Tech Briefs Magazine - August 2022 - 44

Power & Energy
require ions to travel a longer path, limiting
the utilization of electrodes. Temperature
adjustments can alleviate these
negative impacts but may introduce added
complications. The trick is to design a
battery that offers the best balance for
stationary applications.
" Our goal with this research is to identify
a 'sweet spot' to leverage the advantages
of electrode loading and increased
temperatures to maximize the performance
of LTO/LMO battery cells, " Ha
said. " Our research refined material designs
for BTMS specifically, converting
this well-known power chemistry to energy
cells. "
The NREL team further verified their
findings by applying electrochemical modeling
to simulate reactions at different
temperatures and electrode thickness.
This modeling, in alignment with experimental
results, emphasized the impact of
transport limitations and informed strategies
to improve the cell performance. By
allowing batteries to have intermittent rest
during discharge, instead of being fully
discharged as for electric vehicles, the electrode
utilization was significantly improved.
Researchers found this type of
pulsed discharge is well suited for BTMS
stationary applications, where the batteries
will be used only when there is intermittent
demand and then transitioned back
to a resting stage.
Although these optimized LTO/LMO
battery cells offer many advantages, the
research team is also exploring cathode
options that may better meet BTMS system
needs. NREL's expertise in materials
development will be combined with
the cutting-edge electrochemical modeling
used in this project to streamline further
research into new materials and experimental
battery designs for stationary
storage and beyond.
For more information contact David
Glickson at David.Glickson@nrel.gov; 303275-4097.
Photovoltaic
Cell Increases Nighttime Power Generation
The device uses a thermoelectric module to generate voltage and current from the temperature
gradient between the cell and the air.
Stanford University, Stanford, CA
S
olar cells provide power during the
day but saving energy for later use requires
substantial battery storage. Researchers
from Stanford University have
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. The study was
published in Applied Physics Letters.
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 exist44
sky
Radiative
cooling
Solar
cell
TEG
Heat sink
The device generates electricity at night from the temperature difference between the solar cell and
its surroundings. (Image: Sid Assawaworrarit)
ing 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
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square meter, which means lighting
would require about 20 square meters of
photovoltaic area.
The research aims to optimize the thermal
insulation and thermoelectric components
of the device. The team is exploring
engineering improvements to the
solar cell itself to enhance the radiative
cooling performance without influencing
its solar energy harvesting capability.
For more information, contact Larry
Frum at media@aip.org; 301-209-3090.
Tech Briefs, August 2022

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Tech Briefs Magazine - August 2022

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