Going Solar...the best solution for Mars.

louis · 2021-05-24 14:36:42

Spacenut said the efficiency - not the wattage - was 4%. That was wrong. Spacenut posted as follows:

It takes 2 sections of the panels to give you 70 watts that covers a 2 m x 1 m area (2,ooo w) giving you an efficiency less than 4% or less even by there own specs which is horrible on earth let alone getting power out of them for the pair on mars that is going to be less than 30 watts.

So it was 30 watts, not 70 watts Spacenut was quoting. As your figures suggest, the 30W figure is incorrect - less than half the true figure.

Thanks for the reading recommendations. Blake did provide the option of tilted panels - which would be a lower tonnage overall (but would mean more complex deployability).

I wouldn't claim to understand how solar panels are linked up and electricity directed into a mains supply, so probably not much point in my delving ino that in depth. Suffice to say we know it can be done. The wing area of Solar Impulse was 200m2 and was, I believe completely covered in PV cells. I have always been happy to make an allowance of 30 tons for electric connection equipment - cables, converters and all the rest. I am sure where there's a will there's a way to link everything up with that sort of allowance.

kbd512 wrote:

Louis,
1. The nominal Watts per square meter figure corresponds to a fixed Earth TSI value of 1,000W/m^2.
2. 14% of 1,000W/m^2 would generate an output of 140W/m^2. 10% of 1,000W/m^2 would generate an output of 100W/m^2.
3. SpaceNut short-changed you a few Watts, because he simply divided the figure by 2, in order to account for the fact that Mars is roughly twice as far from the Sun as the Earth is.
500W/m^2 * 0.14 = 70W/m^2 <- The figure SpaceNut came up with.
It should be as follows:
593W/m^2 (on average), or 59.3% of the Earth-relative TSI value incident to the surface of Mars. It ranges between 480W/m^2 and 700W/m^2, as Blake noted.
593W/m^2 * 0.14 = 83.02W/m^2 <- average peak power output, assuming the 14% efficiency figure holds under Mars insolation conditions.
83.02W/m^2 is the maximum number of Watts of power, on average, that 1m^2 of Flisom's thin film panel could generate. If the TSI is 480W/m^2, then it's 67.2W/m^2 and if it's 700W/m^2, then it's 98W/m^2. That's peak power at high noon and assumes that sunlight directly strikes the face of the panel.
For the position on Mars that Blake selected, I don't believe the W/m^2 figures hold.
4. You're going to have to read and understand what these documents mean, whether you want to or not. Basic science provided the equations, NASA provided the data, and industry has provided the engineering analysis tools. It's up to you to start using them.
Solar Radiation on Mars
Solar Radiation on Mars: Stationary Photovoltaic Array
Solar Radiation on Mars: Tracking Photovoltaic Array
For the wiring and power inverter mass estimates, you need more information from Flisom to determine what kind of voltage is achievable before running into the dielectric breakdown strength of the active material. Max / transient voltage and amperage info is provided for the triple junction silicon used in spacecraft solar arrays. I have no idea how Blake determined that he could string together 72m^2 of their product without knowing that information. 720 grams for electrical connectors and wiring to carry 1kWe is a very low estimate at a practical working voltage and amperage, even if we invoke advanced materials like CNT / BNNT, and not achievable using conventional Aluminum or Copper wiring at that weight target. Higher voltage is generally preferable to higher amperage, but there's a practical limit to the voltage achievable before arcing occurs on the panel itself. Either the panel itself or some combination of panels and wiring has to deliver the power to the power inverter.

SpaceNut · 2021-05-24 18:47:00

go look at the panel shape as they are not square or even close to being a meter.... in the 2 spec.s that were given....

the first required 2 panels to make up a divisible meter of 2 square meters
https://www.flisom.com/wp-content/uploa … -BL_CH.pdf
only a 2 pg document

Length [mm] 1021 ±2
Width [mm] 411 ±1

0.419 m^2

the second is even worse in shape....
https://flisom.com/wp-content/uploads/2 … terial.pdf
is 3 pages

Length [mm] 742
Width [mm] 372

0.276 m^2

cell efficiency
https://ecowowlife.com/fill-factor-of-solar-cell/

tahanson43206 · 2021-05-25 06:28:36

For Louis about this topic

Is there any reason why you cannot transform yourself into an expert on Solar Panels.

There may be such a reason.

However, if you have your health, and retain a modest energy level, it should be possible for you to gain field experience by asking local solar cell installers to let you tag along and possibly even perform a minor task or two.

Your expressed inability to estimate wiring mass is a major impediment to your being able to offer useful advice.

(th)

Calliban · 2021-05-25 06:44:37

I don't have as much time now as once I did. But reading through the product specifications that SpaceNut, Kbd and Louis have provided, suggest to me that there are a lot of unanswered questions about what is realistically achievable in terms of system mass in the Martian environment. The problem is that none of the proposed low area specific mass thin film concepts has yet progressed to detailed design stage. Hence, we do not know what their final mass is going to be when they are designed to achieve the required reliability under Martian conditions. There are systems that have flown in space, which achieve low area specific mass of ~1kg.m-2 for the panels alone. But these are for small space craft which operate in perfect vacuum and are not subject to any bending forces or vibrational loads after launch and deployment. We do not know what the mass of a Mars surface system will be, because no one has carried out the sort of detailed engineering study that gives us that sort of information. Even the MIT study that Louis referenced a while back, makes assumptions about system mass that are presently unsubstantiated.

A few specific uncertainties come to mind.

(1) The very thin components that Louis is referencing are actually thinner than printer paper. They are not much thicker than the PV material itself. This material is doped silicon ceramic, which is fragile and intolerant of bending. You may see it advertised in flexible sheets, but repeated bending or flexing will give rise to stress fractures which will rapidly degrade performance of the panel. You notice how the images of this material show it glued to a flat substrate? It isn't just pegged to ground over rocks and other imperfections. If it isn't perfectly flat, it will develop stress fractures over time. It needs to be flat. It cannot flex over time when subject to wind loading. How big a problem is that going to be when deployed by men in space suits, over relatively unimproved Martian terrain? I don't know and neither does Louis. Neither do any of the people he is referencing, I suspect. Pretending any certainty would be irresponsible at this point. There will be a certain amount of degradation in assembly and degradation over time due to flexing and stress concentrations. It would need to be estimated following accelerated lifetime testing under Mars analogue conditions.

(2) Films this thin, with relatively little protection from abrasion, will be vulnerable to abrasion damage, during assembly and due to dust abrasion. When the film is less than 0.1mm thick, even dust invisible to the human eye could inflict substantial damage. Removing dust will cause damage. Any dust blown by rocket exhaust will be especially damaging. Do we know how it will fare under Martian conditions? Can we estimate how it will contribute to efficiency degradation over time? I suspect no. And we won't know until we subject the films to Martian analogue conditions in as part of detailed engineering studies.

(3) Thermal design is important. Thermal gradients produce stress fractures in PV films, which degrade efficiency over time. The thinner the panel, the more significant this problem becomes, because the thermal inertia of the panel is proportional to thickness. Martian conditions are far more challenging than those on Earth, because the atmosphere provides very little thermal feedback. Normal operational voltage will change depending upon the temperature of the panel and so will efficiency. Do we know how thin film panels will behave under Martian thermal environment? I suspect not. And professing any certainty when you don't know is irresponsible.

(4) The mass of subsystems is not easily predictable. It will depend upon the voltage output of the panels. The sort of very thin films being proposed here will have low breakdown voltage. This will limit the number of cells that can be connected in series. If you exceed breakdown voltage at any point in your panel, you will get a short circuit that will destroy the entire panel, so some factor of safety is needed. Low breakdown voltage requires connecting panels in parallel, using thicker conductors. Because voltage is low, the resistance of connecting conductors must also be low, to avoid excessive voltage drop between the panel and the inverters. You will need regular inverter-transformers or very thick conductors. And for a system covering tens of acres of ground, as the Starship mission power source inevitably will, the mass of transmission cabling will be considerable. Have these considerations been factored in to system mass estimates? I suspect not. I also suspect, that no one here has the expertise or time to carry out such a study, so again, professing certainty would be irresponsible.

Without accurate information, these questions (and others) could result in order of magnitude differences in system mass. You cannot simply assume that a system is going to work with certain mass limits under Martian conditions, just because you like the idea of it and want to champion the case for it. That sort of thinking has no place in engineering. Engineering for such a high risk environment requires a high degree of certainty.

louis · 2021-05-25 07:15:46

When I see a pile of bovine waste material I walk away, TA - I'm not buying!

I don't need to pretend to be an expert. I keep an eye on everyone else's estimates and I think an upper limit of 30% of mass for PV panels is about right and certainly no one has ever shown me I'm wrong on that. Are you claiming that a PV facility has a greater proportion of electric connection equipment than that?

Blake at Redditt has a figure of 2 tons, about 18% of the system's 11 ton mass, for converters. I was suggesting an overall addition of 30% mass, including cables. It might be possibly too low a proportion if you have ultra thin PV but on the other hand you can afford to use the lightest materials for the Mars Mission - so there may be mass savings there. On the other hand again, the electrical intake may need housing in its own temperature controlled hab in which case perhaps you need to add on a ton. Adding 40% and a ton for a protective hab would make the overall system clock in at 16.4 tons. For the more easily deployed rolls, on Blake's figures, the equivalent would be 20.6 tons.

