Solar thermal aircraft

• US 20050242232A1
• Filed: 04/30/2004
• Published: 11/03/2005
• Est. Priority Date: 04/30/2004
• Status: Active Grant

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Bennett, Charles L.
• Granted Patent: US 7,270,295 B2
• Time in Patent Office: Days
• US Class Current: 244/53.R
• CPC Class Codes: B64D 27/24 using steam or spring force jet aircraft B64D27/16
• CPC Class Codes: Y02E 10/46 Conversion of thermal power into mechanical power, e.g. Rankine, Stirling or solar thermal engines
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft
• CPC Class Codes: Y02T 90/40 Application of hydrogen technology to transportation, e.g. using fuel cells

Abstract

A solar thermal powered aircraft powered by heat energy from the sun. A heat engine, such as a Stirling engine, is carried by the aircraft body for producing power for a propulsion mechanism, such as a propeller. The heat engine has a thermal battery in thermal contact with it so that heat is supplied from the thermal battery. A solar concentrator, such as reflective parabolic trough, is movably connected to an optically transparent section of the aircraft body for receiving and concentrating solar energy from within the aircraft. Concentrated solar energy is collected by a heat collection and transport conduit, and heat transported to the thermal battery. A solar tracker includes a heliostat for determining optimal alignment with the sun, and a drive motor actuating the solar concentrator into optimal alignment with the sun based on a determination by the heliostat.

Claims

1. An aircraft powered by the heat of the sun comprising:

an aircraft body capable of producing lift and sustained free flight when propelled;

heat engine means carried by said aircraft body for producing power;

propulsion means powered by said heat engine means for propelling said aircraft;

heat storage means in thermal contact with said heat engine means for supplying heat thereto;

solar concentration means movably connected to said aircraft body for receiving and concentrating solar energy;

solar tracking means including means for determining whether said solar concentration means is optimally aligned with the sun, and means for actuating said solar concentration means into optimal alignment with the sun based on said determination; and

heat collection/transport means for collecting the concentrated solar energy and transporting heat to said heat storage means.

2. The aircraft of claim 1,

wherein said aircraft body includes an optically transparent section, and said solar concentration means is movably mounted in said optically transparent section so that incident solar flux is transmitted therethrough to said solar concentration means.

3. The aircraft of claim 2,

wherein said optically transparent section is on a fuselage of said aircraft body.

4. The aircraft of claim 2,

wherein said optically transparent section is on a wing of said aircraft body.

5. The aircraft of claim 2,

wherein said solar concentration means is a reflective parabolic trough for concentrating solar energy along a focal axis thereof and adapted to rotate about said focal axis, and said heat collection/transport means is positioned along said focal axis to collect the concentrated solar energy.

6. The aircraft of claim 5,

wherein said means for determining optimal alignment comprises a heliostat mounted on said reflective parabolic trough for rotation therewith about said focal axis.

7. The aircraft of claim 6,

wherein said heliostat is located along a symmetric plane of said reflective parabolic trough and adapted to detect a shadow of said heat collection/transport means for use in the optimal alignment determination.

8. The aircraft of claim 7,

wherein said heliostat includes solar cells symmetrically arranged about said symmetric plane

9. The aircraft of claim 8,

wherein said solar cells include a center cell, and two outer cells on opposite sides of the center cell.

10. The aircraft of claim 9,

wherein, in a sun tracking mode, said heliostat is adapted to detect deviations from optimal alignment of said reflective parabolic trough by detecting voltage differences between said two outer cells.

11. The aircraft of claim 9,

wherein, in a sun searching mode, said heliostat is adapted to locate the position of the sun by detecting the voltage difference between the center cell and the average of the two outer cells.

12. The aircraft of claim 8,

wherein the solar cells of said heliostat provide power to said actuation means to rotate said reflective parabolic trough into optimal alignment with the sun.

13. The aircraft of claim 5,

wherein said heat collection/transport means comprises a heat pipe containing a heat transfer working fluid and connected at one end to said heat storage means.

