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Heat-to-Power Technology and Thermoelectrics: Turning Waste Heat into Tomorrow’s Energy
From powering wearables with body heat to fueling spacecraft, thermoelectrics are recycling wasted heat into clean, reliable power.
Introduction
In the quest for sustainable and efficient energy solutions, heat-to-power technology and thermoelectrics (TEs) are emerging as promising contenders. These technologies leverage the conversion of heat into electrical power, offering a versatile and eco-friendly approach to energy generation. From wearables to homes, vehicles to military equipment, the applications of heat-to-power and thermoelectrics are vast and transformative. This article explores the latest advancements, potential applications, and future prospects of these groundbreaking technologies.
Heat is an inevitable byproduct of most mechanical and electrical systems. Whether it’s from car engines, aircraft turbines, or ship machinery, this “waste heat” is a direct consequence of the laws of thermodynamics. However, what has long been seen as a necessary inefficiency is now emerging as a significant energy opportunity. Heat-to-power technology offers a pathway to reclaim lost energy and reintegrate it into the system, thereby improving efficiency and reducing environmental impact. For instance, vehicles could redirect waste heat from their exhaust systems into electrical power, which in turn could power onboard systems or recharge batteries.
Data Centers and Low-Grade Heat Recovery
Modern data centers are notorious for their enormous energy consumption. Servers and related hardware convert the vast majority—over 98%—of their input electricity into low-grade heat. Not only is this heat traditionally wasted, but even more electricity is required to cool these facilities and maintain optimal performance levels. Emerging thermoelectric technologies, however, now make it feasible to convert this low-temperature waste heat into usable electricity, transforming the energy profile of data centers and helping to offset their considerable carbon footprint.
What are Thermoelectrics?
Thermoelectrics are solid-state devices that convert temperature differences directly into electricity. At the heart of this technology lies the Seebeck effect, where an electric current is generated when there’s a temperature gradient across two dissimilar conductors or semiconductors. This phenomenon occurs when a temperature gradient in a conducting material results in the diffusion of charge carriers, creating a voltage difference. The efficiency of this conversion depends on the material’s electronic and thermal properties.
A thermoelectric harvester generates green energy with numerous advantages, making it ideal for sustainable energy harvesting. It is maintenance-free due to its solid-state design, which ensures high reliability and compactness. Operating silently and efficiently, it converts waste heat into electricity, making excellent use of otherwise lost thermal energy. Thermoelectric generators (TEGs) can function at high temperatures—up to 250°C—and are easily scalable to suit varying energy demands. They can harvest energy from both hot and cold surfaces, further enhancing their versatility. As TEGs do not rely on fossil fuels, they contribute to reducing greenhouse gas emissions, offering a clean, eco-friendly energy solution.
These materials can also function in reverse through the Peltier effect, providing heating or cooling by applying an electrical current. However, their most revolutionary role lies in the ability to harvest energy from waste heat—a nearly ubiquitous byproduct in natural and man-made systems.
Thermophotovoltaics: A High-Efficiency Approach
Thermophotovoltaics (TPV) represent a more advanced form of heat-to-power technology. TPV devices, like solar cells, convert heat into electricity but do so more efficiently. Heat2Power (H2P), a startup co-founded by Professors Stephen Forrest and Andrej Lenert, has developed a patented air-bridge thermophotovoltaic technology that achieves over 44% heat-to-power efficiency, with a clear path to over 50%. This technology can be paired with high-temperature thermal energy storage (TES) systems to provide sustainable, on-demand power.
Thero Electric Generators (TEG)
TEGs utilize the Seebeck effect to directly convert a temperature difference into voltage. They consist of n-type and p-type semiconductor legs connected between two metal plates—one hot and one cold. The difference in temperature causes charge carriers to move, creating electrical current. More advanced devices also incorporate the Peltier and Thomson effects for refined energy conversion.
