A Space Solar Cell

[softdragonz]

I had this strange doubt one sunny afternoon

 

The intensity of sun's heat decreases as we move away from it.

So, sun's heat must be much more intense near Venus than near Earth.

 

If we could design a solar cell and send it to space close to sun ( not that close to burn the cell ) , couldnt we be extracting more energy?

 

The electromagnetic energy then collected can be transported with minimal loss using a wave guide. ;)

[InfiniteNow]

I am not sure, but my guess would be that the energy required to put the collector out into orbit, as well as the transportation of that energy back to Earth and any losses involved would outweigh the slight benefit of collecting more energy by being closer. Costs vs. benefits, ya know?

[cwes99_03]

No. The act of putting it into orbit around the sun would be cost prohibitive. The act of keeping it in repair is even higher.

 

The only reason it collects more when near the sun is that it catches more. So instead increase the size and keep it near earth.

[Kayra]

Just inside the orbit of mercury would give you Approx 10 times the sunlight.

 

The system though would have to be pretty damned robust.

 

Robust usually means expensive.

 

Cost benefit would have to be done to determine if it would be feasible.

 

Cost of getting to orbit is 1/2 the cost of getting to anywhere in our solar system. The rest is just a matter of time.

 

If earth orbit is 1/2 the cost, and and you would require something 10 times more massive to collect the same energy, It is possible that it would be drastically cheaper to send something to a near sun orbit.

 

I would, however, recommend something that is passive rather then active.

[ronthepon]

Well, If such a thing is sent into orbit, between the earth and the sun, we could try to calculate or hasten a guess towards how much closer we could move the collector ner the sun to make it cost optimised...

 

PS: I just can't help but remark on how money and lack of resources, not to mention bodily limits are bogging us science guys down...

[Kayra]

Well, the cost of moving the device closer to the sun once it is in space is negligible. (comparatively speaking)

So the constraint is not how close do we have to move it in order to be cost optimized, but how close can we move it without significantly shortening it's lifespan or incurring required maintenance.

 

The closer we can move it, the more power we can harvest for almost the same investment.

[cwes99_03]

I beg to differ and would require some actual data be put my way before believing these quotes (sorry, Kayra).

 

BTW if half the cost is getting it into orbit, where does the other half go of just keeping it in orbit where it was initially put? The simple math doesn't add up. What you need to show is cost/benefit as Ron recommended.

 

Cost of getting into orbit around earth $xxxxxx.xx

Added cost of size of payload to obtain equal amount of sun's energy $xxxx.xx

Added cost of placing smaller payload in solar orbit at 1/3AU $xxxxxx.xx

Added cost of maintaining smaller payload in solar orbit $xxxxx.xx

Added cost of manpower for placing and maintaining solar orbiter $xxxxxxx.xx

 

Added benefit of placing smaller orbiter near sun vs placing larger orbiter near earth $0.

 

I see a lot of added cost for the distant orbiter and only some added cost of a larger orbiter in the vicinity of the earth.

 

But I digress. The idea is on the right track physically. If we could avoid the extra cost of placing something nearer the sun, yes it would collect more energy per square foot of orbiter. How would you then get it back to earth at that distance?

 

BTW isn't there already a thread on this elsewhere? Why was another thread started?

[Kayra]

cwes99_03, the value was from an offhand remark by Pyrotex

 

Basically, getting something out of our gravity well is one of the most drastic costs involved in almost any space endeavor.

 

Getting to a destination in space follows the rule

"Saving time costs money, how fast do you want to get there"

 

If you do not mind taking 5 to 20 years to get there, a small rocket booster could eventually get you anywhere in the solar system. More exotic solutions would be required if you needed to get to a mercury orbit in 6 months.

 

I am not qualified to give even hints of costing involved, and though many in this forum are. (Buffy for one, Pyrotex for another)

 

One of the aspects of the cost/benefit analysis though would definitely have to take into account the cost of the financial burden. The longer you have this thing traveling in space and not producing an income, the greater the cost of the money used to build it.

 

Sorry I could not be more helpful.

[cwes99_03]

No problem, you examined what I hoped you would, and gave me some valuable info. Maybe Pyro can shed some light on this.

In the meantime you said something that I must also question, but please don't be offended. I have a knack for picking things apart, but am not always right in my assumptions either.

 

You said that saving time costs money. If I wanted to get the rocket into near sun orbit in a short amount of time, yes that may be more costly in fuel considerations. However having it take a couple of years will also be more costly because of the cost of not having something up and running within a year of take off to make money (which you also suggested.) This is a cost benefit analysis.

 

I just was pointing out that to put something into earth orbit would definitely cost less than putting something in near sun orbit in starting costs (the percentage more we'd have to ask Pyro for.) However the other costs in manpower to keep watch over something so far away and to constantly recalculate trajectories and whatnot only affect a near sun mission. You suggested recouping the cost in that you will not have to send up as big of a payload (good job there) but I don't believe that a smaller payload will significantly cut the cost enough compared to the other costs I suggested (mostly because I don't think the reflectors weight will be that much less for a near sun vs a near earth.)