14. The aircraft of claim 13,

wherein said heat pipe has a triangular cross-section forming a single channel containing the heat transfer working fluid.

15. The aircraft of claim 13,

wherein said heat pipe comprises multiple channels in parallel containing the heat transfer working fluid.

16. The aircraft of claim 15,

wherein said multiple channels each have a triangular cross-section.

17. The aircraft of claim 13,

wherein said heat collection/transport means further comprises an optically transparent heat collector envelope coaxially surrounding said heat pipe and supporting a vacuum therebetween, said heat collector envelope allowing concentrated solar energy to be transmitted to said heat pipe while substantially inhibiting conductive and convective heat loss therefrom.

18. The aircraft of claim 17,

wherein said heat collector envelope has an anti-reflection coating that decreases the transmission loss of sunlight to said heat pipe, and minimizes radiative heating of said heat collector envelope by said heat pipe.

19. The aircraft of claim 13,

wherein said heat pipe contains sodium as the heat transfer working fluid.

20. The aircraft of claim 13,

wherein said heat pipe contains lithium as the heat transfer working fluid.

21. The aircraft of claim 13,

wherein said heat pipe has a bend section which slopes downward away from said heat storage means, for draining the heat transfer working fluid away from said heat storage means during dark periods.

22. The aircraft of claim 13,

further comprising a back-reflector adjacent the heat pipe at a side thereof opposite the reflective parabolic trough, for reflecting radiation from said heat pipe back thereto.

23. The aircraft of claim 22,

wherein said means for determining optimal alignment uses a shadow of said back-reflector for said determination.

24. The aircraft of claim 1,

wherein said heat storage means comprises a thermal container and a mixture of lithium hydride and lithium metal contained therein.

25. The aircraft of claim 24,

wherein said mixture of lithium hydride and lithium metal is in substantial equilibrium with dissociation products, including hydrogen gas, and liquid phase lithium and lithium hydride.

26. The aircraft of claim 24,

wherein said thermal container includes an inner containment shell structure and an outer vacuum shell supporting an evacuated space therebetween.

27. The aircraft of claim 26,

wherein said thermal container includes thermal battery insulation in said evacuated space comprising multiple layers of highly reflective material to shield against radiation.

28. The aircraft of claim 1,

wherein said propulsion means includes at least one propeller operably coupled to said heat engine means to be driven thereby.

29. The aircraft of claim 1,

wherein said propulsion means includes at least one ducted fan system operably coupled to said heat engine means to be driven thereby, and said aircraft body has an air inlet and an air outlet which leads air into and out of said at least one ducted fan system, respectively.

30. The aircraft of claim 29,

wherein said at least ducted fan system is located near a stern end of said aircraft body.

31. The aircraft of claim 29,

wherein said air inlet and said air outlet leads air past a cold side heat exchanger of said heat engine means for convective cooling thereof.

32. The aircraft of claim 1,

wherein said heat engine means comprises at least two heat engines.

33. The aircraft of claim 32,

wherein each of said heat engines is independently powered by and associated with a corresponding heat storage means, solar concentration means, solar tracking means, and heat collection/transport means.

59. The aircraft of claims 1, 34 or 35,

wherein said heat engine means is a Stirling engine having a hot side heat exchanger and a cold side heat exchanger.

60. The aircraft of claim 59,

wherein said Stirling engine includes at least one helical groove on one of a crankshaft and a journal surrounding said crankshaft, for self-pressurizing said Stirling engine.

61. The aircraft of claim 60,

wherein said Stirling engine includes a crankcase pressure relief valve for controlling the crankcase pressure and the power output of said Stirling engine.

62. The aircraft of claim 60,

wherein said Stirling engine is hermetically sealed and uses helium as the working fluid therein.

