Panasonic Corp developed a light-concentrating system using 1 x 1mm multi-junction (MJ) compound semiconductor photovoltaic (PV) cells and announced it at EU PVSEC, an international academic conference that runs from Sept 30 to Oct 4, 2013, in Paris.
When Panasonic measured the module conversion efficiency of the system outdoors, it was 34.7%, the company said.
The system concentrates light with 10 x 10mm lenses and 0.95 x 0.95mm cells. The cell's aperture area, which contributes to power generation, is 0.56 x 0.56mm. To make a 50 x 50mm module, 25 (5 x 5) sets of cells and lenses are combined.
The height of the module is 20mm. Its light concentration ratio is 625. The cell is a triple-junction compound semiconductor PV cell using GaAs for its substrate and supplied by Solar Junction Corp.
The new light-concentrating system has the following three features. First, its smaller cells enable to prevent temperature rise, facilitating heat release. Second, with the smaller cells, the variation in the location where lights with different wavelengths are projected is reduced, eliminating the need for the second lens.
Third, with a structure in which the lens is in contact with the cell, the optical loss generated at the interface between the lens and air is reduced. In addition, 50 x 50mm modules can be freely connected like toy blocks to have a desired shape, Panasonic said.
The short-circuit current density, open voltage and fill factor of the module having a conversion efficiency of 34.7% are 10.0mA/cm2, 3.23V and 0.789, respectively. They were measured in Kyoto, Japan, with a wind speed of 1.2m/s and a direct normal irradiance (DNI) of 735W/m2 at a temperature of 30.5°C.