Cheap Solar Electricity?

Nanosolar, a California-based company, has developed a unique technology for producing cost-efficient solar electricity. The company says that the new technology is significantly superior to existing solar cell techniques, both in its versatility and in its availability. Named “Innovation of the Year” by Popular Science Magazine, the technology enables production of several hundred feet of “solar sheet” per minute and relies on recent advances in the field of nano-structured materials.
“Roll-to-Roll” processing (Credit: Nanosolar)
“Roll-to-Roll” processing
(Credit: Nanosolar)

The centerpiece of Nanosolar’s technique is a proprietary ink developed by the company, which is used to print the semiconductor of the solar cell. The ink is based on various proprietary forms of nano-particles and associated organic dispersion chemistry. Once it is deposited on a flexible substrate, the ink’s nano-components align themselves via molecular self-assembly, creating a homogenous mix of nano-particles that ensure the perseverance of the correct atomic ratios of the elements involved even across large areas of deposition. This approach is extremely different from the traditional vacuum deposition processes where one effectively has to “atomically” synchronize various materials sources – a complex process, which significantly limits production efficiency.

The material on which the cells are printed is a highly conductive metal foil substrate . The metal foil is 20 times more conductive than the stainless steel often used in the industry. The company says this property enables major cost reduction on the solar cell’s thin-film bottom electrode. “A thin-film solar cell consists of an absorber semiconductor layer, sandwiched between the top and bottom electrode layers. If the thin films of a solar cell are deposited directly onto a highly conductive metal foil (as opposed to glass or stainless steel), then the bottom electrode gets much simpler because the substrate can do the job of carrying the current” – explained the scientists.

Nanosolar’s technology uses a CIGS (Copper Indium Gallium Diselenide) thin-film semiconductor, capable of achieving considerably higher efficiency rates (up to 19.5%) than are achieved when using other thin-film technologies, such as Cadmium Telluride (CdTe) or Amorphous Silicon. In fact, a thin 1-nanometer-wide film of CIGS can generate as much electricity as a 200-300 nanometer-wide crystalline silicon wafer. However, such maximal efficiency rates can be achieved only in laboratory conditions (at this stage). Using expensive processing technology, mass produced CIGS solar cells usually have efficiency rates of 12%-15%, – making them about half as efficient as their crystalline silicon counterparts.

In conventional silicon solar technology, wafer cells are sorted into performance bins according to their electrical characteristics before the cells are assembled into panels. Nanosolar says that this sorting process may result in grouping poorly-matched cells, because cell transitions are created through scribing after they are already deposited on the glass substrate. In contrast, the company claims that their new approach optimizes the accuracy of cell-matching, resulting in better panel efficiency distribution and yield.

The main advantages of Nanosolar’s technique are its relatively high speed and the highly precise manufacturing process. According to the company, its thin-film solar films are more than 100 times thinner than silicon-wafer cells and therefore, have correspondingly lower materials costs – between 10%-20% of the current industry standard per kilowatt. The “printing” technique is executed in a “roll-to-roll” manner, in which meters-wide and miles-long rolls of solar panels are created and cut to a desirable size, much like the way in which newspapers are printed at printing houses. As opposed to the method of processing separate wafers or glass plates, a roll-to-roll printing process can be maintained for the entire length of the roll, eliminating undesirable start-ups and other cycle overhead costs – a key advantage, according to the company.

Nanosolar provides a 25-year warranty for its products, and claim the cells are tested under much harsher conditions than mandated by official certification standards. During product development, the solar cells are exposed to extreme temperatures, frequent changes in the environment, intense UV light, and humidity. These examinations help the company to study the nature of various degradation mechanisms within a short period of time.

TFOT previously covered several novel solar technologies, including organic solar cells and FirstSolar’s cadmium-telluride (CdTe) semiconductor modules.

You can find more information about Nanosolar’s products on the company’s official website.

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