I absorb people's estimates into my overall thinking. You would learn nothing about PV on Mars from watching humans on Earth tacking on PV panels to roofs on Earth designed to withstand hurricanes, rainstorms, hailstorms and four foot drifts of snow. Much better to read up on solar powered missions already undertaken to Mars and systems like Megaflex.

tahanson43206 wrote:

For Louis about this topic
Is there any reason why you cannot transform yourself into an expert on Solar Panels.
There may be such a reason.
However, if you have your health, and retain a modest energy level, it should be possible for you to gain field experience by asking local solar cell installers to let you tag along and possibly even perform a minor task or two.
Your expressed inability to estimate wiring mass is a major impediment to your being able to offer useful advice.
(th)

louis · 2021-05-25 07:38:32

1. Your comments are fair enough. Clearly the Flisom approach would need to be tested out thoroughly in Mars like conditions. But we do know ultrathin Flisom PV has demonstrated an ability to maintain power in what I would think were pretty high stress conditions - on an airplane wing. Clearly encapuslating protection is required as indicated by Blake at Redditt.

2. No we don't know for sure though there are plenty of flexible PV systems that claim little decline in efficiency over time and we do know about abrasion effects in desert areas. But if we are talking about systems massing as little as 16-21 tons, we can afford to take along replacements. I see no particular reason to think abrasion would reduce efficiency significantly over two years and the Mission One system really doesn't need a lifetime longer than 4 years. We just need expert teams to focus on these issues and test solutions.

3. All true. Flisom does claim its systems are suitable for space applications (where you can get extreme temperature shifts). I've no idea whether that's true or not. Again, we are not looking here for a system that will last 20 plus years.

4. This is a valid concern. The Solar Impulse PV cover the 200M2 wing. Not sure how that was all wired up. For a 70K M2 squared system you'd need 350 of those "wings". My gut feeling is this won't be a major problem. Even if we have 5 tons of cabling, that's not the end of the road for a system starting off at 14 tons for the rolled PV film.

Part of the problem here is that there is no commercial demand for "Mars-appropriate" systems which will, by definition, be extremely expensive at the outset. I personally can't believe Space X haven't addressed this issue with some companies like Flisom. Flisom seem a much more Space X type outfit. Once again, the great benefit of the Space X mission design is that you will know how well your PV is performing on Mars if you get a robot rover to lay out a roll.

Calliban wrote:

I don't have as much time now as once I did. But reading through the product specifications that SpaceNut, Kbd and Louis have provided, suggest to me that there are a lot of unanswered questions about what is realistically achievable in terms of system mass in the Martian environment. The problem is that none of the proposed low area specific mass thin film concepts has yet progressed to detailed design stage. Hence, we do not know what their final mass is going to be when they are designed to achieve the required reliability under Martian conditions. There are systems that have flown in space, which achieve low area specific mass of ~1kg.m-2 for the panels alone. But these are for small space craft which operate in perfect vacuum and are not subject to any bending forces or vibrational loads after launch and deployment. We do not know what the mass of a Mars surface system will be, because no one has carried out the sort of detailed engineering study that gives us that sort of information. Even the MIT study that Louis referenced a while back, makes assumptions about system mass that are presently unsubstantiated.
A few specific uncertainties come to mind.
(1) The very thin components that Louis is referencing are actually thinner than printer paper. They are not much thicker than the PV material itself. This material is doped silicon ceramic, which is fragile and intolerant of bending. You may see it advertised in flexible sheets, but repeated bending or flexing will give rise to stress fractures which will rapidly degrade performance of the panel. You notice how the images of this material show it glued to a flat substrate? It isn't just pegged to ground over rocks and other imperfections. If it isn't perfectly flat, it will develop stress fractures over time. It needs to be flat. It cannot flex over time when subject to wind loading. How big a problem is that going to be when deployed by men in space suits, over relatively unimproved Martian terrain? I don't know and neither does Louis. Neither do any of the people he is referencing, I suspect. Pretending any certainty would be irresponsible at this point. There will be a certain amount of degradation in assembly and degradation over time due to flexing and stress concentrations. It would need to be estimated following accelerated lifetime testing under Mars analogue conditions.
(2) Films this thin, with relatively little protection from abrasion, will be vulnerable to abrasion damage, during assembly and due to dust abrasion. When the film is less than 0.1mm thick, even dust invisible to the human eye could inflict substantial damage. Removing dust will cause damage. Any dust blown by rocket exhaust will be especially damaging. Do we know how it will fare under Martian conditions? Can we estimate how it will contribute to efficiency degradation over time? I suspect no. And we won't know until we subject the films to Martian analogue conditions in as part of detailed engineering studies.
(3) Thermal design is important. Thermal gradients produce stress fractures in PV films, which degrade efficiency over time. The thinner the panel, the more significant this problem becomes, because the thermal inertia of the panel is proportional to thickness. Martian conditions are far more challenging than those on Earth, because the atmosphere provides very little thermal feedback. Normal operational voltage will change depending upon the temperature of the panel and so will efficiency. Do we know how thin film panels will behave under Martian thermal environment? I suspect not. And professing any certainty when you don't know is irresponsible.
(4) The mass of subsystems is not easily predictable. It will depend upon the voltage output of the panels. The sort of very thin films being proposed here will have low breakdown voltage. This will limit the number of cells that can be connected in series. If you exceed breakdown voltage at any point in your panel, you will get a short circuit that will destroy the entire panel, so some factor of safety is needed. Low breakdown voltage requires connecting panels in parallel, using thicker conductors. Because voltage is low, the resistance of connecting conductors must also be low, to avoid excessive voltage drop between the panel and the inverters. You will need regular inverter-transformers or very thick conductors. And for a system covering tens of acres of ground, as the Starship mission power source inevitably will, the mass of transmission cabling will be considerable. Have these considerations been factored in to system mass estimates? I suspect not. I also suspect, that no one here has the expertise or time to carry out such a study, so again, professing certainty would be irresponsible.
Without accurate information, these questions (and others) could result in order of magnitude differences in system mass. You cannot simply assume that a system is going to work with certain mass limits under Martian conditions, just because you like the idea of it and want to champion the case for it. That sort of thinking has no place in engineering. Engineering for such a high risk environment requires a high degree of certainty.

Calliban · 2021-05-25 08:20:09

I don't know who this Blake guy is, or what his qualifications are. However, most thin-film PV deployed on Earth is sandwiched between glass sheets on both sides and mounted on a frame to keep it off the ground. This avoids the sort of bending and abrasion damage that an unprotected PV film would suffer, if it were rolled out onto the ground. It also provides a degree of protection from UV light. Thin film PV panels end up being heavier than crystaline silicon, not the other way around.

You have to wonder why that sort of engineering would be carried out, if it were possible to simply unroll flexible PV films and stake them to the ground with tent pegs or weigh them down with rocks. Even in a desert, you could hire some poor third world serf on slave wages to blow away dust with a leaf blower? Could it be that the engineers that develop these power plants decided that this wasn't a sustainable strategy? I am thinking that they wouldn't be investing extra millions in megatonnes of steel and concrete if they hadn't carried out a cost-benefit study that showed it to be necessary. Could it be that there are problems with that idea that none of the self-professed experts and obsessives that troll the Internet are aware of?

Without a lot of technical knowledge on the subject, I don't think that I or Louis or anyone else here is in a position to advocate anything. We can agree that some ideas are interesting and worthy of further examination. And we can see problems. But are we in a position to be able to establish within reasonable limits, what the mass of a solar power system will be on the surface of Mars for a fuel production facility? Not a chance. All we can really do is reference engineering studies when they become available. Which they don't appear to be at present, beyond concept level that is. I don't know how Louis can strongly advocate a technology that he appears to know little about and isn't that interested in learning about. It is a puzzle to me. Is it a bit like religious scripture, where faith is more important than details?

Last edited by Calliban (2021-05-25 08:24:25)

Calliban · 2021-05-25 08:58:50

An interesting interview with Arvind Shah, an electronics expert who has been working with amorphous silicon PV since 1980. It is certainly interesting to hear what he has to say. Especially his answer to the second question. The Chinese now dominate the global PV module market thanks to cheap coal-based electricity and interest free loans. When both vendors and utilities are able to borrow at rates lower than inflation, or issue bonds that offer similarly low returns, it beggars the question as to why solar electricity is not completely free? I also wonder how sustainable such a strategy is in the long term. We have been living in an effectively zero interest rate environment for 12 years now. What happens when rates return to 5% say?

https://www.pv-magazine.com/2021/04/16/ … he-market/

pv magazine 1: In “Solar Cells and Modules,” which was recently published by Springer, you dedicate a long chapter to amorphous silicon solar cells, which is very much still a niche technology reserved for specific applications. Why hasn't this technology been deployed in rooftop PV arrays?

Arvind Shah: The main problem of this technology is the low conversion efficiencies that have so far been attained. Commercially, only about 7 % module stabilized efficiency was reached with a single junction. On a rooftop, space is limited. Therefore, wafer-based crystalline silicon solar modules with over 20% commercial efficiency are preferred.

pv magazine 2: Hydrogenated amorphous silicon layers are used to manufacture highly efficient heterojunction solar cells, but when they are used for amorphous silicon solar cells, they result in cell efficiencies of just 7%. Are these low efficiencies not sufficiently balanced by lower production costs and simplified manufacturing processes?

