Ultra thin PV film

louis · 2019-09-22 06:12:18

Well it would be a very small town...200 people maybe.

On Earth, how you lay out an array is a matter of economics. All else being equal, you are looking for the cheapest method and of course there are time constraints. So that's how you end up with your balance of labour and capital equipment. But of course, on Earth, PV sysems have to be very robust because of the powerful weather phenomena. The same issues do not apply on Mars, where the wind force for any given speed is, if I recall correctly, about 5% of that on Earth and where there are no thunderstorms, hailstones, lightning, or hurricanes and even the tornadoes are harmless affairs.

In terms of how we lay out the arrays I am feeling it will probably be a mix between ATK-style PV "fans" which could be deployed very quickly and provide the basic power for the base and rovers and other PV which would essentially power the propellant production plant.
The other PV might be ultra thin PV film that is rolled out. Or it might be concertinaed panelling. Or it might be thin PV film that is attached to wires stretched between poles. I can see a number of approaches working.

Don't forget we've also got PV panels attached to the six Starships that have landed in the vicinity. They might also be able to make a very useful contribution to overall power supply.

As for the rather supercilious comment at the end, yes am I aware energy is mission-critical. But can I point out Musk and his team are committed to a solar energy approach as far as I can see. I've never heard Musk mention nuclear power for the Space X mission. It's not as though he would use it if he thought it was a better option - this is the guy who has "Nuke Mars" on his T Shirt, so he's not afraid of judicious use of nuclear energy where appropriate. You might take along a few RTGs for emergency back up power if necessary but that's about it I would say. Solar energy is tried and tested on Mars and will provide a failsafe energy supply.

kbd512 wrote:

Louis,
If you have a plan that requires a constant average of 400kW, then you're talking about a solar system of the type that would supply a small town with electricity, but that's just to produce enough propellant to get the rocket back. For use on Mars, we're now talking about something with a nominal capacity rating well into the low MegaWatt range. In other words, the type of array that's built over the course of a year with unlimited labor and fossil fuel supplies of the type that don't need to be kept cryogenically cold, just to power the construction equipment that makes that possible.
Unlike robotic rovers, humans don't have a "temporary shutdown" or "hibernation" mode. They have a "permanent shut down" mode called "death". That's what this plan is really advocating for because it categorically refuses to acknowledge the limits of current solar panel and construction technology, which are well understood in engineering, substituting a personal fantasy you find pleasing for engineering reality.

kbd512 · 2019-09-22 14:29:46

Louis,

Irrespective of what Elon Musk thinks, NASA will test KiloPower reactors in space because the agency is not operating under any delusions about how fast MegaWatt-class or multi-hundred KiloWatt-class solar arrays can be set up. RTG's produce a few hundred Watts of power at most. KiloPower, as the name suggests, can produce between 1kWe and 10kWe of output. The output of RTG's scales linearly with increasing mass. The output of KiloPower does not.

SpaceNut · 2019-09-22 14:53:35

A changing of solar array types and mounting to automated tech to allow them to work is not a plan as you need to pick one. We did talk about thin film flexible laying on the ground and how it could be damaged, the glass thin film solar panels while less possible to damage requires frame transport to align them with dust cleaning periodically, the ATK are the highest of efficiency but these come with the mounting problem as well as how to inter connect them without a human to do that work....
Me I think an ATK fan lander with it batteries would make for a possible means since these would be moveable as they would not be that heavy on mars and to inter connect them is to run cables from each to a centralized power hub for distribution....men required for finishing connections. One could add a motorized wheel set to do the moving via radio command...

kbd512 · 2019-09-22 16:27:26

SpaceNut,

The primary problems with solar arrays in deserts here on Earth is degradation of output from accumulation of dust and abrasion of the hard glass coating protecting the photovoltaic cells under them. I fail to see how this won't be a problem on Mars since it hasn't been solved here on Earth where there is every incentive imaginable to solve the problem.

If the array is small enough and it can be periodically cleaned, then it should work. If the array spans multiple football fields, it should be pretty obvious that some kind of machine, which also requires maintenance and power to function, must perform that work. As of right now, we're not using such machines here on Earth. In the Middle East, human laborers remove the dust by hand using water and soft rags, so as not to damage the arrays. The arrays we're sending to Mars are far more delicate than anything we use here on Earth.

SpaceNut · 2019-09-22 16:41:58

I agree with the desert sand abrasivness being simular to mars but washing with water will not really work on mars for a cleaning solvent.

