Space Solar Power?  Golly that sounds great.  I’ll use it to power my Moller Sky Car or maybe my new Palm Cobalt handheld, which I can play some Duke Nukem Forever on.  Then I’ll head on over to the Superconducting Supercolider and watch the NASP take off.    In other words:  It’s not going to happen.  Just because they say it has a schedualed time does not mean it is ever going to come to be.

PG&R recently signed a deal for “Space Solar Power.”   Apparently realizing that solar power doesn’t really work for grid power here on the ground they’ve decided to try an even more outlandish idea with the hope that it might actually fool someone into thinking this is seriously going to happen.

Via MSNBC:

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.

San Francisco-based Pacific Gas & Electric said it was seeking approval from state regulators for an agreement to purchase power over a 15-year period from Solaren Corp., an 8-year-old company based in Manhattan Beach, Calif. The agreement was first reported in a posting to Next100, a Weblog produced by PG&E.

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.

Well, this kind of thing got all kinds of attention and the webblogs and boards were going nuts about how this is the next big step toward “sustainable” (TM) energy.  After all, solar power is proven as a viable way of powering satellites, right?   So why not just beam it down to earth.   Granted, 200 megawatts is a pitifully small amount of power for something like the California gird, but nobody really knows what a megawatt is anyway, right?

Perhaps I’m in the minority of people in my thinking, but the first thing that came to mind when I heard this “official announcement” was the announcement that Pan American World Airlines was opening a waiting list to be on the first season of flights on their earth-moon service.   Of course, Pan Am never transported a passenger to space, much less to a lunar vacation and the company folded years ago, something which PG&E will also be doing if they actually take this seriously (which I’m sure they don’t).

The plan calls for the bump and dump…. er… I mean startup company to launch a satellite to geostationary orbit, where it will receive sunlight for all but a small portion of the day. From there, it will beam back power to a collection area in California by means of microwaves.   The collection area is supposed to be small enough to be reasonably maintaintained (and not defeat the purpose by receiving energy that is as defuse as sunlight) but large enough that the beam it receives will not be so narrow that it will end up cooking anything should it miss the target.

They claim that they can get this project going by 2016 and for a cost of about 2 billion dollars.  If they could achieve this, it would make it the most expensive 200 megawatts on this planet or, for that matter, anywhere else.   Of course they won’t actually get it built for that cost or any cost, because it would take more energy to launch the stupid thing than it is likely to ever produce and the real cost of such a venture would be much higher than two billion.   (Perhaps it could be done for two hundred billion)

Here is why:

The International Space Station uses some of the most advanced large space solar arrays in existence.   Each section is made of extremely lightweight flexible solar cells that are launched folded into a small package and then are deployed from the station.   The solar wing each contain over 250,000 individual photovoltaic cells and are 112 feet long by 39 feet wide when fully deployed.   Each of the arrays weighs about 2,400 lbs or just over one metric ton.   Together the eight solar wings on the space station can generate about 110 kilowatts when in direct sunlight.

So, if a space-based PV solar system is going to generate 200 megawatts, it will need roughly 14,500 of the solar panels that the space station has.  Of course that does not include the other systems on such a space-solar system.   There would need to be voltage regulators, gyroscopes, to keep it pointed in the right direction, thrusters to insert it into the proper orbit and to occasionally correct for drift caused by tidal forces and solar winds.  It would also need a powerful microwave transmitter and an extremely large and high gain antenna system.   Of course, it would also need some kind of structure or truss system to attach all this stuff together.

The solar wings on the space station already represent the bleeding edge in extremely lightweight space solar collectors.  Geostationary orbit would allow for a bit longer exposure to the sun with only brief periods during which the earth blocks the sun, but improved efficiency is not likely to happen, at least not beyond a small amount.   One big issue with space solar cells is that they need to be efficient but at the same time be relatively resistant to the degradation that can be caused by not only intense sunlight but cosmic rays, solar winds and other sources of radiation.

How much would this end up weighing?   It’s anyone’s guess, but based on the solar panel area alone, it’s going to have to be at least 15 thousand metric tons.   20,000 metric tons might be a good conservative estimate for such a spacecraft.   Really, however, this is pretty hypothetical.    The weight is likely to be increased if the solar collector needs to be assembled from multiple parts.   This is because docking and joining sections complicates things and necessitates that each section have its own propulsion and guidance system.