Arvind Shah: Potentially, the production costs of amorphous silicon solar panels could indeed be lower than those of wafer-based crystalline silicon solar modules. But this would only occur once high enough production volumes would be reached. We should take note of the fact that the main factors influencing the production costs of any solar module are the cost of electricity and the investment costs. Now, around 2011, when Chinese manufacturers took over the photovoltaic solar market, they were doing this based on exceedingly low electricity prices, not available anywhere else in the whole world, and interest-free loans from their government. No wonder that they were able to sell solar modules at prices not attainable anywhere else in the whole world.

pv magazine 3: With technological improvements and cost reductions, what kind of efficiencies can be reached in the future? What is the maximum theoretical efficiency these cells could reach?

Arvind Shah: My own institute, the PV Lab Neuchâtel, founded by me in 1984, was in 2011 working in close collaboration with a company called Oerlikon Solar. The latter had attained module efficiencies around 12% for large-area modules, albeit with a much more complicated structure called the Micromorph structure, involving both amorphous silicon and microcrystalline silicon. Oerlikon Solar was not a module producer, but a provider of equipment for manufacturing modules. The companies that made modules with the equipment from Oerlikon Solar had initially a small volume, hence relatively high production costs. These companies were unable to compete in the global market with crystalline silicon moving faster than expected, and they all had to stop activities within a few years. As for the maximum theoretical efficiency these cells may reach, this is a very difficult question. The answer depends on the assumptions you make. If you make realistic assumptions, the limit you can reach is around 16 % for a triple-junction cell. For such a cell, the production costs could be low if you find a way to decrease the cost of equipment and to accelerate the deposition rate of the microcrystalline layer, which are both real challenges.

pv magazine 4: Amorphous solar cells have big problems with stability and suffer from the “Staebler–Wronski effect” (SWE), which consists of a particular form of light-induced degradation. Is there room for improvement here?

Arvind Shah: No. During the years 1980 to 2000, there have been numerous attempts to improve the stability of amorphous silicon, by using purer gases, by modifying the deposition parameters, by avoiding/reducing the incorporation of oxygen, iron, and other foreign atoms into the amorphous silicon layer, or by using a totally different deposition process. None of these approaches were successful.

pv magazine 5: How do amorphous solar cells compare to perovskite solar cells in terms of instability?

Arvind Shah: It is true that both types of cells suffer from stability problems. However, there are important differences. Amorphous silicon solar cells show initial degradation and their efficiency stabilizes after about two years of normal exposition to sunlight, Furthermore, the decrease in efficiency observed in amorphous silicon is fully reversible – the original state can be recovered through annealing at about 200 C. Moreover, the instability observed in amorphous silicon solar cells depends on their operation temperature – if the latter is high, let's say around 70 C, as commonly encountered in tropical countries, the degradation is much less pronounced. Finally, the degradation in amorphous silicon is a purely physical process, no chemical changes are involved. In contrast with this, we observe for perovskite solar cells that their degradation process, once initiated, apparently continues until the cell is fully degraded. In addition, only a part of the degradation processes observed in today’s perovskite cells during long-term operation is reversible; degradation also depends here on the operation temperature, but it is accelerated, not reduced at higher operation temperatures. Finally, in perovskite cells, the irreversible degradation phenomenon is associated with chemical changes.

pv magazine 6: In your book, you explain that amorphous silicon does not have a real bandgap. Can you explain what this means?

Arvind Shah: Yes, I can explain this, but a precise explanation will need concepts from solid-state physics, which readers will, in general, be unable to understand. I will therefore attempt to give an intuitive and approximate explanation here. In crystalline semiconductors, there exists a clear bandgap between the upper edge of the valence band and the lower edge of the conduction band. Within this bandgap, there are practically no electronic states at all. In amorphous semiconductors, such as amorphous silicon, what was previously a real bandgap is now a region filled with electronic states such as bandtail states, due to the amorphous, chaotic nature of the material, and midgap states, due to dangling bonds or broken bonds. Therefore, no real bandgap exists in amorphous silicon.

pv magazine 7: Unlike other solar cells, amorphous silicon cells have a “p-i-n” structure. How does this structure influence their behavior and performance?

Arvind Shah: The “p-i-n” structure, used for amorphous silicon solar cells, consists mainly of an intrinsic layer. This layer extends over more than 90% of the whole solar cell, whereas the doped layers – the p and n layers – make up less than 10% of the cell. Intrinsic layers of amorphous have a far better quality than doped layers. Furthermore, within the whole i-layer of the p-i-n structure, there exists an internal electric field – a field that helps in transporting and collecting the carriers. All this contributes to obtaining for amorphous silicon solar cells, a reasonable efficiency of about 9-10% efficiency at cell level, whereas with the traditional pn-structure, like those used in all other types of solar cells, one would not attain more than 1%, in the case of amorphous silicon.

pv magazine 8: The deposition process in the manufacturing of these cells is made mostly through plasma-enhanced chemical vapor deposition (PECVD). Will this process remain the only option for technology developers in the future?

Arvind Shah: Yes. Many other deposition processes have been tried out. No other process has produced results as good as those obtained with PECVD. At some moment, in the early 2000s, there was a lot of hope for hot-wire deposition. But this process has not created an advantage, although it is at present nevertheless used by some companies for making heterojunction cells.

pv magazine 9: What kind of improvements are needed in manufacturing processes to open up more commercial possibilities for this technology? How big could this niche become?

Arvind Shah: Personally, I do not see any improvements here. Japanese and European researchers tried very hard in the early 2000s to find new, alternative materials to be included in multijunction thin-film silicon cells, such as silicon-germanium alloys and special, elaborated forms of silicon-carbon alloys. They did not succeed in finding any viable options.

pv magazine 10: Do you exclude the possibility that amorphous silicon cells and panels may be used for rooftop or off-grid applications in the future?

Arvind Shah: No, fundamentally I do not exclude that possibility. However, I very much doubt that anybody will invest massively in this technology today. I will give you here some examples, where amorphous silicon cells and panels would be the ideal choice: windows with selected grades of transparency, greenhouses. Amorphous silicon will also continue to be used for energy scavengers (Internet of Things, watches), because of its high efficiency in indoor conditions and its facility of patterning. Finally, most of the know-how developed for amorphous silicon has now allowed the emergence of valuable and cost-effective manufacturing processes for silicon heterojunction solar cells. My successor, Professor Ballif, who took over as head of the PV Lab in 2005, now concentrates on developing the “solar module of the future,” for the period 2030 to 2040. A module based on a crystalline silicon heterojunction bottom cell and a perovskite top cell. The goal is to reach commercial module efficiencies of 30% at module prices well below €0.30 per watt. In these modules, amorphous interface layers will be a key factor. These modules will constitute a basis for the renaissance of the European photovoltaic industry.

Last edited by Calliban (2021-05-25 09:18:37)

louis · 2021-05-25 14:25:33

Well there is already a system for laying out PV flat on the ground which I've featured before:

https://www.youtube.com/watch?v=D_D8I4CY9r0

https://www.renovagen.com/technology/

This is very much the sort of PV solution for Mission One to Mars I have in mind but obviously using a thin film PV system that will work well on Mars for at least four years.

On Earth you can deploy 16 Kws peak in two minutes. Of course rolls would have to be replaced on a robot rover. That would take time. I think deployment of the whole system - maybe 70,000 sq metres - shouldn't take longer than 10 sols - that would be 700 sq metres per sol or 26.5 x 26.5 metres.

Flexible solar hasn't been a good economic solution on Earth because at both utility and domestic scale you want the system to survive the worst the weather can throw at it, you want to it to maintain efficiency over 20 plus years and you want it to have as high an efficiency as your cost profile can bear, to get the most out of the system. Things are gradually changing because efficiencies for thin film are increasing so at some point they might cross over into being more cost effective. But cost effectiveness is very low down the priority list on Mars for the first few missions.

Calliban wrote:

I don't know who this Blake guy is, or what his qualifications are. However, most thin-film PV deployed on Earth is sandwiched between glass sheets on both sides and mounted on a frame to keep it off the ground. This avoids the sort of bending and abrasion damage that an unprotected PV film would suffer, if it were rolled out onto the ground. It also provides a degree of protection from UV light. Thin film PV panels end up being heavier than crystaline silicon, not the other way around.
You have to wonder why that sort of engineering would be carried out, if it were possible to simply unroll flexible PV films and stake them to the ground with tent pegs or weigh them down with rocks. Even in a desert, you could hire some poor third world serf on slave wages to blow away dust with a leaf blower? Could it be that the engineers that develop these power plants decided that this wasn't a sustainable strategy? I am thinking that they wouldn't be investing extra millions in megatonnes of steel and concrete if they hadn't carried out a cost-benefit study that showed it to be necessary. Could it be that there are problems with that idea that none of the self-professed experts and obsessives that troll the Internet are aware of?
Without a lot of technical knowledge on the subject, I don't think that I or Louis or anyone else here is in a position to advocate anything. We can agree that some ideas are interesting and worthy of further examination. And we can see problems. But are we in a position to be able to establish within reasonable limits, what the mass of a solar power system will be on the surface of Mars for a fuel production facility? Not a chance. All we can really do is reference engineering studies when they become available. Which they don't appear to be at present, beyond concept level that is. I don't know how Louis can strongly advocate a technology that he appears to know little about and isn't that interested in learning about. It is a puzzle to me. Is it a bit like religious scripture, where faith is more important than details?

