The Micro- and Nanotechnology Research Group of the Universitat Politècnica de Catalunya (UPC) has produced silicon photovoltaic cells with a conversion efficiency of 20.5 percent, the highest level achieved in Spain using this material. This figure is comparable to results obtained by leading research groups in the field at the international level. The cells developed by the UPC researchers have surpassed the 15 percent barrier — the average efficiency of the most common photovoltaic cells. Specifically, a conversion efficiency (of incident light to electric power) of 20.5 percent has been achieved, which means the energy produced per unit of area can be increased by one third. For example, thanks to the high efficiency of this new cell type, only 4.8 m² of photovoltaic panels would be needed to meet one family's annual energy needs (an average of about 4 kWh per day). This compares to an area of 6.5 m² for traditional cells. Pablo Ortega and Gema López, members of the UPC team responsible for developing the high-efficiency photovoltaic cells. (Image: UPC) The cells are made of crystalline silicon and work in a simple way, much as conventional cells do. The light captured by the cells generates charges that are drawn off at the panel contacts and transformed into an electric current. “The goal is to generate a lot of charges that don’t get lost — that make it to the contacts,” said Alcubilla, a member of the research group. Finally, after the light from the sun has been converted into electric current, it is fed into the power grid for domestic and industrial use. The key to the success of the project was therefore to minimize losses, and by pursuing this approach the UPC researchers have managed to produce the most efficient silicon cells in Spain. “We've done a lot of work on the conception and development of new materials and structures, and on the technology needed to optimize the entire process and achieve high levels of efficiency,” said Alcubilla. The next step is to develop procedures that facilitate large-scale production. The result achieved in this research (which has involved 38 trials since 2002) is comparable to those obtained in other research projects carried out in countries that are taking the lead in the field of photovoltaic energy. The maximum efficiency obtained for cells of this type is 24.7 percent, a record set by an Australian group at the University of New South Wales. Photovoltaic energy around the world According to the International Energy Agency, with over 4000 MW, Spain is one of the countries with the most photovoltaic capacity installed. The leader is Germany, with 7203 MW installed. According to the European Photovoltaic Industry Association, in 2009 total installed capacity worldwide was 22,787 MW, with the European Union (EU) accounting for 15,943 MW. In fact, in two years, from 2007 to 2009, the EU became the leader in the sector, tripling the number of photovoltaic installations in member countries. Japan was a distant second with 2633 MW. According to data provided by Red Eléctrica Española, in 2010 solar energy met 2 percent of the total demand for electric power in Spain and represents 6.25 percent of the total covered by renewables, a category that includes hydroelectric energy, wind power, solar thermal, biomass, geothermal energy, marine energy, and other sources. For more information, visit: www.upc.edu