By Timothy Dalton
Photovoltaic cells (the individual units of a solar panel) have been around since the 1970s. But until now, they have not been cost or energy effective enough for widespread adoption as an energy source. IBM Research’s latest foray into solar technology, a second-generation Ultra High Concentrator Photovoltaic (UHCPV) system, converts 30 percent of the sunlight that hits it to Direct Current – versus the 20 percent efficiency of conventional solar panels.
Now, what started out as a joint project between IBM Research and King Abdulaziz City for Science and Technology (KACST) through the KACST IBM Nanotechnology Center of Excellence has branched to sunny spots in the United States – Boulder, CO, and Tucson, AZ.
IBM’s inspiration to develop these new photovoltaics came from researching silicon technology for CMOS microprocessors after a client posed the question “what can [IBM] do with your technology in the field of renewable energy?” during the 2006 Innovation Jam.
This started our Materials Science research down the path of looking for ways to further extend our technology into the green space.
New Materials for Improved Efficiency
Traditional solar cells are simple to manufacture because they’re made of silicon. And they only have one p-n junction, or interface between differently doped silicon layers, to convert sunlight to electricity. So, they’re low cost, but their efficiency drops as temperatures climb. Our UHCPV system, on the other hand, can operate at a solar concentration of 1,600 suns because we utilize a compound semiconductor solar cell based on gallium arsenide (GaAs) in a triple junction (three p-n junctions) configuration. The triple junctions convert more sunlight into electricity than the silicon cells, per square centimeter.
The increased efficiency is not free: triple junction cells cost more to manufacture. But UHCPV systems use less cell area than a flat panel system, and have the additional advantage of being less sensitive to temperature, and maintaining high efficiency at high temperatures.
Following the Sun
Tucson and Boulder were chosen for their good DNI (Direct Normal Incidence) of solar radiation – or simply put, these two cities get a lot of sunlight. Tucson has more than 300 “sunny” days per year, according to the National Climate Data Center. Boulder has more than 200.
For now, UHCPV’s major advantage in solar energy is confined to regions like Tucson and Boulder – clear skies with high DNI. But we’re continuing to optimize the design with hopes of licensing it to a photovoltaic manufacturer that can partner with us to go to market.