Calliban · 2021-05-25 14:40:34

louis wrote:

Well there is already a system for laying out PV flat on the ground which I've featured before:
https://www.youtube.com/watch?v=D_D8I4CY9r0
https://www.renovagen.com/technology/
This is very much the sort of PV solution for Mission One to Mars I have in mind but obviously using a thin film PV system that will work well on Mars for at least four years.
On Earth you can deploy 16 Kws peak in two minutes. Of course rolls would have to be replaced on a robot rover. That would take time. I think deployment of the whole system - maybe 70,000 sq metres - shouldn't take longer than 10 sols - that would be 700 sq metres per sol or 26.5 x 26.5 metres.
Flexible solar hasn't been a good economic solution on Earth because at both utility and domestic scale you want the system to survive the worst the weather can throw at it, you want to it to maintain efficiency over 20 plus years and you want it to have as high an efficiency as your cost profile can bear, to get the most out of the system. Things are gradually changing because efficiencies for thin film are increasing so at some point they might cross over into being more cost effective. But cost effectiveness is very low down the priority list on Mars for the first few missions.

Do you know any of this, or are you guessing?

Last edited by Calliban (2021-05-25 14:44:34)

louis · 2021-05-25 14:47:23

Calliban wrote:

An interesting interview with Arvind Shah, an electronics expert who has been working with amorphous silicon PV since 1980. It is certainly interesting to hear what he has to say. Especially his answer to the second question. The Chinese now dominate the global PV module market thanks to cheap coal-based electricity and interest free loans. When both vendors and utilities are able to borrow at rates lower than inflation, or issue bonds that offer similarly low returns, it beggars the question as to why solar electricity is not completely free? I also wonder how sustainable such a strategy is in the long term. We have been living in an effectively zero interest rate environment for 12 years now. What happens when rates return to 5% say?
https://www.pv-magazine.com/2021/04/16/ … he-market/

You've made similar claims before now but whenever I research the subject I find that business loans are around 6% - so a real interest rate of probably 4% or more. The Chinese operate a form of state capitalism in any case, so if they decide to promote an industry, they might well decide to give 0% loans. That's their business and we are the fools if we let them crush our industries on that basis. It ain't rocket science as someone said. But so many of our politicians are in a corrupt relationship with the CCP China regime that they no longer act in our interest.

pv magazine 1: In “Solar Cells and Modules,” which was recently published by Springer, you dedicate a long chapter to amorphous silicon solar cells, which is very much still a niche technology reserved for specific applications. Why hasn't this technology been deployed in rooftop PV arrays?
Arvind Shah: The main problem of this technology is the low conversion efficiencies that have so far been attained. Commercially, only about 7 % module stabilized efficiency was reached with a single junction. On a rooftop, space is limited. Therefore, wafer-based crystalline silicon solar modules with over 20% commercial efficiency are preferred.
pv magazine 2: Hydrogenated amorphous silicon layers are used to manufacture highly efficient heterojunction solar cells, but when they are used for amorphous silicon solar cells, they result in cell efficiencies of just 7%. Are these low efficiencies not sufficiently balanced by lower production costs and simplified manufacturing processes?
Arvind Shah: Potentially, the production costs of amorphous silicon solar panels could indeed be lower than those of wafer-based crystalline silicon solar modules. But this would only occur once high enough production volumes would be reached. We should take note of the fact that the main factors influencing the production costs of any solar module are the cost of electricity and the investment costs. Now, around 2011, when Chinese manufacturers took over the photovoltaic solar market, they were doing this based on exceedingly low electricity prices, not available anywhere else in the whole world, and interest-free loans from their government. No wonder that they were able to sell solar modules at prices not attainable anywhere else in the whole world.

Doesn't really explain why the declining PV cost graph showed similar steep falls prior to 2011, does it? Anyway, pretty irrelevant to this thread which is whether solar is the best energy solution for Mars.

pv magazine 3: With technological improvements and cost reductions, what kind of efficiencies can be reached in the future? What is the maximum theoretical efficiency these cells could reach?
Arvind Shah: My own institute, the PV Lab Neuchâtel, founded by me in 1984, was in 2011 working in close collaboration with a company called Oerlikon Solar. The latter had attained module efficiencies around 12% for large-area modules, albeit with a much more complicated structure called the Micromorph structure, involving both amorphous silicon and microcrystalline silicon. Oerlikon Solar was not a module producer, but a provider of equipment for manufacturing modules. The companies that made modules with the equipment from Oerlikon Solar had initially a small volume, hence relatively high production costs. These companies were unable to compete in the global market with crystalline silicon moving faster than expected, and they all had to stop activities within a few years. As for the maximum theoretical efficiency these cells may reach, this is a very difficult question. The answer depends on the assumptions you make. If you make realistic assumptions, the limit you can reach is around 16 % for a triple-junction cell. For such a cell, the production costs could be low if you find a way to decrease the cost of equipment and to accelerate the deposition rate of the microcrystalline layer, which are both real challenges.

Efficiency for one type of cell...not very interesting really.

pv magazine 4: Amorphous solar cells have big problems with stability and suffer from the “Staebler–Wronski effect” (SWE), which consists of a particular form of light-induced degradation. Is there room for improvement here?
Arvind Shah: No. During the years 1980 to 2000, there have been numerous attempts to improve the stability of amorphous silicon, by using purer gases, by modifying the deposition parameters, by avoiding/reducing the incorporation of oxygen, iron, and other foreign atoms into the amorphous silicon layer, or by using a totally different deposition process. None of these approaches were successful.
pv magazine 5: How do amorphous solar cells compare to perovskite solar cells in terms of instability?
Arvind Shah: It is true that both types of cells suffer from stability problems. However, there are important differences. Amorphous silicon solar cells show initial degradation and their efficiency stabilizes after about two years of normal exposition to sunlight, Furthermore, the decrease in efficiency observed in amorphous silicon is fully reversible – the original state can be recovered through annealing at about 200 C. Moreover, the instability observed in amorphous silicon solar cells depends on their operation temperature – if the latter is high, let's say around 70 C, as commonly encountered in tropical countries, the degradation is much less pronounced. Finally, the degradation in amorphous silicon is a purely physical process, no chemical changes are involved. In contrast with this, we observe for perovskite solar cells that their degradation process, once initiated, apparently continues until the cell is fully degraded. In addition, only a part of the degradation processes observed in today’s perovskite cells during long-term operation is reversible; degradation also depends here on the operation temperature, but it is accelerated, not reduced at higher operation temperatures. Finally, in perovskite cells, the irreversible degradation phenomenon is associated with chemical changes.
pv magazine 6: In your book, you explain that amorphous silicon does not have a real bandgap. Can you explain what this means?
Arvind Shah: Yes, I can explain this, but a precise explanation will need concepts from solid-state physics, which readers will, in general, be unable to understand. I will therefore attempt to give an intuitive and approximate explanation here. In crystalline semiconductors, there exists a clear bandgap between the upper edge of the valence band and the lower edge of the conduction band. Within this bandgap, there are practically no electronic states at all. In amorphous semiconductors, such as amorphous silicon, what was previously a real bandgap is now a region filled with electronic states such as bandtail states, due to the amorphous, chaotic nature of the material, and midgap states, due to dangling bonds or broken bonds. Therefore, no real bandgap exists in amorphous silicon.
pv magazine 7: Unlike other solar cells, amorphous silicon cells have a “p-i-n” structure. How does this structure influence their behavior and performance?
Arvind Shah: The “p-i-n” structure, used for amorphous silicon solar cells, consists mainly of an intrinsic layer. This layer extends over more than 90% of the whole solar cell, whereas the doped layers – the p and n layers – make up less than 10% of the cell. Intrinsic layers of amorphous have a far better quality than doped layers. Furthermore, within the whole i-layer of the p-i-n structure, there exists an internal electric field – a field that helps in transporting and collecting the carriers. All this contributes to obtaining for amorphous silicon solar cells, a reasonable efficiency of about 9-10% efficiency at cell level, whereas with the traditional pn-structure, like those used in all other types of solar cells, one would not attain more than 1%, in the case of amorphous silicon.
pv magazine 8: The deposition process in the manufacturing of these cells is made mostly through plasma-enhanced chemical vapor deposition (PECVD). Will this process remain the only option for technology developers in the future?
Arvind Shah: Yes. Many other deposition processes have been tried out. No other process has produced results as good as those obtained with PECVD. At some moment, in the early 2000s, there was a lot of hope for hot-wire deposition. But this process has not created an advantage, although it is at present nevertheless used by some companies for making heterojunction cells.
pv magazine 9: What kind of improvements are needed in manufacturing processes to open up more commercial possibilities for this technology? How big could this niche become?
Arvind Shah: Personally, I do not see any improvements here. Japanese and European researchers tried very hard in the early 2000s to find new, alternative materials to be included in multijunction thin-film silicon cells, such as silicon-germanium alloys and special, elaborated forms of silicon-carbon alloys. They did not succeed in finding any viable options.
pv magazine 10: Do you exclude the possibility that amorphous silicon cells and panels may be used for rooftop or off-grid applications in the future?
Arvind Shah: No, fundamentally I do not exclude that possibility. However, I very much doubt that anybody will invest massively in this technology today. I will give you here some examples, where amorphous silicon cells and panels would be the ideal choice: windows with selected grades of transparency, greenhouses. Amorphous silicon will also continue to be used for energy scavengers (Internet of Things, watches), because of its high efficiency in indoor conditions and its facility of patterning. Finally, most of the know-how developed for amorphous silicon has now allowed the emergence of valuable and cost-effective manufacturing processes for silicon heterojunction solar cells. My successor, Professor Ballif, who took over as head of the PV Lab in 2005, now concentrates on developing the “solar module of the future,” for the period 2030 to 2040. A module based on a crystalline silicon heterojunction bottom cell and a perovskite top cell. The goal is to reach commercial module efficiencies of 30% at module prices well below €0.30 per watt. In these modules, amorphous interface layers will be a key factor. These modules will constitute a basis for the renaissance of the European photovoltaic industry.