The TEG device is composed of one or more thermoelectric couples. The simplest TEG consists of a thermocouple, comprising a pair of P-type and N-type thermoelements or legs connected electrically in series and thermally in parallel. Furthermore, the sign of the Seebeck coefficient depends on the type of carriers (electrons e− and holes h+) conducting the electric current. The p-type elements are made of semiconductor materials doped such that the charge carriers are positive (holes) and Seebeck coefficient is positive. The n-type elements are made of semiconductor material doped such that the charge carriers are negative (electrons) and the Seebeck coefficient is negative. A number of thermoelectric couples n form a TEG system wired electrically in series and sandwiched between two ceramic plates to maximise the output voltage from the TEG.
The voltage generated is proportional to the temperature difference between the junctions, and TEGs are often configured into arrays to increase power output. A single TEG can produce between 1 and 125 watts, while modular designs can yield up to 5 kilowatts with temperature gradients exceeding 70°C.
Since TEGs produce low and often variable voltages, a DC-DC converter is typically employed to stabilize and scale the output. These converters—boost, buck, or Cuk types—are essential for matching the generator’s output to the needs of external loads, such as sensors or communication devices.
Applications Across Various Sectors
Thermoelectric generators (TEGs) are solid-state devices that can convert temperature gradients directly into electricity using the Seebeck effect. They are ideal for applications in harsh or remote environments where conventional power sources are impractical.
Thermal energy harvesting, in particular, is invaluable in environments where waste heat is readily available. The versatility of energy harvesters allows them to power devices ranging from nanowatts to hundreds of milliwatts, making them suitable for applications ranging from smartwatches to industrial sensors.
From individual vehicles and transport trucks to remote sensors in heavy industries like glass and metal production, TEGs are unlocking new energy frontiers. As Boona, a postdoctoral researcher at Ohio State, explains, “Over half of the energy we use is wasted and enters the atmosphere as heat. Solid-state thermoelectrics can help us recover some of that energy. These devices have no moving parts, don’t wear out, and require no maintenance—but they need to become more efficient and cost-effective to scale broadly.”
Powering Wearables with Body Heat
Thermoelectrics offer a unique advantage for wearable devices by harvesting energy directly from the human body. The human body emits a continuous stream of thermal energy—roughly 100 watts at rest. While most of this heat dissipates into the surrounding environment, advances in thermoelectric materials are allowing us to recapture even small amounts of it, down to milliwatt levels. This opens the door to a new class of wearables that can function independently of conventional charging.
Recent studies have focused on developing flexible inorganic thermoelectrics, such as silver selenide on nylon substrates, which can generate power from body heat. This innovation could significantly reduce or eliminate the need for charging wearable devices, making them more convenient and sustainable.
Smartwatches, fitness bands, and biometric monitors are now being developed with embedded thermoelectric generators that can extend battery life or eliminate the need for charging altogether. For medical applications, thermoelectric-powered sensors can provide real-time health monitoring without intrusive batteries or wires. In the military domain, smart uniforms with thermoelectric textiles could power communications, GPS units, or even body-worn sensors using nothing but body heat.
Homes and Buildings
Modern homes contain countless sources of heat—ranging from kitchen appliances and heating systems to solar-exposed walls and electronics. Thermoelectric panels and films, strategically installed on radiators, ovens, or even window panes, can passively harvest this ambient heat and convert it into electricity.
In residential and commercial settings, thermoelectric generators can convert waste heat from heating systems, appliances, and even solar panels into usable electricity. This not only reduces energy consumption but also enhances the overall efficiency of the home or building. TPV technology, with its high efficiency and scalability, can be integrated into thermal energy storage systems to provide reliable, on-demand power.
These systems could be integrated alongside solar photovoltaic systems to provide a hybrid approach to renewable energy. When sunlight is unavailable, thermoelectric modules could continue producing power from retained heat or internal sources. By transforming walls and ceilings into energy-harvesting surfaces, future homes could significantly reduce their reliance on grid electricity and increase energy self-sufficiency.
Greening the Automotive Industry
Vehicles are among the most wasteful systems when it comes to heat. Internal combustion engines, for example, lose nearly two-thirds of their fuel energy as heat through exhaust systems and radiators. By integrating thermoelectric generators into these hot zones—such as exhaust pipes or engine blocks—automakers can convert a portion of this thermal waste into usable electricity.
