Vision Show 2009: A Solar Vision

Appropriately enough for a talk given in the Valley of the Sun, the keynote at the Vision Show in Phoenix in early April concerned solar power.

Peter Klaerner, a staff process engineer at SolFocus of Mountain View, Calif., spoke about concentrating photovoltaics (CPVs), his company's specialty. He noted that machine vision could play a vital role in a number of manufacturing steps in CPV. That could be good news for vision companies.

The interaction between vision and solar could also be good for solar. After finishing the talk, Klaerner was answering questions and mentioned one of the manufacturing challenges in CPV. That's when a member of the audience came up with a possible solution on the spot. Klaerner then told the vision vendor's rep, "See me later and we'll talk about it."

Unlike the solar panels found on rooftops and elsewhere, concentrating photovoltaics require direct sunlight and tracking of the sun. That's because they concentrate sunlight, either through lenses or mirrors, as much as 500 times.

The payoff is that only a small amount of photovoltaic material is needed as compared to the more common rooftop PVs. Efficiencies can be much higher, with current triple junction compound semiconductor cells achieving a 40 percent figure versus the 15 percent or so of single junction silicon PVs.

CPVs also do better in hotter climates. The power output of CPV falls less than 5 percent from its rated value when the temperature hits 40 °C, according to data presented by Klaerner. For silicon photovoltatics, the corresponding figure is a drop of more than 25 percent. So in hot climates, CPV puts out 20 percent more energy for the same rated power than conventional PVs.

However, concentrating photovoltaics face some manufacturing challenges. Among them, Klaerner noted, are component quality and alignment. The quality is impacted by the shape, reflectivity, and absorption of the optical structures. For SolFocus, for example, one concern is the concentrator. This consists of a primary and secondary mirror and an optical rod, all of which focus sunlight down onto a postage stamp-sized semiconductor chip.

A mirror with problems reduces the amount of light that makes it to the chip. But mirrors are difficult to inspect because they're reflective and curved. That's where the solution proposed by the keynote audience member comes in. A vision system placed at the mirror's focus, with the right optics and lighting, could potentially easily and thoroughly inspect the whole structure.

Additional innovations could help other manufacturing steps. Such solutions, Klaerner readily acknowledged, might be easier for a vision expert to come up with than they would be for a solar process engineer.

Of course, it isn't just CPVs that could benefit from such techniques, a fact that's attracted attention. For example, just before the Vision show, Dalsa Corporation of Waterloo, Ontario announced its entrance into the solar cell inspection market. For a more complete discussion of this trend and what it means, see the GreenLight section of the May 2009 Photonics Spectra.

Hank Hogan, Photonics Spectra contributing editor
hank@hankhogan.com