I am not quite following the relevance of the above. It may be the case that thin film has not yet found a big market on Earth - that doesn't mean it's wrong for Mars, or at least early missions on Mars which has an entirely different and less adverse weather conditions (excluding temperature fluctuations and occasional weak-wind dust storms).

louis · 2021-05-25 15:01:35

Calliban wrote:

louis wrote:
Well there is already a system for laying out PV flat on the ground which I've featured before:
https://www.youtube.com/watch?v=D_D8I4CY9r0
https://www.renovagen.com/technology/
This is very much the sort of PV solution for Mission One to Mars I have in mind but obviously using a thin film PV system that will work well on Mars for at least four years.
On Earth you can deploy 16 Kws peak in two minutes. Of course rolls would have to be replaced on a robot rover. That would take time. I think deployment of the whole system - maybe 70,000 sq metres - shouldn't take longer than 10 sols - that would be 700 sq metres per sol or 26.5 x 26.5 metres.
Flexible solar hasn't been a good economic solution on Earth because at both utility and domestic scale you want the system to survive the worst the weather can throw at it, you want to it to maintain efficiency over 20 plus years and you want it to have as high an efficiency as your cost profile can bear, to get the most out of the system. Things are gradually changing because efficiencies for thin film are increasing so at some point they might cross over into being more cost effective. But cost effectiveness is very low down the priority list on Mars for the first few missions.
Do you know any of this, or are you guessing?

The deployment time is from the Renovagen tech spec. I used that as the basis for a very rough guesstimate of max roll out time on Mars. Most of the time would be spent detaching and attaching rolls of PV, I would imagine. Under human supervision you'd have a team of robots working. A robot rover with trailer would bring rolls of PV from the Starship to the array site. The site would have been staked out with transponders by robot rovers acting under human supervision. Once the pioneers had checked the transponder system, the robots would work to a pre-ordained computer system in the same way farm robots on Earth do. Deployment robots would come up to the trailer and attach a roll to their carrier and then take it to the area to be laid out. Attachment robots would then come along and deploy the attachment system - this might be the equivalent of an industrial robot arm driving titanium "tent spikes" into the ground. Or it might involve the robots place rocks at intervals.Or it might involve some application of superglue. Whatever works best.

I've definitely read of labs getting into the 20% plus area with thin film.

https://www.researchgate.net/publicatio … _beyond_20

I think I saw a new record of 26% or thereabouts.

Calliban · 2021-05-25 16:02:31

Here is the brochure for Rapid T from Renoven.
https://www.renovagen.com/wp-content/up … ochure.pdf

It is an impressive system. I might even be tempted to buy one.
Unit weight = 1500kg.
Power = 11kWp.
Average power under Martian equatorial conditions = 1.8kW.
Power/mass = 1800/1500 = 1.2W/kg.

A 1.2MW power supply based upon these units, would weigh 1000 metric tonnes. Whilst it is impressive within it's limitations, it is at least an order of magnitude too heavy to be useful on Mars.

A note on laboratory based solar cell efficiency. It is the efficiency of a single cell, under idealised light conditions, temperature and of course at beginning of life. It is not very indicative of what can be expected of modules under real conditions, across their operating life. Amorphous silicon cells lose 10-30% of efficiency in the first six months of life on Earth. This is due to formation of dangling bonds in amorphous silicon following irradiation. How quickly this will happen under Martian conditions, I do not know. The UV and thermal conditions are far more severe.

Last edited by Calliban (2021-05-25 16:11:44)

louis · 2021-05-25 17:47:10

Silly to mock like that. The "whole unit" includes all the electrical gear housed in a vehicle and there is nothing to suggest that the electric gear couldn't handle more PV strips - in fact the technical brochure refers to the ease with which you can line up the PV roll outs. In addition there is a 120 KwH battery battery set up which is adding a lot of mass relative to the PV array.

So it's not relevant to reference all that specifically as what would be required on Mars. Rapid Roll is essentially a mobile energy system that can deliver constant power 24/7 for military and disaster relief applications (and some other niche uses) without need for shipping diesel.

On Mars, the system is not required to be mobile, it can be static. The array system does not have to deal with rainstorms, ice storms, hailstorms, thunder and lightning, floods or whatever. It can certainly be less robust. The ratio of mass of batteries to the PV array can be much lower.

My interest in this was more as a deployment system.

I'm getting a peak figure of around 93 watts per sq metre from the PV array. So that might indicate around 10% efficiency. Indications are we can do better than that if we are prepared to pay for more efficiency.

Calliban wrote:

Here is the brochure for Rapid T from Renoven.
https://www.renovagen.com/wp-content/up … ochure.pdf
It is an impressive system. I might even be tempted to buy one.
Unit weight = 1500kg.
Power = 11kWp.
Average power under Martian equatorial conditions = 1.8kW.
Power/mass = 1800/1500 = 1.2W/kg.
A 1.2MW power supply based upon these units, would weigh 1000 metric tonnes. Whilst it is impressive within it's limitations, it is at least an order of magnitude too heavy to be useful on Mars.
A note on laboratory based solar cell efficiency. It is the efficiency of a single cell, under idealised light conditions, temperature and of course at beginning of life. It is not very indicative of what can be expected of modules under real conditions, across their operating life. Amorphous silicon cells lose 10-30% of efficiency in the first six months of life on Earth. This is due to formation of dangling bonds in amorphous silicon following irradiation. How quickly this will happen under Martian conditions, I do not know. The UV and thermal conditions are far more severe.

SpaceNut · 2021-05-25 19:48:31

prepared surface sand no grass for mars nothing sharp to tare or puncture the thin skins self contained with a FUCHS MHL320 just sitting around...

Solar cell panels to batteries are still energy mismatched for kw hrs in to be stored...temporary use design not intended for long term as a portable power source,

no temperature ratings for rollout or use on a frozen ground....

louis · 2021-05-26 12:27:28

I don't think ground prep will be that onerous. probably just get robot rovers to clear away rocks above a certain size. All this can be tested on Earth. We could even create a replica of the designated PV array zone. If the PV roll can function on Earth in rocky deserts and if it can survive Mars conditions in the lab, all should be set fair.

Generally the rule with a PV system on Mars will be to "make hay while the sun shines". It is a mismatch I accept, since the time you want to be charging things is also the time you want to be working. This argues for detachable battery packs for the smaller robot rovers and for fast chargers. Any tasks that can be undertaken during maximum insolation should be carried out - so that would be the period for peak propellant manufacture (though it might need to be kept going at 24/7), for heating up domestic and industrial hot water, for recharging batteries and for doing the laundry.

SpaceNut wrote:

prepared surface sand no grass for mars nothing sharp to tare or puncture the thin skins self contained with a FUCHS MHL320 just sitting around...
Solar cell panels to batteries are still energy mismatched for kw hrs in to be stored...temporary use design not intended for long term as a portable power source,
no temperature ratings for rollout or use on a frozen ground....

SpaceNut · 2021-05-26 18:50:57

Here is why it matters
UNDERSTANDING BATTERY AMP HOURS

Battery Amp Hours Explained (And Other Battery Terms)

How to Calculate Battery Amp Hours

Solar panels follow the slow charge model of which it takes many hours at current going in to charge the cells properly. Some battery's use 1/10 of the amp/hr rating for the charging current value and it depends on battery chemistry...

https://ntrs.nasa.gov/api/citations/201 … 012929.pdf
Atmospheric Opacity Measurements for VL-1, VL-2 and the MER Rovers

https://www.lpi.usra.edu/meetings/lpsc2011/pdf/1122.pdf

https://www.boulder.swri.edu/~layoung/p … 97Mars.pdf

https://mars.nasa.gov/mgs/sci/lpsc98/1784.pdf

kbd512 · 2021-05-27 11:03:54

Some general observations:

1. The people making the proposals seem very unaware or even dismissive of the practical limitations of the equipment they propose using. It must stem from a fundamental ignorance about electricity, which also happens to be fundamental to evaluating practical vs grossly impractical ideas. Blake doesn't seem to think there's a voltage and amperage limitation for electricity flowing through a printed conductor that's thinner than a human hair, on an insulator that's essentially a grocery store bag, nor a practical limit to the deployment of something that thin.

How else could he believe that 720 grams of wiring and connectors was sufficient to permit 1,000W of power to flow through a 36m long string of panels in an efficient manner, or at all, for that matter?

Why is it that he thinks lightweight aerospace power inverters are a practical solution, purely based upon their weight? Is he unaware that these systems also sacrifice efficiency for sake of weight reduction?