And this solar satellite would certainly need to be assembled in space, because no launch system could launch this thing in one shot, or even come close to it.  The upcoming Ares-V will be the largest launch system ever developed and will have a capacity of 188,000 kg to low earth orbit.   The Saturn V was capable of launching 118,000 kg to low earth orbit and the (never flown) Energia-Vulkan would have been able to launch about 175,000 kg.   Of course, the payload to geostationary orbit would be less than the LEO capacity.   While the exact capacity to GEO is unknown, launching this system just to LEO orbit would require well over one hundred launches of the Ares-V.    Putting it in geostationary orbit might take as many as 150-200 or more.

However, the Ares-V is currently only planned for use by NASA for space exploration missions.  Also, it won’t make it’s first test flight until at least 2018.   Commercially avaliable launch systems like the Russian Proton and US Atlas V would require several thousand flights to put the system in geostationary orbit.

But this is really all just theoretical anyway, because even if they could manage to get hundreds of the world’s largest rockets committed to launching a massive 200 megawatt solar collector there are still a number of problems.   Also, this is not accounting for loss involved.   If you want 200 megawatts of usable power on the receiver side, you will need far more than 200 megawatts of collection capacity.

Problems to be solved (aside from launching this monstrosity into geostationary orbit):

1.  Figure out how to keep the damn thing in the same place -  Most geostationary satellites use reaction wheels to maintain orientation and small thrusters to compensate for drift caused by factors like the solar wind, the pull of the moons gravity and so on.   Of course, this satellite would dwarf any previous ones and hence would need an enormous system to maintain placement and attitude.   With such enormous surface area it’s difficult to know how forces like the solar winds and particle radiation may effect the satellite.  This is going to mean more thrusters are needed more often to compensate for such forces.   Even with ion thrusters, it’s going to take a lot of energy and fuel to keep this massive thing from drifting out of geostationary orbit.

2.   Make it play nice with other GEO satellites – The Clark Belt is crowded with communications satellites and interference from a massive radio transmitter of any kind would be unwelcome.   Even if the transmitter were not on the same frequency as the other satellites, the sheer power could flood the circuitry of any dish pointed in the general direction of the satellite.   It could also block communications if it came between the satellite and the receiver and could reflect back to earth the up links to the satellites.

3.   Protect the system from meteorites and orbital debris – There is not a huge amount of orbital debris at the altitude this would be situated at, but being so enormous in size would present a very large target.   At least one communications satellite, the European Olympus satellite was destroyed by a meteor strike. Although this is a rare occurrence, no other structure has had such a large area to be struck by a meteor or by space junk.   Several satellites have experienced damage to solar cells due to meteor strikes, as solar cells are the most sensitive part of the spacecraft to even tiny meteor impacts.     This thing is going to be all solar panel, so there’s hardly much point in trying to shield them.

4.  Beaming the power down to earth  -In theory it is possible to transmit large amounts of energy via microwave.   The process is pretty lossy due to the conversion of electricity to microwaves and back to electricity along with the losses which occur due to atmospheric absorption,  scattering, reflections off of anything that comes between the transmitter and receiver (satellites, aircraft, meteorites, water droplets etc).   However, in theory it can be done, while still having much of the power at the receiver.   The bigger problem is creating a narrow enough beam to transmit the power to the receiver station without it being defused over a large area and mostly lost.

Satellites do have spot-beam microwave transmitters, but getting a beam with a spread of nearly zero and a very narrowly defined border is really pushing the tolerances of transmission antennas.   Remember that at a distance of  36, 000 kilometers, even the slightest spread in the beam will make for a very large area on the ground covered and thus power density being extremely low.   Extreme high directionality requires extremely high gain antennas which are generally very large in size.

Due to their low efficiency and power, masers are out of the question, but the microwave transmitter would need to achieve uniformity and concentrations approaching that of a laser beam.

5.  Keeping the beam rock steady and correctly aimed - Not just steady, but extremely steady.  So steady that even the slightest vibrations, which could be caused by a switch closing or a minuscule imbalance in one of the gyroscopes could cause the beam to wobble by miles from the receiver station.   Mirrors or light sources have long been used as a method of making tiny movements visible by moving a beam a noticeable distance.    This same principal will apply to such a narrow-beamed satellite.   The massive antenna must be kept pointed at the receiver station without even the slightest movement.   Moving a millionth of a degree could move the beam entirely out of the receiver area.

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This entry was posted on Friday, May 1st, 2009 at 2:00 am and is filed under Bad Science, Enviornment, Obfuscation, Politics, Space, inverse square. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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