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#1 2008-03-29 06:37:14

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,648

Re: Ultra thin PV film

Does anybody have any views on whether ultrathin photovoltaic film would work on Mars.

I would say at the outset that

1. I don't think wind and dust storms are a problem. I am sure we can weigh down the film with regolith and we can control dust through various measures, including blowers.

2. I don't think the lower output compared with say the Mars Rover solar panels is an issue.  The reduced mass is an incredible gain. Calculations I have done previously suggest we might be able to power a colony of six people from just a few hundred Kgs of the stuff. Land is not a problem - there is plenty of that, though obviously when we start to go some distance cabling can become an issue.

I think the main issue is whether the film would disintegrate in the extreme cold of Mars? (take a look at the Nanosolar site if you want to see what I am talking about).

Assuming that would be an issue, is there a solution? 

One possibility is to raise the temperature of the film itself, by maybe incorporating heating elements, which would keep it above a certain temperature. However, I am not sure whether that would drive the system into negative values  and make it useless.

Another possibility is perhaps to encase the film in a thin transparent  plastic coating which is resistant to degradation as this might (?) protect the thin film.

Does anyone one know how the problem of degradation of materials has been solved with the Mars Rover solar panels?


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#2 2008-04-06 12:05:46

Terraformer
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From: Lancashire
Registered: 2007-08-27
Posts: 3,225
Website

Re: Ultra thin PV film

I don't think wind and dust storms are a problem. I am sure we can weigh down the film with regolith and we can control dust through various measures, including blowers.

You took a different stance when talking about greenhouses. Please explain.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#3 2008-04-06 13:09:24

louis
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From: UK
Registered: 2008-03-24
Posts: 5,648

Re: Ultra thin PV film

There's a difference between energy generation and food production.

If the light goes because of a dust storm, you simply aren't producing energy. But the system is still there after the dust storm abates.

If the light goes in your greenhouse then your crops die and you starve. When the dust storm abates, the crops are gone.

Big difference. Of course, the energy system has to have built into it energy storage in various forms in order to tied you over the dust storm periods.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#4 2019-07-14 16:01:23

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,282

Re: Ultra thin PV film

Bumping for technology developement not sure how CNT's would work in this form of how they are made.

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#5 2019-07-14 18:27:01

kbd512
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Registered: 2015-01-02
Posts: 3,316

Re: Ultra thin PV film

SpaceNut,

More "thinking out loud" follows...

Given advances in printing methods, the material encasing the photovoltaic material is substantially heavier than the photovoltaic material.  That material is a plastic that's resistant to degradation from UV and chemical exposure.  I'm not sure how to make it much lighter than it already is.  We don't know how to make sheets of Graphene of unlimited size, but ideally we'd use Graphene instead of conductive ink as the on-cell electrical interconnects to reduce resistance losses.  The CNT's wouldn't work very well as the substrate material.  However, doped CNT's would be a much better choice than Copper or Aluminum for wiring, being substantially lighter and just as conductive as Copper.

Ascent Solar's bare modules produce 1,100We/kg to 1,400We/kg, dependent upon voltage (cell interconnect configurations).  The "lightweight" flexible modules encased in plastic are 200We/kg.  That means most of the mass is in the packaging, just like all space-rated Lithium-ion batteries.

So, perhaps the solar power satellite proposed by Louis was actually a better way to generate megawatts of power.  You need ~2,000kg/MW for a solar power satellite in orbit.  Conceptually, the solar power satellite could test Aerojet-Rocketdyne's new X-3 200kW ion engines with its megawatts of onboard power.  If we limit these things to 2MW each, then existing microwave guns developed for our nuclear fusion program / ITER are already COTS hardware.  Mars is about 2x further from the Sun than Earth and the 1.1kWe/kg to 1.4kWe/kg power ratings are for bare modules in Earth orbit.  The durable plastic-encased thin film solar panels are 5,000kg/MW or 10,000kg/MW on the surface of Mars, assuming every day is a crystal clear day.  The plastic won't do anything for durability in space, so the mass to protect the module from abrasive blowing dust can be eliminated entirely if the generating station is in orbit around Mars.