The VFGs that airliners use to supply ship's power may only weigh a few tens of kilos for an output of 100kVa+, but they also rely upon massive amounts of ram air cooling and are around 80% efficient, at best. Losing 20% of your power to heat may be acceptable for something powered by massive multi-MW-output turbofan engines, but it's never going to be practical to power a vehicle on Mars, because all that waste heat has to go somewhere. The markedly more efficient synchronous AC motor-generators used by Tesla vehicles are drastically more efficient, at the expense of added weight, yet cooling is still challenging for these 96%+ efficient motors.

2. Practical systems that are both usable long-term and deployable using the proposed methods are much heavier and much better protected, but that greatly affects the fantastic power-to-weight ratio of thin films, bringing them much closer to existing triple-junction silicon-based cells, which begin and end life with much higher efficiency, thus much less total surface area is required, in comparison to equivalent thin film PV. If it's possible to coat the thin film with cover glass and still have it deployed from a roll, this would make it much more attractive as a long term solution, even at the expense of added weight. If that's not possible, then I stand by my assertion that a cover glass-eqipped, triple-junction silicon wafer-based solution, mounted to a very light aerospace material backer board, is the correct way to do this to minimize weight and maximize power output per unit area.

3. The more off-panel wiring and power conditioning equipment is required, the less attractive the overall solution becomes, since all of that stuff requires assembly and maintenance, and none of it is particularly lightweight in the quantities required for a practical solution. Any panel that must operate at low voltage requires power inverter equipment that boosts the voltage to minimize transmission losses and prevent undesirable on-panel electrical effects (arcing from excessive voltage or resistive heating from excessive current flow) from destroying the panels.

4. In an ideal world, the solar arrays and all ancillary power conversion equipment would be matched to the loads they're intended to supply power to. For example, if we had a direct current Hydrogen electrolysis unit that requires 480V of input electrical power, then a nearby solar array would provide that 480V or something nominally above that to contend with transmission losses, and then the required power conditioning equipment is minimized. All of the real-world power conditioning equipment is not light, requires substantial cooling to radiate away waste heat, and in general also requires routine maintenance (nothing crazy, but the requirement is there, nonetheless, so we should minimize the numbers and types of spares required for logistical support). We need some kind of standardization. All US Navy ships use 480V 3-phase AC power and 120V single phase AC power for lighter loads, for example, so we need to use existing commercial electrolysis units and power conditioning equipment in our model.

5. A practical solution needs to adapt existing commercial equipment, rather than undefined theoretical examples. I've posted about this before in other threads. A correctly-sized Sabatier reactor is the only piece of equipment without a good commercial analog- there are lab / bench top experimental models and then there are gigantic continuous process units used in refineries that simply wouldn't be feasible to import from Earth, because the individual pieces of equipment are the size of things like the primary coolant loop pumps used see in GW-class PWRs. It's not easy to estimate power consumption and performance between examples that consume a few kWs at most, to hundreds of MWs. We need an ISO shipping container sized / truck transportable petrochemical refinery in a box. Maybe such a thing exists, but I'm still hunting for it.

If you want this to work for a real world implementation, then minimization or repurposing of waste heat in power transmission and conversion is the name of the game. Heat is also energy and that energy needs to be directly utilized in the propellant manufacturing process, or materials refining processes, etc. We need a Mars-bespoke solution. This is very important to the overall efficiency of any feasible solution, but especially critical for a solar-only solution, if using the "make hay while the making's good" methodology.

6. I haven't responded more often on the forum because thinking about how to best achieve this has been preoccupying my mind, since it's so important to any prospective solution. This is intended to address tahanson's question, "Is this feasible to do, under any plausible scenario, using the technology that we have?" We need a matrix of coefficients of practical performance so we can then approach the problem from a "first principles" perspective, or what NASA would consider a "parametric performance analysis model". Reasonable assumptions can be made about performance by using the performance of existing equipment. There must be a good reason that no proposal has moved past the proposal stage. I believe it's related to the fact that we've never had an analog requirement with similar performance demands placed upon the entire system. It's simple to conceptualize by hand-waving away all the important details, but astonishingly complex to actually implement. This requires a team of engineers from multiple different disciplines.

Calliban · 2021-05-27 15:40:58

Kbd512, well done for an excellent and well researched post.

Regarding waste heat: On Earth, power transformers are usually oil filled when power goes above about 2MVA. The oil serves a dual function of providing insulation and providing a convective medium for removing waste heat. The larger the transformer is, the lower the surface area to volume ratio, so thermal design becomes more challenging as power rating increases. On Earth, transformers rely upon atmospheric convection to remove waste heat. On Mars, high heat output components would need to rely on a combination of radiation heat loss and ground heat sinking. I cannot foresee much use for waste heat, aside from perhaps greenhouse heating. The heat is distributed over many acres of area and is low quality (<100°C). I doubt it would be that useful in driving chemical processes, but I could be wrong.

In terms of a COTS solar solution, Renovagen has already developed one, which Louis has referenced on numerous occasions.
https://www.renovagen.com/wp-content/up … ochure.pdf

It would appear to be relatively easy to deploy. Unfortunately, under Martian equatorial conditions, each 1500kg trailer would produce average power of 1.8kW, giving a power-weight of 1.2W/Kg. A 1.2MW mission power supply would weight 1000 metric tonnes. This is a real system that has been developed and tested.

Louis seems to think it will be straightforward shaving weight off of this sort of system. On what basis? Too many people seem to assume that technology is some sort of black box, which will provide any solution with any combination of properties, so long as some benevolent entity is willing to pour enough money into R&D. That view ignores the fact that developing a new product is a trade off between different properties. Making something lighter, often means making it weaker and less durable. It is possible to manufacture thin-film solar panels that are as thin as A4 printer paper. But these are fragile ceramic films, vulnerable to damage from bending, dust contamination and UV. There are no technological solutions that allow a panel to get both lighter and more durable. Likewise the problem introduced by breakdown voltage of very thin films. We can have low voltage thin films and thick conductors and regular inverters and transformers. Or thicker films, higher voltages and less transmission infrastructure. But no amount of technology will change the basic design options. The trailer for the renovagen product could be made from aluminium alloy to reduce weight. But of course aluminium has fatigue and cracking problems that we need to be taken into account. In real engineering design, improvements in one area always require tradeoffs in others.

I cannot offer much guidance on how a methane oxygen synthesis plant can be integrated with a solar power system. But I do know that in any system dealing with high temperatures and pressure, thermal shocking is a problem that receives a lot of attention. It can result in the formation of microcracks that later grow rapidly and catastrophically. There are limits to the rate of heating and cooling. That will be the case for any chemical reactor, which is going to be a stainless steel lined pressure vessel, containing an active catalyst. It will also be the case for electrolysis cells. These things cannot be switched on and off at a moments notice. They need preheating and materials flowing into them need to be preheated to the correct temperature. Generally it makes much more sense to run a propellant synthesis plant at constant high loads, 24/7. It is also the most efficient solution in terms of utilising the plant efficiently as an asset with both high capital and shipping costs. So I suspect (but do not know) that it will be more efficient to use some sort of energy storage system (batteries?) to provide a 24/7 constant power supply to the propellant plant.

One final point. There seems to be a general assumption that capital costs and development costs for anything sent to Mars can be ignored, because they are small compared to carriage costs and total mission costs. That assumption is obviously only true up to a point.

Last edited by Calliban (2021-05-27 16:58:17)

louis · 2021-05-27 17:23:24

kbd512 wrote:

Some general observations:
1. The people making the proposals seem very unaware or even dismissive of the practical limitations of the equipment they propose using. It must stem from a fundamental ignorance about electricity, which also happens to be fundamental to evaluating practical vs grossly impractical ideas. Blake doesn't seem to think there's a voltage and amperage limitation for electricity flowing through a printed conductor that's thinner than a human hair, on an insulator that's essentially a grocery store bag, nor a practical limit to the deployment of something that thin.
How else could he believe that 720 grams of wiring and connectors was sufficient to permit 1,000W of power to flow through a 36m long string of panels in an efficient manner, or at all, for that matter?
Why is it that he thinks lightweight aerospace power inverters are a practical solution, purely based upon their weight? Is he unaware that these systems also sacrifice efficiency for sake of weight reduction?
The VFGs that airliners use to supply ship's power may only weigh a few tens of kilos for an output of 100kVa+, but they also rely upon massive amounts of ram air cooling and are around 80% efficient, at best. Losing 20% of your power to heat may be acceptable for something powered by massive multi-MW-output turbofan engines, but it's never going to be practical to power a vehicle on Mars, because all that waste heat has to go somewhere. The markedly more efficient synchronous AC motor-generators used by Tesla vehicles are drastically more efficient, at the expense of added weight, yet cooling is still challenging for these 96%+ efficient motors.

Did you read Blake's responses in the comments? Here they are:

"I'm treating "the grid" as a separate system. The wiring mass depends on the voltage the system runs at, and I'd assume high voltage, maybe as high as 20 kV.

This kind of stuff really doesn't weigh much if designed for aerospace use (like DC-DC converter in electric drones), I'd be really surprised if the power grid (putting aside generation and storage) masses in at more than few tons.

One thing that i did not see any mention of, (and maybe it is not a problem at all) is thermal buildup.

