Solyndra - Technology

Technology

Solyndra designed, manufactured, and sold solar photovoltaic (PV) systems composed of panels and mounting hardware for large, low-slope commercial rooftops. The panels perform optimally when mounted horizontally and packed closely together, thereby, the company claimed, covering significantly more of the typically available roof area and producing more electricity per rooftop on an annual basis than a conventional panel installation.

The solar panels developed by the company were claimed to be unlike any other product ever tried in the industry. The panels were made of racks of cylindrical tubes (also called tubular solar panels), as opposed to traditional flat panels. Solyndra rolled its CIGS thin films into a cylindrical shape and placed 40 of them in each 1-meter-by-2-meter panel. Solyndra designers thought the cylindrical solar panels absorbed energy from any direction (direct, indirect, and reflected light).

Each Solyndra cylinder, one inch in diameter, is made up of two tubes. The company used equipment it had developed to deposit CIGS on the outside of the inner tube, which includes up to 200 CIGS cells. On top of the CIGS material, it added an "optical coupling agent", which concentrates the sunlight that shines through the outer tube. After inserting the inner tube into the outer tube, each cylinder is sealed with glass and metal to exclude moisture, which erodes CIGS's performance. The hermetic sealing technology is commonly used in fluorescent lamps.

When combined with a white roof (the fastest growing segment of the commercial roof industry with over 1 billion square feet installed in 2008 and required for any new commercial construction in California), the company claimed that systems that employ the panels on a given rooftop could produce significantly more electricity in a given year. It was thought that on a white roof, the panels can capture up to 20% more light than a black roof. (Note: it is difficult to cite a specific reference for this because the exact gain depends on the latitude of the installation (i.e. sun angle). Solyndra's on-line energy modeling tool allowed designers to specify the roof albedo, and energy output varied as a function of albedo. Twenty percent is cited as typical figure and was validated by careful testing and modeling by the Fraunhofer Institute, among others. However, this report is not available on-line.)

The other advantage claimed by the company was that the panels did not have to move to track the Sun. The panels are always presenting some of their face directly perpendicular to the Sun. The daily production of flat solar panels has an output curve that has a clear peak while Solyndra claimed their system produced more power throughout the day.

The Solyndra panels allow wind to blow through them. According to the company, these factors enable the installation of PV on a broader range of rooftops without anchoring or ballast, which are inherently problematic. Solyndra claimed that wind and snow loads are negligible and that its panels are lighter in weight per area.

The company claimed the cells themselves convert 12 to 14 percent of sunlight into electricity, an efficiency better than competing CIGS thin-film technologies. However, these efficiencies are for the cells laid flat. The company did not post any numbers about performance when the cells are rolled up. The Solyndra 100/200 spec sheet doesn't mention the cells or the panel efficiencies directly. However, calculating from the data provided shows the high-end 210 panel has a field efficiency of about 8.5%.

In 2006, Solyndra began deploying demonstration systems globally. The company stated the total count was 14 systems and that these systems were each instrumented with sensitive radiation, wind speed, temperature, and humidity measurement devices to aid in the development of energy yield forecasting software tools. The company's website claimed there were more than 1,000 Solyndra systems installed around the world, representing 100 megawatts of power.