Solar Power Satellites and Microwave Power Transmission

[seminar class]

presented by:
Andrew K. Soubel

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Solar Power Satellites and Microwave Power Transmission
Background
 1899-1990
 Nikola Tesla
 1856-1943
Innovations:
– Alternating current
– Wireless power transmission experiments at Wardenclyffe
 Wardenclyffe
 1899
– Able to light lamps over 25 miles away without using wires
– High frequency current, of a Tesla coil, could light lamps filled with gas (like neon)
 1940’s to Present
 World War II developed ability to convert energy to microwaves using a magnetron, no method for converting microwaves back to electricity
 1964 William C. Brown demonstrated a rectenna which could convert microwave power to electricity
Brief History of Solar Power
 1940-50’s Development of the Photovoltaic cell
 1958 First US Satellite that used Solar Power
 1970’s Oil embargo brought increased interest and study
Solar Power from Satellites
 1968’s idea for Solar Power Satellites proposed by Peter Glaser
– Would use microwaves to transmit power to Earth from Solar Powered Satellites
 Idea gained momentum during the Oil Crises of 1970’s, but after prices stabilized idea was dropped
– US Department of Energy research program 1978-1981
Details of the DOE Study
 Construct the satellites in space
– Each SPS would have 400 million solar cells
 Use the Space Shuttle to get pieces to a low orbit station
 Tow pieces to the assembly point using a purpose built space tug (similar to space shuttle)
 Advantages over Earth based solar power
 More intense sunlight
 In geosynchronous orbit, 36,000 km (22,369 miles) an SPS would be illuminated over 99% of the time
 No need for costly storage devices for when the sun is not in view
– Only a few days at spring and fall equinox would the satellite be in shadow
 Continued
 Waste heat is radiated back into space
 Power can be beamed to the location where it is needed, don’t have to invest in as large a grid
 No air or water pollution is created during generation
Problems
 Issues identified during the DOE study
– Complexity—30 years to complete
– Size—6.5 miles long by 3.3 miles wide
 Transmitting antenna ½ mile in diameter(1 km)
 Cost—prototype would have cost $74 billion
 Microwave transmission
– Interference with other electronic devices
– Health and environmental effects
 1980’s to Present
 Japanese continued to study the idea of SPS throughout the 1980’s
 In 1995 NASA began a Fresh Look Study
– Set up a research, technology, and investment schedule
NASA Fresh Look Report
 SPS could be competitive with other energy sources and deserves further study
 Research aimed at an SPS system of 250 MW
 Would cost around $10 billion and take 20 years
 National Research Council found the research worthwhile but under funded to achieve its goals
Specifications
 Collector area must be between 50 (19 sq miles) and 150 square kilometers (57 sq miles)
 50 Tons of material
– Current rates on the Space Shuttle run between $3500 and $5000 per pound
– 50 tons (112,000lbs)=$392,000,000
 There are advantages
 Possible power generation of 5 to 10 gigawatts
– “If the largest conceivable space power station were built and operated 24 hours a day all year round, it could produce the equivalent output of ten 1 million kilowatt-class nuclear power stations.”
 Possible Designs
 Deployment Issues
 Cost of transporting materials into space
 Construction of satellite
– Space Walks
 Maintenance
– Routine
– Meteor impacts
 Possible Solutions
 International Space Station
 President’s plan for a return to the moon
 Either could be used as a base for construction activities
Microwave Power Transmission
How the power gets to Earth
 From the Satellite
 Solar power from the satellite is sent to Earth using a microwave transmitter
 Received at a “rectenna” located on Earth
 Recent developments suggest that power could be sent to Earth using a laser
Microwaves
 Frequency 2.45 GHz microwave beam
 Retro directive beam control capability
 Power level is well below international safety standard
 Microwave vs. Laser Transmission
 Microwave
– More developed
– High efficiency up to 85%
– Beams is far below the lethal levels of concentration even for a prolonged exposure
– Cause interference with satellite communication industry
 Laser
– Recently developed solid state lasers allow efficient transfer of power
– Range of 10% to 20% efficiency within a few years
– Conform to limits on eye and skin damage
Rectenna
“An antenna comprising a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power.”
 Microwaves are received with about 85% efficiency
 Around 5km across (3.1 miles)
 95% of the beam will fall on the rectenna
Rectenna Design
 Currently there are two different design types being looked at
– Wire mesh reflector
 Built on a rigid frame above the ground
 Visually transparent so that it would not interfere with plant life
– Magic carpet
 Material pegged to the ground
 5,000 MW Receiving Station (Rectenna). This station is about a mile and a half long.
Rectenna Issues
 Size
– Miles across
 Location
– Aesthetic
– Near population center
 Health and environmental side effects
– Although claim that microwaves or lasers would be safe, how do you convince people
Current Developments
 SPS 2000
 Details
 Project in Development in Japan
 Goal is to build a low cost demonstration model by 2025
 8 Countries along the equator have agreed to be the site of a rectenna
 10 MW satellite delivering microwave power
– Will not be in geosynchronous orbit, instead low orbit 1100 km (683 miles)
– Much cheaper to put a satellite in low orbit
– 200 seconds of power on each pass over rectenna
 Power to Mobile Devices
 If microwave beams carrying power could be beamed uniformly over the earth they could power cell phones
 Biggest problem is that the antenna would have to be 25-30 cm square
Low Orbit
 Communications industry proposing to have hundreds of satellites in low earth orbit
 These satellites will use microwaves to beam communications to the ground
 Could also be used to beam power
 Since a low orbit microwave beam would spread less, the ground based rectenna could be smaller
 Would allow collectors on the ground of a few hundred meters across instead of 10 kilometers
 In low orbit they circle the Earth in about every 90 minutes
Issues
 Would require a network of hundreds of satellites
– Air Force currently track 8500 man made objects in space, 7% satellites
 Would make telecommunications companies into power companies
Reliability
 Ground based solar only works during clear days, and must have storage for night
 Power can be beamed to the location where it is needed, don’t have to invest in as large a grid
 A network of low orbit satellites could provide power to almost any point on Earth continuously because one satellite would always be in range
 Legal Issues
 Who will oversee?
 Environmental Concerns
 International