[Kayra]

No problem, you examined what I hoped you would, and gave me some valuable info. Maybe Pyro can shed some light on this.

In the meantime you said something that I must also question, but please don't be offended. I have a knack for picking things apart, but am not always right in my assumptions either.

 

Not easy to offend me really :).

 

 

I just was pointing out that to put something into earth orbit would definitely cost less than putting something in near sun orbit in starting costs (the percentage more we'd have to ask Pyro for.) However the other costs in manpower to keep watch over something so far away and to constantly recalculate trajectories and whatnot only affect a near sun mission. You suggested recouping the cost in that you will not have to send up as big of a payload (good job there) but I don't believe that a smaller payload will significantly cut the cost enough compared to the other costs I suggested (mostly because I don't think the reflectors weight will be that much less for a near sun vs a near earth.)

 

Hmm.. interesting questions.

 

Assuming we do not have to have manpower on the unit itself, then the ground based manpower would have to be committed either way, regardless of distance. Extra manpower would likely be required for the Trip though.

 

Constant recalculation of trajectories is not inherently costly. Constantly changing course would be costly because all fuel requirements would have to be sent on the original mission. This would increase the amount of mass that would have to be moved off earth and into the new orbit. Once in orbit, the entire structure will not have to be moved to change the direction of the beamed energy. The energy is focused in front of the collector on a smaller mirror. This mirror will be used to determine beamed energy direction. This also allows the main collector to remain pointed directly at the sun at all times.

 

 

While the reflectors will not have weight, they will have mass proportional to their size. Even if we used reflectors of the same size, we could gather 10 times the energy near the sun. Even with losses, it should be easily over 7 times. The cost benefit would definitely like that fact :)

[Pyrotex]

...Hmm.. interesting questions....:)

Several SF authors with scientific credentials have addressed this problem, you will be happy to know. :) Including Robert Forward and Isaac Asimov.

 

Converting solar energy to electricity is like pumping water through a 1 inch pipe. You can plug it into a small tank, a large tank, or the ocean, but that pipe is only gonna pass just so much water. Increasing the pressure may give you some gains, but those gains decline rapidly. If you want more water, you have to have more pipes.

 

So it is with solar energy. At the orbit of Mercury, the solar "pressure" is greater, but conversion systems do not operate entirely on how much light there is. They have their limits. Taking a solar cell to Mercury's orbit may give you twice the power, and then burn out, but it won't give you 10 times as much.

 

Unless you think on a gargantuan scale, like Asimov and Forward did. The latter's idea was to place a "ring" around Mercury, 20,000 miles across and held in place not by orbital velocity but by radiation pressure from the Sun. We're talking not megawatts, not gigawatts, but thousands of terawatts!!!

 

Converting electricity to micowaves can be done in klystron tubes with 95%+ efficiency, beamed with 99%+ efficiency, captured in a large microwave antenna (in Earth orbit or elsewhere) with 95%+ efficiency, and converted to electricity with 95%+ efficiency. This has been experimentally confirmed. Total system efficiency can be 90% or better. However, the receiving antenna at Earth would have to several hundreds of miles wide.

 

You can get by with a smaller receiving antenna (tens of miles) by using infrared lasers instead of microwaves. This drops your efficiency by another 10% or so.

 

The cost of building in space is MOSTLYa function of the Delta-V to get there. The amount of velocity you need to build. It can be in any direction, doesn't matter. Getting to Mercury adds the DVs to get to low Earth orbit (7 km/sec), injection into Venus trajectory (about 7 km/sec), traj.correction at Venus (1 km/sec or less, depending) and (5-10 km/sec) to get into Mercury orbit. Total, about 25 km/sec.

 

Getting into Solar orbit takes 7 km/s + getting into elliptical transfer orbit to sun closer than Mercury (about 25 km/sec) + circularizing Solar orbit (about 25 km/sec) for a total of 57 km/sec or more.

 

We have: Low Earth orbit = 7

High Earth orbit, at geosync or L1 = 12-14

Mercury orbit = 27

Sun orbit inside Mercury = 57 km/s

No contest, build your solar collector in high Earth orbit.

All values are approximate but relatively reasonable. Discretion is advised.

[Kayra]

There you have it.

The orbit I wanted for the system was even worse, it was a solar polar orbit.

 

Interesting.

A Mercury orbit would give us about 8 times more sunlight then an earth orbit, at 4 times the cost of getting there.

I guess the cost benefit analysis would determine if the energy harnessed over the lifetime of the units operation would be worth it or not.

 

Pyro, what if we did no conversion at all? Just beamed solar energy back in it's raw form? simplified equipment, drastically reduced maintenance, etc. 30% loss getting it through the atmosphere though :). The energy could be split into many "Pipes" for easier conversion and distribution.

 

The business end of it could simply be the delivery of so much solar energy, and let the ground/orbital businesses purchase it. They can do with it as they like. (capitalism at it's best)

 

Hmm, I suspect that we would end up with a hybrid system. Collector near mercury concentrating and beaming raw sunlight to an earth orbit conversion and transmission system.