I have more faith in a lander deploying a few microwave dishes than 10+ football fields worth of solar panels, never mind keeping all those panels clean during a dust storm.  That begs the question...  Can the rest of a microwave power transmission system, irrespective of conversion losses, be engineered to be more mass efficient than a solar power array that has to be constructed and continually maintained on the surface of Mars for years at a time?  The Mars orbiters have fared far better than any of the surface rovers and landers.

You have 8,000kg/MW as the trade space to play with, so if you can put a solar power satellite in a geosynchronous-type orbit and come substantially under that figure for the complete power system, then perhaps that's a better alternative since the satellite will make rated power for almost the entire time it's overhead.  Keep in mind that during a dust storm, a solar power satellite still makes 100% of rated power and attenuation of microwaves from the dust is unlikely to be as severe as the loss of power from dust-coated panels and a nearly opaque atmosphere.  The other obvious advantage is beaming power to multiple locations at the same time.  If the ships land 10km+ away from each other, you can supply the juice to both at the same time.  The wiring runs could theoretically be reduced, so long as you're not overly-worried about a power satellite frying things that stray into the path of the power beam.  Fewer things on the surface are prone to being knocked over by a rocket taking off nearby.  Any ultra-light panels with little to no connection to the ground would have to be at least several kilometers away from the landing zone or risk being blasted into the next zip code by the exhaust from a Starship landing or taking off.

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#6 2019-07-14 19:14:28

kbd512
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Posts: 3,316

Re: Ultra thin PV film

Regarding the Gyrotron:

New Results of Development of Gyrotrons for Plasma Fusion Installations

According to the document, a 960kW output 170 GHz gyrotron is 2.6m long, weighs 250kg, and is 50% efficient.  So, a pair of these things and 2MW/4,000kg worth of Ascent Solar's thin film arrays is still just 4,500kg, or less than half of the surface mass for equivalent power.  This also excludes the mass of the propellant required to soft land on Mars.  We have so much mass margin here that I bet that a complete Argon-fueled electrically propelled solar power satellite would have equivalent or less mass when compared to any equivalent array landed on the surface.

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#7 2019-07-14 19:53:35

tahanson43206
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Registered: 2018-04-27
Posts: 2,163

Re: Ultra thin PV film

For kbd512 re #5 ...

Thanks for mentioning Louis having brought up solar powered satellites as an option for Mars ...

In your post, you mentioned microwave dishes, so I decided to offer an alternative that might be worth considering ...

https://en.wikipedia.org/wiki/Space-based_solar_power

Microwave power transmission[edit]
William C. Brown demonstrated in 1964, during Walter Cronkite's CBS News program, a microwave-powered model helicopter that received all the power it needed for flight from a microwave beam. Between 1969 and 1975, Bill Brown was technical director of a JPL Raytheon program that beamed 30 kW of power over a distance of 1 mile (1.6 km) at 9.6% efficiency.[47][48]
Microwave power transmission of tens of kilowatts has been well proven by existing tests at Goldstone in California (1975)[48][49][50] and Grand Bassin on Reunion Island (1997).[51]

Comparison of laser and microwave power transmission. NASA diagram
More recently, microwave power transmission has been demonstrated, in conjunction with solar energy capture, between a mountain top in Maui and the island of Hawaii (92 miles away), by a team under John C. Mankins.[52][53] Technological challenges in terms of array layout, single radiation element design, and overall efficiency, as well as the associated theoretical limits are presently a subject of research, as it was demonstrated by the Special Session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" held during the 2010 IEEE Symposium on Antennas and Propagation.[54] In 2013, a useful overview was published, covering technologies and issues associated with microwave power transmission from space to ground. It includes an introduction to SPS, current research and future prospects.[55] Moreover, a review of current methodologies and technologies for the design of antenna arrays for microwave power transmission appeared in the Proceedings of the IEEE[56]

The concept I remember from discussion of SPS for Earth was use of microwave antenna farms with antenna raised above the surface, so animals could graze under the antenna. The intensity of the beam under those circumstances was described as modest and not harmful, with the tradeoff being the size of the area of land to be allocated for the purpose.   On Mars (I am presuming) there would be plenty of available land. 

Robots would have to install the antenna and the wires between them, but my guess is the materials required and the complexity would be less than would be true for solar PV panels, and (again guessing) the lifetime of a field of antenna would be longer than would be true for PV panels.

