Cooling mechanism increases solar energy harvesting for self-powered outdoor sensors

July 07, 2020

WASHINGTON, July 7, 2020 -- Sensors placed in the environment spend long periods of time outdoors through all weather conditions, and they must continuously power themselves in order to collect data. Many, like photovoltaic cells, use the sun to produce electricity, but powering outdoor sensors at night is a challenge.

Thermoelectric devices, which use the temperature difference between the top and bottom of the device to generate power, offer some promise for harnessing naturally occurring energy. But, despite being more efficient than photovoltaics, many thermoelectric devices flip the sign of their voltage, meaning the electrical current changes the direction of its flow, when environmental temperatures change, so the voltage drops to zero at least twice a day.

"The sign of the thermoelectric device depends on the temperature difference between the top and bottom of the device," author Satoshi Ishii said. "Cooling can be used to create a temperature difference compared to the ambient temperature, and if there is a temperature difference, thermoelectric generation is possible."

In a study published this week in Applied Physics Letters, by AIP Publishing, the authors tested a thermoelectric device made up of a wavelength-selective emitter that constantly cools the device during the day using radiative cooling, the dispersion of thermal energy from the device into the air. As a result, the top of the device is cooler than the bottom, causing a temperature difference that creates constant voltage through day and night and various weather conditions.

The authors compared a broadband emitter with a selective emitter, showing the selective emitter avoids the problem of the voltage dropping to zero during environmental changes in temperature.

"For the selective emitter, it is best to have emissivity close to unity in the atmospheric window, approximately 8 to 13 micrometers, where the atmospheric transmittance is high and thermal emission can effectively radiate into space, which in turn cools the device," Ishii said.

The device they tested is comprised of a 100-nanometer-thick aluminum film on the bottom of a glass substrate. The authors discovered that other sources of heat, such as the roof where a sensor might be mounted, can augment its ability to generate voltage.

"A large temperature difference results in a large thermoelectric voltage," Ishii said. "Using the heat on the backside of the device makes the temperature difference between the bottom and top larger, so heat from behind the device is beneficial for thermoelectric generation."
The article, "Radiative cooling for continuous thermoelectric power generation in day and night," is authored by Satoshi Ishii, Thang Duy Dao and Tadaaki Nagao. The article will appear in Applied Physics Letters on July 7, 2020 (DOI: 10.1063/5.0010190). After that date, it can be accessed at


Applied Physics Letters features rapid reports on significant discoveries in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See

American Institute of Physics

Related Temperature Articles from Brightsurf:

History of temperature changes in the Universe revealed
How hot is the Universe today? How hot was it before?

A drop in temperature
In the nearly two centuries since German physician Carl Wunderlich established 98.6°F as the standard ''normal'' body temperature, it has been used by parents and doctors alike as the measure by which fevers -- and often the severity of illness -- have been assessed.

Kitchen temperature supercurrents from stacked 2D materials
A 'stack' of 2D materials could allow for supercurrents at ground-breakingly warm temperatures, easily achievable in the household kitchen.

Get diamonds, take temperature
Measuring the temperature of objects at a nanometer-scale has been a long challenge, especially in living biological samples, because of the lack of precise and reliable nanothermometers.

Chemical thermometers take temperature to the nanometric scale
Scientists from the Coordination Chemistry Laboratory and Laboratory for Analysis and Architecture of Systems, both of the CNRS, recently developed molecular films that can measure the operating temperature of electronic components on a nanometric scale.

How reliable are the reconstructions and models for past temperature changes?
Understanding of climate changes during the past millennia is crucial for the scientific attribution of the current warming and the accurate prediction of the future climate change.

New method measures temperature within 3D objects
University of Wisconsin-Madison engineers have made it possible to remotely determine the temperature beneath the surface of certain materials using a new technique they call depth thermography.

Who takes the temperature in our cells?
The conditions in the environment are subject to large fluctuations.

Taking the temperature of dark matter
Warm, cold, just right? Physicists at UC Davis are using gravitational lensing to take the temperature of dark matter, the mysterious substance that makes up about a quarter of our universe.

Thermal siphon effect: heat flows from low temperature to high temperature
In this work, researchers study (both thermal and electric) energy transport in physical networks that rewired from 2D regular lattices.

Read More: Temperature News and Temperature Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to