Wondering if we can do a containing carpet like vacuum device for cleaning the arrays where under the hood sends out the cleaner while a sweeper vacuum cleans up the residue from the process.

Spraying the array glass with an anti-static coating would aid the dust from building up between several washings to limit energy drop over time from dust build up.

kbd512 · 2019-09-22 18:02:25

SpaceNut,

That's actually an interesting idea. Something that generates an electrostatic charge potential between the surface of the array and some sort of fabric that traps the dust and then dumps the dust might work, too. That would "pull" the dust off the array without damaging the surface. That's preferable to flinging the dust back into the atmosphere through electrostatic repulsion because it might simply land on other panels in the array, given the large size of the array.

SpaceNut · 2019-09-22 18:35:37

https://en.wikipedia.org/wiki/Triboelectric_effect
https://en.wikipedia.org/wiki/Static_electricity
http://www.swedishelectrostatics.com/le … tatic.html

A liquid solution
https://www.instructables.com/id/Creati … tic-Spray/

For electronics we use an ion generator air flow device that blows over the area which work is within so this would work for mars as well...

https://www.aircontrolindustries.com/us … ir-knifes/

louis · 2019-09-22 18:38:29

I've suggested before that on Mars robot rovers could be programmed to fix angled posts to the ground which have a couple of parallel wires attached between them. The wires are under tension. The rovers then hook the PV thin film on to the wires. That approach could work.

I think a lot of the connecting gear can be designed for easy rover installation.

My vision would include rovers with compressed gas tanks going up and down the rows every couple of sols blowing off any dust accumulation.

If we can design cars that can park themselves, we can design rovers that can lay out a simple solar array.

I like the ATK fans as well. They might be the best solution...

I expect there are a number of potential solutions.

SpaceNut wrote:

A changing of solar array types and mounting to automated tech to allow them to work is not a plan as you need to pick one. We did talk about thin film flexible laying on the ground and how it could be damaged, the glass thin film solar panels while less possible to damage requires frame transport to align them with dust cleaning periodically, the ATK are the highest of efficiency but these come with the mounting problem as well as how to inter connect them without a human to do that work....
Me I think an ATK fan lander with it batteries would make for a possible means since these would be moveable as they would not be that heavy on mars and to inter connect them is to run cables from each to a centralized power hub for distribution....men required for finishing connections. One could add a motorized wheel set to do the moving via radio command...

SpaceNut · 2019-09-22 18:56:18

Thin wire for connecting panels do not conduct the current to the batteries and would be resistive meaning that they would disapate the enrgy before getting to the battery. Wires for the panels need to be larger in order to pass the current to the batteries with less lose. The higher the wattage the larger the wires to reduce lose as heat in the conductor.

louis · 2019-09-23 03:15:05

I wasn't referencing electric cable wire - I was referring to fence wire.

SpaceNut wrote:

Thin wire for connecting panels do not conduct the current to the batteries and would be resistive meaning that they would disapate the enrgy before getting to the battery. Wires for the panels need to be larger in order to pass the current to the batteries with less lose. The higher the wattage the larger the wires to reduce lose as heat in the conductor.

SpaceNut · 2019-09-23 16:40:40

sort of hamock style where the support frame for mounting is a guidewire which will sag and twist in the wind not allowing for alignment to remain constant throughout the day let alone the mars seasons.

louis · 2019-09-23 17:09:08

No - wire under tension as I indicated.

The winds on Mars are of very low force. The maximum is probably equal to 16 mph on Earth or something like that. On earth I see fence wire under tension every day and I don't see sagging or twisting - even in the much more powerful wind on Earth.

SpaceNut wrote:

sort of hamock style where the support frame for mounting is a guidewire which will sag and twist in the wind not allowing for alignment to remain constant throughout the day let alone the mars seasons.

SpaceNut · 2019-09-24 20:56:22

I think you are talking about 17-Gauge Electric Fence Wire for temporary or movable grazing applications. Although it has less weight to support it has a similar breaking strength to heavier gauges. Its a copper center with steel jacket but its not all the large in diameter. Heavy zinc coating for long life and durability 12-1/2 Gauge High Tensile Smooth Wire is used for livestock.

https://www2.gov.bc.ca/assets/gov/farmi … fences.pdf

It requires posts set close together to maintain the ability to hold mass as the guage even though its got a high strength its still will sag with distance as the mass of the panels add up when connected to it. The post will need to also be quite strudy so that the weight will not pull it down as well.

louis · 2019-09-25 15:29:18

Mars gravity will help regarding the infrastructure mass.

