Wireless Power Transmission for Solar Power Satellites By

Wireless Power Transmission for Solar Power Satellites By B. Ravindra Reddy (MT 097109)

Outline l l l Background Solar Power Satellite Microwave Power Transmission Current Designs Conclusion

Background 1899 -1990

Nikola Tesla l l 1856 -1943 Innovations: – Alternating current – Wireless power transmission experiments at Wardenclyffe

Wardenclyffe l 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 l l 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 l 1940 -50’s Development of the Photovoltaic cell l 1958 First US Satellite that used Solar Power l 1970’s Oil embargo brought increased interest and study

Details of the DOE Study l Construct the satellites in space – l l 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 l l l 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 l Waste heat is radiated back into space l No air or water pollution is created during generation

Problems l Issues identified during the DOE study – Complexity— 30 years to complete – Size— 6. 5 miles long by 3. 3 miles wide l Transmitting antenna ½ mile in diameter(1 km)

Continued l l Cost—prototype would have cost $74 billion Microwave transmission – – Interference with other electronic devices Health and environmental effects

1980’s to Present l l 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 l l 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 l l Cost of transporting materials into space Construction of satellite – l 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 l Received at a “rectenna” located on Earth l Recent developments suggest that power could be sent to Earth using a laser l

Microwave vs. Laser Transmission l 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 l 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 l Around 5 km across (3. 1 miles) l 95% of the beam will fall on the rectenna l

Current Developments

Details l l l 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 l l 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 l Would require a network of hundreds of satellites – l Air Force currently track 8500 man made objects in space, 7% satellites Would make telecommunications companies into power companies

Reliability l l 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 l 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 l l 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