Renewable Report: Can plastic film increase solar panel efficiency?

SolOptics creates its custom lens structure design configurations for solar manufacturers through innovative software and modeling. The company wants to license its technology to plastic processors who work with PET, OPP, PVC, APET, acrylic, or other clear plastics, and with plastics processors that could emboss, extrude, calendar, cast, or mold custom-designed structures for varying solar panels.  

Integrating materials that are low cost to purchase and manufacture into photovoltaics is desired as the solar industry seeks to reduce production costs and speed products to market. Patterning thin, lightweight, transparent or translucent, durable plastics or polymer films could help shift the industry away from more expensive glass solar panels.

New manifestation of an old concept
The concept of using optics to increase the amount of light striking a solar cell is not new. It has been the basis of concentrated solar power (CSP) for years, and seen tremendous success at companies like SolFocus, Emcore, and Amonix.  Others have also offered aftermarket add-ons to photovoltaic (PV) solar panels to increase efficiency, such as flat waveguide optics or Fresnel lenses. However, creating total internal reflection devices as a film applied to glass or perhaps eventually replacing glass is new.

Beyond Validation
SolOptic's arrays of non-concentrating optical micro-lenses boost solar cell efficiency three ways: they increase the path length of light and the amount of light that enters the cell, while reducing the amount of light reflected away from the cell.

As a concept, increasing the path length of light entering a photoconductor and reducing the amount of light reflected has been embraced by the solar industry as a valid way to boost efficiency by "texturizing" the surface of PV cells themselves. Texturizing is now common practice in silicon solar cell processing, and is performed through many different means. Most silicon solar cells appear black colored now due to the texturized silicon and other anti-reflective coatings applied during processing.

SolOptics applies the same concept to the light before it enters the silicon or thin film solar panels, either with a film applied to glass or by creating structures in the glass itself. This approach was validated to increase efficiency during outdoor testing in late 2010 at the National Renewable Energy Laboratory, and recently awarded a patent (with three others pending).

Scalable and cost effective is key
In 2008, a group at MIT found that solar efficiencies could be improved by trapping light in the cell longer by applying coatings and diffraction gratings to the cells, but was deemed not commercially feasible for cost and scalability reasons. The fine dimensions needed for creating diffraction gratings by texturizing glass involved holographic lithography using laser rastering, too slow and costly to scale for processing large surface areas. Even systems that contained multiple laser beams simultaneously working at once were slow, as well as expensive.

In contrast, SolOptics' patent mentions that arrays of structures could be achieved by embossing techniques that do not require such fine patterning as in the past.

Officials at the company estimate manufacturing costs to implement their technology to be less than $0.01/Watt (and quote installed costs at <$0.10/Watt), an attractive price for solar manufacturers. In terms of square footage, manufacturing costs for an average 280Watt solar panel that has 21sq ft of surface area would work out to about $2.80/panel, or $0.13/sq ft.

Since rolls of film could be applied to existing glass in the field and would not require specialized equipment for installation, this low cost efficiency boosting concept could be an attractive opportunity for plastics manufacturers and suppliers to consider.

More Info:

Solar Power 2011

Plastics in Photovoltaics 2011 Conference

Polymers in Photovoltaics 2012 Conference

About the Author: Debbie Sniderman writes, owns, and consults with VI Ventures, an R&D and manufacturing consulting company for renewable energy products and technologies. She can be contacted at [email protected].