What about the electrical performance of the solar cells? As electronics professionals, we tend to focus on this rather than the secondary aspects of marketing or mechanical design. In terms of energy harvesting performance, Solyndra promised that cylindrical modules required only their shape to track the sun rather than costly mechanical systems. They reasoned that a curved surface would collect rays at all the sun's angles throughout the day.
Figure 2: The module construction employed by Solyndra is revealed in this cross-section view showing the inner tube coated with the photosensitive CIGS thin film covered with a coupling element to provide a light concentrating effect.
Without data to compare side-by-side, we should be slow to judge. But to a first order, it appears questionable that the cylindrical modules could actually achieve what was advertised. The sun passing across a fixed flat surface definitely produces a constantly varying angle of incidence. Peak output occurs during a relatively short portion of the day as the ray angle is perpendicular to the solar cell surface. Solyndra cited this as their key differentiator.
There is no disputing the fact that the sun strikes the surface of a curved solar cell at right angles throughout much of the day. However, the surface area subjected to this optimal angle is extremely small compared to a flat panel leaving less photovoltaic material exposed to strong sunlight for energy conversion.
Solyndra's process of forming the solar cell material over 360° of the tube along with the gaps between the tubes enabled the harvesting of light passing through the panel and reflected from the surface behind. Although a reflective backdrop improved power output from the Solyndra panels, it is difficult to make a case for their design compared to a panel with 100% fill factor capturing only incident light. There would be little to be gained by leaving large gaps and collecting reflections compared to simply covering the area receiving the direct sunlight.
Figure 3: This Solyndra marketing graphic was used to highlight the ability of the tubular design to accept light through a full 360°.
Solyndra marketing materials pointed to the improvement in solar energy harvesting early and late in the day compared to a crystalline silicon flat panel. If the solar panels were directly tied to a load, a longer window of useful energy would be a big advantage.
Solyndra's datasheet compared output from a standard crystalline flat panel with 15° tilt to their tubular design. Although the Solyndra output was strikingly higher both early and late in the day, peak output at midday was lower than the crystalline panel. The net effect was an increase in total daily energy supplied by the Solyndra panel, but the improvement was only 7%.
Without an independent comparison test, we cannot be entirely certain, but the comparison of outputs even as shown in Solyndra's own marketing collateral was not compelling enough to warrant a much higher price tag for their panels. With feed-in-tariffs in effect, the goal is to sell the most power back to the utility company. That was Solyndra's prime market, but their design offered only a mild performance benefit.
The tubular design for Solyndra solar panels forced them to focus on some niche markets. There is no doubt that their panels allowed light through. One angle was the energy collected after reflection from the surface behind the panels.
Looking to situations where there is value in allowing some light through, Solyndra attempted to market the tubular module concept to greenhouses. They took that one step further to position their product for greenhouses in climates where partial shade is advantageous. Solyndra panels would provide the perfect protection for plants growing underneath while producing electrical energy for greenhouse operations (http://www.solyndra.com/technology-products/greenhouse/