This reclaimed power can reduce the load on the alternator, improving fuel economy and lowering emissions. For electric vehicles, thermoelectric modules can enhance battery efficiency and extend range by supplementing power from the vehicle’s internal heat. Major automakers have already begun incorporating TEGs in prototype systems, recognizing their potential to support greener, more efficient transportation platforms.
The automotive industry is a major consumer of energy, and thermoelectrics offer a way to recover and utilize waste heat from engines and exhaust systems. Automotive thermoelectric generators (ATGs) have been shown to increase fuel efficiency by up to 3.45%, with projections for even greater improvements in hybrid vehicles. TPV technology could further enhance this efficiency by providing a more effective way to convert waste heat into electricity.
Consumer Electronics that Charge Themselves
The proliferation of Internet of Things devices now brings with it a demand for non-toxic, portable power sources. Modern electronics—from smartphones to laptops—generate significant heat during use. This thermal output, while typically dissipated through passive or active cooling systems, represents a latent energy source. By embedding thermoelectric micro-generators within the casings or heat sinks of consumer devices, manufacturers can convert heat into supplemental electrical energy.
Thermoelectrics offer one of the fastest paths to realizing self-powered sensors,” says Hippalgaonkar. Devices like heart rate monitors require just a few hundred microwatts, and materials with a ZT of 1 can generate about 50 microwatts per square centimeter with a 10°C temperature difference. PHAROS’s latest material could potentially produce 10 microwatts per square centimeter—bringing wearable thermoelectric power tantalizingly close to practical use. As commercial interest grows, Hippalgaonkar expects progress to accelerate rapidly.
Such systems could prolong battery life or provide a continuous trickle charge that reduces power draw during standby. In remote or off-grid environments, this capability becomes even more valuable, enabling devices to operate independently of traditional power sources. As thermoelectric materials become smaller and more flexible, we can expect future phones, tablets, and gadgets to harvest their own heat to charge themselves.
Space and Beyond: Thermoelectrics in Extreme Environments
Thermoelectrics have already proven their reliability in the most extreme environments. NASA’s Mars rover, Curiosity, and the interstellar spacecraft Voyager 2 both rely on thermoelectric generators powered by nuclear decay, offering decades of maintenance-free power. Researchers like Kedar Hippalgaonkar and Jianwei Xu at A*STAR’s Institute of Materials Research and Engineering believe that this same principle can be applied to lower-grade heat sources here on Earth. As Hippalgaonkar notes, “An enormous amount of low-grade waste heat is being dumped into the environment. Converting this into electricity is a big opportunity that shouldn’t be missed.”
Mission-Critical Use in Military Equipment
In defense scenarios, energy independence is more than a convenience—it’s a matter of operational security and effectiveness. Soldiers today depend on a growing array of electronic systems, from communications equipment to night-vision goggles and body-worn sensors. Carrying spare batteries adds significant weight, and resupply can be both risky and difficult in hostile environments.
Thermoelectric systems offer a tactical advantage by generating power from body heat, vehicle exhausts, or external heat sources such as stoves or engine blocks. By integrating thermoelectric elements into helmets, body armor, or backpack frames, troops can power essential electronics with no need for external charging infrastructure. These systems are silent, have no moving parts, and emit no detectable signatures, making them ideal for stealth operations.
Thermoelectrics and TPV systems are particularly valuable in military and aerospace applications, where reliability and efficiency are paramount. These technologies can provide power for remote installations, unmanned vehicles, and space probes. For example, radioisotope thermoelectric generators (RTGs) have been used to power space missions, including the Mars Curiosity rover. The high efficiency and durability of TPV devices make them ideal for these demanding environments.
