Thermoelectric generator contrasts heat of Sun and cold of space
Engineers at Japan’s National Institute for Materials Science (NIMS) have developed a new type of thermoelectric generator that produces an electric current through a temperature gradient. By absorbing heat from the Sun on one surface and emitting it from another, the device can generate electricity day and night.
It’s a basic principle of physics that heat moves from hotter objects to colder ones. Thermoelectric generators tap into that, where the temperature gradient between two surfaces causes electrons to move from the warmer one to the cooler one, thereby creating an electric current. This is called the Seebeck effect, and in theory these thermoelectric materials, paints and generators could be put to work to recycle waste heat from almost anywhere, such as engines, exhaust pipes, power plants, and even clothing or cookware.
In the new study, the NIMS researchers developed a solar-powered thermoelectric generator based on a variation of the principle called the spin Seebeck effect. In this case, the current emerges from the flow of the electrons’ spins, produced by magnetic materials in each electrode.
The new design is made up of four layers, each with an important job to play. The top two layers are transparent to allow sunlight to pass through to the bottom two layers, which absorb it. That means the top layer stays cool, the bottom layer stays warm, and the two middle layers generate electricity from the resulting temperature gradient.
A major factor that limits how useful thermoelectric generators can be is that the cold side can’t get rid of the heat fast enough, so the temperature gradient levels out. The new device gets around this by venting its excess heat straight into space. That’s thanks to the topmost layer, a paramagnet made of gadolinium gallium garnet (GGG), which emits infrared radiation that passes directly through the atmosphere.
The second layer is a ferromagnet made of yttrium iron garnet, which produces the spin current from the temperature gradient. The third layer down is a paramagnet made of platinum, which converts that spin current into a useable voltage. And the final layer is coated in blackbody paint, to absorb sunlight and hold onto heat.
The team says that this design allows the device to continue generating electricity day and night, since the bottom layers retain their heat for a while. It works best in clear weather, the engineers say, because clouds can block the infrared radiation from escaping.
That said, they admit that the efficiency of the current version is still pretty low. They plan to try to boost that by tweaking the design and the materials.
The research was published in the journal Science and Technology of Advanced Materials.