Advanced studies for new photovoltaic technologies capable of operating even at night

A solar panel that works at night and 'a contradiction in terms. In a word: impossible. But Steven Novack, Idaho National Laboratory of the U.S. Department of Energy, has developed a new concept of solar panels intended to create a revolution in the industry. And most of all overcome the major limitation of solar panels: no sun, and at night, they do not produce energy, with the obvious limitations that this' implies.

INFRARED - Novack began with an observation of fact: about half 'of the available energy of the solar spectrum at the Earth in the infrared band (Ir). And part of this is re-emitted as heat from the ground during the night. If the night and 'cover, in part, the infrared are reflected back to the ground. That's why 'in the deserts, where the cloud cover and' absent, at night the temperature drops considerably and it's cold: the heat is dispersed through the atmosphere and into space as radiation Ir.

MICROANTENNE - Realizing a system of microantenne wavelength infrared (above 700 nanometers), laboratory tests have verified the possibility 'to collect 84% of the re-emitted photons from the ground. A real operating system used on a large scale could rise to 46%. It 'still an efficiency far greater than that of the best current photovoltaic panels, whose silicon cells does not exceed 20% in the best conditions. Actually 'traditional panels have efficiency even less,' cause if the cells are not precisely positioned at an angle with respect to the angle of the sun if it becomes hot or too past the optimum operating temperature, the production of electricity collapses to a fraction of the nominal value. The microantenne, instead, are able to absorb infrared in a wide angular range.

DIODES - A difference of the photovoltaic cells, which absorb photons to release electrons and generate energy, microantenne work in another way. Enter into resonance with the wavelength of Ir generating an alternating current, but at a frequency too high to be used. The alternating current (AC) should be transformed into direct current (DC), but there is a problem. The silicon semiconductor diodes that convert AC to DC do not work at high frequencies generated, explains Aimin Song, engineer nanoelectronic University 'of Manchester. Also when they are shrunk to the size of microantenne, the diodes become less conductive. But Song and, independently, Garret Moddel University 'of Colorado at Boulder, are solving this crucial problem with the creation of a diode capable of using newly developed high optical frequencies.

PLYWOOD - Once you overcome the problem of the diodes, the ideal would be to make a plywood panel capable of operating at different frequencies. Is therefore able to absorb sunlight during the day, both the infrared emitted from the ground at night and even those sent back to earth from the clouds. Then a panel that works both day and night. In practice, the squaring of the circle.

NMS - In addition to the diodes, the problem is to produce microantenne the size of the infrared radiation: a few hundred nanometers (a nanometer and 'one-millionth of a millimeter). At the time the research group of Novack to Idaho Falls has created microantenne capable but 'to operate only in the far infrared, but seem possible within a few months microantenne able to work even in the middle and near infrared spectrum.

Nanotubes - a major impetus to this technology that could revolutionize the world of solar energy, can 'get by carbon nanotubes, developed by Michael Strano, Han Jae-hee and Geraldine Paulus of Mita' in Boston. The group, in Nature Materials of last Sept. 12, announced that he had found a way to make the microantenne Novack of using carbon nanotubes. Strano and his colleagues have created a sort of long fiber thousand nanometers and 400 nanometers thick, composed of approximately 30 million nanotubes. The costs of carbon nanotubes have been halved in recent years more 'times and, according to Strange, in the near future will come down to a few cents per pound (a little less than a pound). The nanotubes have so far achieved 87% efficiency in the ratio of energy produced than absorbed, but the research team is working on an advanced version with an efficiency of 99 percent.

DENMARK - The nanotubes are proving very promising and are studied also at the Center for Nanoscience at the University 'of Copenhagen. In particular Peter Krogstrup Niels Bohr Institute, in collaboration with other researchers funded by the company 'SunFlake, is focusing on the purity of the nanofibers, in which the electronic structure and' perfectly uniform throughout the material. An important aspect, as more 'nanotubulo and' pure and greater 'efficiency. In Denmark, however, 'the research, which appeared on the November 2010 issue of Nano Letters, focuses on different nanofibers, carbon but not gallium and arsenic.

RESEARCH AND WILL OF INVESTMENTS - About 2 billion people have no access to electricity, almost all countries in the Third World. Renewable energy, in particular solar, could meet the needs of at least half 'of the population without electricity, according to studio estimates Bernoni and Efrem made for the second edition of Good Energy Award. The development of the new generation of photovoltaics night just seems destined to close this gap. And without increasing emissions of greenhouse gases. It 'just a matter of will' to invest resources in research in this direction.




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