New Mars Forums

Louis, in an overflow of enthusiasm, it appears you may have created this topic in error.

Would you like to remove it and try again?

(th)

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.

Elon Musk may order SN20 to launch into orbit anyway. Yes, I agree with everything everyone has said. But Elon is following a rapid development schedule. Remember what NASA did with Saturn V. It was standard practice to test each stage separately. They did test each stage separately in a static test stand. But standard procedure called for launching each stage separately before combining them. They didn't, Apollo 4 was an "all up" test of the full stack. Yes, again, they did test each stage separately in static test stands before doing this. But they didn't launch stages separately. Elon may want to do the same thing, just to keep development pace rapid.

In case someone from SpaceX is reading this, let me give a warning. For Saturn V, they did test each stage in a static test stand. This included the first stage with all 5 engines tested at full thrust, and full duration burn, while held down in a static test stand. This gave engineers the data they needed to ensure it works. And engineers could examine engines and full stage after each test. And not everything worked the first time.

F-1 engines were tested in a separate engine test stand before integration with the stage. They had a problem at first: oscillation until the engine exploded. These were the largest rocket engines ever built. Engineers resolved that problem with baffles, designed to dampen oscillation. For the Russian N-1 rocket, they didn't build a test stand capable to testing a full stage. One Russian politician didn't believe in space, so took away money for the test stand, used it for some aircraft thing. So the first test of the Block A stage was the "full up" test of the rocket. This caused a pogo problem, the rocket exploded (RUD). Second test flight: RUD as soon as it clearing the tower. Third test flight: eddies at the tail of the rocket caused uncontrolled roll. This increased until guidance system went into gimbal lock, vehicle disintegrated due to structural loads. Fourth test flight: normal operation until shutdown of 6 core engines to reduce aerodynamic stress. Abrupt engine shutdown caused a hydraulic shock wave through the propellant feed system. In plumbing this is called pipes "hammering". This caused propellant feed lines to burst. RUD.

Wikipedia: N1 rocket - Launch history

Experience of N1 is particularly appropriate considering N1 had 30 engines. Super heavy booster has how many?

The trouble is I can see both sides
There is the scientist looking to Mars as a great untouched living Laboratory
And then there is the engineer who will transform the planet to provide homes for a human population

Do you know what is the worst problem both ideas are not only honourable but also right

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....

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.

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.

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.