New TEG device generates electricity day and night using solar and radiative cooling

How does the thermoelectric generator work?

A TEG generates electricity in the presence of a temperature gradient. Electrons begin to flow from the hot area to the cold area of the material and generate an electric current. While this is the principle of a TEG, the current produced is usually not sufficient to do any meaningful work and its production is also unstable.

To improve on conventional TEGs, the researchers developed a new type of TEG, which has two additional components. One is the ultra-broadband solar absorber (UBSA) that can capture sunlight to heat one side of the generator. The other is the radiative cooling emitter (RCE) which is placed on the other end, where it releases the heat, leading to a temperature gradient and the production of electricity.

In outdoor experiments, conducted with this setup, the researchers found that the new TEG design generated 166.2 mV of output voltage during clear daytime conditions. This is sufficient to power a small device or sensor.

Under cloudy daytime conditions, the TEG produced an output of 95mV while it generated 14.7mV during clear nighttime conditions.

Since, the UBSA and RCE can be used with flexible substrates too, the TEG can be used to power wearable devices.

"Our innovative method for combining solar heating with radiative cooling allows the TEG to generate electricity that is uninterrupted,” said Haoyuan Cai, a member of the research team in a press release.

“This could improve access to critical services, particularly in remote or underdeveloped areas where traditional power sources are not available" he added.

The research findings were published in the journal Optics Express.

Abstract

Passive power generation has recently stimulated interest in thermoelectric generators (TEGs) using the radiative cooling mechanism. However, the limited and unstable temperature difference across the TEGs significantly degrades the output performance. In this study, an ultra-broadband solar absorber with a planar film structure is introduced as the hot side of the TEG to increase the temperature difference by utilizing solar heating. This device not only enhances the generation of electrical power but also realizes all-day uninterrupted electrical output due to the stable temperature difference between the cold and hot sides of the TEG. Outdoor experiments show the self-powered TEG obtains maximum temperature differences of 12.67 °C, 1.06 °C, and 5.08 °C during sunny daytime, clear nighttime, and cloudy daytime, respectively, and generates output voltages of 166.2 mV, 14.7 mV, and 95 mV, respectively. Simultaneously, the corresponding output powers of 879.25 mW/m2, 3.85 mW/m2, and 287.27 mW/m2 are produced, achieving 24-hour uninterrupted passive power generation. These findings propose a novel strategy to combine solar heating and outer space cooling by a selective absorber/emitter to generate all-day continuous electricity for unsupervised small devices.