What Stirling Engines Are Used For

Stirling engines are used for quiet, fuel-flexible power generation (especially remote power and some combined heat and power), air-independent propulsion in several submarines, high-reliability cryocoolers and heat pumps (reverse Stirling), niche solar dish–Stirling systems, converting waste or flare gas to electricity, and in educational and historical demonstrations. Below is a detailed look at where and why they are deployed today.

Electric Power Generation and Combined Heat and Power (CHP)

Because Stirling engines are external-combustion machines that can run on many heat sources, they are used where reliability, fuel flexibility, and low maintenance matter more than peak power density. They also appear in small CHP systems that capture both electricity and usable heat.

• Remote and off‑grid power: Free‑piston Stirling generators provide 24/7 electricity for remote monitoring, cathodic protection, pipeline and well‑pad equipment, environmental sensors, and telecom relays.
• Oil and gas methane abatement: In North America and elsewhere, Stirling generators powered by natural gas or waste/flare gas replace methane‑venting pneumatic devices by supplying instrument air and electricity—reducing emissions and improving safety.
• Micro‑CHP in buildings: A number of European boilers integrated small Stirling engines to generate electricity while providing space and water heating. Several product lines were reduced or discontinued as markets shifted, but the concept remains technically sound where heat demand is steady.
• Biogas and landfill gas: Stirling engines can use low‑quality or variable gas streams (with proper cleanup) to produce power at small scale, useful for sites where reciprocating engines clog or require frequent service.

In these roles, Stirling engines trade lower power density for long service intervals, quiet operation, and the ability to use diverse heat sources—from clean fuels to challenging off‑gases.

Submarine Air‑Independent Propulsion (AIP)

Several non‑nuclear submarines use Stirling engines for AIP to extend underwater endurance without snorkeling. The engines burn diesel with stored liquid oxygen, driving generators quietly and efficiently at low speeds.

• Sweden: Gotland‑ and Södermanland‑class submarines use Kockums‑designed Stirling AIP modules.
• Singapore: Archer‑class boats (ex‑Västergötland) include Swedish Stirling AIP refits.
• Japan: Early Sōryū‑class submarines used Kawasaki‑built Stirling AIP before later boats shifted to large lithium‑ion batteries.
• China: Several Yuan‑class (Type 039A/B) submarines are widely reported to use domestic Stirling‑type AIP systems.

Stirling AIP systems are valued for quiet, steady underwater cruising and reduced acoustic signatures compared with alternatives, though navies increasingly mix AIP with advanced batteries depending on mission profiles.

Cryocoolers and Heat Pumps (Reverse Stirling)

Running the thermodynamic cycle in reverse, Stirling machines act as high‑efficiency cryocoolers and heat pumps. These sealed, often free‑piston devices provide reliable cooling from roughly 30–200 K (and sometimes to lower temperatures in staged systems) for sensors and instruments.

• Infrared imaging and seekers: Compact Stirling cryocoolers chill focal plane arrays in thermal cameras and missile seekers for defense and industrial monitoring.
• Space instruments: Satellites and space telescopes use Stirling or Stirling‑type cryocoolers to cool detectors; long‑life units with moving parts isolated magnetically have logged years of continuous operation in testing and flight.
• Scientific and industrial systems: Laboratory cryostats, superconducting devices, and specialty liquefaction or cold‑trap applications use Stirling coolers where low vibration, efficiency, and long life are critical.

This is one of the most active commercial domains for Stirling technology today, with suppliers emphasizing durability, efficiency, and low vibration for sensitive instruments.

Solar Thermal and Renewable Heat‑to‑Power

Stirling engines can convert concentrated solar heat and other renewable thermal sources to electricity. While solar photovoltaics dominate most markets, dish–Stirling systems achieved record solar‑to‑electric efficiencies and remain of technical interest.

• Dish–Stirling: Parabolic dishes focus sunlight onto a receiver heating a Stirling engine; net solar‑to‑electric efficiencies above 30% were demonstrated at test sites in the U.S. and Europe.
• Biomass and concentrated waste heat: Engines coupled to clean biomass burners or focused industrial heat can generate small‑scale power with low local emissions.

