Space-based power

[pfrit]

At 85% efficiency?

Currently I believe the efficiency is in the 1E-6 range. Roughly .0001% That is a lot of zeros to make up with better engineering.

Oh, come on. You feel bad about that one. That is not an apple to apple comparison. That is not an inefficient transmiter, atmospheric absorbtion or an inefficient rectenna(actually satelites don't use a rectenna). Thats from a moderately focused beam and a small target. Not the same thing at all and you know that. Consider your hand slapped. I was trying to say that the hardware is mature. Not that TV stations use acres wide receiving stations to make sure that they get every bit of redundant signal or that the landside transmiter is required to have a 1/10th second arc accuracy. Heck, the satelites broadcast to thousands of miles^2 at once! They are trying to make it a diffuse signal. And the transmiters are meant to be error tolerant.

[pfrit]

Folks,
Go to the source. SSI has been into this for DECADES. Their data should help this discussion.

I have to agree with the sceptics on this. Not mature technology. All I am saying is that it is a path that could lead to useful tech and the core tech is fairly mature. Not the whole package. The real barrier is not the tech, but the expense and political issues. OTOH, the original post talked about 100-125 tons to lift for project success and that could be affordable. How much does the ISS weigh? What is its finacial return? (More than 300 tons and zero) OK, technically the ISS wieghs nothing, but that is just quibbling

[gblaze42]

One other issue with solar cells is the limited lifetime of the cell, they tend to degrade over time, in the radiation and heat of space, I would think it would degrade quickly. So all these SPS units would need to be replaced at some point.

Actually, they degrade slower. Solar cell degradation comes mostly from fogging of the covering material. That comes from oxygen. Older cell coverings also had problems with UV, but for space based systems, that has never been an issue. My understanding of current systems is that life time in space is a function of dust collection on the cells. You can't hose them off in space and they tend to have an unavoidable magnetic charge that attracts dust.

I beg to differ, solar cells tend to degrade do to sunlight, in a matter of days even, it's been known for 20 some years. Also the newer thin-film solar cells have higher tendency to degrade in efficiencies.

See here http://www.mrc.iastate.edu/research/Biswas.pdf

[pfrit]

I beg to differ, solar cells do tend to degrade in sunlight, in a matter of days even, it's been known for 20 some years. Also the newer thin-film solar cells have higher tendency to degrade in efficiencies.

See here http://www.mrc.iastate.edu/research/Biswas.pdf

I could be wrong. I had learned that the damage to solar cells arose from UV light. That was overcome by putting a layer over the cell that blocked the UV. The UV then slowly fogged the blocking material. The link you provided did not state what "light" caused the damage, just that it was sunlight, but the implication was that it was from the light the cell was designed to convert to electricity. OTOH, 15-20% damage in the first few days of use seems to run counter to what I had learned. OTOOH, I am not an expert and I do not own any PV cells (other than a toy that rocks its head). OTOOOh, I am out of hands.

[gblaze42]

I beg to differ, solar cells do tend to degrade in sunlight, in a matter of days even, it's been known for 20 some years. Also the newer thin-film solar cells have higher tendency to degrade in efficiencies.

See here http://www.mrc.iastate.edu/research/Biswas.pdf

I could be wrong. I had learned that the damage to solar cells arose from UV light. That was overcome by putting a layer over the cell that blocked the UV. The UV then slowly fogged the blocking material. The link you provided did not state what "light" caused the damage, just that it was sunlight, but the implication was that it was from the light the cell was designed to convert to electricity. OTOH, 15-20% damage in the first few days of use seems to run counter to what I had learned. OTOOH, I am not an expert and I do not own any PV cells (other than a toy that rocks its head). OTOOOh, I am out of hands.

The graph shows a decline by 14% in the first seven years of the satellite's operation. Individual degradation events caused by specific solar proton events can also be seen. The largest drop in power was caused by the July 14, 2000 and the November 4 and 23, 2001 Solar Proton Events which reduced performance by nearly 2% in each instance. Without the solar proton events, the degradation would have been approximately 10% due to the generally constant cosmic-ray background rates found at the satellite's location at the 'L1' point. These two events cost the satellite two years of ordinary lifespan. This is the typical rate that satellite designers expect, and upon which estimates of satellite lifetimes are based. It is expected that solar panels will degrade by about 20-25% during the 10 to 15-year lifetimes of modern GEO satellites. Solar panel are oversized at launch by 25% to allow for this loss of power at the end of the mission lifetime. The problem is that solar flares and proton storms can upset these calculations and cause a satellite to end its service several years earlier, at a large cost to profit margins.

This is from 'Effects of Space Weather on Technology Infrastructure', 2003, NATO Science Series vol. 176 p. 116 and emphasizes what I was trying to say.