SpaceNut wrote:

I think you are talking about 17-Gauge Electric Fence Wire for temporary or movable grazing applications. Although it has less weight to support it has a similar breaking strength to heavier gauges. Its a copper center with steel jacket but its not all the large in diameter. Heavy zinc coating for long life and durability 12-1/2 Gauge High Tensile Smooth Wire is used for livestock.
https://www2.gov.bc.ca/assets/gov/farmi … fences.pdf
It requires posts set close together to maintain the ability to hold mass as the guage even though its got a high strength its still will sag with distance as the mass of the panels add up when connected to it. The post will need to also be quite strudy so that the weight will not pull it down as well.

elderflower · 2019-09-26 05:24:48

Will covering the Martian surface with solar panels, or anything else that can keep thermal radiation from escaping into space, result in a rise in local average surface temperature as it would on earth? Could this result in melting brine creating mud?

louis · 2019-09-26 12:46:07

Terraformation? Sounds good!

The Starships need to land on flat rock, so I guess the surrounding surface will be of similar nature.

Longer term, it may be an issue.

elderflower wrote:

Will covering the Martian surface with solar panels, or anything else that can keep thermal radiation from escaping into space, result in a rise in local average surface temperature as it would on earth? Could this result in melting brine creating mud?

SpaceNut · 2019-09-26 19:00:22

As the insight probe has shown that mars being hard would make the posts needed for mounting the panels an even bigger problem.

Sure the heat from the say time would rise around the panels but not sure that the ground would get all that warm as the ground would be in the shade of the panels.

elderflower · 2019-09-27 04:23:02

Assume 20% conversion of incoming solar radiation to electrical energy by our panels, we still have 80% left. Some will be reflected, some transmitted and some absorbed. The absorbed fraction will heat the panels and they will radiate thermal IR, some to space and some to the ground beneath. Adding this to the transmitted fraction of the incoming radiation still gives a gain of energy to the surface beneath the panels. Normally, during the night heat will be radiated from the surface into Space which is virtually an infinite heat sink, but with panels overhead this will be interrupted. It is now the panels which are radiating into space and the ground is radiating to the panels. Because of this the panels are a bit warmer and so is the ground.
I think we can neglect conduction as the panel is not in contact with the ground, and convection as the atmosphere is very close to a vacuum.

Last edited by elderflower (2019-09-27 04:23:51)

Calliban · 2019-09-27 10:17:08

I am a little sceptical of this whole ultra-lightweight thin-film PV thing. There are hard limits on how thin and lightweight you can build these systems. Here on Earth, we do have thin-film PV solar farms in the MW range. It is the semi-conductor that is thin, not the panels.

Individual PV cells discharge at <1volt and are combined in series to build up a 12-24v open circuit voltage. Some facilities are able to push that higher. But with thin film, output voltage is limited by the extreme thinness of the semiconductor, which must function as insulation between the two phases and will fry and short circuit if you push output voltage too high. So to build up high power levels, you are talking low voltage and high current, which requires thick conductors on the face and backing plates, to avoid excessive resistance losses and thick cables with cells wired in parallel.

On top of this comes the fragility of thin film PV coatings. These are damaged or destroyed by mechanical flexing, abrasion and oxidation and a stiff backing plate (usually glass) is used to keep them flat and a front plate is required to shield out UV and prevent abrasion.

That is not to say that a power system based upon these panels cannot be made to work with a passable power to weight ratio. But estimates I have seen suggest a few 10s watts per kg average power at Mars surface. And that is without any allowance for storage. Using the energy with either no or minimal storage is probably the best idea anyhow; as it allows much superior power-weight on the power supply side, which will generally dominate mission mass. But it does severely limit the productivity of any downstream equipment, as the PV array will only generate large amounts of power about a third of the day at the equator and more or less at higher latitudes, depending upon the time of year. So your propellant plant will either take 3 times longer to produce the same output, or it must be scaled 3 times larger. The same is true if you are using PV powered LEDs for food production. Then there are issues around deploying the PV array; keeping it free of dust accumulation and maintaining survivable levels of power during dust storms.