(th)

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#8 2019-07-14 20:57:39

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,282

Re: Ultra thin PV film

We have talked about solar beamed back from orbit to the land below and what the power levels are which we know is involved.

We complain now about cellphone radiation so being under a recieving antenna would not be for man....

here are a few topics which ae containing microwave solar transmission as key words.

Microwave Sattelites - Sending solar energy to from orbits

A novel method for energy needs on Mars
Louis' Solar Power Strategy
Power generation on Mars

I am sure that there are many more with the recieving element and frequency of reception....

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#9 2019-07-15 03:10:59

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,648

Re: Ultra thin PV film

I think the last time I looked up this subject, solar power microwave or laser beams were still only capable of sending power a km or so at most- and not a v. powerful beam at that. I think Japan is in the lead. So although it's a technology of great promise, which would answer all countries' energy needs, potentially, I think it's unlikely to be there in the next 10 years.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#10 2019-07-15 16:27:40

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,282

Re: Ultra thin PV film

The plastic substrate with ink layers withan another protection plastic layer bonded to the first creating a sandwich of solar cell worked fine in space where the solar intensity and near zero structure to support them works good for the components mass but probably will do poorly as it ages and has micrometeor strikes to will distroy the cells over time.
Nasa did do a rollup flexible cell design but it failed to retract and was tossed overboard as yesterdays junk when they got all of the test data from it.

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#11 2019-07-15 19:48:01

kbd512
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Registered: 2015-01-02
Posts: 3,316

Re: Ultra thin PV film

More thinking out loud, but trying to find a way to do this without nuclear reactors...

As long as we're considering the infrastructure required, what if we just kept all the power to make return-to-Earth propellant in orbit?

We could avoid the hard requirement for fission reactors if we're smarter about how we use solar power.  The surface environment is brutal for photovoltaics and Lithium-ion batteries.  The dust and insolation levels during dust storms kill everything we send there, so let's skip that to the extent we can.  Even if we had robots running around every day with CO2 guns to blow the dust off the panels, it would only craze the plastic over time and there are multiple football fields of panels to keep relatively clean.  RTG's can supply always-available local power for life support functions, given the low power consumption of the new generation of life support systems.  We're talking about a few kilowatts at most and we'll have power galore during the day to make propellant or recharge batteries.  The satellites could also supply process heat for chemical reactions or for fusing / baking regolith bricks.

Perhaps we could use Na/NiCl2 batteries since those don't explode, can operate over wider temperature ranges, and last for many years.  Sodium Nickel-Chloride is not quite as energy-dense as Lithium-ion, but still 200Wh/kg+.  Lithium-ion needs to be operated outside to avoid fireworks from runaway reactions and the associated release of toxic chemicals.  Since Na/NiCl2 could be kept inside or warm at night from its own internal heat- it's a molten salt battery, the packaging mass requirements are lower.

CO + CO2 has an Isp which is entirely sufficient to reach orbit.  Zubrin stated that CO + O2 would come at an energy cost of about ~10MWh/t.  Well, if the Mars Ascent Vehicle was around the size of NIMF, the propellant could be made purely from Martian atmosphere in less than a year.  We just need MOXIE to make CO and O2, which is what it's designed to do, and will actually be tested on Mars prior to arrival.

If we also had a non-nuclear / solar-powered PROFAC in orbit that was powered by the Solar Power Satellites / SPS, it could make Argon for electric propulsion cruise power and CO/O2 for orbital transfer.  These devices skim the upper atmosphere to collect propellants over weeks to months of operation.  The propellants can then be transferred to departure stages in higher orbits.  The SPS supplies power for propulsion instead of a nuclear reactor, drastically reducing the mass of the device.  Since we don't carry return propellant from Earth, nor even from the surface of Mars, the energy requirements plummet.  Any orbit-to-orbit transfer propulsion system combining SEP with CO/O2 is much more controlled than screaming interplanetary reentries.  The SPS could also provide supplemental braking power for new comers.  CO/O2 will provide TEI thrust, whereupon an Argon-fueled SEP cruise stages take over.

