What a Stirling Engine Is Used For

A Stirling engine is used to turn heat—sourced from combustion, the sun, radioisotopes, nuclear fission, or industrial waste heat—into mechanical power and electricity, and in reverse as an efficient cooler. Today its most common roles are in cryogenic coolers, quiet submarine propulsion, off‑grid and industrial power systems, and specialized research and demonstration projects. Below is a deeper look at where and why it’s used, how it works, and what limits wider adoption.

What Is a Stirling Engine?

The Stirling engine is a closed‑cycle, external‑combustion heat engine that works by cyclically compressing and expanding a sealed working gas (typically helium or hydrogen) at different temperatures. A regenerator inside the engine temporarily stores and returns heat during the cycle, boosting efficiency. Because combustion happens outside the working fluid loop—or there may be no combustion at all, just a heat source—the engine is fuel‑agnostic and can run on anything that provides a temperature difference, including waste heat or sunlight. Operated in reverse, the same thermodynamic cycle functions as a high‑efficiency heat pump or cryocooler.

Where It’s Used Today

Although Stirling engines are not mainstream for cars or grid power, they occupy important niches where quiet operation, fuel flexibility, low maintenance, or very high efficiency at small scale matter most. The following examples illustrate current, real‑world deployments and active development areas.

• Cryogenic cooling and refrigeration: “Reverse‑Stirling” cryocoolers provide precise, vibration‑controlled cooling for infrared sensors, night‑vision and space instruments, and ultra‑low‑temperature medical freezers (for example, vaccine storage). Brands in this space include Stirling Ultracold and multiple aerospace cryocooler suppliers.
• Submarine air‑independent propulsion (AIP): The Royal Swedish Navy’s Gotland‑class and planned A26 submarines use Stirling AIP modules to run quietly underwater using stored liquid oxygen and diesel, extending submerged endurance without snorkeling.
• Remote and industrial power: Free‑piston Stirling generators supply off‑grid electricity and mechanical work for telemetry, cathodic protection, and instrument air—especially at oil and gas sites seeking to eliminate methane venting. These systems can run on pipeline gas, biogas, or other fuels with long maintenance intervals.
• Waste‑heat recovery and combined heat and power (CHP): Small Stirling units can convert low‑to‑moderate temperature waste heat into electricity while providing useful heat for buildings or processes. Commercial adoption has been niche after early micro‑CHP waves, but pilots and specialized installations persist.
• Solar thermal power: Dish‑Stirling prototypes have demonstrated high solar‑to‑electric conversion efficiency using concentrated sunlight; however, cheap photovoltaics curtailed most large‑scale projects, leaving this as a research and specialty area.
• Space power research: NASA and the U.S. Department of Energy continue developing free‑piston Stirling converters for potential Dynamic Radioisotope Power Systems and small fission reactors, aiming for higher efficiency than thermoelectric generators on future missions.
• Education and hobbyist models: Desk‑top engines and lab rigs remain popular for teaching thermodynamics and demonstrating external‑combustion principles safely.

Taken together, these use cases play to the Stirling engine’s strengths—quiet, efficient, and fuel‑flexible operation—where those attributes justify costs and engineering complexity.

Why Engineers Choose Stirling Engines

The value proposition rests on efficiency at small scale, compatibility with many heat sources, and low acoustic and emissions profiles. The points below summarize the most cited advantages in current deployments.

• Fuel and heat‑source flexibility: Works with combustion (gas, diesel, biofuels), concentrated solar, nuclear heat, radioisotopes, or industrial waste heat.
• High efficiency for small machines: Regeneration and external combustion yield competitive efficiencies versus many small internal‑combustion engines and thermoelectrics.
• Quiet, low‑vibration operation: Especially true for free‑piston designs, important for submarines, scientific instruments, and remote sites.
• Low local emissions with external combustion: Enables cleaner combustion or catalytic burners and easier after‑treatment.
• Long service intervals: Sealed, few-wear designs (notably free‑piston) can run for years with minimal maintenance.
• Reversible operation: When driven mechanically or electrically, the cycle functions as an efficient cooler or cryocooler.

