Stirling Engines

Size Range

1 KW to 25 KW

Technology

The Stirling engine is an external combustion engine allowing, in theory, for a range of fuel sources such as combustible gas or solar energy. The heat supplied to the engine causes the working fluid to expand, moving the piston. A displacer then transfers the fluid into the cold zone of the engine where it is recompressed by the working piston. The fluid returns to the hot region of the engine and the cycle continues (see figure below). The purpose of the regenerator is to capture heat from the working fluid as it moves from the hot to cold part of the engine with the heat being given back to the fluid on its return journey - this reduces the amount of fuel needed to reheat the working fluid. The noise created by a Stirling engine is considerably less than other technologies due to the low number of moving parts and the absence of internal combustion.

 

Sterling Engine Schematic
Source: A Collinson- The Future of Embedded Generation

Performance and Efficiency

  • High theoretical efficiencies
  • Current operational efficiencies 12% to 20%, due to material and design limitations.
  • Up to 90% efficient with heat recovery.

Fuel Types

  • Fuel versatility: can use and waste-heat stream.
  • Current focus on solar and waste-heat applications
  • Natural Gas
  • Biomass


Pictured is a Sterling Engine technology designed to run on biomass.
Source: Stirling Denmark 

Application Types

Residential, Rural

  • Stirling engines are suitable for residential or portable applications. The small size and quiet operation mean that they would integrate well into a domestic environment;
  • There is the possibility of using a solar dish to heat the Stirling engine eradicating the need for combustion of a fuel.

Advantages and Disadvantages

Advantages Disadvantages
  • Few moving parts, limiting wear on components and reducing vibration levels;
  • Constant burning of fuel as opposed to pulsed combustion reduces noise;
  • Low emissions of NOx and unburned fuel;
  • Fuel versatility.
  • High cost and reliability issues;
  • Low electrical efficiency.

Economic Performance

Cost Range for Stirling Engines
Installed Capital Cost ($/kW)2,000 – 5,000
Operating and Maintenance ($c/kWh)0.1 – 3.5
Levelized Cost ($c/kWh) 
8000hrs/year 5.0 – 9.5
4000hrs/year8.0 – 19.0
Source: WADE, 2006

As with other emerging technologies, the ultimate commercial success of Stirling engines depends upon economies of scale being achieved through mass production. There are a number of material-related issues specific to the design architecture that must be addressed. Once this has been achieved, costs of Stirling engines, and other emerging DE technologies, will fall. The high costs and small size of Stirling engines limits the applicability of this technology in developing regions.
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