Anyway, this drops our power requirements by at least half, if not to a quarter of what LOX/LCH4 requires, to say nothing of all the propellant transfer missions saved and the tons of propellant to take things to and from the surface of Mars.

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#12 2019-07-15 20:41:53

tahanson43206
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Registered: 2018-04-27
Posts: 2,163

Re: Ultra thin PV film

For kbd512 ....

Re #11 ...

? Phobos ?

(th)

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#13 2019-07-15 22:39:13

kbd512
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Registered: 2015-01-02
Posts: 3,316

Re: Ultra thin PV film

tahanson43206,

It might be a good storage depot for equipment and cryogenic propellants.  After you make the propellant in low Mars orbit, instead of constantly providing electrical power to keep it cold, you could then use the power satellites to send it to the shadow of Phobos, where it could just sit there and chill out.  Since you need less of it by using SEP in conjunction with chemical, and only as much propellant from the surface as you need to return crew to orbit, there are a lot of other things you could do with the excess power, namely construction and farming.  Equally important, this would be a mission-enabler for a set of precursor exploration missions intended to characterize the best sources of water / minerals / metals / radiation protection (lava tubes, craters, canyons).

Maybe we could skip most of the batteries and use heat engines, either molten salts or Argon, to power equipment using microwave heating from orbit.  That limits the number of critical computer-controlled systems that can be killed by radiation or exposure.  Despite their inefficiency, heat engines work pretty reliably here on Earth and there's no reason it won't work on Mars.  It could give crewed surface vehicles functionally unlimited power without massive batteries.  Given enough power sat launches, there'd always be satellites overhead to provide power, no matter where you happened to be.  Polar exploration would be extraordinarily difficult without this technology, but we could get all the water we wanted by melting chunks of ice.

Many years ago, Lockheed-Martin figured out how to make high-powered airborne lasers achieve maximum coherency at a point in space beyond the emitter aperture using a technology called "adaptive optics" (fancy terminology that just means electromagnetically "bending" a lens to cause the laser to achieve maximum coherency on the target- in ABL's case Sidewinder missiles).  We've also figured out how to do that with microwaves:

Pinpoint microwave resolution could lead to wireless power transfer

They took a 30cm microwave beam and focused it on a target 1.5cm in diameter.  Basically, the receiving station could have a very small CNT rectifying antenna, or a molten salt tank, with a power density approaching a small nuclear reactor.

Useful for understanding delivered power:

Environmental impact of high power density microwave beams on different atmospheric layers

Space Launch Applications:

Space Applications of High Power Microwaves

PROFAC paper:

PROFAC and PHARO: Changing Perceptions of an Idea in Aerospace

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#14 2019-07-16 06:02:03

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,648

Re: Ultra thin PV film

I am not sure the surface environment is "brutal" for PV. At least, we know PV systems have worked on Mars for multiples of their specified life - over a decade in some cases I think.  We also know that PV systems on Earth still work well in Arizona and the Sahara after much worse dust storms. The wind power on Mars is very weak so I don't think we have any evidence that there will be significant damage. Dust particles as far as I know don't do any damage in and off themselves - it is only through powerful impact that they do lasting damage. Obviously we are looking for space rated PV owing to the absence of a thick Earth-like atmosphere.

The requirement for Mission One is simply to enable the establishment of a permanent base. Mission Two will bring in further PV power equipment and the people on Mars will have access to a large store of methane and oxygen to run generators by then.

Let's suppose your Mission One system degrades by 20% over 4 years and that you bring in a similar size system for Mission 2. That means at the end of four years you have a capacity that is 170% over the 100% starting point at Year Zero on Mission One. But you still only have to prepare one Starship for return, even if you've doubled the number of people from 6 to 12.

You can stick with a single Starship return probably for the first decade but your energy system is growing all the time, allowing you to grow food indoors and to produce large stocks of storage fuel that will see you through any sort of disaster that might come your way.

Yes there will be degradation in output through dust accumulation (rather than dust damage).  Robots to blow off dust make perfect sense. If you have 56K sq. metres of PV then blow cleaning them at a rate of maybe 2000 sq. metres a day (400 sq metres per hour for say a 5 hour single shift) ie just under 7 sq. metres per minute or just over ten seconds per sq. metre: blow sequence (6 seconds), move (4 seconds)....so one clean every 28 sols.  If I'm being optimistic then use two robot rovers. They don't need to be v. large - similar to the bomb-defuser tracked robots. 

