Abstract • We wish to demonstrate a small portable Stirling cycle electrical
generator system to power USB electronics.
• The system will require the design of a solar collector component, a
Stirling engine component, and an electrical generator, power
conditioner and power storage component.
• A beta type Stirling engine was selected with a single power piston, a
single displacer piston, crankshaft, and flywheel to connect to a
permanent magnet DC generator.
Background Information • Harvesting energy from renewable sources offers a method of
providing power at remote locations using local resources.
• Overall system efficiency of Stirling engines can outperform silicon
based photovoltaic systems in many cases.
• Stirling cycle generators can use any heat source to produce
electricity, such as solar radiation, geothermal or waste heat
sources, or even simple combustion of waste biomass.
Stirling Cycle • The Beta Type Stirling Engine
consists of one cylinder containing a
displacer piston and a power piston ,
coupled to a flywheel.
• The working fluid on the far side of
the cylinder is heated by an external
heat source and the opposite side is
cooled by a heat sink.
• As the working fluid on the hot side
expands, it pushes the power piston
towards the cold end of the cylinder.
• On the cold end the gas contracts ,
pulling the power piston back
towards the hot side.
• The displacer piston acts as a
shuttle, moving hot gas towards the
cold side and vice versa. The power
piston and displacer piston rods are
linked to the flywheel 90 degrees out
of phase, producing output power.
Parabolic Mirror
Beta Type Stirling Engine
Crank Shaft and Gearing
PMDC Motor
Buck-Boost Converter
Battery Charge Circuit
USB Output 5V 10W
Arduino with thermocouple
Motor Power FET
System Implementation
Acknowledgments Dr. Alan Raisanen
Mr. Robert Kraynik
Mr. David Hathaway
Stirling Engine Design Assumptions:
• 10% efficiency between the parabolic reflector and engine output
(1300 W/m2 exerted by the sun)
• 50% efficiency between the generator input and USB output
• Beale number of 0.15
• Operating speed of 1000 rpm
Resulting design targets:
• 200 Watt solar power collected
• 20 Watt mechanical output
• 10 Watt electrical output
Resulting Values:
• Mirror collection area of 1.658 ft3
• Displaced fluid volume of 6.39 in3
Generator and Power Conditioning • An Arduino powered from a 6 Volt lead acid battery monitors the
temperature difference between the hot and cold side of the Stirling engine to
determine when to “kick start” the engine by driving the generator as a motor.
• Generator voltage is converted to 5 Volts USB at a maximum of 10 Watts
through a buck-boost converter, as well as converted to 7 Volts to charge
the lead acid battery through a power resistor.
Will Tierney • Bryan Abbott • Phil Glasser • Mike Scionti
Dr. Chris Hoople
Dr. Sergey Lyshevski
USB output begins when motor reaches ~1570 RPM.
Buck-boost can begin operating when generator voltage
reaches 4.6V, and can operate in a boost mode down to
3.6V once powered on, and up to 18V (above the
maximum voltage for this motor).
Generator Test Results
Custom electronics input and USB output shown above
at full load of 1.915A (9.745W), 5.05Vavg, 0.45Vp-p ripple
within USB specification. Successfully charged cell
phones with power conditioning board shown right.
