Sunlight concentration: holograms and lenses
Prism Solar Technologies use holograms to concentrate light onto photovoltaic (PV) cells. This allows increased output per cell on partially transparent silicon PV windows. From the MIT Technology Review:
Holograms have advantages that make up for their relatively weak concentration power. They can select certain frequencies and focus them on solar cells that work best at those frequencies, converting the maximum possible light into electricity. They also can be made to direct heat-generating frequencies away from the cells, so the system does not need to be cooled. […]
Also, different holograms in a concentrator module can be designed to focus light from different angles — so they don’t need moving parts to track the sun.
Cost savings are a major factor for the development of this technology:The system needs 25 to 85 percent less silicon than a crystalline silicon panel of comparable wattage, Lewandowski says, because the photovoltaic material need not cover the entire surface of a solar panel. […]
The high demand for solar cells in Germany and other European countries “has now outstripped the supply, which has [led to] a silicon shortage and a shortage of manufacturing in the photovoltaic world,” he says.Although the idea of holographic solar concentrators has been around since the early 1980s, no one has developed them commercially yet, according to Professor Stojanoff, who has investigated the technique extensively. His company, Holotec GmbH in Aachen, Germany, researches and manufactures holographic materials. Also, Northeast Photosciences, a Hollis, NH-based company, came close to manufacture, before it went defunct for reasons unrelated to the technology or to finance, he says.
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Stellaris, another player in this field, use small lenses to concentrate the light; from Mass High Tech:
By using small lenses, about 6 millimeters high, that concentrate light onto narrow strips of thin-film photovoltaic material, Stellaris is able to create a solar module that uses less photovoltaic material and is able concentrate sunlight at a ratio between 2-to-1 and 3-to-1 […].
The lens technology is based on non-imaging optics, which gives its glazing material unique aesthetic properties, something Paull believes will help penetrate the building and architectural market, integrated with hard materials like industrial curtains or shingles.
“You can actually see through the glazing, as the energy is being integrated. It’s like a hologram,” he said.
