Follow Slashdot stories on Twitter


Forgot your password?
Space Power

PG&E Makes Deal For Solar Power From Space 392

N!NJA writes "California's biggest energy utility announced a deal Monday to purchase 200 megawatts of electricity from a startup company that plans to beam the power down to Earth from outer space, beginning in 2016. Solaren would generate the power using solar panels in Earth orbit and convert it to radio-frequency transmissions that would be beamed down to a receiving station in Fresno, PG&E said. From there, the energy would be converted into electricity and fed into PG&E's power grid."
This discussion has been archived. No new comments can be posted.

PG&E Makes Deal For Solar Power From Space

Comments Filter:
  • by Jacques Chester ( 151652 ) on Tuesday April 14, 2009 @08:35AM (#27568669)

    Plus in space solar power is available constantly, rather than being affected by night time, winter hours and weather. As they point out you don't have to pay for the real estate, just the trip to get there.

    And it gives more consistent power because you don't get dust settling on the panels. I realise that sounds stupid, but dust can reduce efficiency by a lot in a few years; your costs go up because you have to pay people to be cleaning acres and acres of solar panels.

  • by muffen ( 321442 ) on Tuesday April 14, 2009 @08:41AM (#27568725)
    I saw a documentary [] on Discovery a few months ago, it was an episode part of "Discovery Project Earth".
    I found it extremely fascinating and was wondering if it would just die or if there would be some actual results from the project, seems like we are getting somewhere now!

    I remember from the documentary that the biggest problem was the beam being split in two, rather than one focused beam. Hopefully they found a solution to this problem.
    Anyways, I strongly suggest watching the documentary if you are interested in this, it really shows how the idea was born and all the small advancements they made which resulted in a successful test.
  • by Jacques Chester ( 151652 ) on Tuesday April 14, 2009 @08:53AM (#27568827)

    There are a number of points you can choose that are geostationary and in shadow less than 2% of the time (as I recall the 1970s proposal). Other schemes call for having multiple satellites that hand off to each other. This proposal is I think of the former variety.

  • Interlock (Score:5, Informative)

    by Doc Ruby ( 173196 ) on Tuesday April 14, 2009 @08:55AM (#27568861) Homepage Journal

    These beaming systems have interlocks pointed back from the ground receiver to the satellite. If the two get out of alignment, the satellite immediately loses the ground signal, and immediately stops transmitting.

    Besides, the beamed power density doesn't have to be very high per square meter. If it's just concentrated 5x from its density in space, it's 6.5KW:m^2. At this system's 2MW transmission rate, is only 308m^2, or a square 17.5m on a side. If it's really RF, even if the interlock failsafe failed, the beam wouldn't do much except fry some unshielded electronics in the way until something else shut it down. I'm sure the multiple layers of government regulators will ensure a lot of "deadman switches" to stop the only thing that everyone guesses could go wrong.

  • by ATestR ( 1060586 ) on Tuesday April 14, 2009 @09:00AM (#27568931) Homepage
    which means the array will be in the earth's shadow just less than half the time.

    Not really. A Geostationary orbit (over the same point) would cut through Earth's shadow for about 45 minutes on orbits where the orbital inclination lines up with the sun... generally in the spring and fall. Other times, the orbit is up to 23 degress off the Earth-Sun plane, and not in the shade at all. Since this power interruption would occur at "midnight", it probably won't affect peak power usage at all. And if you put two of the things up, at least 10,000 apart in orbit (about 45 degrees of arc, well within the allowable angle of incidence), your have continuous power, with only one being in shadow at the same time.

  • by Jacques Chester ( 151652 ) on Tuesday April 14, 2009 @09:01AM (#27568943)

    1. Orbital solar platforms cannot be used as weapons unless you are trying to drop them on someone (which is true of anything in orbit). The energy they put out is the wrong frequency; it doesn't interact with human biology at all.

