Electricity from waste heat

How far are thermoelectric generators from recovering waste heat at scale in cars, industry and wearables?

Thermoelectric generators turn a temperature difference directly into electricity with no moving parts. Radioisotope versions have powered NASA spacecraft and Mars rovers for decades. Recovering waste heat from car exhausts, factories or the body is still at prototype or laboratory stage. BMW reported exhaust-heat generators giving 200 to 250 watts in 2008 and 2009 prototypes, with a 2 per cent fuel saving in customer testing. A 2022 laboratory rig reached 1.21 per cent overall efficiency. The main gaps are low efficiency, the cost and supply of tellurium, durability at high temperature and proof on real vehicles and real skin.

AI illustration · Illustrative scene, not a photograph of the specific device or experiment.
WHERE WE AREEngineering prototypes

Getting closer. Prototypes exist, but not in real-world use.

Radioisotope thermoelectric generators are flight-proven, but they run on nuclear decay heat rather than waste heat, so they are a separate, niche case. For waste heat, the sources reviewed show vehicle prototypes that BMW reported from 2008 and 2009, a Ford vehicle demonstration planned for 2011 with no measured result found, and a laboratory rig in 2022. They show no production system in cars or industry, so waste-heat recovery is at engineering prototype. Wearable generators are at laboratory stage.

The tech tree

Everything recorded on Vrulum that this future needs, oldest foundations at the top and the goal at the bottom. Lines show what each step requires.

What it takes: Electricity from waste heat Unlocked Being researched Locked
  1. 2008Thermoelectric generatorsPilot and early commercial Unlocked.
  1. 2008Exhaust-heat generator prototypes reported by BMWDone Unlocked.
  2. 2011Ford vehicle demonstration on a FusionIn progress Being researched.
  3. 2013Five per cent fuel economy gain on the US06 cycleIn progress Being researched.
  4. 2022Laboratory waste-heat rig at kilowatt heat inputDone Unlocked.
  5. 2022Wearable generator running on body heatIn progress Being researched.
  6. Date not recordedRadioisotope generators powering spacecraftDone Unlocked.
  7. Date not recordedRadioisotope output over mission lifeDone Unlocked.
  8. Date not recordedProduction waste-heat generator in cars or factoriesNot started Locked.
  1. GoalElectricity from waste heatGoalRequires: Thermoelectric generators, Radioisotope generators powering spacecraft, Radioisotope output over mission life, Exhaust-heat generator prototypes reported by BMW, Ford vehicle demonstration on a Fusion, Five per cent fuel economy gain on the US06 cycle, Laboratory waste-heat rig at kilowatt heat input, Wearable generator running on body heat, Production waste-heat generator in cars or factories. Locked.

The road so far

4 of 8 steps done, 3 in progress.

  1. DoneRadioisotope generators powering spacecraft

    NASA's overview says radioisotope thermoelectric generators convert heat from radioactive decay into electricity using thermocouples, and that RTGs have no moving parts. It lists New Horizons and the Perseverance and Curiosity Mars rovers among the spacecraft they power, and says more than two dozen NASA missions have flown radioisotope power systems. [1]

  2. DoneRadioisotope output over mission life

    NASA's MMRTG fact sheet gives about 110 W of electrical power at the start of life and an estimated 72 W at 17 years of design life. It gives a beginning-of-life system efficiency of 6 per cent, and about 2,000 W of thermal power from the plutonium-238 fuel. These are design figures for a nuclear heat source, not for waste heat. [2]

  3. Done · 2008Exhaust-heat generator prototypes reported by BMW

    BMW's first exhaust-system generator, shown in 2008, gave a maximum of 200 W. A 2009 generator fitted to the radiator of the exhaust gas recirculation system produced 250 W in customer testing, and CO2 emissions and fuel consumption were reduced by 2 per cent. BMW's 2011 article gives 600 W for its latest exhaust-system generation. These are company-reported prototype results. [3]

  4. In progress · 2011Ford vehicle demonstration on a Fusion

    Ford's 2011 DOE presentation planned a vehicle-level demonstration on a Fusion with a 3.0 L V-6 engine, with an anticipated peak of about 500 W and a US06 test cycle. Its next steps were to install and test the generator and compare actual with modelled performance. The sources reviewed do not report a measured Ford result, and the status is as of 2011. [4]

  5. In progress · 2013Five per cent fuel economy gain on the US06 cycle

    A 2013 DOE project presentation by Gentherm set a project objective of a 5 per cent fuel economy improvement from converting engine waste heat, measured on the US06 cycle, alongside a production cost analysis for 100,000 units a year. Its slides show milestones and early US06 engine dynamometer power results, but the sources reviewed give no measured fuel economy gain. BMW's 2009 customer testing reported 2 per cent. [5][3]

  6. Done · Jan 2022Laboratory waste-heat rig at kilowatt heat input

    A 2022 study simulated the waste heat of a 2.0 L petrol engine with an electric heater and 20 bismuth telluride modules. At 3 kW of heat input, the rig gave a maximum of 36.4 W, a measured thermoelectric efficiency of 2.88 per cent and a maximum overall efficiency of 1.21 per cent after the pump and blower power were counted. No real vehicle was tested. [6]

