Beamed Space Solar Power Plant To Open In 2016?

Eric_S writes "Anybody who managed to get a decent city going in Sim City 2000 remembers the microwave power plant; now it seems like a real-world equivalent might be coming up on the horizon. The Pacific Gas and Electricity Company, per this 'interview' with the CEO of Solaren on their affiliated site, announced PG&E's plans to buy 200MW of base-load power from a Solaren beamed space solar power plant by 2016." I wish the skeptic in me would be quiet.

Comments

Human Size Ants

[NReitzel]

Because you haven't run the numbers on the beam power density. The Microwave beam is wide, because it's trivial and cheap to make a huge ground antenna, and because agriculture can be carried out under the antenna. THe beam power density can be held down to just a few times noon sunlight power, and still deliver plenty of energy.

That way, both airplane and albatross are safe to transit the beam area.

Re:Human Size Ants

[QuoteMstr]

First of all, the power being there doesn't mean that you absorb it. We're talking about microwaves (and not the cooking kind). It's not visible light or ultraviolet. You won't notice a thing. You won't get a sunburn.

Second, rectennas are stupidly efficient: 87%. We can barely get to 50% with solar. Furthermore, it's a lot cheaper to build a kilometer of rectenna than a kilometer of solar panels, and you can actually use the land underneath for something useful. And also unlike conventional solar, this thing would work all day and all night, every day of the year.

Re:Human Size Ants

[Bakkster]

Somethings seems wrong with this reasoning.

First, a "few times" noon sunlight power, I think would be pretty brutal. To take you literally, it would be like standing in the sun at noon where the sun is say three times brighter than it is. I'm not a physicist, so feel free to tell me why a three times more power sun at noon wouldn't be a problem for me.

Sunlight has two components that make it uncomfortable or dangerous. First is the infrared, which is the heat energy. Second is the Ultraviolet, which can damage skin cells. Because the energy is not in infrared or UV radiation, you will experience neither of these effects. If you're worried about microwave radiation, remember that this includes the frequencies that make up the WiFi, Bluetooth, and AM/FM radio waves that pass through your body all the time.

Secondly, Doesn't a "few times" noon sunlight power mean that your getting only a "few times" what you'd be getting from the sun by itself, which isn't all that much. Doesn't sound like your going to deliver the concentrations of power that cities need.

So, I'm inclined not to put too much stake in what you said.

Converting electrical power to and from microwave radiation is an order of magnitude more efficient than solar. Also remember that the solar panels placed in space have a large surface area than the antenna, receive more solar energy per area (due to not having losses due to the ozone layer, etc), and can beam power 24/7. So imagine if the sun was 4x more powerful, and the solar panels were 80% efficient, rather than 20%. Using these (thumbnail estimate) numbers, that makes microwave 16x more efficient per unit area than solar. It becomes even more efficient when you take into account that the sun is not as bright at other times of the day (such as 8AM, or 11PM).

And yes, I am an Electrical Engineer.

Re:Human Size Ants

[Bakkster]

This orbiting solar plant would have to be in a geosynchronous orbit to beam the energy to the antenna. It could not beam power 24/7.

You are correct, this was a slight overstatement.

However, the ammount of time where the satellite is in darkness is significantly less than when a ground based solar panel is in darkness. As well, when not in darkness, the solar energy density is very close to its average maximum, which is significantly more than even the noon-time maxiumum for a ground-based solar. In other words, a solar panel on earth generates less energy at 7PM than at noon (due to light passing through additional atmosphere, and even less if the panel is not aimed), but a satellite produces nearly the same amount of power whenever it is in sunlight.

The earth will occlude the sun for about 20 degrees of its 360 degree rotation at geostationary orbit. So the system will not be in sun for 1 hour, 20 minutes each day. Not 24 hour power (more like 22.7 hour), but still much better than solar. A pumped storage or other facility would still allow nighttime off-peak energy to be used during this "dark" time, or during peak hours.

Re:Human Size Ants

[Bakkster]

So imagine if the sun was 4x more powerful, and the solar panels were 80% efficient, rather than 20%.

And yes, I am an Electrical Engineer.

The issue is that the best cells in the world are still in the high 30% range... And yes, I do build satellites for a living, and will certainly not invest my money in this company.

Many ground based photovoltaic cells are not operating at this maximum efficiency. Regardless, microwave power efficiency will always be greater than solar. I only intended the efficiency numbers as a rough estimate.

As a satellite designer you should also recognize that it's the solar power density in space, rather than panel efficiency, that make solar so useful in space. The panels receive more energy from the sun, regardless of how efficiently they convert this energy to electricity. In space, it's about 1300W/m^2, at the equator it's about 1000W/m^2 at noon on a sunny day.

If we want another thumbnail calculation, a square meter solar panel in space gets 1300W 22.7hours a day, making an average power of 1230W. For a panel at the equator on a sunny day, assuming it gets full sun 12 hours a day, its power is only 500W on average. Any practical application (not at the equator, cloudy days, additional shade, etc) will reduce this number farther.

