Irish and Spanish researchers are finding an environmentally friendly way to generate energy from body heat using a thermoelectric generator made from wood waste. Smartwatches and fitness trackers, among other things, could be operated. But the potential of the technology is even greater.
The human body continually radiates heat – more than you might think. According to a calculation by Cornell University in the US state of New York, it corresponds to about 19 matches per square foot per hour. Or as ETH Zurich writes: On average, the human body continuously emits around 100 watts of thermal energy.
Scientists from the universities of Limerick and Valencia want to use this energy. In a study published in “Advanced Functional Materials” you have not only developed a method for converting body heat into electrical current. The technology is also particularly sustainable.
Basics from Darmstadt
The conversion is based on thermoelectric generators (TEG) made of semiconductor elements that are able to generate electricity with small temperature differences. These considerations are not new; research into them has been going on for several years. However, cadmium, lead or mercury are often used to produce them, writes project leader Muhammad Muddasar from the University of Limerick in “Conversation”. “But we discovered that thermoelectric materials can also be made from wood – a safe and sustainable alternative.”
Strictly speaking, the Spanish and Irish researchers are continuing the work of a team at TU Darmstadt led by Steffen Hardt, which discovered the process: Energy conversion takes place in a material with tiny nanochannels filled with a highly concentrated salt solution. If one side of the material is warmer than the other, a thermoelectric effect occurs.
The temperature difference causes the ions (charged atoms) in the salt solution to move. Positive ions drift towards the cooler side while negative ions move towards the warmer side. This creates voltage (potential difference) from which electricity can be generated.
Lignin membranes
Muddasar's team's research project uses membranes made from lignin, a by-product of paper and pulp production that is produced in large quantities. These are biopolymers, a substance that occurs in the cell walls of plants and acts as a type of glue. It allows plants to remain strong and stable by connecting the cells together. This is called lignification.
About 20 to 30 percent of the dry matter of a woody plant is lignin. According to Research and Markets, around 50 million tons of lignin are produced annually in paper and pulp production worldwide. It is usually used thermally. That is, it is burned to produce heat or electricity.
However, because of its high carbon content, low cost and biological renewability, lignin is increasingly being used industrially. Because it is an important precursor for the sustainable synthesis of chemicals, polymers and materials that can replace or complement current petroleum-based products.
Industrial future
Generating electricity from body heat for smartwatches and other portable electronic devices (wearables) is just the first step. In the future, the lignin TEGs will also be used to convert waste heat in industry into electricity. According to Muddasar, 66 percent occur in the range below 200 degrees, which is suitable for using the technology.
It can be used in many areas, he writes. This ranges from energy supply in remote areas to the supply of sensors and devices in everyday applications. Their environmentally friendly nature also makes them a promising solution for sustainable energy production in buildings and infrastructure.
Also storage solution with lignin
Efficient, cost-effective and sustainable storage of energy is just as important as its production. Normally, supercapacitors are used for such application scenarios, which can quickly store and release electricity.
The problem here is the use of carbon materials from fossil fuels, says Muddasar. But his research group has discovered that lignin can be the solution here too. Porous carbon obtained from this could serve as an electrode in supercapacitors to store energy.
This approach offers a sustainable solution without harmful chemicals and dependence on fossil fuels, concludes Muddasar. “This innovation in energy storage technology could power everything from consumer electronics to wearable technology to electric vehicles.”
