Solar Power Satellites and Microwave Power Transmission

Andrew K. Soubel

Energy Law Spring 2004

Chicago-Kent College of Lawsoubel@msn.com

Outline

Background Solar Power Satellite Microwave Power Transmission Current Designs Legal Issues Conclusion

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)

Continued

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

Continued

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 beamRetro directive beam control capabilityPower 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 groundVisually 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

Continued

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

Continued

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

NASA

Funding the research In charge of space flight for the United States Would be launching the satellites and doing

maintenance

FCC

Federal Communications Commission– The FCC was established by the

Communications Act of 1934 and is charged with regulating interstate and international communications by radio, television, wire, satellite and cable.

Environmental

Possible health hazards– Effects of long term exposure– Exposure is equal to the amount that people receive

from cell phones and microwaves

Location– The size of construction for the rectennas is

massive

International

Geosynchronous satellites would take up large sections of space

Interference with communication satellites Low orbit satellites would require agreements

about rectenna locations and flight paths

Conclusions

More reliable than ground based solar power In order for SPS to become a reality it several

things have to happen:– Government support– Cheaper launch prices– Involvement of the private sector