The efficiency of conventional stacked-layer solar cells is compromised because some incoming light is reflected or lost as heat, instead of being absorbed and converted to electricity. Researchers at United Innovations in San Marcos, CA, have developed a new approach that captures incoming photons in a spherical cavity treated with a highly reflective coating and lined with multiple photovoltaic cells. Each cell is covered by a filter that transmits only those photons whose wavelengths match the cell’s highest sensitivity range; other photons are reflected within the cavity until they are absorbed by the proper cells. With support from the National Renewable Energy Laboratory of the U.S. Department of Energy, United Innovations has built a prototype and is testing the efficiency of the basketball-size cavity, which generates 1.5 kilowatts, says president Ugur Ortabasi. A computer model predicts that 48 percent of the captured solar energy will be converted into electricity. That would smash the industry record (34 percent), but to achieve it in practice may take several years.