The device continuously generates electricity by absorbing solar radiation and cooling. (Image Credit: STAM)
Scientists from Japan's National Institute for Materials Science developed a magnetic hybrid device capable of continuously generating electricity by harvesting two energy types on each side. This system could eventually be applicable for off-grid IoT sensors if it undergoes more upgrades.
For 200 years, Scientists have realized that electricity can be produced through a temperature gradient. By changing material parameters and implementing new principles, researchers were able to develop thermoelectric conversion technologies. For instance, they discovered that magnetic materials generate thermoelectric voltage by inducing a flow of electric spins along a temperature gradient known as the spin Seebeck effect. Also, the device produces more voltage if its length increases perpendicular to the gradient. Scientists want to develop more efficient, thin thermoelectric devices based on the Seebeck effect. However, increased thinness poses a challenge toward maintaining the temperature gradient between the top and bottom.
The team's magnetic hybrid system solves this issue by harvesting two energy types: radiative cooling at the top and solar radiation at the bottom. "It is really important to take full advantage of renewable energy in order to achieve a more sustainable society," explains Satoshi Ishii. "Daytime radiative cooling and solar heating have both been used to improve a variety of thermoelectric applications. Our device uses both types of energy simultaneously to generate a thermoelectric voltage."
The device contains four layers. The top paramagnetic insulator layer is made of gadolinium gallium garnet. It's transparent to sunlight and releases thermal radiation, allowing it to cool down. Afterward, sunlight passes through the transparent ferromagnetic layer composed of yttrium iron garnet. Due to its transparency, light can pass through it before reaching the bottom two light-absorbing layers that are made of paramagnetic platinum and blackbody paint. The bottom layer retains its warmth thanks to the sunlight absorption. Lastly, the ferromagnetic layer generates spin current as a result of the temperature gradient between the device's top and bottom layers. It then converts into an electric voltage in the paramagnetic platinum layer.
Overall, the system performs more efficiently on clear days. That's because clouds decrease the necessary temperature gradient by blocking infrared radiation from passing through the atmosphere while reducing solar heating. However, the thermoelectric generation efficiency isn't sufficient. So the team plans on boosting its efficiency through design improvements, different material combinations, and developing solutions for thermoelectric generation.
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