Nuclear power offers huge logistical advantages, but the development costs are intimidating. On Earth, new nuclear power projects have been rendered unworkable by overbearing regulatory systems and a general lack of established supply lines and scale economies, which collectively push the price of new projects through the roof. These are institutional problems; not engineering and physics problems. But they ruin profitability all the same. No matter how good something has the potential to be, it is always possible to screw it up.

I suspect that Musk took one look at the financial, political and legal minefield that he would have to negotiate to build a space nuclear reactor and decided that it was just easier and more affordable to go with solar based infrastructure, even with all its obvious problems.

Last edited by Calliban (2019-09-27 10:19:10)

louis · 2019-09-27 14:19:39

Some points:

1. For a Space X style mission, you are going to have to manufacture methane and oxygen as propellant-fuel for the return journey. So with relatively lightweight methane generators as part of that mission you can use the propellant also as your fuel for electricity generation and thus your primary means of energy storage (though there will be chemical batteries as well not least some 2.4 Mwhs of Tesla batteries at a minimum, used to activate the fins).

2. I query whether nuclear power really has such huge logistical advantages. At the very least you need to take two reactors for failsafeness, it's far less flexible and the safety issues cannot be simply waved away. Be that as it may, I agree with you that the "financial, political and legal minefield" would discourage anyone from deploying nuclear reactors on Mission One to Mars.

3. PV is much better than steady nuclear power for high energy demand work e.g. smelting, should that be required. Remember the six Starships themselves will be providing additional PV power as well - not sure I've seen an estimate of that yet but in the artist illustrations the PV "fins" look pretty large, so we are probably talking of at least 200 Kws max from those.

4. With methane-oxygen storage of PV power you can maintain a fairly even electrical input into the propellant production facility.

5. The meteorological conditions on Mars, leaving aside cold temperatures, are benign compared with Earth. You certainly don't need robust glass insulation.

Calliban wrote:

I am a little sceptical of this whole ultra-lightweight thin-film PV thing. There are hard limits on how thin and lightweight you can build these systems. Here on Earth, we do have thin-film PV solar farms in the MW range. It is the semi-conductor that is thin, not the panels.
Individual PV cells discharge at <1volt and are combined in series to build up a 12-24v open circuit voltage. Some facilities are able to push that higher. But with thin film, output voltage is limited by the extreme thinness of the semiconductor, which must function as insulation between the two phases and will fry and short circuit if you push output voltage too high. So to build up high power levels, you are talking low voltage and high current, which requires thick conductors on the face and backing plates, to avoid excessive resistance losses and thick cables with cells wired in parallel.
On top of this comes the fragility of thin film PV coatings. These are damaged or destroyed by mechanical flexing, abrasion and oxidation and a stiff backing plate (usually glass) is used to keep them flat and a front plate is required to shield out UV and prevent abrasion.
That is not to say that a power system based upon these panels cannot be made to work with a passable power to weight ratio. But estimates I have seen suggest a few 10s watts per kg average power at Mars surface. And that is without any allowance for storage. Using the energy with either no or minimal storage is probably the best idea anyhow; as it allows much superior power-weight on the power supply side, which will generally dominate mission mass. But it does severely limit the productivity of any downstream equipment, as the PV array will only generate large amounts of power about a third of the day at the equator and more or less at higher latitudes, depending upon the time of year. So your propellant plant will either take 3 times longer to produce the same output, or it must be scaled 3 times larger. The same is true if you are using PV powered LEDs for food production. Then there are issues around deploying the PV array; keeping it free of dust accumulation and maintaining survivable levels of power during dust storms.
Nuclear power offers huge logistical advantages, but the development costs are intimidating. On Earth, new nuclear power projects have been rendered unworkable by overbearing regulatory systems and a general lack of established supply lines and scale economies, which collectively push the price of new projects through the roof. These are institutional problems; not engineering and physics problems. But they ruin profitability all the same. No matter how good something has the potential to be, it is always possible to screw it up.
I suspect that Musk took one look at the financial, political and legal minefield that he would have to negotiate to build a space nuclear reactor and decided that it was just easier and more affordable to go with solar based infrastructure, even with all its obvious problems.

Last edited by louis (2019-09-27 16:37:53)

SpaceNut · 2019-09-27 16:50:23

One issue for batteries is that the useage rate whrs is not the is not the battery capacity whrs. When you operate a battery near the rating of the batteries is internal heat builds up to quickly and will cause the battery to breakdown shorting out. The next is the cell barrier issue that happens for nicad, lithium and even lead acid. This will cause the battery to not fully charge and when a cell is drawn down to far the battery can also require to much power to overcome the low cell barrier as well which can also damage the battery.
There is a good chance that depending on the draw on the batteries that they will be dead and may not be chargeable when we can deploy panels.

