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Wednesday, June 2, 2010

Japaneses Firm Shimizu Plan to Build a Solar Power Plant On the Moon

Dreams are free as the old saying goes. This one sounds about as realistic as planning to build a full scale copy of the Death Star.

Japanese construction firm Shimizu Corporation wants to build a 400 km wide, 11,000 km long belt of PV solar panels around the equator of the moon and plan to transmit the power back to earth wirelessly via a network of 20 km diameter antenna.

Using Robots tele-operated from Earth 24 hours a day, Shimizu say they can make everything from Oxygen and water through concrete and the solar cells themselves from Lunar soil.

This project is even more fantastic than the Japanese plan to build a 1000 MW solar satellite by 2030, despite the fact such an array is 8000 times the size of the solar array on the International Space Station and Japan haven't even managed manned space flight yet with their own space vehicles.

The only problem we have with any of this is that wireless power transmission using RF has not been proven at any distance over 1 mile. To transmit power from geostationary orbit a wireless power transmission system must be energy efficient over 35,299 km (22,000 miles)! From the Moon we're talking 384,403 km (238,857 miles).

Japanese researchers are also considering laser power transmission but laser signals are almost completely blocked by cloud cover and again this technology is untested for long distance power transmission.

Radio and Laser signals suffer from free-space path loss, which is proportional to the square of the distance between the transmitter and receiver and is also proportional to the square of the frequency of the radio signal.

A radio signal 'spreads out' when it leaves the antenna according to Inverse-square law. As much of that signal as possible has to be captured by the antenna aperture at the receiving end to achieve high efficiency. Any energy that spreads out and does not make it to the receiving antenna is considered a loss of efficiency.

Wireless power experiments to date have tired to get around these limits by using extremely focused antenna such as parabolic dishes and co-phased arrays at very close range. They still have yet to deal with loss due to distance as all such successful tests have only been conducted over a mile or less.

Where a conventional wire based long distance high voltage power transmission line is around 95% energy efficient, the longest distance wireless power transmission test to date, between two Hawaiian Islands 148 kms apart, had an efficiency of less than 1/1000th of 1%.

At this stage in time, the technology to do this simply does not exist.


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