A thermoelectric generator that can simultaneously harvest radiative cooling and solar heating to generate electricity has been engineered at the National Institute for Materials Science (NIMS) in Japan.

The device is constructed with magnetic materials that generate thermoelectric voltage by inducing a flow of electron spins along a temperature gradient, called the spin Seebeck effect. The magnetic layers provide continuous radiative cooling at the top of the generator and absorb heat from the sun at the bottom.

A weak, transparent paramagnet top layer of gadolinium gallium garnet emits thermal radiation to provide cooling as solar radiation is transmitted to a transparent ferromagnetic layer made of yttrium iron garnet. The two bottom-most light-absorbing layers assembled with paramagnetic platinum and blackbody paint stay warm due to sunlight absorption. The spin current is generated in the ferromagnetic layer due to the temperature gradient between the top and bottom of the device and is converted to electric voltage in the paramagnetic platinum layer.

The design allows the device to continue generating electricity at night by radiative cooling. Such continuous voltage generation may be useful for outdoor energy harvesting systems to power off-grid applications.

A paper on this research is published in Science and Technology of Advanced Materials.