Special solar cells have a combined efficiency of 42.8% when illuminated by sunlight at standard terrestrial conditions, say researchers with a University of Delaware-led consortium of industrial companies, national laboratories, and universities.
That bests the current record of 40.7%, noteworthy in a field where gains of 0.2% are the norm and 1% is seen as highly significant. The work is said to be an important milestone toward the 50% efficiency goal set by Darpa’s very high efficiency solar cell (VHESC) program.
VHESC solar cells use a special lateral optical concentrating system that splits sunlight into three different energy bins of high, medium, and low, and directs them onto cells of various light-sensitive materials that cover the solar spectrum. The stationary concentrator’s wide acceptance angle captures large amounts of light and eliminates the need for complex tracking devices. The 40.7%-efficient system, for comparison, needs sophisticated tracking optics and a table-sized concentrating lens more than 30 cm thick.
The VHESC devices are <1 cm thick and give about 20 magnification. A low profile and lack of moving parts could let the units mount on laptop computers, for example. Lightweight solar battery chargers incorporating VHESC technology could integrate into common battlefield devices such as night-vision goggles, radios, and GPS navigation systems.
American soldiers today carry packs weighing nearly 100 lb, of which about 20 lb is a three-day supply of batteries for powering gear. The Darpa program aims to dramatically shrink the battery logistics pipeline and give soldiers more electrical power in a smaller package.