Solar cell keeps working long after sun sets
Harvesting energy from the temperature difference between photovoltaic
cell, surrounding air leads to a viable, renewable source of electricity at night

Date:
April 5, 2022
Source:
American Institute of Physics
Summary:
Researchers have constructed a photovoltaic cell that harvests
energy from the environment during the day and night, making use
of the heat leaking from Earth back into space. At night, solar
cells radiate and lose heat to the sky, reaching temperatures a
few degrees below the ambient air. The device under development
uses a thermoelectric module to generate voltage and current from
the temperature gradient between the cell and the air. The setup
is inexpensive and, in principle, could be incorporated within
existing solar cells.



FULL STORY ========================================================================== About 750 million people in the world do not have access to electricity
at night. Solar cells provide power during the day, but saving energy
for later use requires substantial battery storage.


========================================================================== InApplied Physics Letters, by AIP Publishing, researchers from Stanford University constructed a photovoltaic cell that harvests energy from the environment during the day and night, avoiding the need for batteries altogether. The device makes use of the heat leaking from Earth back
into space -- energy that is on the same order of magnitude as incoming
solar radiation.

At night, solar cells radiate and lose heat to the sky, reaching
temperatures a few degrees below the ambient air. The device under
development uses a thermoelectric module to generate voltage and current
from the temperature gradient between the cell and the air. This process depends on the thermal design of the system, which includes a hot side
and a 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 in their device during the day, when it runs in reverse
and contributes additional power to the conventional solar cell, and
at night.

The setup is inexpensive and, in principle, could be incorporated within existing solar cells. It is also simple, so construction in remote
locations with limited resources is feasible.

"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.

Using electricity at night for lighting requires a few watts of power. The current device generates 50 milliwatts per square meter, which means
lighting would require about 20 square meters of photovoltaic area.

"None of these components were 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 aims
to optimize the thermal insulation and thermoelectric components of the
device. They are exploring engineering improvements to the solar cell
itself to enhance the radiative cooling performance without influencing
its solar energy harvesting capability.


========================================================================== Story Source: Materials provided by American_Institute_of_Physics. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Sid Assawaworrarit, Zunaid Omair, Shanhui Fan. Nighttime electric
power
generation at a density of 50 mW/m2 via radiative cooling
of a photovoltaic cell. Applied Physics Letters, 2022; 120 (14):
143901 DOI: 10.1063/5.0085205 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220405115222.htm

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