A new device works like a solar panel, except it doesn’t harvest energy from the sun. It captures energy from the cold night sky.
A prototype of the device produced enough electricity at night to power a small light bulb. A bigger version might one day light rooms or charge phones. It also could power electronics in remote or low-resource areas that lack electricity.
The core of this new night-light is a thermoelectric generator. It harnesses the temperature difference between Earth and outer space. The generator then uses that difference to create electricity.
As long as one side of it is cooler than the other, the generator can produce electricity. The cooler side faces the sky and is attached to an aluminum plate. That plate is sealed beneath a transparent cover and surrounded with insulation to keep out heat. This plate stays cooler than the surrounding air by shedding any heat it absorbs as infrared radiation. That radiation can zip up through the transparent cover and on toward outer space.
The bottom of the generator is attached to an exposed aluminum plate. That plate is warmed by the local air. At night, the top plate can get a couple of degrees Celsius cooler than the bottom of the generator.
Researchers tested a 20-centimeter prototype one clear December night in Stanford, Calif. The generator produced up to about 25 milliwatts of power per square meter of device. That was enough power to light a small light-emitting diode, or LED bulb. Further improvements might boost its production to at least 500 milliwatts per square meter. To do that, the system might need more insulation around the cool top plate.
The researchers described their achievement online September 12 in Joule.
“It’s a very clever idea,” says Yuan Yang. A materials scientist, he works at Columbia University in New York City and was not involved in the work. “The power generation is much less than solar panels,” he notes. Solar panels generally produce at least 100 watts (not milliwatts) per square meter. But this new generator may be useful for backup power, Yang says. It might also provide a bit of energy to people living off the electric grid.
A typical lamp bulb might consume a few watts of electricity, notes Shanhui Fan. He is an electrical engineer at Stanford University in California who worked on the device. So something that took up a few square meters (square yards) of roof space might light a room with energy from the night sky.
The device also could help power remote weather stations or other environmental devices, says Aaswath Raman. He is a materials scientist who worked on the device at the University of California, Los Angeles. This may be useful in polar regions that don’t see sunlight for months at a time, Raman says. “If you have some low-power load and you need to power it through three months of darkness, this might be a way.”
aluminum A metallic element, the third most abundant in Earth’s crust. It is light and soft, and used in many items from bicycles to spacecraft.
atmosphere The envelope of gases surrounding Earth or another planet.
diode An electronic part that works like a one-way valve for electric current.
electrical engineer An engineer who designs, builds or analyzes electrical equipment.
electricity A flow of charge, usually from the movement of negatively charged particles, called electrons.
electronics Devices that are powered by electricity but whose properties are controlled by the semiconductors or other circuitry that channel or gate the movement of electric charges.
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
generator A device used to convert mechanical energy into electrical energy.
grid (in electricity) The interconnected system of electricity lines that transport electrical power over long distances. In North America, this grid connects electrical generating stations and local communities throughout most of the continent.
infrared A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means “below red.” Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X-rays, radio waves and microwaves. Infrared light tends to record the heat signature of an object or environment.
LED (short for light emitting diode) Electronic components that, as their name suggests, emit light when electricity flows through them. LEDs are very energy-efficient and often can be very bright. They have lately been replacing conventional lights for home and commercial lamps.
materials scientist Someone who studies how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application.
online (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.
prototype A first or early model of some device, system or product that still needs to be perfected.
radiation (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.
watt A measure of the rate of energy use, flux (or flow) or production. It is equivalent to one joule per second. It describes the rate of energy converted from one form to another — or moved — per unit of time. For instance, a kilowatt is 1,000 watts, and household energy use is typically measured and quantified in terms of kilowatt-hours, or the number of kilowatts used per hour.