What if we were to say that the heat produced by the human body is also a waste product of our metabolism? According to a study from the Cornell University Ergonomics Web, every square foot of the human body emits heat equivalent to about 19 matches per hour. However, much of this heat escapes into the atmosphere.
According to Muhammad Muddasar, PhD candidate at the School of Engineering, University of Limerick, this heat can be harnessed to produce energy. While his research has shown it is possible, Muddasar and his colleagues are working on methods to capture and store body heat for energy generation using eco-friendly materials.
The aim is to develop a device that generates energy and stores it, essentially functioning as a built-in power bank for wearable technology. By tapping into body heat as a power source, this innovation could dramatically extend the battery life of devices like smartwatches, fitness trackers, and GPS units, potentially allowing them to operate for days, weeks, or indefinitely without recharging.
“It isn’t just our bodies that produce waste heat. In our technologically advanced world, substantial waste heat is generated daily, from the engines of our vehicles to the machines that manufacture goods,” he said.
What Muddasar is trying to achieve
According to the PhD candidate, “Typically, this heat is also released into the atmosphere, representing a significant missed opportunity for energy recovery. The emerging concept of waste heat recovery seeks to address this inefficiency. By harnessing this otherwise wasted energy, industries can improve their operational efficiency and contribute to a more sustainable environment.”
Muddasar identified the “thermoelectric effect” as a phenomenon that can help turn the heat mentioned above into electricity. All it requires is a temperature difference that will generate an electric potential as electrons flow from the hot side to the cool side, creating usable electrical energy.
Thermoelectricity is a two-way process. It can refer to how a temperature difference between the two sides of a material generates electrical power, or to the reverse. In the reverse process, applying an electric current through a material can create a temperature difference between its two sides, which can be used to heat or cool things without combustion or moving parts. This is a field in which MIT (Massachusetts Institute of Technology) has been doing pioneering work for decades.
Muddasar explains that conventional thermoelectric materials are often made from cadmium, lead, or mercury. These materials come with environmental and health risks that limit their practical applications. However, he has found a solution in the form of wood, which is a safer and more sustainable alternative, to give his “waste heat production” idea a concrete form.
“Wood has been integral to human civilisations for centuries, serving as a source of building materials and fuel. We are uncovering the potential of wood-derived materials to convert waste heat, often lost in industrial processes, into valuable electricity,” he explained, reiterating that this approach will enhance energy efficiency and redefine how we view everyday materials as essential components of sustainable energy solutions.
In collaboration with the University of Valencia, Muddasar’s team at the University of Limerick has already developed a sustainable method to convert waste heat into electricity using Irish wood products, particularly lignin, a byproduct of the paper industry.
Speaking about the material, the International Lignin Institute states, “Lignin is an organic substance that binds the cells, fibres, and vessels that constitute wood and the lignified elements of plants, such as straw. After cellulose, it is the most abundant renewable carbon source on Earth. Between 40 and 50 million tons per year are produced worldwide as a mostly non-commercialised waste product. As a natural and renewable raw material, obtainable at an affordable cost, lignin’s substitution potential extends to any products currently sourced from petrochemical substances.”
“Our study shows that lignin-based membranes, when soaked in a salt solution, can efficiently convert low-temperature waste heat (below 200°C) into electricity. The temperature difference across the lignin membrane causes ions (charged atoms) in the salt solution to move. Positive ions drift toward the cooler side, while negative ions move toward the warmer side. This separation of charges creates an electric potential difference across the membrane, which can be harnessed as electrical energy,” the research body noted.
Since around 66% of industrial waste heat falls within this temperature range, this innovation presents a significant opportunity for eco-friendly energy solutions.
This new technology has the potential to make a big difference in many areas. Industries such as manufacturing, which produce large amounts of leftover heat, could see major benefits by turning that waste heat into electricity. This would help them save energy and reduce their impact on the environment.
This technology could be used in various settings, from providing power in remote areas to powering sensors and devices in everyday applications. Its eco-friendly nature makes it a promising solution for sustainable energy generation in buildings and infrastructure.
The trouble with storage
According to Muddasar, capturing energy from waste heat is just the first step; the most critical challenge lies in effectively storing the end product. One option could have been supercapacitors—energy storage devices that rapidly charge and discharge electricity, thus becoming an essential tool for applications requiring quick power delivery.
A supercapacitor is a battery-like device that stores and releases electricity. Instead of storing energy in the form of chemicals, supercapacitors store electricity in a static state, making them better at rapidly charging and discharging energy.
Additionally, supercapacitors don’t degrade in the same way as lithium-ion batteries, which improves the lifespan of electric vehicles and reduces the environmental impact of lithium-ion power cells. Supercapacitors enjoy a clear advantage over lithium-ion and nickel-cadmium batteries due to their ability to charge and discharge rapidly.
However, Muddasar believes that to capture energy from waste heat and store it, a supercapacitor is not the ideal option because its reliance on fossil fuel-derived carbon materials raises sustainability concerns, underscoring the need for renewable alternatives in its production.
“Our research group has discovered that lignin-based porous carbon can serve as an electrode in supercapacitors for energy storage generated from harvesting waste heat using a lignin membrane. This process allows the lignin membrane to capture and convert waste heat into electrical energy, while the porous carbon structure facilitates rapid movement and storage of ions. By providing a green alternative that avoids harmful chemicals and reliance on fossil fuels, this approach offers a sustainable solution for energy storage from waste heat,” he concluded.