Efficient low-cost system for producing power at night
Rooftop radiative cooling system could provide lighting power when solar energy is unavailable

Date:
August 13, 2020
Source:
The Optical Society
Summary:
Researchers have designed an off-grid, low-cost modular energy
source that can efficiently produce power at night. The system
uses commercially available technology and could eventually help
meet the need for nighttime lighting in urban areas or provide
lighting in developing countries.



FULL STORY ========================================================================== Researchers have designed an off-grid, low-cost modular energy source
that can efficiently produce power at night. The system uses commercially available technology and could eventually help meet the need for nighttime lighting in urban areas or provide lighting in developing countries.


========================================================================== Although solar power brings many benefits, its use depends heavily on
the distribution of sunlight, which can be limited in many locations and
is completely unavailable at night. Systems that store energy produced
during the day are typically expensive, thus driving up the cost of
using solar power.

To find a less-expensive alternative, researchers led by Shanhui Fan from Stanford University looked to radiative cooling. This approach uses the temperature difference resulting from heat absorbed from the surrounding
air and the radiant cooling effect of cold space to generate electricity.

In The Optical Society (OSA) journal Optics Express, the researchers theoretically demonstrate an optimized radiative cooling approach that
can generate 2.2 Watts per square meter with a rooftop device that
doesn't require a battery or any external energy. This is about 120
times the amount of energy that has been experimentally demonstrated
and enough to power modular sensors such as ones used in security or environmental applications.

"We are working to develop high-performance, sustainable lighting
generation that can provide everyone -- including those in developing
and rural areas - - access to reliable and sustainable low cost lighting
energy sources," said Lingling Fan, first author of the paper. "A modular energy source could also power off-grid sensors used in a variety of applications and be used to convert waste heat from automobiles into
usable power." Maximizing power generation One of the most efficient ways
to generate electricity using radiative cooling is to use a thermoelectric power generator. These devices use thermoelectric materials to generate
power by converting the temperature differences between a heat source
and the device's cool side, or radiative cooler, into an electric voltage.

In the new work, the researchers optimized each step of thermoelectric
power generation to maximize nighttime power generation from a device that would be used on a rooftop. They improved the energy harvesting so that
more heat flows into the system from the surrounding air and incorporate
new commercially available thermoelectric materials that enhance how
well that energy is used by the device. They also calculated that a thermoelectric power generator covering one square meter of a rooftop
could achieve the best trade-off between heat loss and thermoelectric conversion.

"One of the most important innovations was designing a selective emitter
that is attached to the cool side of the device," said Wei Li, a member
of the research team. "This optimizes the radiative cooling process so
that the power generator can more efficiently get rid of excessive heat."
The researchers demonstrated the new approach by using computer modeling
to simulate a system with realistic physical parameters. The models
reproduced previous experimental results faithfully and revealed that the optimized system designed by the researchers could come close to what has
been calculated as the maximum efficiency using thermoelectric conversion.

In addition to carrying out experiments, the researchers are also
examining optimal designs for operating the system during the day, in
addition to nighttime, which could expand the practical applications of
the system.

This work is supported by the U.S. Department of Energy under Grant
No. DE- FG02-07ER46426.


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


========================================================================== Journal Reference:
1. Lingling Fan, Wei Li, Weiliang Jin, Meir Orenstein, Shanhui
Fan. Maximal
nighttime electrical power generation via optimal radiative cooling.

Optics Express, 2020; 28 (17): 25460 DOI: 10.1364/OE.397714 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200813152246.htm

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