A simular problem occurs with the solar panels in that they are damaged by the curent draw as it approached the max output power.

Calliban · 2019-09-27 17:03:31

"2. I query whether nuclear power really has such huge logistical advantages. At the very least you need to take two reactors for failsafeness, it's far less flexible and the safety issues cannot be simply waved away."

Not really. Out of all of the mechanical systems that you take with you, the reactor will be most reliable. What it does need, is more than one power generation loop. It has redundancy built into it, but there only has to be one core. I don't understand why solar would be more flexible.

"The meteorological conditions on Mars, leaving aside cold temperatures, are benign compared with Earth. You certainly don't need robust glass insulation."

Wind loadings are lower. Thermal cycles are far more severe. Dust contamination is likely to be a problem. The UV environment is quite challenging.

"3. PV is much better than steady nuclear power for high energy demand work e.g. smelting, should that be required."

That doesn't make any sense to me. I cannot see any scenario in which an intermittent power source would be superior to a 24/7 power source. With high temperature processes like smelters, you ideally want to maintain constant temperature conditions. Thermal cycling is not good for refractory linings. And if you have the monetary and mass investment in a smelter, how is it in any way superior to run it part time?

"With methane-oxygen storage of PV power you can maintain a fairly even electrical input into the propellant production facility."

You are talking about burning propellant in an engine or fuel cell, to make power for propellant production? Am I reading that right?

SpaceNut · 2019-09-27 17:14:33

The 10 kw systems that nasa is developing is being design to not melt down and needs no coolant as its self contained with I think salts for the means to radiate heat.

Its the battery capacity that allows for the higher currents as the panels are low current devices. You would use extra batteries to lower the current draw on each to keep them from over heating when under the higher current useages.

That would be a backup system for using surplus methane and oxygen for power and I think its a last resort to out last a dust storm should the sun be totally blocked out for a long period of time. At that time we would be in emergency power useage protocal so as to conserve energy.

Calliban · 2019-09-27 17:36:30

SpaceNut wrote:

The 10 kw systems that nasa is developing is being design to not melt down and needs no coolant as its self contained with I think salts for the means to radiate heat.
Its the battery capacity that allows for the higher currents as the panels are low current devices. You would use extra batteries to lower the current draw on each to keep them from over heating when under the higher current useages.
That would be a backup system for using surplus methane and oxygen for power and I think its a last resort to out last a dust storm should the sun be totally blocked out for a long period of time. At that time we would be in emergency power useage protocal so as to conserve energy.

Got it. That makes more sense. One could in fact use one of the vehicles to generate small amounts of emergency power from the alternator.

The Martian surface has huge day-night temperature variations. If we could makes solar thermal panels from local materials, it should be possible to store heat and cold from day and night respectively, in tanks of fluid or masses of soil and rock. A sterling engine could run between the hot a cold stores, generating constant power across the day night cycle.

louis · 2019-09-28 02:57:23

Re 2 A nuclear reactor of the type proposed has never been tested on Mars. In fact they haven't yet been built even (I am referring to the Kilopower units). So we know nothing about how well they would fit in with a human mission. PV panels have been tested on several missions. PV panels carry no risk to health of the mission crew.

As for flexibility, if I want to provide power for a outpost base, I can take along some solar panels. If I have just the one nuclear reactor I am limited to charging up batteries at the main base. If there is just one nuclear reactor, I have to cable everything back to that reactor.

Yes, the thermal cycles are more severe. I think that is the main challenge. But I think there are solutions to that.
UV is probably not going to be a major issue on a two year mission. A relatively fast rate of deterioration in the panels is going to be much more acceptable on such a mission, compared with on a commercial solar farm on Earth.

Wind loadings are much, much lower so the equivalent as far as I can make out be about 16 MPH on Earth as the reference point for the strongest ever recorded wind on Mars.

In order to provide a reasonably steady energy supply on Mars the peak power of your PV panel system has to be much higher than the average (and therefore much higher than the constant electricity supply from the equivalent nuclear power installation). Yes, you could bring along more nuclear reactors if you want to match that peak power, but then you would have a mass penalty to deal with. It's an advantage, I am not saying it's the critical factor. But, also, solar power does follow the day-night cycle and even more than on Earth, I don't think we'll be looking to undertaking much activity at night...humans, rovers and diggers will I imagine be safely tucked up in bed after dark!