[Pyrotex]

...Pyro, what if we did no conversion at all? Just beamed solar energy back in it's raw form? simplified equipment, drastically reduced maintenance, etc. ...

ROTFLMAO :) :)

 

uhhhhhhh... sorry. You really got me on that one.

 

{ahem} Kayra, we ALREADY get beamed solar energy in its raw form. It is called "sunlight" and you're absolutely correct -- it reduces the need for equipment down to nothing but a clear sky and a good set of shades.

 

LOL... LOL... :) Oh, that was good. Thanks a million!!!

[Kayra]

ROTFLMAO :) :)

 

uhhhhhhh... sorry. You really got me on that one.

 

{ahem} Kayra, we ALREADY get beamed solar energy in its raw form. It is called "sunlight" and you're absolutely correct -- it reduces the need for equipment down to nothing but a clear sky and a good set of shades.

 

LOL... LOL... :) Oh, that was good. Thanks a million!!!

 

SMACK!!!!

 

Smeghead :)

I was speaking of a concentrated form :)

You have been spending to much time that that spaceship design forum.

[Pyrotex]

...I was speaking of a concentrated form :)...

ooooohhhhh! "concentrated" -- yes.

There are not many ways to concentrate sunlight. Mirrors and lenses. Even a giant Fresnel lens would be massive. One ton per acre? You will need a million acres?

 

A single lens will only focus the light somewhere, say just outside the Moon's orbit. Sunlight is so many wavelengths that it will not achieve perfect focus, so the beam will have a minimum size. The end product, "concentrated sunlight" is not going to be easily converted into power because of the energy flux -- number of photons per cubic meter. Anything you put into that stream will melt and vaporize. Perhaps liquid cooled mirrors. Then you have to use a Thermal Cycle engine (turbines etc) to get power. Very inefficient.

 

That's why beam microwaves and infrared is preferred. There are "loopholes" at those frequencies making conversion so easy and simple that very little energy is wasted as heat -- which could burn up the system. The best solar cells convert only 20% at best. 80% of your solar inferno is just going to flash-vaporize the solar cells.

[InfiniteNow]

ooooohhhhh! "concentrated" -- yes.

There are not many ways to concentrate sunlight.

 

Well, duh... you just need to heat up this "sunlight" so it evaporates! Then, you could put it in a little can and store in the freezer and mix it with water when you are ready to use. Geesh... always making everything so complicated.

[Kayra]

Quoting myself from

http://hypography.com/forums/computers-technology/4423-solar-energy-6.html

 

 

Hmm, I did not realize diffraction was such a major issue. :)

 

I was only considering capturing raw sunlight in a 100KM diameter reflective umbrella. Aimed at earth and capture it using a 1 KM diameter reflective umbrella.

 

Energy leaving the sun should be something like 300 GWH. About ....... You could suffer considerable losses and still have a fair amount of power.

 

Beaming raw sunlight through the atmosphere as straight sunlight would likely cost you an additional 20% of the remaining power. Limitations in existing materials would demand that this energy be split up and sent to multiple locations in order to harness it.

 

Conversion in space to Microwave is another option that has been studied rather rigorously. (http://en.wikipedia.org/wiki/Solar_power_satellite) One of the issues I have with this sort of technology is that it will rely on Solar cells. A technology that is far from ready and whos lifespan is still indeterminate. you can not spend vast amounts of money on a power generation system that will last 8, 10, 12 years, decreasing in efficiency each year.

 

Any suggestions on how to send the raw sunlight that far? What it's losses would be? If the total that reaches the earth orbital reciever is less then 10% then it would be the same as building the 100 KM diameter umbrella reflector right here in earth orbit.

 

And

Yep

And the 10,000 motorized mirrors that all have to be moved to face the sun. Surfaces that get scoured by sand constantly. Maintenance on a system like that has already proven to be substantial.

 

Imagine if you had that capability, but it came straight down on the system. 24/7/360 (it would be obscured a few days out of the year during equinox. Few hours each day). No massive mirror farm that had to be constantly aligned. practically no moving parts at all.

 

In fact, there would probably be enough energy (if it could be focused tight enough) to create a fast ignition inertial fusion system.

 

The design for the collectors I had in mind was an inversed umbrella of stiff cloth. Spun at high speed, it would use centripedal force to hold it's shape, and solar pressure to keep the parabolic form.

 

The edge would have to be studded with many Ion thrusters powered by the sun. These would be used to spin up, sping down, and correct the orbit of the system.

 

Would this work?

 

The design for the collectors I had in mind was an inversed umbrella of stiff cloth. Spun at high speed, it would use centripedal force to hold it's shape, and solar pressure to keep the parabolic form.

 

The edge would have to be studded with many Ion thrusters powered by the sun. These would be used to spin up, sping down, and correct the orbit of the system.

 

Would this work?

 

 

http://www.space.com/businesstechnology/technology/carbonsail_000302.html

 

Sorry for not distilling the info in the other posts. I have to go fix a punch machine computer :) (integrated with windows 3.11 no less :) )