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.