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Solar power beamed from space within a decade?

By

February 22, 2009

Artists visualization of a solar satellite (Image: Space Energy via Mafic Studios)

Artists visualization of a solar satellite (Image: Space Energy via Mafic Studios)

February 23, 2009 The concept of Space-Based Solar Power (SBSP) has been doing the rounds for decades with fantastic claims of 24 hour a day solar power beamed from space via microwave to any point on earth. A start up company called Space Energy, Inc says it plans to develop SBSP satellites to generate and transmit electricity to receivers on the Earth's surface. To do this, the company plans to create and launch a prototype satellite into low earth orbit (LEO). The hitch: this concept is based on as yet unproven technology.

SBSP was theorized over 40 years ago by renowned scientist Dr. Peter Glaser. Since then, in response to periodic energy crises, the idea has been re-evaluated from time to time by the U.S. Department of Energy, NASA, major aerospace companies and countries such as Japan and India.

Solar power satellites are large arrays of photovoltaic panels assembled in orbit, which use microwave radio waves to transmit solar power to large receiving antennas on Earth. The resulting power can either supplement, or be a substitute for, conventional electricity sources.

The advantage of placing solar collectors in geosynchronous Earth orbit (GEO), about 36,000 kilometres (22,500 miles) above Earth, is that it uses the constant and unobstructed output of the Sun, unaffected by the Earth's day/night cycle.

By contrast, ground-based solar power provides a vital and valuable addition to the Earth's energy needs, but is limited by these factors:

  • Weather
  • Variable seasons
  • Atmospheric blocking of sunlight
  • Poor direct sunlight at higher and lower latitudes
Because none of these factors applies in outer-space, an orbiting SBSP station can supposedly provide an estimated 6-8 times more power than a comparable solar cell on the Earth's surface.

Here’s where the entire concept falls flat. Space Energy, Inc claims that a successful long-range wireless power transmission test was conducted in mid-2008, that supposedly transmitted a microwave beam (similar to the kind that would be used to transmit energy from space to Earth) between two Hawaiian Islands across 148 kilometres - more than the distance from the surface of the Earth to the boundary of space. They claim this test demonstrated the technical feasibility of transmitting SBSP to Earth.

Less than 1/1000th of 1% received

Unfortunately for Space Energy, Inc and the entire concept of space based solar power, the actual test results conducted for a Discovery channel documentary proved a total failure. The former NASA executive and physicist who organized the experiment, John Mankins, admitted in a press conference that the $1 Million budget spent of the experiment resulted in less than 1/1000th of 1% of the power transmitted being received on the other island.

The most successful test of wireless power transmission over any distance at high efficiency was conducted by Bill Brown in 1975. Using a NASA deep space tracking dish they transmitted 30kw over 1.6 km (1 mile) at 82.5% efficiency at the Goldstone Deep Space Communication Complex. A Since Geostationary orbit is 36,000 km (22,500 miles) away from earth the space based power station needs to efficiently transmit power over twenty thousand times further than has ever been achieved to date.

Researchers at the Japan Aerospace Exploration Agency (JAXA) have begun to develop the hardware for a SBSP satellite they hope to launch by 2030. They will begin testing this month of a microwave power transmission system designed to beam the power from the satellites to Earth. In a series of experiments to be conducted at the Taiki Multi-Purpose Aerospace Park in Hokkaido, the researchers will use a 2.4-meter-diameter transmission antenna to send a microwave beam over 50 meters to a rectenna (rectifying antenna) that converts the microwave energy into electricity and powers a household heater. The researchers expect these initial tests to provide valuable engineering data that will pave the way for JAXA to build larger, more powerful systems.

This hardware will then have to be scaled up from 50 meters to a distance of 36,000 km and from a 2.4 meter antenna to a ground receiving stations that measure 3 kilometres across and that can receive 1 gigawatt (1 million kilowatts) of electricity — enough to power approximately 500,000 homes.

Japan developing Laser transmission

The Japanese scientists have also experimented with direct conversion of sunlight into a high powered laser to transmit power wirelessly back to earth using light. Using solar plates made from chromium, a ceramic material that absorbs the sunlight, and neodymium, which converts it into laser light, these solar panels demonstrated a 42% solar-to-laser energy conversion efficiency – an impressive figure that outperforms previous technology by a factor of four. Unfortunately cloud cover has an adverse effect of laser transmissions, perhaps why they are also testing a microwave system.

Comparing the energy provided by Space Based power with a conventional ground based solar PV or thermal system of the same 3 km size as the receiving antenna shows that earth based systems are more than competitive. Using a value of 1.4kW per square meter as the radiant solar intensity at the Earth's surface with a 20% power conversion efficiency a ground based solar plant could generate 2.5 gigawatt (only during daylight of course) compared to the Space satellites 1 gigawatt. Many solar thermal power generation plants now incorporate thermal energy storage therefore providing the 24 hour a day base load at a small fraction of the cost of developing and launching solar power station that would be larger than the International Space Station into geostationary orbit.

