Newer thin-film cell technologies, while using cheaper fabrication methods, consume even scarcer exotic materials. Moreover, at typical sunlight intensities, PV cells are relatively inefficient, requiring large panels for a given peak power output.

Increased PV cell efficiencies and minimizing the use of costly materials and fabrication techniques will reduce costs. One promising way to accomplish this is with concentrator PV (CPV) systems, which use an inexpensive optical element (usually made of glass) covering a large sun-lit area to greatly concentrate the light onto a small PV cell. Higher light intensities enable higher efficiencies in converting sunlight to electricity and significantly reduce the required size of the PV cell. One important limitation of CPV, however, is the need to keep the concentrator surface aligned with the sun. For CPV to become cost-competitive with conventional PV technology, CPV designs must become less stringent in their alignment requirements (i.e. higher acceptance angles)

Description

A researcher at the University of California, Merced has invented a CPV design that features much wider acceptance angles and maintains a high level of efficiency, a high concentration factor, and more uniform illumination.

The UC Merced researchers had previously developed CPV systems featuring glass sheets functioning in a Cassegrain reflective or a Fresnel lens configuration, and a non-imaging secondary element at the focal point that evenly distributes the concentrated light over a small PV cell. In their new CPV invention, the secondary element was replaced with an element that has a reflective inner surface.

This new secondary element uses specular reflections and (optionally) total internal reflections to achieve more uniform illumination of the small PV cell at wide acceptance angles. As with previous designs, this CPV can be used with both silicon PV cells and with multi-junction PV cells.

Applications

This invention may become a preferred design for CPV systems, helping make CPV more competitive as compared to fixed panel arrays for solar electricity generation.

Advantages

This novel Fresnel lens concentrator design offers a number of potential benefits over previous concentrator technologies, including:
• simple design with few parts,
• relatively low material costs,
• high optical efficiency,
• high angular tolerance to improve tracking requirements,
• uniform light distribution over photovoltaic cells, and
• suitability for use with advanced cell technologies.
As compared to their previous Fresnel lens concentrator design, this invention, with its novel secondary element, offers more uniform illumination at wide acceptance angles.

Patent Status

Patent Pending

Inventor

Roland Winston
Weiya Zhang
Kevin Balkoski