1. 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. 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. 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. 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. 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/m 2 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 ft 3 Displaced fluid volume of 6.39 in 3 Stirling Engine Design Assumptions: 10% efficiency between the parabolic reflector and engine output (1300 W/m 2 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 ft 3 Displaced fluid volume of 6.39 in 3 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. 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), 5.05V avg, 0.45V p-p ripple within USB specification. Successfully charged cell phones with power conditioning board shown right.