Paul Evans

7 Comments

Paul, there are reasons to be down on space based solar power, but microwave power transmission is not one of them. The field is *extremely* well understood, and has been for a long time, almost back to Newton.

What is the hard part is getting millions of tons of parts to GEO. If you can get the transport down in the range of $100/kg, then power sats are close to ten times less expensive than the next best solution, nuclear.

But to do that requires a new look at the rocket equation and ISPs from 550 to 1500. That seems to be possible, but only for traffic models of half a million tons up.

Keith Henson

H. Keith Henson
23rd February, 2009 @ 11:05 pm PST

Planet-importing solar power is a horrible idea! The people who propose it have not done an environmental impact study of even the most cursory sort. First, it increases the total energy of the atmosphere because virtually all of it will wind up as heat. Something we can do without just now. Second, it continually ionizes a column of the atmosphere passing through it. Any idea what the effect of that might be? Third, because of the requisite size of such a project, space garbage and meteorites will destroy any collector within a short time. Fourth, how do you repair it? The cost of launching a repair are many millions of $. Fifth, the same money spent on Earth-based collectors produces MUCH more power.

Anyone who invests in such an undertaking is throwing away their money!

HaPPI
24th February, 2009 @ 01:31 am PST

Importing solar power does NOT increase total energy to the atmosphere or Earth. Heat from the Earth is radiated to space and does not accumulate unless it is trapped by greenhouse gases. The waste heat from microwave power is far less than from any other energy source, because it is 90% efficient conversion at the receiver, compared to efficiencies of less than 50% for most coal powered and nuclear powered stations. Space solar power injects far less heat into the atmosphere than existing power systems.

Charles F. Radley
25th February, 2009 @ 08:01 pm PST

"Total failure"? I disagree. First, the microwave power WAS transmitted. Surely that is not "total" failure. Second, the distance of the transmission is among the longest of its kind, comparable to the distance from the earth's surface into space. World's records are certainly not a "failure".

The physics and engineering of microwave power transmission and antenna gain have been in textbooks for decades, and can now be found easily on the internet. These equations tell exactly why the power received was so low for this demonstration; and they also tell exactly why a large scale solar power satellite with a large receiving antenna can achieve much higher transmission efficiency. The answer is in the wavelength of the electromagnetic signal, and the aperture (sizes) of both the transmitting and the receiving antenna. When combined with phased array technology (for pointing the beam), a large orbital transmitter can deliver some 50% of its power to a large terrestrial rectenna (reports are available within www.nasa.gov and www.nss.org). Compared to other methods for electrical power conversion and transmission, this is not bad.

The first automobiles, the first computers, the first airplanes, all could be labelled "total failures" if performance metrics (cost, efficiency, speed) are compared to the incredible machines these have evolved into today. But when viewed as an early feasibility demonstration indicative of the need for further study and development, these tests were, in my opinion, successful.

Facebook User
28th February, 2009 @ 04:39 am PST

Looks like it all comes down to the space elevator.

Richard Belihomji
2nd January, 2010 @ 04:21 pm PST

H. Keith Henson said:

"What is the hard part is getting millions of tons of parts to GEO."

I love your optimism for microwave technology. As for the issue of transportation, this may be a feasible solution. To allow for large and light-weight panels, application of practical origami could be used along with recent advances in mass-produced, thin-film photovoltaics. The folding method for a football field sized diffraction lens called Eyeglass could be used to deploy massive solar panels. Here is a link: https://www.llnl.gov/str/March03/Hyde.html

Also, cheap and very light solar panels can be produced by Nanosolar. Not only is the printed sheet light, but it would require less (read: lighter) weather protection due to the obvious lack of weather in space. Here is a link to Nanosolar's website: http://www.nanosolar.com/

Cameron Rogers
16th January, 2010 @ 10:27 pm PST

The idea of cheap solar energy beamed form space, 24 hours a day sounds great but the technical problems and costs involved make it one for the back burner I think. We have plenty of renewable power waiting to be tapped on earth which, if it had the financial support could be making inroads right now into reducing carbon dependancy and reliance on supplies from unreliable sources. I am well aware that wind power has in many cases proved itself to give no real carbon benefit due to its unreliablity but areas such as concentrating solar power and tidal offer very reliable sources and are far easier and cheaper to develop. Even the oil industry didn't go for the tough locations first.

I am currently setting up a site, http://www.realitygreen.co.uk to focus on what is realistic and what isn't when it comes to sustainable living and reducing our carbon footprint. The site will launch officially in the next couple of months but I am interested to hear from others who also feel there is a lot of unrealistic marketing going on.

chris_
27th January, 2010 @ 02:22 am PST
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