Commercial deployment has been limited due to cost, complexity, and PV’s rapid price decline, but dish–Stirling remains a niche option where direct‑normal irradiance is high and maintenance capacity exists.

Waste Heat and Industrial Off‑Gases

Because the working fluid is sealed and the heat is supplied externally, Stirling engines can utilize dirty or variable heat sources that would damage internal‑combustion engines. Careful heat‑exchanger design is crucial to control fouling and corrosion.

• Metals and glass industries: Projects have targeted flue streams or off‑gases (e.g., ferroalloy CO‑rich gases) for small‑to‑medium power recovery.
• Cement and ceramics: Pilot efforts have explored installing engines near hot zones to tap steady thermal gradients.
• Oilfield flare reduction: Using waste gas to run Stirling generators both generates power and mitigates methane and black‑carbon emissions compared with open flaring.

Economics hinge on fuel cleanup, exchanger longevity, and maintenance access; where those are managed, Stirling engines provide a durable path to turn otherwise wasted heat into power.

Education, Hobby, and Historical Uses

Beyond industry, Stirling engines play a role in STEM education and have a rich history as safe, simple “hot‑air” engines for light mechanical work in the 19th and early 20th centuries.

• Demonstration models: Desk‑top and classroom engines visualize thermodynamics and energy conversion with candles or small burners.
• Historical machinery: Hot‑air engines once powered fans, pumps, and small workshops where simplicity and safety outweighed power needs.

These applications continue to make the Stirling cycle accessible to students and hobbyists, emphasizing clarity over power density.

Advantages and Limitations

Stirling engines occupy a niche shaped by their cycle’s strengths—sealed working fluid, external heat, and potential for high reliability—and by practical constraints in materials, cost, and size.

• Advantages: Fuel‑flexible external combustion; very quiet with low vibration; long service intervals (especially free‑piston designs); potential for high efficiency when well‑matched to a heat source (e.g., dish–Stirling); low local emissions with proper burners.
• Limitations: Higher upfront cost and complex heat exchangers; lower power density than piston or turbine engines; slower transient response; engineering challenges with sealing and high‑temperature materials; performance falls with low temperature differentials; tough competition from PV, batteries, fuel cells, and modern ICEs.

The best fits are steady, long‑duration duties where reliability, low noise, and fuel flexibility justify the capital cost.

Who Makes and Uses Them Today

A range of companies and sectors continue to field Stirling technology, particularly in remote power, cryogenics, and naval propulsion.

• Qnergy (U.S.): Free‑piston Stirling generators for remote power and instrument‑air systems in oil and gas, utilities, and industrial sites.
• Microgen Engine Corporation (Europe): Free‑piston Stirling cores supplied for micro‑CHP boilers; deployments have narrowed but technology remains available via OEMs in select markets.
• Ricor, Thales Cryogenics, Honeywell, AIM and others: Stirling cryocoolers for infrared sensing, defense, and space payloads.
• Sunpower (AMETEK) and NASA partners: Free‑piston Stirling convertors used in long‑duration laboratory tests and space‑related R&D for dynamic radioisotope power systems.
• Saab Kockums (Sweden) and Kawasaki (Japan): Builders and licensees of Stirling AIP modules for conventional submarines.

Activity is strongest where long life, low maintenance, and specialized performance (quiet, cryogenic, or AIP) confer clear advantages over alternatives.

Outlook

Near‑term growth is most likely in remote, autonomous power (including methane emission reduction and instrument air), defense and space cryocooling, and select AIP submarine fleets. Micro‑CHP prospects are mixed as many regions electrify heating and expand heat pumps, while dish–Stirling remains a technical niche overshadowed by inexpensive solar PV. Ongoing research—particularly in materials, free‑piston designs, and dynamic space power—continues to refine performance and lifetime.