Again, safe battery usage on Mars is well established. Yes, statistical risks might rise but this will be a safety-first mission. I am sure any battery storage will incorporate monitoring and fire suppression.

Solar power satellites will be perfect for Mars, but the technology is still several decades away it would seem.

I don't see any problem with an essentially PV Plus Storage mission with storage achieved via either methane/oxygen (given we have to produce it in any case - if we are talking about a Space X mission) or chemical batteries.  The technology is all there, as far as I can see. Barring something statistically improbably - like a meteor impact that could equally destroy a KP reactor - I think this is a failsafe route.

The main issue is the trade off between mass and efficiency for PV.  Obviously you want to hit the sweet point there.


kbd512 wrote:

More thinking out loud, but trying to find a way to do this without nuclear reactors...

As long as we're considering the infrastructure required, what if we just kept all the power to make return-to-Earth propellant in orbit?

We could avoid the hard requirement for fission reactors if we're smarter about how we use solar power.  The surface environment is brutal for photovoltaics and Lithium-ion batteries.  The dust and insolation levels during dust storms kill everything we send there, so let's skip that to the extent we can.  Even if we had robots running around every day with CO2 guns to blow the dust off the panels, it would only craze the plastic over time and there are multiple football fields of panels to keep relatively clean.  RTG's can supply always-available local power for life support functions, given the low power consumption of the new generation of life support systems.  We're talking about a few kilowatts at most and we'll have power galore during the day to make propellant or recharge batteries.  The satellites could also supply process heat for chemical reactions or for fusing / baking regolith bricks.

Perhaps we could use Na/NiCl2 batteries since those don't explode, can operate over wider temperature ranges, and last for many years.  Sodium Nickel-Chloride is not quite as energy-dense as Lithium-ion, but still 200Wh/kg+.  Lithium-ion needs to be operated outside to avoid fireworks from runaway reactions and the associated release of toxic chemicals.  Since Na/NiCl2 could be kept inside or warm at night from its own internal heat- it's a molten salt battery, the packaging mass requirements are lower.

CO + CO2 has an Isp which is entirely sufficient to reach orbit.  Zubrin stated that CO + O2 would come at an energy cost of about ~10MWh/t.  Well, if the Mars Ascent Vehicle was around the size of NIMF, the propellant could be made purely from Martian atmosphere in less than a year.  We just need MOXIE to make CO and O2, which is what it's designed to do, and will actually be tested on Mars prior to arrival.

If we also had a non-nuclear / solar-powered PROFAC in orbit that was powered by the Solar Power Satellites / SPS, it could make Argon for electric propulsion cruise power and CO/O2 for orbital transfer.  These devices skim the upper atmosphere to collect propellants over weeks to months of operation.  The propellants can then be transferred to departure stages in higher orbits.  The SPS supplies power for propulsion instead of a nuclear reactor, drastically reducing the mass of the device.  Since we don't carry return propellant from Earth, nor even from the surface of Mars, the energy requirements plummet.  Any orbit-to-orbit transfer propulsion system combining SEP with CO/O2 is much more controlled than screaming interplanetary reentries.  The SPS could also provide supplemental braking power for new comers.  CO/O2 will provide TEI thrust, whereupon an Argon-fueled SEP cruise stages take over.

Anyway, this drops our power requirements by at least half, if not to a quarter of what LOX/LCH4 requires, to say nothing of all the propellant transfer missions saved and the tons of propellant to take things to and from the surface of Mars.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#15 2019-07-16 14:54:51

louis
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From: UK
Registered: 2008-03-24
Posts: 5,648

Re: Ultra thin PV film

Alta Devices have developed lightweight thin PV film for space-rated applications.

https://www.altadevices.com/space-innov … echnology/

Sounds like their sort of technology might be right for Mars.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#16 2019-07-16 17:20:11

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 18,282

Re: Ultra thin PV film

Public service anouncement

The website tried to negotiate an inadequate level of security.

www.altadevices.com uses security technology that is outdated and vulnerable to attack. An attacker could easily reveal information which you thought to be safe. The website administrator will need to fix the server first before you can visit the site.

