Maryland [US]April 18, 2008 (ANI): A new Stanford University study has shown that solar cells can harvest energy from the surrounding environment and continue to function after the sun sets. This eliminates the need for batteries.
The findings of the study were published in the journal, ‘Applied Physics Letters’.
Researchers have developed a photovoltaic solar cell that draws energy from the surrounding environment day and night. It makes use of heat leaking from Earth into space. Solar cells radiate heat to the sky at night, and reach temperatures that are just a few degrees below ambient air.
The thermoelectric module is used to generate current and voltage from the temperature gradient between cells and air. This setup is very affordable and could be integrated into existing solar cells.
The study found that approximately 750,000,000 people around the world don’t have access to electricity at nights. Although solar cells can provide power throughout the day, storing energy for later use is essential.
Solar cells lose heat to the atmosphere at night and radiate heat to the skies, reaching temperatures that are a few degrees lower than the ambient air. The thermoelectric module generates voltage and current from the temperature gradient of the cell and the ambient air. This process is dependent on the thermal design of this system, which includes a hot and cold side.
“You want the thermoelectric to have very good contact with both the cold side, which is the solar cell and the hot side, which is the ambient environment,” said author Sid Assawaworrarit. “If you don’t have that, you’re not going to get much power out of it.”
The team demonstrated power generation using their device during the day. It runs in reverse and adds more power to the solar cell.
The setup is very affordable and could theoretically be integrated into existing solar cells. It is also very simple so it is possible to build in remote locations that have limited resources.
“What we managed to do here is build the whole thing from off-the-shelf components, have a very good thermal contact, and the most expensive thing in the whole setup was the thermoelectric itself,” said author Zunaid Omair.
A few watts is required to light up electricity at night. The current device produces 50 milliwatts per square foot, which would mean that lighting would need approximately 20 square meters of solar area.
“None of these components was specifically engineered for this purpose,” said author Shanhui Fan. “So, I think there’s room for improvement, in the sense that, if one really engineered each of these components for our purpose, I think the performance could be better.”
The team is working to optimize the thermoelectric and thermal insulation components of the device. They are investigating engineering improvements to the solar cells to increase its radiative cooling capability without affecting its solar energy harvesting capabilities. (ANI)
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