Hologram PV windows

A novel approach to solar PV has been quietly hatching in Tucson for a number of years. I’ve been on their trail since early ’98, but until very recently they were in strict stealth-mode, and it was impossible to get a handle on what they were doing. (It was refreshing to see a startup that understood the benefits of laying low until they have something to show.)

TerraSun’s patent issued quietly in March ’99 (# 5,877,874), and then in mid May of this year, they did a press release and launched an effort to raise money and identify potential customers and strategic partners (suppliers and sales channels). The company has been funded up to now by part-owner Apogee Enterprises (nasdaq APOG), an $800 million major manufacturer of architectural window products (www.apog.com).

Their PV technology uses holographic optics to concentrate light onto standard silicon cells. Imagine a multi-layer window pane with solar cells arrayed across it in long bands, leaving clear spaces inbetween. If a band of cells is 1″ wide, then the clear space would be from 1″ to 4″ wide. A holographic film, sandwiched between layers of glass, directs the incoming light into the solar cells. Solar concentration ratios of 1.5 have already been demonstrated, and the company believes they can reach ratios of 4-5.

There are several implications. One, as with any concentration scheme, less area of silicon is needed, which presumably lowers cost. Two, the wavelengths of light directed into the cell can be optimized. Three, the window remains transparent, allowing the passage of light, ideal, for example, for skylights. Four, the wavelengths of this transmitted light can be tuned, for example to reject heat. TerraSun has coined a term “Power Window” to describe a product which produces on peak electricity, while allowing the passage of daylight. (The company estimates this approach will be competitive with the various semi-transparent thin-film PV approaches that others are developing.)

With the growing interest in BIPV (building integrated PV), and energy efficiency in general (e.g. low emissivity coatings for windows), TerraSun expects to exploit huge opportunities not only in PV, but eventually in other applications of holographic optics as well. They see energy as perhaps only the first area of application for holographic optics, which is the company’s real strength. (Using holograms as optical devices is a relatively new and little-known idea. In effect, holograms can be made to act as lenses, mirrors, filters, etc., processing light instead of just recording images.)

The company’s website is http://www.terrasun.com. Much more information is available from the company, in particular, a confidential business plan.

Glenn Rosenberg, 520-512-1995 grosenberg@terrasun.com