  7. In progress · 24 Feb 2022Wearable generator running on body heat

    A 2022 study measured a wearable generator on a thermally insulating film, not live skin. With a 5.5 degree Celsius temperature difference, body heat alone gave 2.19 microwatts per square centimetre. With body heat and light together it reached 15.33 microwatts per square centimetre. [7]

  8. Not startedProduction waste-heat generator in cars or factories

    The sources reviewed show no production thermoelectric waste-heat system in vehicles or industry. Ford's 2011 presentation listed a business case for production feasibility as a next step. Goldsmid's 2014 review says the cost and scarcity of tellurium may make bismuth telluride alloys unsuitable for large-scale use. [4][8]

Why it matters

Engines, factories and power plants give off large amounts of heat that is usually lost. A solid-state generator that recovers even part of it could save fuel, and small generators that run on body heat could power sensors without batteries. Whether this works at scale depends on efficiency, cost and materials that do not rely on scarce elements.

What stands in the way

  • Conversion efficiency is low. The 2022 rig reached 1.21 per cent maximum overall efficiency, and Goldsmid (2014) estimated about 2 per cent for a 400 K heat source and a 360 K sink, where the Carnot limit is 10 per cent.
  • Tellurium is scarce and costly. Goldsmid (2014) says its cost and scarcity may make bismuth telluride alloys unsuitable for large-scale use, and tellurium is volatile, so it can be lost from the material over time.
  • High-temperature durability is hard. Gentherm's 2013 programme planned antimony sublimation suppression and hermetic sealing to limit material erosion and oxidation.
  • Cost per watt has to fall. Ford's 2011 presentation gave regulatory values of about $0.50 to $1.00 per watt (US CAFE) and $3 to $5 per watt (EU), and listed a $/W target at the design point. The sources reviewed give no measured production cost.
  • Vehicle results are small and hard to compare. BMW's customer testing reported a 2 per cent fuel saving, and the sources reviewed do not show a production vehicle with a 5 per cent gain.
  • A single peak ZT does not describe device efficiency. A 2018 preprint argues that single-value ZT misrepresents how efficiently a device converts heat, because material properties change with temperature (Ryu, Chung and Park).
  • Body-heat figures are not proven on skin. The 2022 wearable tests used an insulating film, so the output of a worn device is not yet shown.

Published forecasts

What others have predicted. These are their estimates, not ours.

WhoForecastTimeframeMade
Unnamed researchers, quoted in a BMW Group press article by Osama El-SherifResearchers forecast that thermoelectric generators will save up to 5 per cent fuel under real everyday driving conditions in the future. Customer testing of the 2009 system had reported a 2 per cent reduction. [3]Not given30 Aug 2011

Signals to watch

  • A measured fuel economy gain of about 5 per cent over the US06 cycle from a thermoelectric exhaust system, the target set in the 2013 programme.
  • A published waste-heat module or system efficiency that states the hot-side and cold-side temperatures and the electrical output in watts.
  • A production order or supplier announcement for an exhaust thermoelectric generator from a car maker.
  • A factory or power plant waste-heat trial with a stated output, cost and payback period.
  • Wearable generators reported on live human skin, with skin temperature, air temperature and power density all stated.
  • Thermoelectric materials with less tellurium shown at module level in peer-reviewed tests.

Sources

  1. government report
    Radioisotope Power Systems: Overview
    NASA Science, 28 Apr 2025.
  2. government report
    Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), NASA fact sheet NF-2020-05-619-HQ
    NASA, May 2020.
  3. company announcement
    Looking for the next gram.
    Osama El-Sherif. BMW Group, 30 Aug 2011.
  4. other
    Thermoelectric Waste Heat Recovery (2011 DOE Thermoelectrics Applications Workshop presentation slides)
    US Department of Energy, 2011 Thermoelectrics Applications Workshop (presentation by Ford Research & Advanced Engineering), 2011.
  5. other
    Thermoelectric Waste Heat Recovery Program for Passenger Vehicles
    Doug Crane. US Department of Energy, project presentation (Gentherm Inc.), 17 May 2013.
  6. peer reviewed paper
    Experiments on Waste Heat Thermoelectric Generation for Passenger Vehicles
    Jianfei Chen, Wei Xie, Min Dai et al.. Micromachines, 10 Jan 2022.
  7. peer reviewed paper
    Operation of Wearable Thermoelectric Generators Using Dual Sources of Heat and Light
    Myeong Hoon Jeong, Kwang-Chon Kim, Jin-Sang Kim et al.. Advanced Science, 24 Feb 2022.
  8. review article
    Bismuth Telluride and Its Alloys as Materials for Thermoelectric Generation
    H. Julian Goldsmid. Materials (MDPI), 28 Mar 2014.
  9. preprint
    Thermoelectric degrees of freedom determining thermoelectric efficiency
    Byungki Ryu, Jaywan Chung, SuDong Park. arXiv, 26 Oct 2018.

Last reviewed 21 Oct 2026.