I have analyzed that one in the past, quite recently actually. Basically you can treat the solar panel as a perfect blackbody and work out the equilibrium temperature in martian sunlight, it basically comes to like 60 C even if you don't allow for any heat exchange out the back and that temperature is not a problem for these kind of solar cells. But in reality the temperature will stabilize at something like 20-30 C in direct sunlight, really not a problem.

Waste heat would be a problem when it comes to power conversion, perhaps the power regulator/convertor on each array would need a radiator panel. These really don't need to weigh much though and can be passive using heat pipes and lightweight fins (some carbon fiber composites have extremely good thermal conductivity along the grain of the fibers). It is yet another thing to be designed, but it's not going to be mass-prohibitive."

"For sure and I'm not saying the mass would be negligible, however when these things are built on Earth mass is rarely a serious consideration, it just has to be light enough to not be unduly unwieldy with cost being the overriding concern.

A setup which has to be launched by rocket will use improbably high voltages to reduce the conductor mass and it will use aerospace grade power regulation (for example aerospace DC-DC converter are generally in the ballpark of 10 kW/kg so the convertors for a 10 MW system would be maybe around 2 t). It also almost certainly won't meet the safety standards of Earthly nations, offering an excessively high risk of electrocution and short-circuiting were it to be deployed under Earthly conditions.

I do know that the numbers for an industrial system on Earth will be incredibly wrong, off by one or even two orders of magnitude."

2. Practical systems that are both usable long-term and deployable using the proposed methods are much heavier and much better protected, but that greatly affects the fantastic power-to-weight ratio of thin films, bringing them much closer to existing triple-junction silicon-based cells, which begin and end life with much higher efficiency, thus much less total surface area is required, in comparison to equivalent thin film PV. If it's possible to coat the thin film with cover glass and still have it deployed from a roll, this would make it much more attractive as a long term solution, even at the expense of added weight. If that's not possible, then I stand by my assertion that a cover glass-eqipped, triple-junction silicon wafer-based solution, mounted to a very light aerospace material backer board, is the correct way to do this to minimize weight and maximize power output per unit area.

Well I would agree of course everything needs to be tested and that until a flexible roll system with ultra thin Flisom style PV film has been tested, no one can assert anything with absolute confidence but I do feel positive about this approach.

3. The more off-panel wiring and power conditioning equipment is required, the less attractive the overall solution becomes, since all of that stuff requires assembly and maintenance, and none of it is particularly lightweight in the quantities required for a practical solution. Any panel that must operate at low voltage requires power inverter equipment that boosts the voltage to minimize transmission losses and prevent undesirable on-panel electrical effects (arcing from excessive voltage or resistive heating from excessive current flow) from destroying the panels.

If the sealed Flisom PV film is feasible then I really can't see the additional mass from connecting equipment being a problem. You could add 30, 40 or 50 tons and it would still look great from a total mass point of view.

4. In an ideal world, the solar arrays and all ancillary power conversion equipment would be matched to the loads they're intended to supply power to. For example, if we had a direct current Hydrogen electrolysis unit that requires 480V of input electrical power, then a nearby solar array would provide that 480V or something nominally above that to contend with transmission losses, and then the required power conditioning equipment is minimized. All of the real-world power conditioning equipment is not light, requires substantial cooling to radiate away waste heat, and in general also requires routine maintenance (nothing crazy, but the requirement is there, nonetheless, so we should minimize the numbers and types of spares required for logistical support). We need some kind of standardization. All US Navy ships use 480V 3-phase AC power and 120V single phase AC power for lighter loads, for example, so we need to use existing commercial electrolysis units and power conditioning equipment in our model.

I presume you would accept, as is generally true in the space industry, that where there is a trade off between mass and cost lower mass will be favoured. So all else being equal, electric connection equipment will be as a low mass as possible. If the whole PV system comes in at $500 million, or even $1billion that just won't be a problem for Missions 1 to 5.

5. A practical solution needs to adapt existing commercial equipment, rather than undefined theoretical examples. I've posted about this before in other threads. A correctly-sized Sabatier reactor is the only piece of equipment without a good commercial analog- there are lab / bench top experimental models and then there are gigantic continuous process units used in refineries that simply wouldn't be feasible to import from Earth, because the individual pieces of equipment are the size of things like the primary coolant loop pumps used see in GW-class PWRs. It's not easy to estimate power consumption and performance between examples that consume a few kWs at most, to hundreds of MWs. We need an ISO shipping container sized / truck transportable petrochemical refinery in a box. Maybe such a thing exists, but I'm still hunting for it.
If you want this to work for a real world implementation, then minimization or repurposing of waste heat in power transmission and conversion is the name of the game. Heat is also energy and that energy needs to be directly utilized in the propellant manufacturing process, or materials refining processes, etc. We need a Mars-bespoke solution. This is very important to the overall efficiency of any feasible solution, but especially critical for a solar-only solution, if using the "make hay while the making's good" methodology.

I doubt that a propellant plant facility suitable for Mars is commercially available. That is something that will need to be a bespoke solution. But I am sure all the various elements already exist as separate items for various purposes and that a competent team of engineers can create a working facility. I am doubtful it could be shipped as one unit, if you were looking to offload it - although you could probably set it up in one Starship (that might be the easiest solution). If we are offloading the facility, it will probably need its own hab...I'm thinking in terms of maintenance and temperature control, operating it out in the open on Mars would present too many problems.

6. I haven't responded more often on the forum because thinking about how to best achieve this has been preoccupying my mind, since it's so important to any prospective solution. This is intended to address tahanson's question, "Is this feasible to do, under any plausible scenario, using the technology that we have?" We need a matrix of coefficients of practical performance so we can then approach the problem from a "first principles" perspective, or what NASA would consider a "parametric performance analysis model". Reasonable assumptions can be made about performance by using the performance of existing equipment. There must be a good reason that no proposal has moved past the proposal stage. I believe it's related to the fact that we've never had an analog requirement with similar performance demands placed upon the entire system. It's simple to conceptualize by hand-waving away all the important details, but astonishingly complex to actually implement. This requires a team of engineers from multiple different disciplines.

I am pretty sure, if memory serves, that NASA have commissioned a number of detailed studies, but they have always been "20 years away" from a Mars Mission so there has never been an incentive to take the proposals further. Space X is the only credible commercial buyer for a Mars propellant production facility. As long as the facility is enclosed in a temperature controlled environment I am really not sure what the problem is...this is basic science and engineering. On Mars there may be residual but important issues such as venting gases. But venting of gases is a well established space technology. Are you sure you aren't overthinking this?

louis · 2021-05-27 17:43:49

Calliban wrote:

Kbd512, well done for an excellent and well researched post.
Regarding waste heat: On Earth, power transformers are usually oil filled when power goes above about 2MVA. The oil serves a dual function of providing insulation and providing a convective medium for removing waste heat. The larger the transformer is, the lower the surface area to volume ratio, so thermal design becomes more challenging as power rating increases. On Earth, transformers rely upon atmospheric convection to remove waste heat. On Mars, high heat output components would need to rely on a combination of radiation heat loss and ground heat sinking. I cannot foresee much use for waste heat, aside from perhaps greenhouse heating. The heat is distributed over many acres of area and is low quality (<100°C). I doubt it would be that useful in driving chemical processes, but I could be wrong.

Longer term (not in the early missions) I think any waste heat will be "gratefully received" by farm habs and will be absolutely crucial in efficient farming on Mars.

In terms of a COTS solar solution, Renovagen has already developed one, which Louis has referenced on numerous occasions.
https://www.renovagen.com/wp-content/up … ochure.pdf
It would appear to be relatively easy to deploy. Unfortunately, under Martian equatorial conditions, each 1500kg trailer would produce average power of 1.8kW, giving a power-weight of 1.2W/Kg. A 1.2MW mission power supply would weight 1000 metric tonnes. This is a real system that has been developed and tested.

Well again, I say that's just silly. You can't take a military-disaster zone system and apply it to Mars. All the requirements are totally different. What you can do is say: yes, that's a simple and credible deployment system. On Earth mass is not a huge consideration as it is on a Mars Mission - I can obviously immediately think of better solutions than having a huge heavy steel stand at one end of the system. On Mars a robot rover (used for multiple purposes) could grip one end.

Louis seems to think it will be straightforward shaving weight off of this sort of system. On what basis? Too many people seem to assume that technology is some sort of black box, which will provide any solution with any combination of properties, so long as some benevolent entity is willing to pour enough money into R&D. That view ignores the fact that developing a new product is a trade off between different properties. Making something lighter, often means making it weaker and less durable. It is possible to manufacture thin-film solar panels that are as thin as A4 printer paper. But these are fragile ceramic films, vulnerable to damage from bending, dust contamination and UV. There are no technological solutions that allow a panel to get both lighter and more durable. Likewise the problem introduced by breakdown voltage of very thin films. We can have low voltage thin films and thick conductors and regular inverters and transformers. Or thicker films, higher voltages and less transmission infrastructure. But no amount of technology will change the basic design options. The trailer for the renovagen product could be made from aluminium alloy to reduce weight. But of course aluminium has fatigue and cracking problems that we need to be taken into account. In real engineering design, improvements in one area always require tradeoffs in others.

Bit of a cheek to say I don't understand trade-offs when I've mentioned them several times in this thread. There are clearly hundreds of ways a Mars Rapid Roll system would be of lower mass than an Earth based system. We know how light the Flisom system is. The only issue is can it be sealed and made usable on Mars as Blake suggests. I am happy to accept that no one really knows the answer to that. But I don't see any formidable road blocks.