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#17 2019-07-16 17:22:59

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,282

Re: Ultra thin PV film

Solar panels in the desert are glass not thin film plastic....

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#18 2019-07-17 17:12:59

louis
Member
From: UK
Registered: 2008-03-24
Posts: 5,648

Re: Ultra thin PV film

Have you got any evidence to show that thin film plastic cannot be used in desert conditions?  They are used on high flying planes. They are space rated - resistant to high UV. I am not clear what you are claiming.



SpaceNut wrote:

Solar panels in the desert are glass not thin film plastic....


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#19 2019-07-17 19:17:31

kbd512
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Registered: 2015-01-02
Posts: 3,316

Re: Ultra thin PV film

Louis,

In order for a plastic sheet to be flexible, it has to be soft.  If something is soft, then it can be scratched by abrasive powder.  The regoliths on the moon and Mars are abrasive powders.  The thin film CIGS cell technology from Ascent Solar is ink-jet printed on a thin, soft (and therefore flexible) plastic substrate.  The solar panels on our Spirit and Opportunity rovers were bare, non-flexible silicon wafer-based cells.  They were much more robustly built, therefore heavier, and attached to a rigid backing plate for deployment.  JPL's contractors fabricated wiring onto the top of those panels to create an electrostatic field to repel dust particles.  From time to time, they sent electricity back through the wiring on the panels to remove some of the dust.  However, at no time was all the dust removed.  The wind, weak as it is, also removed some of the dust.  It also caused dust accumulation at other times.  That was why they always looked like trucks that had been through a mud hole.  Curiosity looks pretty much the same as Spirit and Opportunity.  Unfortunately, all that dust also seriously affected power output, as well as the servos, motors, and bearings.

This isn't really news, though:

[Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)

Here's Curiosity:

Curiosity is still dirty! How will the ExoMARS Rover keep its solar panels dust-free and collecting sufficient power?

A little more detail on how dust affects the panels:

Managing PV Power on Mars – MER Rovers

An answer regarding why there were no "wipers" installed on the dust panels (response from Mark Adler, Mars Exploration Rover Spirit Mission Manager):

Why weren't wipers installed on the solar panels of the Spirit and Opportunity?

From the article:

As for the various means, wiper blades are quite heavy and complex, prone to failure (as anyone with a car knows), could not be flexible enough in the extremely cold environment to both cover the cell surfaces and not damage them, and most importantly, the best possible wiper blades wouldn't even work very well! The atmospheric dust particles are incredibly fine, on the order of three microns in diameter, and adhere to the panels by van der Waals forces, so the wiper blades wouldn't be able to get all of the dust off. Quite a bit would be left. If some sand somehow also made it up on the panels (maybe kicked up by the wheels), then the wipers could damage the cells by rubbing sand on them. So forget wipers. They're a terrible idea.

The reasonable approaches were articulated panels that could be turned vertically to allow the expected low level of winds to blow the dust off; electrostatic repulsion, which would lift the dust and again allow the low winds to blow the levitated dust away; and a simple compressed air tank and a blower arm to directly blow the dust off. These means could also be used in combination. But simply making the panels bigger was a better solution than all of those.

As it turned out, Mars has been generous enough to provide solar panel cleaning for us. What Mars taketh, Mars sometimes giveth back. We certainly didn't expect that, but it has extended the life of the rovers from months to years. Many years. Each Martian year there is a season in which solar panel cleaning events occur overnight, erasing many months of accumulation in a single night. This can happen for several nights. It is not deterministic though, and one Martian year Spirit didn't get any cleaning events. That, compounded with some other problems, resulted in the loss of Spirit with the last contact being in March 2010. More than six (Earth) years after landing. Opportunity is still going strong today, coming up on (fingers crossed) 12 years after landing!

So...  Losing 0.29% of the output per Sol for something that has to produce megawatts of power is approaching a very significant degradation of output over the course of a month or so.  That means something has to constantly keep the panels clean.  Your weekly cleaning requirement was about right.

From Nomad Desert Solar (regarding the challenges of using solar panels used in deserts here on Earth):

Problem:

Dust build-up is the greatest technical challenge facing a viable, desert solar industry.