63. The aircraft of claim 62,

wherein said Stirling engine includes a crankcase pressure relief valve for controlling the crankcase pressure and the power output of said Stirling engine, and a sealed chamber connected to said crankcase pressure relief valve and an intake end of said helical groove, for recycling helium released by said crankcase pressure relief valve.

64. The aircraft of claim 59,

wherein said Stirling engine includes cooling fins adjacent the cold side heat exchanger.

34. A solar thermal powered aircraft comprising:

an aircraft fuselage having an optically-transparent section;

wing means extending from said aircraft fuselage and capable of producing lift and sustained free flight when propelled;

a heat engine for producing power and carried by said aircraft fuselage, said heat engine having a heat storage medium in thermal contact therewith for supplying heat thereto;

at least one propulsion device(s) powered by said heat engine for propelling said aircraft;

a solar concentrator movably mounted in said optically transparent section so that incident solar flux is transmitted therethrough to said solar concentrator for receiving and concentrating solar energy;

a solar tracker adapted to determine whether said solar concentrator is optimally aligned with the sun, and actuate said solar concentrator into optimal alignment with the sun based on said determination, for tracking the position of the sun; and

a heat collection and transporting conduit adapted to collect the concentrated solar energy and transport heat to said heat storage medium.

36. The aircraft of claim 34 or 35,

wherein said solar concentrator is a reflective parabolic trough for concentrating solar energy along a focal axis thereof and adapted to rotate about said focal axis, and said heat collection and transporting conduit is positioned along said focal axis to collect the concentrated solar energy.

37. The aircraft of claim 36,

wherein said solar tracker includes a heliostat mounted on said reflective parabolic trough for rotation therewith about said focal axis.

38. The aircraft of claim 37,

wherein said heliostat is located along a symmetric plane of said reflective parabolic trough and adapted to detect a shadow of said heat collection and transport conduit for use in the optimal alignment determination.

39. The aircraft of claim 38,

wherein said heliostat includes solar cells symmetrically arranged about said symmetric plane

40. The aircraft of claim 39,

wherein said solar cells include a center cell, and two outer cells on opposite sides of the center cell.

41. The aircraft of claim 40,

wherein, in a sun tracking mode, said heliostat is adapted to detect deviations from optimal alignment of said reflective parabolic trough by detecting voltage differences between said two outer cells.

42. The aircraft of claim 40,

wherein, in a sun searching mode, said heliostat is adapted to locate the position of the sun by detecting the voltage difference between the center cell and the average of the two outer cells.

43. The aircraft of claim 39,

wherein the solar cells of said heliostat provide power to said actuation means to rotate said reflective parabolic trough into optimal alignment with the sun.

44. The aircraft of claim 36,

wherein said heat collection and transporting conduit comprises a heat pipe containing a heat transfer working fluid and connected at one end to said heat storage medium.

45. The aircraft of claim 44,

wherein said heat pipe has a triangular cross-section forming a single channel containing the heat transfer working fluid.

46. The aircraft of claim 44,

wherein said heat pipe comprises multiple channels in parallel containing the heat transfer working fluid.

47. The aircraft of claim 46,

wherein said multiple channels each have a triangular cross-section.

48. The aircraft of claim 44,

wherein said heat collection and transporting conduit further comprises an optically transparent heat collector envelope coaxially surrounding said heat pipe and supporting a vacuum therebetween, said heat collector envelope allowing concentrated solar energy to be transmitted to said heat pipe while substantially inhibiting conductive and convective heat loss therefrom.

49. The aircraft of claim 48,

wherein said heat collector envelope has an anti-reflection coating that decreases the transmission loss of sunlight to said heat pipe, and minimizes radiative heating of said heat collector envelope by said heat pipe.

50. The aircraft of claim 44,

wherein said heat pipe contains sodium as the heat transfer working fluid.

51. The aircraft of claim 44,

wherein said heat pipe contains lithium as the heat transfer working fluid.

52. The aircraft of claim 44,

wherein said heat pipe has a bend section which slopes downward away from said heat storage medium, for draining the heat transfer working fluid away from said heat storage medium during dark periods.

