Nanosolar: Tubular Thin Films Are Overrated

Nansolar says it can make tubular solar cells too. But it says it doesn't need to.

In a long blog post Wednesday that aimed to discredit competitor Solyndra, Nanosolar CEO Martin Roscheisen said designing and making thin-film tubes isn't so tough. The company even rolled some of its thin film solar cells in a tube to prove it.

But he then proceeded to rebuke many of the claims made by Solyndra about why its solar equipment is superior.

"After all, if there is something that makes business sense about the tubular product concept, we'd surely be the ideal company to manufacture it at lowest cost and bring it to the market in volume!" Roscheisen wrote.

Solyndra is a new player whose unusual thin-film designs have caught a lot of attention in the solar world. The Fremont, Calif.-based startup has developed a way to deposit copper indium gallium selenium (CIGS) on a glass tube.  The tube is then encased in a second glass tube to protect it from moisture, which can seriously erode the CIGS' performance.

The cylindrical shape allows Solyndra's cell to face the sun directly for longer periods of time in a day than a flat solar cell. Hence, cylindrical cells can produce more power.

The tubes are then placed side by side in a 1-meter by 2-meter aluminum frame for installation (see Solyndra Rolls Out Tube-Shaped Thin Film).

Putting CIGS inside a tube is unusual. Other thin-film developers are making cells that lay flat on a panel, the same design as the conventional crystalline silicon solar panels commonly seen on the market today.

Solyndra says its tube and panel designs can capture not only direct sunlight. It also does wonder in capturing light reflected from the ground, especially when installed on a roof made with white membranes. Because the tubes are spaced with a gap in between, the panels can withstand strong wind, the company said.

All these claims have made Solyndra a company to watch. It doesn't hurt that it's announced $1.5 billion worth of contracts with installers in Germany and the United States (see Solyndra Snags $320M with Roofing Firm and Solyndra Signs $250M GeckoLogic Deal).

Roscheisen doesn't see the appeal. The tubular design is flawed because it limits the amount of solar cells facing the sun. In comparison, each flat-plate panel exposes all of cells to the sun, and can be tilted to get the maximum exposure.

"Cost-efficient solar requires maximizing the area of sun collection relative to the area of solar cell material used. So tubes are 50% less efficient to start," Roscheisen wrote.

He also pointed out that solar cells can't produce as much electricity from reflected light as directed light. Besides, dirt and other crud can prevent any white roof from reflecting the light.

And, by the way, Nanosolar can make tubular thin films cheaper, he said. In fact, Nansolar engineers have made prototype tubes that Roscheisen said would cost 70 percent to make than Solyndra's tubes.

How? By printing a sheet of CIGS cells, rolling it up and inserting it into a glass tube. Instead of inserting into another glass tube to prevent moisture, Nanosolar would add a layer of foil inside the tube to seal the cells. This method would cut down on the costs of using glass and depositing CIGS cells on the tube.

Roscheisen told Greentech Media via email that he was able to figure out that the Nanosolar process would cost 70 percent less based on the "substantial cost of the glass tubes as well as the cost of high-vacuum deposition they use."

Even though flat-plate thin-film panels also use a glass backing, Roscheisen maintained that tubular glass costs more than the flat kind.

Solyndra must be posing a serious threat to San Jose, Calif.-based Nanosolar, which started commercial production last year. The company has said much about its sales and production efforts. It's developing two solar power plants in Germany (see Nanosolar to Build 10MW Power Plant).

Roscheisen dismissed the idea that Solyndra has become a strong competitor.

"Solyndra is only beginning to compete in the [commercial rooftop market], and in this segment for only about 3 percent of the buildings which have a white rooftop. So they overlap with us in 1 percent of the markets we already are in," Roscheisen told Greentech Media via email.

Solyndra didn't immediately return calls for comment.