    2. If you can build 25 ton to LEO heavy lifters, James Bondesque schemes are a waste of time. Better to lob nukes. Heck, even throwing a 25 ton block of concrete on a ballistic course would be more far, far more dangerous than 100 years of orbital solar power transmissions.

  • by Jacques Chester ( 151652 ) on Tuesday April 14, 2009 @09:12AM (#27569097)

    The trick to remember is that the Earth is actually quite a small part of the sky when seen from a satellite in geostationary orbit. It seems big to us, but it's just a pale blue dot after all.

  • Re:Bad idea (Score:4, Informative)

    by Jacques Chester ( 151652 ) on Tuesday April 14, 2009 @09:33AM (#27569407)

    Again, no. The microwaves don't interact with organic matter, they pass through. You're not getting cancer from TV broadcasts or mobile phone towers either.

  • I mean, what's the worst that can happen when you're beaming 200 Megawatts of energy into my town?

    Right now a fusion reactor is beaming sunlight (@ 1366W per square meter [], on average) * 271.4 square km [] of energy at luminal frequencies alone which if I do the math right (even at this level it is by no means sure, I could be off by three orders of magnitude or something, yes I am that dyslexic about numbers) works out to about 370 gigawatts.

    The amount of energy is pretty irrelevant by itself, aside from what it can add to the grid.

  • Re:Bad idea (Score:2, Informative)

    by mozzis ( 231162 ) on Tuesday April 14, 2009 @09:39AM (#27569485) Homepage
  • by Doc Ruby ( 173196 ) on Tuesday April 14, 2009 @09:54AM (#27569711) Homepage Journal

    How about I convince you they're planning to deliver only 2MW, not 200MW.

    They say they'll reach a 17GWh:y delivery once the platform is stable. There's 8765.81277 hours in a year, so that's 17 billionWh / 8765.81277h = 1.9393524 million watts.

    The solar "constant" [] in geosync Earth orbit (about 35Km elevation) is 1366W:m^2. That's 1419.73089m^2, or 0.00141973089Km^2, significantly less (0.709865445%) than 0.2Km^2.

  • Re:Bad idea (Score:1, Informative)

    by Anonymous Coward on Tuesday April 14, 2009 @10:05AM (#27569879)

    No. The microwaves are the wrong frequency, they don't interact with water and will pass straight through any living creature.

    I don't know what you're thinking, but maybe you think microwave ovens work on some magic frequency where water resonates? That's an urban legend. Microwaves are easily absorbed by the human body. We're basically salt water which is conductive enough to absorb most of the energy in a microwave at any frequency.

  • Re:makes no sense (Score:5, Informative)

    by icebrain ( 944107 ) on Tuesday April 14, 2009 @10:43AM (#27570457)

    During most of the year, geostationary satellites spend 100% of the time in sunlight. During "eclipse season" (which happens around the spring/fall equinoxes), they get eclipsed, for a few minutes up to about 70 (at the peak of the season). A discussion of this can be found here: []

    During those times, you could redirect from another satellite, use an alternative power source (batteries, capacitors, fueled generators, etc), and/or have a "brownout". Power outages suck, but if you're in a place where conventional power sources are unavailable/impractical/infeasable, it's better than nothing.

  • Re:Bad idea (Score:4, Informative)

    by afidel ( 530433 ) on Tuesday April 14, 2009 @10:46AM (#27570503)
    I see you aren't an electronics geek, it's simple to make a crystal radio that's powered by nothing more than the radio waves floating around you =) Oh and the solution is simple, you use a feedback loop. You have a continue signal on the ground that tells the satellite to send power, if the beam gets misaligned the ground station loses power and the continue signal stops and the satellite shuts down transmission.
  • by Doc Ruby ( 173196 ) on Tuesday April 14, 2009 @10:51AM (#27570571) Homepage Journal

    TFA's math is wrong. TFA says specifically

    [Solaren corporate spokesperson Marshall] said the agreement called for 800 gigawatt-hours of electricity to be provided during the first year of operation, and 1,700 gigawatt-hours for subsequent years.

