Reports from the Heart of the Machine
Editor: Du Wei
The researchers say they designed photovoltaic cell devices that can charge LED lights or mobile phones.
By exploiting the temperature difference between the solar panels and the surrounding space, engineers have created solar cells that can generate electricity at night. Compared to 100 to 200 watts per square meter of electricity generated by daytime solar cells, power can reach 50 milliwatts per square meter at night.
The study, published recently in Applied Physics Letters, was titled "Nighttime electric power generation at a density of 50 mW/m^2 via radiative cooling of a photovoltaic cell" by Stanford University and ASML, respectively.
Address: https://aip.scitation.org/doi/full/10.1063/5.0085205
Shanhui Fan, one of the authors and a professor of electrical engineering at Stanford University, said, "Solar cells that generate electricity at night are economically interesting for low-power density applications such as LED lights, cell phone charging, or charging small sensors."
Shanhui Fan
Fan and colleagues used the concept of radiant cooling, in which a material radiates heat into the sky after absorbing a full day of solar energy. Others have previously exploited this phenomenon to make cooling coatings and energy-efficient air conditioners. And, due to the influence of this phenomenon, the temperature of standard solar cells facing the sky at night is lower than the temperature of the surrounding air, which causes heat to flow from the surrounding air to the solar cell. Fan and others use this heat flow to generate electricity.
Radiant cooling schematic. Source: National School of Applied Sciences, Lyon, France.
To do this, the researchers integrated a photovoltaic cell (PV) with a commercial thermoelectric generator (TEG) module to convert the temperature difference into electrical energy. Among them, TEG is located under the solar cell, and the aluminum plating material between them conducts heat from the solar cell to the TEG. The other side of the TEG is connected to the surrounding air via a radiator. Figure 1 below shows the radiation cooling process of photovoltaic cells at night.
While existing solar panels can generate electricity at night after being modified with TEG, the key to making these devices work well together is that the thermal contact between the solar cells and the TEG is very close, which is a challenge that the retrofit program must overcome.
Design schematics and prototypes of PV-TEG equipment.
In October 2021, the research team tested a prototype of a TEG-integrated solar cell on a rooftop at Stanford University for three days. It turned out that the power generation reached 50 mW per square meter at night. They estimate that in hotter and drier climates, the same device can reach 100 milliwatts per square meter.
Temperature and power measurements for multiple days.
Fan says there's plenty of room for improvement in the future, as the traditional solar cells they use aren't designed for radiant cooling. It emits thermal waves in the mid-infrared range with a wavelength of about 10 microns. By adjusting the emission wavelength, the solar cell can become colder at night, increasing the temperature difference as well as the power generated by the TEG.
He said, "In principle, the thermal emission characteristics of a solar cell can be designed to optimize its radiant cooling performance without affecting the solar performance." Our theoretical calculations suggest that it is possible to reach hundreds of milliwatts or even 1 watt."
Currently, the research team plans to design new solar cells to improve nighttime power generation and expand their prototypes. Cost can be a big problem because TEG is often made from expensive materials. The team hasn't done a detailed cost analysis yet, but Fan believes they'll have to compare the 24-hour solar cell to a nighttime device that generates solar energy during the day and then uses the battery to get electricity at night.
TEG modules have a much longer service life than the usual five-year life of batteries, and according to preliminary calculations from researchers, thermoelectricity may outperform battery methods in some application scenarios.
Reference link: https://spectrum.ieee.org/solar-cell
IJCAI 2022 - Neural MMO Massive AI Team Survival Challenge
On April 14th, the "IJCAI 2022-Neural MMO Massive AI Team Survival Challenge" was officially launched, initiated by Hyperparameter Technology, co-sponsored by MIT, Tsinghua University Shenzhen International Graduate School and AIcrowd, a well-known data science challenge platform.
Themed "Finding the Strongest AI Team in the Future Open World", the tournament achieved higher achievements than other contestants by exploring, searching and fighting in Neural MMO's massive multi-agent environment. The game also sets new rules, evaluates the strategic robustness of agents against new maps and different opponents, and introduces cooperation and role division in AI teams, enriching the content of the game and enhancing the fun.