53. The aircraft of claim 44,

further comprising a back-reflector adjacent the heat pipe at a side thereof opposite the reflective parabolic trough, for reflecting radiation from said heat pipe back thereto.

54. The aircraft of claim 53,

wherein said solar tracker uses a shadow of said back-reflector for said optimal alignment determination.

55. The aircraft of claim 34 or 35,

wherein said heat storage means comprises a thermal container and a mixture of lithium hydride and lithium metal contained therein.

56. The aircraft of claim 55,

wherein said mixture of lithium hydride and lithium metal is in substantial equilibrium with dissociation products, including hydrogen gas, and liquid phase lithium and lithium hydride.

57. The aircraft of claim 55,

wherein said thermal container includes an inner containment shell structure and an outer vacuum shell supporting an evacuated space therebetween.

58. The aircraft of claim 57,

wherein said thermal container includes thermal battery insulation in said evacuated space comprising multiple layers of highly reflective material to shield against radiation.

65. The aircraft of claim 34,

wherein said propulsion device include a propeller operably coupled to said heat engine to be driven thereby.

67. The aircraft of claim 34,

wherein said propulsion device includes a ducted fan system operably coupled to said heat engine to be driven thereby.

35. A solar thermal powered aircraft comprising:

an aircraft fuselage;

wing means extending from said aircraft fuselage and capable of producing lift and sustained free flight when propelled, said wing means having at least two optically-transparent sections; and

associated with each optically-transparent section;

a heat engine carried by said wing means for producing power, and having a heat storage medium in thermal contact therewith for supplying heat thereto;

a propulsion device powered by the corresponding heat engine for propelling said aircraft;

a solar concentrator movably mounted in the corresponding optically transparent section so that incident solar flux is transmitted therethrough to said solar concentrator for receiving and concentrating solar energy;

a solar tracker adapted to determine whether the corresponding solar concentrator is optimally aligned with the sun and to actuate said solar concentrator into optimal alignment with the sun based on said determination, for tracking the position of the sun; and

a heat collection and transporting conduit adapted to collect the concentrated solar energy and transport heat to the corresponding heat storage medium.

66. The aircraft of claim 35,

wherein said propulsion device include a propeller operably coupled to said heat engine to be driven thereby.

68. The aircraft of claim 35,

wherein said propulsion device includes a ducted fan system operably coupled to said heat engine to be driven thereby.

69. An aircraft powered by the heat of the sun comprising:

an aircraft body capable of producing lift and sustained free flight when propelled;

heat engine means carried by said aircraft body for producing power;

propulsion means powered by said heat engine means for propelling said aircraft;

solar concentration means movably connected to said aircraft body for receiving and concentrating solar energy;

solar tracking means including means for determining whether said solar concentration means is optimally aligned with the sun, and means for actuating said solar concentration means into optimal alignment with the sun based on said determination; and

heat collection/transport means for collecting the concentrated solar energy and transporting heat to said heat engine means.

70. A solar thermal power plant comprising:

a heat engine for producing power;

a heat storage medium in thermal contact with a hot side of said heat engine for supplying heat thereto;

an actuable reflective parabolic trough for receiving and concentrating solar energy along a focal axis thereof and adapted to rotate about said focal axis;

a solar tracker adapted to determine whether said reflective parabolic trough is optimally aligned with the sun and to actuate said reflective parabolic trough into optimal alignment with the sun based on said determination, for tracking the position of the sun; and

a heat collection and transporting conduit positioned along said focal axis and adapted to collect the concentrated solar energy and transport heat to said heat storage medium.

71. The solar thermal power plant of claim 70,

wherein said solar tracker includes a heliostat mounted on said reflective parabolic trough for rotation therewith about said focal axis.

72. The solar thermal power plant of claim 71,

wherein said heliostat is located along a symmetric plane of said reflective parabolic trough and adapted to detect a shadow of said heat collection and transport conduit for use in the optimal alignment determination.