From what I can find, and it isn't much, the degradation is due to UV and infrared wavelengths and possibly . Begs the question, if we can use Quantum dots to shift the UV and Infrared hitting the cells to a more conducive wavelength for the solar cell, the efficiencies should actually go up and remain there longer. Might already be solvable.[/img]

[pfrit]

I could live with 2% loss per year. If we assume that 50% of the lift is structure, then that means a 1.25 ton lift a year to keep steady production, based on what the original post claimed. That is a lot, but 10 million dollars a year for maintenance is not that bad... (assuming $5000 per lb lift cost and assuming that the cells are comparitely free). What is the annual maintenance cost of a coal plant? Really, I have no clue what it is.

[MSimon]

Thats from a moderately focused beam and a small target. Not the same thing at all and you know that.

Thank you for making my point for me.

[pfrit]

Thank you for making my point for me.

This is where I say "OK, what is your point?" and you say "If you do not understand, I can't explain" and if you worked for me I would say "Can you explain it to the Unemployment Office?"

[MSimon]

Thank you for making my point for me.

This is where I say "OK, what is your point?" and you say "If you do not understand, I can't explain" and if you worked for me I would say "Can you explain it to the Unemployment Office?"

My point is that there is no microwave power delivery system that is off the shelf.

The physics says it should be possible. There is a long ways between that and reality. Just ask the ITER folks.

Engineering wise there is a lot of difference between delivering a few hundred microwatts and delivering a few hundred megawatts. About 12 orders of magnitude. That is not trivial. Engineering wise.

[MSimon]

Just one for instance.

How do you scale up a 1N23A to be capable of rectifying a kilowatt of power? There are no 1KW microwave diodes that I'm aware of and I follow the microwave industry pretty closely. It is always possible I have missed something. If so educate me.

[pfrit]

Thank you for making my point for me.

This is where I say "OK, what is your point?" and you say "If you do not understand, I can't explain" and if you worked for me I would say "Can you explain it to the Unemployment Office?"

My point is that there is no microwave power delivery system that is off the shelf.

The physics says it should be possible. There is a long ways between that and reality. Just ask the ITER folks.

Engineering wise there is a lot of difference between delivering a few hundred microwatts and delivering a few hundred megawatts. About 12 orders of magnitude. That is not trivial. Engineering wise.

Agreed. However I think this as a complicated integration job. All the parts exist in one form or another and most are fairly mature. From an engineering standpoint, I would think the biggest challenge would be robustness. We could go down a list and talk about existing systems that solve specific issues and in the end have a headache from the challenge of integrating it all in an environment that prevents repair. I don't want to trivialize the problems, but they are nothing compared to the political problem of putting a Death Star hovering over half of the world. Think about it. It violates the ABM treaty and weaponizes space. Sure, we can say we are going it alone because it is the right thing to do. Does that sound like it will work?

[MSimon]

All the parts exist in one form or another and most are fairly mature.

Isn't that the ITER argument? And aren't the immature parts the ones giving ITER fits? A projected 40 or 50 more years of fits?

[pfrit]

All the parts exist in one form or another and most are fairly mature.

Isn't that the ITER argument? And aren't the immature parts the ones giving ITER fits? A projected 40 or 50 more years of fits?

LOL... Seriously, you must agree that if this had a green light we could send up a functional prototype in under 5 years. And by the third one it would probably work for more than a month. Just think about the shorts that this thing would have! How much cable can you send up and how much insulation can you use. And you want to handle anywhere from 100MW and 1GW? Even if you use SC (I think you would have to) there is going to be sparks. If I designed it (and I usually design apps and DBs) I would design it with a huge amount of redundent transmiters just to keep the joules down at any one place.

[pfrit]

Just one for instance.

How do you scale up a 1N23A to be capable of rectifying a kilowatt of power? There are no 1KW microwave diodes that I'm aware of and I follow the microwave industry pretty closely. It is always possible I have missed something. If so educate me.

Here is 10 million. Hire a team and build it. What would you quote as time frame?

[MSimon]

Just one for instance.

How do you scale up a 1N23A to be capable of rectifying a kilowatt of power? There are no 1KW microwave diodes that I'm aware of and I follow the microwave industry pretty closely. It is always possible I have missed something. If so educate me.

Here is 10 million. Hire a team and build it. What would you quote as time frame?

There is the little problem of junction capacitance my friend. Power scales as junction area (and not well either - due to heat dissipation being easier in smaller objects) and capacitance also scales as area.

Currently power diodes are limited to the MHz range. Getting them to the GHz range? Well it is not just engineering. There are a few physics problems as well.

Engineering is not magic. Although it might seem so to the uninitiated.

For $10 million the estimated time frame is roughly infinite. If you have $100 million to $1 billion I might be able to shorten the time frame considerably. No promises. It requires a breakthrough which is in the real world somewhat unpredictable since a path is not evident.