* A 0.4-0.8% per DAY baseline yield loss caused by dust.
* 60% energy yield losses during and after sand storms are widely reported.
* If left more than a day, dust particles from organics, dew and sulfur adhere to the panels.

Solutions:

* Expensive, unreliable, human labour in harsh, remote desert conditions.
* Water (desalinated, transported and wasted).
* Complex, sensitive equipment, that will fail in harsh conditions.
* Cleaning cycles of 7-14 days causing greater output losses, adhered dust and dust storm vulnerability.
* High operational expenses
* Long-term dependence on volatile labour markets

I'm sure labor prices aren't a consideration for Mars, but the autonomous robotics required to assure reliable cleaning will be.

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#20 2019-07-17 19:33:33

louis
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From: UK
Registered: 2008-03-24
Posts: 5,648

Re: Ultra thin PV film

Well dust accumulation is not the same as dust abrasion. Dust accumulation will not be a serious problem on Mars because we will have ways of cleaning the PV arrays - most likely rovers using gas jets.

Dust abrasion is one of the causes of a permanent reduction in power output, but that requires a force (most obviously wind) to drive the dust particles against the PV encapsulation surface. But IIRC the wind power on Mars is 1/8 that on Earth. So I think we can expect far less abrasion.

You are asserting that thin film is much more subject to abrasion than glass, but I have never read that anywhere. Do you have any evidence for the claim?  A soft surface (by not offering resistance to the particle but rather allowing it to "settle")  is as likely to lead to less abrasion I would surmise. But happy to be corrected if you have some evidence!

kbd512 wrote:

Louis,

In order for a plastic sheet to be flexible, it has to be soft.  If something is soft, then it can be scratched by abrasive powder.  The regoliths on the moon and Mars are abrasive powders.  The thin film CIGS cell technology from Ascent Solar is ink-jet printed on a thin, soft (and therefore flexible) plastic substrate.  The solar panels on our Spirit and Opportunity rovers were bare, non-flexible silicon wafer-based cells.  They were much more robustly built, therefore heavier, and attached to a rigid backing plate for deployment.  JPL's contractors fabricated wiring onto the top of those panels to create an electrostatic field to repel dust particles.  From time to time, they sent electricity back through the wiring on the panels to remove some of the dust.  However, at no time was all the dust removed.  The wind, weak as it is, also removed some of the dust.  It also caused dust accumulation at other times.  That was why they always looked like trucks that had been through a mud hole.  Curiosity looks pretty much the same as Spirit and Opportunity.  Unfortunately, all that dust also seriously affected power output, as well as the servos, motors, and bearings.

This isn't really news, though:

[Opportunity: The Amazing Self-Cleaning Mars Rover (Photos)

Here's Curiosity:

Curiosity is still dirty! How will the ExoMARS Rover keep its solar panels dust-free and collecting sufficient power?

A little more detail on how dust affects the panels:

Managing PV Power on Mars – MER Rovers

An answer regarding why there were no "wipers" installed on the dust panels (response from Mark Adler, Mars Exploration Rover Spirit Mission Manager):

Why weren't wipers installed on the solar panels of the Spirit and Opportunity?

From the article:

As for the various means, wiper blades are quite heavy and complex, prone to failure (as anyone with a car knows), could not be flexible enough in the extremely cold environment to both cover the cell surfaces and not damage them, and most importantly, the best possible wiper blades wouldn't even work very well! The atmospheric dust particles are incredibly fine, on the order of three microns in diameter, and adhere to the panels by van der Waals forces, so the wiper blades wouldn't be able to get all of the dust off. Quite a bit would be left. If some sand somehow also made it up on the panels (maybe kicked up by the wheels), then the wipers could damage the cells by rubbing sand on them. So forget wipers. They're a terrible idea.

The reasonable approaches were articulated panels that could be turned vertically to allow the expected low level of winds to blow the dust off; electrostatic repulsion, which would lift the dust and again allow the low winds to blow the levitated dust away; and a simple compressed air tank and a blower arm to directly blow the dust off. These means could also be used in combination. But simply making the panels bigger was a better solution than all of those.