I cannot offer much guidance on how a methane oxygen synthesis plant can be integrated with a solar power system. But I do know that in any system dealing with high temperatures and pressure, thermal shocking is a problem that receives a lot of attention. It can result in the formation of microcracks that later grow rapidly and catastrophically. There are limits to the rate of heating and cooling. That will be the case for any chemical reactor, which is going to be a stainless steel lined pressure vessel, containing an active catalyst. It will also be the case for electrolysis cells. These things cannot be switched on and off at a moments notice. They need preheating and materials flowing into them need to be preheated to the correct temperature. Generally it makes much more sense to run a propellant synthesis plant at constant high loads, 24/7. It is also the most efficient solution in terms of utilising the plant efficiently as an asset with both high capital and shipping costs. So I suspect (but do not know) that it will be more efficient to use some sort of energy storage system (batteries?) to provide a 24/7 constant power supply to the propellant plant.
One final point. There seems to be a general assumption that capital costs and development costs for anything sent to Mars can be ignored, because they are small compared to carriage costs and total mission costs. That assumption is obviously only true up to a point.

I agree that propellant production sounds like the sort of process that needs to be continued 24/7. But equally I feel confident quantities can fluctuate quite substantially. It's more a question of not letting tanks empty, not letting residues build up. I've no technical knowledge for saying it but I would be surprised if a propellant production facility that had an optimal running rate of x couldn't operate at x - 70% of x. That's the sort of margin I think is likely to determine the size of the plant for a PV system. A nuclear power system can operate at x all sol long (assuming material supply) but with a PV based system you would probably operate at x plus 150% during peak PV. So that could mean the propellant plant facility might have to be up to 1.5 times more mass than with a nuclear power solution. But I don't think the facility will be that huge - my guess is something like 20 tons maybe for a nuclear power solution...so up to 35 tons for a PV power solution. An extra 15 tons. But of course there is no nuclear power solution available for 2024. So that's all moot.

SpaceNut · 2021-05-27 20:30:01

Calliban wrote:

In terms of a COTS solar solution, Renovagen has already developed one, which Louis has referenced on numerous occasions.
https://www.renovagen.com/wp-content/up … ochure.pdf
It would appear to be relatively easy to deploy. Unfortunately, under Martian equatorial conditions, each 1500kg trailer would produce average power of 1.8kW, giving a power-weight of 1.2W/Kg. A 1.2MW mission power supply would weight 1000 metric tonnes. This is a real system that has been developed and tested.

Thats 10 starships....and nothing else....

I think I gave an estimate of 5 ships long ago with the higher efficiency cells but even thats to many ships to make fuel and only that...

This is how to compensate for summer to winter which is the lowest levels of power.

56f089a8d619bdc13d3d069f_WEB_Nait-Reference-Array-Angles.jpg

kbd512 · 2021-05-27 20:46:53

Louis,

I read the entire post, every single comment in the thread, and then carefully considered each point. In point of fact, I read through multiple times, then considered how we could actually do what he was talking about doing. Long story short, we're not going to be doing exactly what he described, because some of his assertions ignore basic electrical principles, such as the ampacity of Copper wiring.

1. Regarding "treatment of the power distribution subsystem as a separate entity", there is no such thing in an actual implementation. There is no, "this is the power generation subsystem mass, and this is the power distribution system mass, so if the power generation subsystem mass is low enough, then the power distribution subsystem mass doesn't matter". That kind of assertion doesn't hold water for any aerospace application, period. The mass of all required components of any actual power generating solution has to be shipped to Mars, so total mass for every bit of the power generation, distribution, and storage subsystems absolutely does matter.

2. I'm not talking about or even the slightest bit worried about "cooling the solar panels" due to shadowing or the Sun striking the panels. Given proper design and deployment that's not an actual problem. I'm talking about cooling all the power conversion equipment.

Regarding CFRP composite radiators, these would have pedestrian thermal conductivity, which is why radiator panels aren't constructed from CFRP. I've posted about Carbon Fiber (no composite, just the fibers) radiators under some of the nuclear power topics. Individual strands of carbon fibers bonded to heat pipes have excellent thermal conductivity and much lower mass than CFRP composites. CFRP would increase both mass and volume, as well as decrease thermal conductivity, providing no tangible benefit for a radiator.

Regarding aerospace power conversion equipment, the reason these aerospace systems are so inefficient is that 20%+ of the input power is lost as waste heat to economize on mass, because it's attached to an aircraft generating tens of MWs of power for a few hours at most, per flight, through an atmosphere that provides lots of cold, dense air to cool the "light but inefficient" power conversion equipment. On the surface of Mars, that's simply throwing away otherwise usable power that we can't afford to throw away, because it only increases the mass of the solar panels and provides no actual benefit. Increasing the solar panel mass to contend with gross power inverter inefficiency is a pointless endeavor.

3. There is no on-panel printed conductor, thinner than a human hair, that's also capable of carrying 1kWe, never mind 7kWe, without melting the plastic substrate or arcing over to the other conductor pathways printed onto the panel's surface, unless we're now talking about something other than the actual Flisom photovoltaic technology. The printed conductor grid on the surface of the panel has a 4.5mm spacing, which is why the product literature states that the panel dimensions can be increased in multiples of 4.5mm units.

If you up the voltage to something crazy like 1,296V (36V per panel multiplied by 36), then any attempt to carry that on-panel will arc over and destroy the panel because that will exceed the dielectric breakdown strength of the active semi-conductor material. Alternatively, conductive Iron Oxide dust sitting on top of the panel will help to complete the circuit. Either way, that's a hard no-go. If you increase the amperage, then temperature increases from resistive heating to the point that it melts the substrate. Let's assume that Blake's 36m panel is operating at 72V (2m wide panels). That's 98A of current at high noon, on the Martian equator, during the summer. No piece of plastic the same thickness as a shopping bag, with a conductive pathways less than 1mm wide, would survive that without melting, period.

If the circuit traces are pure Copper 30 microns / 0.03mm thick (obviously they're less conductive inks printed onto the plastic substrate), same 30 micron thickness as the panel, which is technically possible using a bonded film protective plastic layer on both sides, then the circuit trace has to be 261mm wide to carry 98A of current, for a 30C temperature rise. This assumes a 20C ambient atmospheric temperature at noon on the equator during the summer time. The 72m^2 of panel surface area would generate a nominal 7,056We at high noon, assuming a 14% conversion efficiency.

700W per square meter * 0.14 conversion efficiency * 72 square meters of panel = 7,056We

PCB Trace Width Calculator - Printed Circuit Board Width Tool - This Javascript web calculator calculates the trace width for printed circuit board conductors for a given current using formulas from IPC-2221 (formerly IPC-D-275).

261mm would account for 1/8th of the entire surface area of 2m^2 panel. All the visible circuit traces clearly don't account for that much surface area. The only way to achieve higher voltage is to chop up the panel into smaller segments wired in parallel. It should go without saying that raising the operating temperature to 50C, totally ignoring the temperature rise associated with sunlight, will reduce panel efficiency. You're losing 824 Watts of power to resistive heating along the 36m long conductor pathways by operating at 72V. That's obviously spread over 446 conductor elements, but that's a LOT of power to lose. Can the panel survive that, long-term, without de-laminating? Not likely. 720 grams of wiring to carry that kind of power? It had better be doped CNT or Graphene wiring, because no Copper wire with that kind of mass can carry that kind of current without literally glowing red hot.

Are we still talking about designing a solar power generating facility, or the world's largest and most expensive toaster?

tahanson43206 · 2021-05-28 06:43:57

https://www.brown.edu/news/2021-05-06/perovskite

The weakest of those interfaces is the one between the perovskite film used to absorb light and the electron transport layer, which keeps current flowing through the cell.
“A chain is only as strong as its weakest link, and we identified this interface as the weakest part of the whole stack, where failure is most likely,” said Padture, who directs the Institute for Molecular and Nanoscale Innovation at Brown. “If we can strengthen that, then we can start making real improvements in reliability.”
To do that, Padture drew on his experience as a material scientist, developing advanced ceramic coatings used in aircraft engines and other high-performance applications. He and his colleagues began experimenting with compounds known as self-assembled monolayers or SAMs.
“This is a large class of compounds,” Padture said. “When you deposit these on a surface, the molecules assemble themselves in a single layer and stand up like short hairs. By using the right formulation, you can form strong bonds between these compounds and all kinds of different surfaces.”
Padture and his team found that a formulation of SAM with silicon atom on one side, and iodine atom on the other, could form strong bonds with both the election transport layer (which is usually made of tin oxide) and the perovskite light-absorbing layer. The team hoped that the bonds formed by these molecules might fortify the layer interface. And they were right.

(th)

kbd512 · 2021-05-28 08:14:38

tahanson43206,

That's an interesting application of materials science to help solve some of the toughness problems of wafer-based cells, but reaching 80% EOL cell efficiency after only 4,000 hours of service doesn't make it seem very promising in the near term, unless this was some kind of torture testing. In the long term, this discovery could be fairly significant. However, I'm looking for near-term improvements to manufacturing processes that can increase cell durability and efficiency. I do like the fact that the researchers did "tear-down inspection" after testing. One wonders why we haven't done something similar with all of our solar cells, or maybe we have, at some point, but knowing "what's going on inside" can only help inform future manufacturing process improvements.

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