System Efficiency and Challenges
The efficiency of the thermoelectric energy harvesting system is defined as the ratio of the electrical energy output (used or stored) to the total energy input. This efficiency also contains the electrical efficiency of TEGs, the heat exchangers efficiency, as well as the efficiency of the DC-DC converter. The total energy input especially depends on the energy obtained from the hot source. Also, the total energy input depends to a lesser extent on the mechanical energy needed to operate the thermoelectric energy harvesting system (e.g., pressure losses in the heat exchangers or cooling of the cold heat sink).
Although current thermal energy harvesting systems operate at relatively low efficiencies (5–15%), ongoing improvements in thermoelectric materials have already surpassed 10% conversion efficiency in lab settings. The ultimate goal is to make these systems both economically and functionally viable across a wide range of industries.
Despite the promising outlook, several challenges remain. Current thermoelectric materials and TPV devices need further improvements in efficiency and cost-effectiveness to become widely adopted. Additionally, integrating these technologies into existing systems requires careful consideration of compatibility and scalability. Ongoing research and development efforts are focused on addressing these challenges and unlocking the full potential of heat-to-power and thermoelectrics.
Recent Breakthroughs
Recent breakthroughs in flexible thermoelectric generators (TEGs) are bringing self-powered wearables closer to reality. Researchers at North Carolina State University have significantly improved their 2017 prototype by using graphene-doped silicone elastomers to enhance thermal conductivity sixfold. This innovation allows flexible TEGs to approach the efficiency of rigid devices while maintaining skin comfort—critical for health monitors that track vitals like heart rate and glucose levels without battery replacements. Meanwhile, Stanford scientists have demonstrated nighttime power generation through radiative cooling, achieving 25 mW/m² using simple, scalable aluminum disk emitters. Though output remains modest, optimized designs could make this a viable complement to solar energy.
In industrial applications, companies like PwrCor are commercializing disruptive heat-to-power systems that convert ultra-low-grade waste heat (150–212°F) into electricity. Their proprietary piston-engine cycle outperforms traditional Rankine systems, offering data centers and manufacturers a way to monetize previously wasted energy. Similarly, GMZ Energy’s 1,000W TEGs—now being tested in military vehicles like the Bradley Fighting Vehicle—highlight the potential for fuel savings in transportation. These systems leverage nanostructured half-Heusler alloys to withstand high temperatures while muffling engine noise, aligning with DARPA’s MATRIX program goals for energy-efficient military tech
Flexible and Wearable Energy Harvesting Devices
Material Science Innovations Driving TE Adoption
For many years, the adoption of thermoelectric systems was limited by low conversion efficiencies—typically around 5 to 8 percent. But material science has changed the game. Breakthroughs in nanomaterials, topological insulators, and low-dimensional systems have pushed performance to new levels while lowering production costs.
Materials like bismuth telluride (Bi₂Te₃) remain staples for room-temperature applications, while compounds like skutterudites and silicon-germanium alloys have emerged as high-temperature solutions for automotive and industrial applications. Flexible and printable materials like graphene, MXenes, and other two-dimensional materials are opening doors for lightweight, foldable, and wearable thermoelectric devices that can be embedded nearly anywhere.
Thermophotovoltaic Innovations
Future Prospects and Challenges
Market Growth and Innovation
The global market for thermoelectric generators is projected to grow significantly, reaching up to $1.44 billion by 2030. This growth is driven by increasing demand for energy-efficient solutions and advancements in material science and engineering. Innovations such as flexible thermoelectrics and high-efficiency TPV devices are expanding the potential applications and markets for these technologies.
Conclusion
Heat-to-power technology and thermoelectrics represent a significant step forward in the pursuit of sustainable and efficient energy solutions. From powering wearable devices to enhancing the efficiency of homes, vehicles, and military equipment, these technologies offer a versatile and eco-friendly approach to energy generation. As advancements continue to drive improvements in efficiency and cost, the future looks bright for heat-to-power and thermoelectrics.
The future of energy isn’t just electric—it’s thermoelectric. By reclaiming wasted heat and turning it into usable power, we’re paving the way for more efficient, self-sustaining systems in every aspect of life. As research advances and adoption grows, thermoelectrics are set to play a critical role in the world’s transition toward energy resilience and autonomy—one degree at a time.
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