Technion researchers have developed a technology that could improve the efficiency of photovoltaic cells by nearly 70 percent.Sunlight offers an infinite source of renewable energy. If we add the amount of solar energy that is absorbed by the Earth’s atmosphere, land and oceans every year, we end up with approximately 3,850,000 EJ (exajoules or 10^18 joules). This is equivalent to: 2.7 million earthquakes of the same size as the Tohoku earthquake in Japan (2011); 40 000 times the total energy consumption in the United States; and 8000 times the total consumption in the whole world.
The energy resource of the sun is awesome, and as fossil fuels decline in supply and global warming increases, the heat is on to find new means to generate power to supply a rapidly expanding global population.
The leading technology today is the photovoltaic cell. Currently, photovoltaic cells use a narrow range of the solar spectrum: radiation outside the range is wasted. This energy loss limits the maximum efficiency of current solar cells to around 30 percent.
At the laboratory of Prof. Carmel Rotschild in the Faculty of Mechanical Engineering, a new strategy is underway to increase these low levels of efficiency. The team’s method is based on an intermediate process that occurs between sunlight and the photovoltaic cell. The photoluminescence material they created absorbs the radiation from the sun, and converts the heat and light from the sun into an “ideal” radiation, which illuminates the photovoltaic cell, enabling higher conversion efficiency. As a result, the device’s efficiency is increased from 30 percent (the conventional value for photovoltaic devices), to 50 percent.
The inspiration for the breakthrough comes from optical refrigeration, where the absorbed light is reemitted at higher energy, thereby cooling the emitter. The researchers developed a technology that works similarly, but with sunlight.
“Solar radiation, on its way to the photovoltaic cells, hits a dedicated material that we developed for this purpose, the material is heated by the unused part of the spectrum,” says graduate student Assaf Manor, who led the study as part of his PhD work. The group aims to demonstrate a full operating device with record efficiency within five years’ time. If they are successful, this could become a disruptive technology in solar energy.
The study was conducted with the assistance of the Grand Technion Energy Program (GTEP) and the Russell Berrie Nanotechnology Institute (RBNI) at Technion.