Summary

Stirling engines are used where their unique strengths matter: quiet, reliable, fuel‑flexible generation for remote sites and some CHP; stealthy, efficient AIP for submarines; high‑reliability cryocooling and heat pumping; selective renewable and waste‑heat applications; and education. While they are unlikely to displace mainstream engines or PV‑battery systems broadly, they provide durable solutions in specialized, high‑value niches.

What are the disadvantages of a Stirling engine?

Stirling engines have several disadvantages, including poor power density (low power for their size and weight), high cost, and slow throttle response due to the time it takes for heat exchangers to warm up and respond to power changes. Other drawbacks include the need for large, expensive heat exchangers, potential difficulties with working gas leakage at high pressures, and a low maximum thermal efficiency compared to internal combustion engines because of heat transfer limitations.
 
Low Power-to-Weight Ratio 

• Stirling engines are typically heavier and larger than internal combustion engines to produce the same amount of power. This makes them less suitable for applications where weight is a concern, like vehicles.

Slow Response and Start-Up Time 

• It takes time for the engine’s heat exchangers and flywheel to reach operating temperature and speed. 
• The engines have poor throttle response, meaning they can’t quickly adjust to changing power demands, making them less ideal for applications requiring frequent stopping and starting. 

High Cost 

• Stirling engines are generally more expensive to manufacture than other engine types, partly due to the complexity of their heat exchangers and overall construction.

Large and Expensive Heat Exchangers 

• Efficient heat transfer is crucial for Stirling engines, which necessitates large and costly heat exchangers. These radiators also need to dissipate a large amount of waste heat.

Working Gas Leakage 

• At high pressures, it is difficult to prevent the working gas (like helium) from leaking out of the engine, which reduces efficiency and proper operation.

Lower Practical Efficiency 

• While the ideal Stirling cycle is very efficient, real-world engines cannot achieve total efficiencies as high as internal combustion engines. This is because practical limitations in heat transfer and fluid flow reduce performance.

Why are Stirling engines not used anymore?

Stirling engines aren’t widely used due to poor power-to-weight ratio, slow response times for variable loads, high manufacturing costs, and challenges with heat transfer and sealing expensive working fluids like helium. While highly efficient in theory and quiet, their bulky size, high cost, and slow start-up make them less practical for applications like cars and large power plants compared to more established technologies like internal combustion engines and steam turbines.
 
Key Disadvantages

• Low Power Density: Stirling engines are bulky for the amount of power they produce, making them unsuitable for weight-sensitive applications like cars. 
• Slow Start-up and Response: They require time for the engine’s heat exchangers to warm up and cannot easily change their operating speed or power output. 
• High Cost: The complex design, specialized materials, and less efficient mass production make them expensive compared to alternatives. 
• Complex Heat Exchangers: Efficient operation requires intricate heat exchangers, which add to the engine’s complexity and cost. 
• Working Fluid Issues: The ideal working fluid, helium, is expensive and prone to leaking through seals, especially in large volumes, according to Quora. 
• Heat Transfer Limitations: Heat must transfer into and out of the engine’s working gas through solid walls, which is less efficient than direct combustion in an internal combustion engine. 

Where They Are Still Used
Despite their limitations, Stirling engines are still used in some specialized applications where their unique benefits are crucial: 

• Submarines: Their quiet operation makes them suitable for stealthy environments. 
• Cogeneration Units: They can repurpose waste heat from other generators in industrial and agricultural settings. 
• Solar Power: They can convert concentrated solar energy into electricity, as seen in some solar power plants. 
• Niche Applications: They are also utilized in applications requiring constant, steady power output, such as auxiliary generators for boats and vehicles. 

Does NASA use Stirling engines?

The advanced Stirling radioisotope generator (ASRG) is a radioisotope power system first developed at NASA’s Glenn Research Center. It uses a Stirling power conversion technology to convert radioactive-decay heat into electricity for use on spacecraft.

What are Stirling engines used for today?

Although today the Stirling engine is most commonly used to power submarines, auxiliary power generators, large scale solar power, or as small models and toys, they have the potential to be developed for use in a much larger, successful market if the proper research is able to be applied.