New way to generate energy from temperature changes

Posted Feb 18, 2018 by Tim Sandle
A new system, based on graphene, can draw power from daily temperature swings. The technology can harness temperature fluctuations of many kinds in order to produce electricity.
Taken at 6.30 in the morning a few weeks ago.
Gemma Fox
The new thermoelectric device comes from the Massachusetts Institute of Technology (MIT) and it draws power from the daily cycle of temperature swings. The concept is generating power when one side of the device is at a different temperature from the other side. This process produces sufficient to power remote sensors and several types of communications systems.
The device, which is called a thermal resonator, has been placed on the roof of an MIT building for many months to test out the concept. The energy-harvesting device looks like a simple black box but trials suggest it can introduce a new means of energy capture and storage. The prototype efficiently generates wooer as the result of the fluctuations in ambient temperature that occur during the day-night cycle. The key advantage over other systems is that the device does not need to be exposed to direct sunlight.
In the trials the device, reacting to a 10-degree-Celsius temperature difference (between night and day), generated 350 millivolts of potential and 1.3 milliwatts of power.
The most challenging part of the development of the device was identifying a suitable material that material that is has a characteristic termed thermal effusivity. This is a property that describes how effectively a material can capture heat from its surroundings, store it and release it.
The material selected was a metal foam formed of copper. This was then coated with a layer of graphene to enhance the thermal conductivity. The foam was next infused with octadecane, which is a phase-change material that resembles a wax. Octadecane can change between solid and liquid at a particular range of temperatures. Through the material heat is collected from one side and it gradually radiates through to the other.
According to the lead researcher, Professor Michael Strano: "We've built the first thermal resonator. It's something that can sit on a desk and generate energy out of what seems like nothing. We are surrounded by temperature fluctuations of all different frequencies all of the time. These are an untapped source of energy."
The research has been reported to the journal Nature Communications, and the research paper is titled "Ultra-high thermal effusivity materials for resonant ambient thermal energy harvesting."
In related energy news, the U.S. regulators have permitted large-scale energy storage using batteries for the first time, disrupting the monopoly held by state power grids. See the Digital Journal article "Market barriers removed for energy storage technology."