    1700 GWh in an 8700 hour year is just under 2MW. 200MW is enough power for 100,000 homes at 2KW each (a low average), so even their math that 1700GWh is "the annual consumption of 250,000 average homes" is wrong. I think their quoting the numbers in the contract is more reliable than their arithmetic.

  • Re:Bad idea (Score:3, Informative)

    by rufty_tufty ( 888596 ) on Tuesday April 14, 2009 @11:20AM (#27571017) Homepage

    You are aware that there are different frequencies of microwaves yes? Some that do agitate water (and heat it up) and others that don't. As long as the power satellite uses one of the frequencies that don't, then yes I'd happily spend an indefinite amount of time in its path.
    Just like I'll consume as much plutonium as you're willing to consume caffeine.

  • Re:Bad idea (Score:1, Informative)

    by Anonymous Coward on Tuesday April 14, 2009 @11:33AM (#27571239)

    Again, no. The microwaves don't interact with organic matter, they pass through. You're not getting cancer from TV broadcasts or mobile phone towers either.

    Microwaves react to water molecules, radio waves do not. Two different parts of the electromagnetic spectrum.

    To prove this put your hand on top of your cell phone. Then put your hand in a microwave oven.

    Notice a difference?

  • Re:Bad idea (Score:3, Informative)

    by drinkypoo ( 153816 ) <> on Tuesday April 14, 2009 @12:07PM (#27571837) Homepage Journal

    The transmitting antenna of the system will presumably be a phased array which among other things can detect direction and strength of incoming signals. Sample the transmitting antennas at the same point in the wave each time (the aiming signal will be broadcast at a multiple of the power wave) and you don't even need any separate system. I would propose to do it with an analog system on sapphire insulator or similar, with redundant systems... not with a microprocessor. Hence you get your 'failsafe' aspect. But someone probably knows an even better way. But using a laser has the major disadvantage that it is generally interfered with by clouds, while the frequencies intended for power transmission interact very little with water, and using a separate RF system has the disadvantage that one radio system must be shielded or otherwise isolated from the other.

  • Re:Bad idea (Score:3, Informative)

    by Lloyd_Bryant ( 73136 ) on Tuesday April 14, 2009 @12:12PM (#27571949)

    Ummm The receiver is on the ground. You know, so it can receive the power from the sat.
    The sat. is shooting out the laser beam from orbit to ground.

    So... if the sat rotates enough to be off target, then the ground based receiver can no longer see the laser, not the satellite like you said. Which still leaves the issue of, how do you tell the laser it's pointing wrong, fast enough to prevent it from messing other stuff up?

    The only solution is to use some type of GPS system with a very fine precision, so the satellite can calculate its actual orientation instantly.
    The laser would also need to be mounted on some type of gyroscopic stabalizer, so that if the sat's orientation changes suddenly the laser will get blocked until the power can cut off.

    I messed up with the word "receiver" on that one. Let me rephrase:
    Have a sensor on the satellite with a very limited field of view, and a laser (or maser, or maybe just a plain microwave beam) sent from the ground station to the satellite. If the satellite's orientation changes enough to cause it to miss the target, the sensor would no longer "see" the signal from the ground station, and trigger a shutdown of the power beam.

  • Re:Bad idea (Score:3, Informative)

    by Brandon30X ( 34344 ) on Tuesday April 14, 2009 @08:57PM (#27580681)

    You answered your own question. It cant produce a narrow beam, which is the same reason why it cant cook anybody. You have a large diameter beam (kilometers in diameter) at a low power density (similar to the energy density of sunlight) and a huge rectenna array (say, covering many farmers fields by being upheld on stilts). Yes, this works. I have studied it. Smarter people than you or I have studied it. I swear to god NOBODY on slashdot understands power density. Every frikin time this subject comes up its always "its a weapon!"

    Now economic viability and possible electronic interference you can go and argue all you want.

"Don't worry about people stealing your ideas. If your ideas are any good, you'll have to ram them down people's throats." -- Howard Aiken