Wireless Power Transmission for Solar Power Satellites By B.Ravindra Reddy (MT097109)

Wireless Power Transmission for Solar Power Satellites

By

B.Ravindra Reddy

(MT097109)

Outline

Background Solar Power Satellite Microwave Power Transmission Current Designs 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

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.

Continued

Waste heat is radiated back into space

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

Possible Designs

Deployment Issues

Cost of transporting materials into space Construction of satellite

– Space Walks

Maintenance– Routine– Meteor impacts

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

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

Current Developments

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

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

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

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