Obviously, the power is more efficient per unit area, both of ground and solar panel. If the costs of the satellite are low enough (to be determined), the beamed energy plant will be much more efficient.

Science/tech illiteracy

[StCredZero]

But this hare-brained idea will heat the atmosphere

Fail.

Most power generation schemes are *heat engines.* The typical efficiency is less than 40%. Microwave transmission starts at 50% efficiency, and is likely to get better. For the same amount of electric power, you're going to have less waste heat than with coal, nuclear, or natural gas power plants.

Re:woot!

[socsoc]

This is a dupe of http://science.slashdot.org/story/09/04/14/0317236/PGampE-Makes-Deal-For-Solar-Power-From-Space. They announced this in April.

Hell, the linked interview in summary is in the original story from MSNBC.com. This submission contains nothing new to add...

Re:My religion, or yours?

[Quantumstate]

Based on Wolfram Alpha the Earth gets about 1.3 kW per square meter. with the earth being 6.4*10^6 m radius with find the area facing the sun is pi*r^2 = 1.28*10^14. Multiplied by the power gives 1.67*10^17 W hitting the earth. Now since the power company wants to sell 2*10^8 W of power we can conclude that the extra energy reaching the Earth would be in the region of 0.0000001%.

Re:Bullshit

[hardburn]

It's not just the lack of night, but not having the atmosphere block out a lot of light before it hits your solar cells.

Sim City was fiction. The microwave beams here aren't concentrated enough to be useful as any sort of weapon, either purposely or accidental. The frequencies choosen need to be transparent to water (since it'll have to cut through a lot of it to get to the surface), and the "beam" is spread over a wide area to make simple rectenna receivers possible.

Re:Miss

[AlecC]

A bit more subtle: The transmitter is using a phased array, and the locking phase is a reflection of the signal from the ground. This is a completely fail-safe system: It doesn't have a machine that says "reference signal gone": if the reference signal disappears, the beam turns into a glow by the laws of physics, not by any allegedly safe automation. And the beam can *only* be aimed at something with an appropriate reflector, so even a mad scientist cannot redirect the beam to a city.

Re:My religion, or yours?

[john.r.strohm]

Actually, no, it won't heat the atmosphere significantly.

"Atmospheric heating from microwave loss" is another word for "atmospheric attenuation". The trick is you choose microwave frequencies that are not significantly absorbed by nitrogen, oxygen, and water (dihydrogen monoxide), and that knocks out your atmospheric attenuation problem right there.

This is Physics 102, people.

Your real losses are going to be in beamforming and beam wander. You fix beam wander by using a BIG receiving antenna (which also lets you use low power density in the beam: win-win).

Re:For specific applications, YES! (Remote Militar

[QuoteMstr]

Yes, invulnerable. There's a huge difference between hitting a satellite in low earth orbit and geosynchronous orbit, which is a few times higher up and which requires a lot more delta-v to reach.

Re:For specific applications, YES! (Remote Militar

[blind biker]

You are right, the Solaren CEO does say it would be in geosynchronous orbit.

My bad. I was wrong, you were right.

Re:Miss

[QuoteMstr]

Are there any purely electric space propulsion systems?

If you're talking about attitude of a spacecraft in orbit, then as a matter of fact, there are purely electric systems: magnetic torquers. Lots of satellites use them, including Hubble.

Re:Miss

[Verteiron]

Changing electrical energy into thrust? You got it. Space agencies have been using it for years. And, as an added bonus, it makes a neat blue glow when you do it!

Re:Miss

[AlecC]

No, they cause all the transmitters to drift out of phase, so that instead of a coherent beam, you have a wide-angle glow. Transmission is done by a phased-array antenna, as used on most modern radar systems. If these all transmit in a carefully calculated phase relationship, interference directs all the energy into a tight beam. If the phase between the transmitters is random, which it will become if not positively locked to a reference beam, all interference disappears and the energy is dissipated in all directions. All you have to do is ensure that the reference phase is derived not from on board, but from the ground: when the reference beam disappears the transmitters lose phase and the beam broadens into nothing. The transmitters will probably lose lock easily anyway, but you can deliberately unstable if you want. To start the system requires someone on the ground to fire a fairly powerful beam from the target area up to the satellite; to maintain it requires a well-aligned reflector.

Davis-Besse reactor

[stabiesoft]

Maybe we can build them safely, but maintenance is another issue. This is the same plant that almost went postal in 1985. See http://www.cleveland.com/powerplants/plaindealer/index.ssf?/powerplants/more/1095759100318143.html for just one reference.

Re:In Space

[petermgreen]

Your math is wrong, you are forgetting that you are dealing with sqare units (the common notation for square units is rather confusing which doesn't help). There are 10000 square centimeters in a square meter and 1000000 square meters in a square kilometer. You also seem to be in a bit of a mess with the units of various figures.

200,000 W = 200,000,000 mW

200,000,000 mW / 50 (mW/cm^2 )= 4,000,000 cm^2
4,000,000 cm^2 = 400 m^2
sqrt(400 m^2/3.14) ~= 128m

so a 128m diameter receiver, not small but not massive either.