"You are talking about burning propellant in an engine or fuel cell, to make power for propellant production? Am I reading that right?"

I am talking about using methane-oxygen as a convenient energy store to back up solar power, most likely required during worst case dust storm scenario. It's convenient because it reduces the need to bring mass-heavy chemical batteries (although it looks like Space X's mission will include chemical batteries to the tune of 2,400 KwHs of potential storage - for the fin actuation requirements).

I can't envisage using the methane-oxgygen to power the propellant production plant, as there will always be residual solar power even in the worst dust storm and that should be sufficient to keep the plant "ticking over" if that is an issue. But the solar power approach does mean you "make hay while the sun shines", so there will be more peaks and troughs.

A straightforward methane generator (but would need to be specially adapted for oxygen supply) in a purpose built hab should do the trick. I looked into it once...I think a suitable power output model comes in at about 400 Kg. You could use methane and oxygen to power rovers as well, though I am not proposing that for Mission One. It would not be much of a drain on the propellant production. You would probably wouldn't need more than 10 sols' worth of production from the propellant plant to produce the energy-generation methane and oxygen store, remembering that you need to produce something like 1000 tons of propellant-fuel in total over maybe 650 sols.

Calliban wrote:

"2. I query whether nuclear power really has such huge logistical advantages. At the very least you need to take two reactors for failsafeness, it's far less flexible and the safety issues cannot be simply waved away."
Not really. Out of all of the mechanical systems that you take with you, the reactor will be most reliable. What it does need, is more than one power generation loop. It has redundancy built into it, but there only has to be one core. I don't understand why solar would be more flexible.
"The meteorological conditions on Mars, leaving aside cold temperatures, are benign compared with Earth. You certainly don't need robust glass insulation."
Wind loadings are lower. Thermal cycles are far more severe. Dust contamination is likely to be a problem. The UV environment is quite challenging.
"3. PV is much better than steady nuclear power for high energy demand work e.g. smelting, should that be required."
That doesn't make any sense to me. I cannot see any scenario in which an intermittent power source would be superior to a 24/7 power source. With high temperature processes like smelters, you ideally want to maintain constant temperature conditions. Thermal cycling is not good for refractory linings. And if you have the monetary and mass investment in a smelter, how is it in any way superior to run it part time?
"With methane-oxygen storage of PV power you can maintain a fairly even electrical input into the propellant production facility."
You are talking about burning propellant in an engine or fuel cell, to make power for propellant production? Am I reading that right?

New Mars Forums

Announcement

#51 2019-09-22 06:12:18

Re: Ultra thin PV film

#52 2019-09-22 14:29:46

Re: Ultra thin PV film

#53 2019-09-22 14:53:35

Re: Ultra thin PV film

#54 2019-09-22 16:27:26

Re: Ultra thin PV film

#55 2019-09-22 16:41:58

Re: Ultra thin PV film

#56 2019-09-22 18:02:25

Re: Ultra thin PV film

#57 2019-09-22 18:35:37

Re: Ultra thin PV film

#58 2019-09-22 18:38:29

Re: Ultra thin PV film

#59 2019-09-22 18:56:18

Re: Ultra thin PV film

#60 2019-09-23 03:15:05

Re: Ultra thin PV film

#61 2019-09-23 16:40:40

Re: Ultra thin PV film

#62 2019-09-23 17:09:08

Re: Ultra thin PV film

#63 2019-09-24 20:56:22

Re: Ultra thin PV film

#64 2019-09-25 15:29:18

Re: Ultra thin PV film

#65 2019-09-26 05:24:48

Re: Ultra thin PV film

#66 2019-09-26 12:46:07

Re: Ultra thin PV film

#67 2019-09-26 19:00:22

Re: Ultra thin PV film

#68 2019-09-27 04:23:02

Re: Ultra thin PV film

#69 2019-09-27 10:17:08

Re: Ultra thin PV film

#70 2019-09-27 14:19:39

Re: Ultra thin PV film

#71 2019-09-27 16:50:23

Re: Ultra thin PV film

#72 2019-09-27 17:03:31

Re: Ultra thin PV film

#73 2019-09-27 17:14:33

Re: Ultra thin PV film

#74 2019-09-27 17:36:30

Re: Ultra thin PV film

#75 2019-09-28 02:57:23

Re: Ultra thin PV film

Board footer