73. The solar thermal power plant of claim 72,

wherein said heliostat includes solar cells symmetrically arranged about said symmetric plane

74. The solar thermal power plant of claim 73,

wherein said solar cells include a center cell, and two outer cells on opposite sides of the center cell.

75. The solar thermal power plant of claim 74,

wherein, in a sun tracking mode, said heliostat is adapted to detect deviations from optimal alignment of said reflective parabolic trough by detecting voltage differences between said two outer cells.

76. The solar thermal power plant of claim 74,

wherein, in a sun searching mode, said heliostat is adapted to locate the position of the sun by detecting the voltage difference between the center cell and the average of the two outer cells.

77. The solar thermal power plant of claim 73,

wherein the solar cells of said heliostat provide power to said actuation means to rotate said reflective parabolic trough into optimal alignment with the sun.

78. The solar thermal power plant of claim 73,

wherein said heat collection and transporting conduit comprises a heat pipe containing a heat transfer working fluid and connected at one end to said heat storage medium.

79. The solar thermal power plant of claim 78,

wherein said heat pipe has a triangular cross-section forming a single channel containing the heat transfer working fluid.

80. The solar thermal power plant of claim 78,

wherein said heat pipe comprises multiple channels in parallel containing the heat transfer working fluid.

81. The solar thermal power plant of claim 80,

wherein said multiple channels each have a triangular cross-section.

82. The solar thermal power plant of claim 78,

wherein said heat collection and transporting conduit further comprises an optically transparent heat collector envelope coaxially surrounding said heat pipe and supporting a vacuum therebetween, said heat collector envelope allowing concentrated solar energy to be transmitted to said heat pipe while substantially inhibiting conductive and convective heat loss therefrom.

83. The solar thermal power plant of claim 82,

wherein said heat collector envelope has an anti-reflection coating that decreases the transmission loss of sunlight to said heat pipe, and minimizes radiative heating of said heat collector envelope by said heat pipe.

84. The solar thermal power plant of claim 78,

wherein said heat pipe contains sodium as the heat transfer working fluid.

85. The solar thermal power plant of claim 78,

wherein said heat pipe contains lithium as the heat transfer working fluid.

86. The solar thermal power plant of claim 78,

wherein said heat pipe has a bend section which slopes downward away from said heat storage medium, for draining the heat transfer working fluid away from said heat storage medium during dark periods.

87. The solar thermal power plant of claim 78,

further comprising a back-reflector adjacent the heat pipe at a side thereof opposite the reflective parabolic trough, for reflecting radiation from said heat pipe back thereto.

89. The solar thermal power plant of claim 70,

wherein said heat storage means comprises a thermal container and a mixture of lithium hydride and lithium metal contained therein.

90. The solar thermal power plant of claim 89,

wherein said mixture of lithium hydride and lithium metal is in substantial equilibrium with dissociation products, including hydrogen gas, and liquid phase lithium and lithium hydride.

91. The solar thermal power plant of claim 89,

wherein said thermal container includes an inner containment shell structure and an outer vacuum shell supporting an evacuated space therebetween.

92. The solar thermal power plant of claim 91,

wherein said thermal container includes thermal battery insulation in said evacuated space comprising multiple layers of highly reflective material to shield against radiation.

93. The solar thermal power plant of claim 70,

wherein said heat engine is a Stirling engine having a hot side heat exchanger and a cold side heat exchanger.

94. The solar thermal power plant of claim 93,

wherein said Stirling engine includes at least one helical groove on one of a crankshaft and a journal surrounding said crankshaft, for self-pressurizing said Stirling engine.

95. The solar thermal power plant of claim 94,

wherein said Stirling engine includes a crankcase pressure relief valve for controlling the crankcase pressure and the power output of said Stirling engine.

96. The solar thermal power plant of claim 94,

wherein said Stirling engine is hermetically sealed and uses helium as the working fluid therein.