These advantages align with applications that prize reliability, low noise, and the ability to make use of otherwise hard‑to‑tap heat sources.

Why It Isn’t Everywhere

Despite intriguing benefits, the Stirling engine faces practical barriers that have curbed mass adoption in transportation and utility‑scale power. The limitations below are the ones most often encountered by developers and buyers.

• Cost and complexity: Precision heat exchangers, high‑temperature materials, and hermetic seals add expense, especially at low volumes.
• Power density and response: Compared with internal‑combustion engines, many Stirling designs have lower specific power and slower load‑following.
• Working‑gas challenges: Helium is costly and hydrogen can permeate seals; maintaining charge over long lifetimes is nontrivial.
• Thermal management: Large, durable hot‑ and cold‑side exchangers are bulky and must withstand thermal cycling.
• Market competition: Photovoltaics, lithium‑ion storage, and mature internal‑combustion engines are cheaper or more familiar for many use cases.

These constraints mean Stirlings tend to succeed where their unique attributes outweigh cost and engineering hurdles, rather than in commodity power markets.

Common Configurations and Modes

Different mechanical layouts and operating modes tailor the Stirling concept to specific jobs. Below are the most common variations you’ll encounter.

• Alpha, beta, and gamma kinematics: Piston arrangements that balance simplicity, sealing, and heat‑exchanger design trade‑offs.
• Free‑piston Stirling engines (FPSE): No crankshaft; a resonant piston and linear alternator enable sealed, low‑maintenance generators and cryocoolers.
• Engine vs. cooler: As a heat engine, it produces shaft power or electricity from a temperature gradient; run in reverse, it pumps heat, achieving deep cryogenic temperatures for sensors and freezers.

This design flexibility helps manufacturers optimize performance for quiet propulsion, precision cooling, or rugged remote power.

What’s New and What’s Next (2024–2025)

Recent activity underscores the Stirling engine’s niche momentum. In industry, free‑piston Stirling systems are scaling for methane‑emissions mitigation and off‑grid power at oil and gas sites, replacing pneumatic devices that vent gas. In life sciences, Stirling‑based ultra‑low‑temperature freezers remain in demand for biobanking and high‑reliability cold chains. In defense and space, Stirling cryocoolers continue to support thermal imaging and satellite instruments, while NASA and the DOE are advancing Stirling converters for dynamic radioisotope and fission surface power concepts. In naval applications, Sweden is carrying forward Stirling AIP in its next‑generation A26 submarines, even as other fleets shift toward large battery packs. Meanwhile, micro‑CHP for homes has pulled back from earlier commercial peaks, with activity now limited to pilots and specialized retrofits. Falling costs for solar PV and batteries continue to shape where Stirling makes sense.

Summary

A Stirling engine is used wherever quiet, efficient, and fuel‑flexible conversion between heat and power—or, in reverse, precision cooling—is valuable. That includes cryocoolers for sensors and medical freezers, air‑independent propulsion in some submarines, remote and industrial power systems (including methane‑reduction projects), selective waste‑heat recovery and CHP, solar‑thermal prototypes, and ongoing space‑power research. Its strengths are counterbalanced by cost, complexity, and power‑density limits, keeping the technology focused on niches where those trade‑offs pay off.

What are the negatives of Stirling engines?

For its ideal approaching Carnot efficiency and wide acceptance of heating resources, Stirling engines are foreseen to be the eternal promise in the future. However, in practical use, Stirling engines still own the drawbacks of high cost and low thermal efficiency.

What can you do with a Stirling engine?

• Utility-Scale Power Plants: Solar Stirling engines can be used in large solar power plants to convert solar energy into electricity.
• Distributed Generation: They can be deployed in smaller, distributed systems to provide electricity in remote areas or for off-grid applications.

Where are Stirling engines used today?

Many non-automotive applications for Stirling engines are established or are in prospect including miniature cryogenic refrigerators for missile guidance and night vision equipment, natural gas and propane fired drivers for refrigeration, heat pumps, cogeneration sets and irrigation pumps, trickle chargers and low, …

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.