Getting More Energy from the Sun

Solar energy continues to grow as a valuable resource amid concerns over a depleting fuel supply and the decline in the earth’s environment. Although improvements in how solar energy is collected and used have been implemented, solar is still a long way from being our primary source of energy. Thanks to the discovery of researchers working to improve the use of solar energy, we may be able to get even more energy from the sun’s rays than first imagined. About 20% of the energy from the solar spectrum is unavailable to cells made from silicon, meaning they are unable to utilize it. According to an article printed in Science Daily News, researchers from the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg worked with their colleagues at the University of Bern, Switzerland and the Heriot-Watt University in Edinburgh, Scotland to determine how at least part of this radiation could be made usable with the use of a practical up-converter. Although the technology used has been in existence since the 1960s, only since 1996 have researchers investigated its potential for use with solar cells. Stefan Fischer of the ISE reported that the researchers had been successful at adapting both the solar cells and up-converter to get the most efficient results to date. Another issue of concern for the researchers is in managing to get the up-converter to utilize the infrared radiation for the solar cells. Solar cells absorb visible and near-infrared light as the radiation falls on them. However, the infrared portion is not absorbed, but goes directly through them. The radiation on the back-side runs into the up-converter, which is a microcrystalline powder made from sodium yttrium fluoride that has been embedded in the polymer. Scientists replaced a part of the yttrium with erbium, an element that is active in the optical range, and which will be responsible for the up-conversion. Light that falls on the up-converter causes the erbium ions to be raised to a higher energy state, having an effect like multiple people climbing on a ladder. An ion that “jumps down” from the highest state emits light that has energy equivalent to all those particles that assisted it on the climb up. The up-converter collects the energy from the cells, and then transfers it to a single cell. This high energy cell becomes visible to the solar cells so that they can utilize it.