97. The solar thermal power plant of claim 96,

wherein said Stirling engine includes a crankcase pressure relief valve for controlling the crankcase pressure and the power output of said Stirling engine, and a sealed chamber connected to said crankcase pressure relief valve and an intake end of said helical groove, for recycling helium released by said crankcase pressure relief valve.

98. The solar thermal power plant of claim 93,

wherein said Stirling engine includes cooling fins adjacent the cold side heat exchanger.

88. The solar thermal power plant of claim 88,

wherein said solar tracker uses a shadow of said back-reflector for said optimal alignment determination.

99. An improved Stirling engine of a type having a crankcase with opposing hot and cold heat exchanging ends, a piston capable of reciprocating within said crankcase between the hot and cold heat exchanging ends, a crankshaft coupled to said piston and extending out from said crankcase so that reciprocation of said piston rotates said crankshaft, and a journal surrounding said crankshaft, the improvement comprising:

at least one helical groove on a surface of one of said crankshaft and said journal and bounded by a surface of the other one of said crankshaft and said journal, said helical groove(s) communicating between an inner crankcase volume and the ambient atmosphere so that the relative motion between the rotating crankshaft and said journal pumps ambient atmosphere into said crankcase to self-pressurize the same.

100. The improvement of claim 99,

wherein said helical groove(s) is adapted to self-pressurize the crankcase during operation of said improved Stirling engine.

101. The improvement of claim 100,

wherein said Stirling engine includes a crankcase pressure relief valve for controlling the crankcase pressure and the power output of said Stirling engine.

102. The improvement of claim 99,

wherein said Stirling engine includes cooling fins adjacent the cold side heat exchanger.

103. An improved Stirling engine of a type having a crankcase with opposing hot and cold heat exchanging ends, a piston capable of reciprocating within said crankcase between the hot and cold heat exchanging ends, a crankshaft coupled to said piston and extending out from said crankcase so that reciprocation of said piston rotates said crankshaft, and a journal surrounding said crankshaft, the improvement comprising:

a working fluid within an hermetically sealed crankcase;

a crankcase pressure relief valve for controlling the crankcase pressure and the power output of said Stirling engine;

a closed reservoir for receiving working fluid released from said crankcase pressure relief valve; and

at least one helical groove on a surface of one of said crankshaft and said journal and bounded by a surface of the other one of said crankshaft and said journal, said helical groove(s) communicating between an inner crankcase volume and said closed reservoir so that the relative motion between the rotating crankshaft and said journal pumps the working fluid into said crankcase to self-pressurize the same, whereby the working fluid released from said crankcase is recycled back into said crankcase.

104. The improvement of claim 103,

wherein the working fluid is helium.

105. The improvement of claim 103,

wherein the working fluid is hydrogen.

106. The improvement of claim 105, further comprising:

a hydrogen permeable cap capping the hot end of the Stirling engine; and

a lithium-hydride based thermal storage medium in contact with said hydrogen permeable cap and the hot side of said Stirling engine;

wherein the slow loss of hydrogen from the lithium-hydride is balanced by a slow gain from the Stirling engine hydrogen working fluid through said hydrogen permeable cap, whereby the hydrogen containment of the thermal battery is extended.

107. A thermal battery for use with a heat engine, comprising:

a thermally insulated container; and

a heat storage medium contained in said thermally insulated container and in thermal contact with a hot side of a heat engine for supplying heat thereto, said heat storage medium comprising a mixture of lithium hydride and lithium metal.

108. The thermal battery of claim 107,

wherein said mixture of lithium hydride and lithium metal is in substantial equilibrium with dissociation products, including hydrogen gas, and liquid phase lithium and lithium hydride.

109. The thermal battery of claim 107,

wherein said thermally insulated container includes an inner containment shell structure and an outer vacuum shell supporting an evacuated space therebetween.

110. The thermal battery of claim 107,

wherein said thermally insulated container includes thermal battery insulation in said evacuated space comprising multiple layers of highly reflective material to shield against radiation.