As it turned out, Mars has been generous enough to provide solar panel cleaning for us. What Mars taketh, Mars sometimes giveth back. We certainly didn't expect that, but it has extended the life of the rovers from months to years. Many years. Each Martian year there is a season in which solar panel cleaning events occur overnight, erasing many months of accumulation in a single night. This can happen for several nights. It is not deterministic though, and one Martian year Spirit didn't get any cleaning events. That, compounded with some other problems, resulted in the loss of Spirit with the last contact being in March 2010. More than six (Earth) years after landing. Opportunity is still going strong today, coming up on (fingers crossed) 12 years after landing!

So...  Losing 0.29% of the output per Sol for something that has to produce megawatts of power is approaching a very significant degradation of output over the course of a month or so.  That means something has to constantly keep the panels clean.  Your weekly cleaning requirement was about right.

From Nomad Desert Solar (regarding the challenges of using solar panels used in deserts here on Earth):

Problem:

Dust build-up is the greatest technical challenge facing a viable, desert solar industry.

* A 0.4-0.8% per DAY baseline yield loss caused by dust.
* 60% energy yield losses during and after sand storms are widely reported.
* If left more than a day, dust particles from organics, dew and sulfur adhere to the panels.

Solutions:

* Expensive, unreliable, human labour in harsh, remote desert conditions.
* Water (desalinated, transported and wasted).
* Complex, sensitive equipment, that will fail in harsh conditions.
* Cleaning cycles of 7-14 days causing greater output losses, adhered dust and dust storm vulnerability.
* High operational expenses
* Long-term dependence on volatile labour markets

I'm sure labor prices aren't a consideration for Mars, but the autonomous robotics required to assure reliable cleaning will be.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#21 2019-07-17 19:48:37

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,316

Re: Ultra thin PV film

Louis,

I'm not saying it's impossible, but you're really stacking the deck against your survival.

The people I've quoted in the previous post are all telling you the exact same things I've been saying.

All the simple / easy solutions aren't.  No such thing as a free lunch.

Things you don't think are major problems are very difficult to overcome here on Earth, never mind Mars.

Thin film with protective plastic is no better, weight-wise, than heavier but more durable silicon wafer, but does require significantly more surface area.  It can be stored in less volume, though, which is an important consideration at this scale.  On the plus side, it does produce significantly more power at off-optimal Sun angles and that is very important.

Space has more radiation, but it also has a lot more power, no dust, nearly 100% of available power is on tap until the power satellite slips over the horizon, far less propellant and available payload capacity has to be spent on power provisioning, and deployment is vastly simplified.  I didn't think this was possible in the past due to the inefficiency of available high power gyrotrons, but ongoing research for our fusion program has substantially improved their efficiency.

A simple CNT wire can make a suitable rectifying antenna, which is extraordinarily light, or you could have a heat engine with a power density approaching that of many nuclear reactors, but without the substantial mass requirements.  At least in theory, this seems like a pretty good way to use solar power and heat engines to provide lots of power wherever it's required.  If your drilling operation is 20km+ away from the landing site, you don't need to erect a solar array there, you just point one satellite or a "spot beam" at the drill site's rectenna.

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#22 2019-07-17 20:10:41

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,282

Re: Ultra thin PV film

https://en.wikipedia.org/wiki/First_Solar

cadmium telluride (CdTe)-based photovoltaic (PV) modules, which produce electricity with a thin CdTe film on glass

These typically have a metal backer or extra heavy pane glass thats tempered. Glass is heavy to deliver to mars....

This not what is truely a thin film solar cell as its not flexible....

Panels that are glass protected as earlier described
300px-02-09-15_First_Solar_Desert_Sunlight_Solar_Farm_(15863210084).jpg

https://en.wikipedia.org/wiki/Topaz_Solar_Farm

They use the First  CdTe photovoltaic modules based on thin-film technology....Other types of glass panels use the crystal grown process which make them heavier still.

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#23 2019-07-17 20:20:09

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,316

Re: Ultra thin PV film

Louis,

I'm asserting that fine dust abrades soft plastic.

You can believe it doesn't as much as you wish, but it won't change how that process works.

Regarding something harder being less subject to abrasion damage than something softer, I can't believe you need evidence of that.

Did you skip shop class in high school where you sanded both wood and metal with a piece of sand paper?

Unless my eyes and muscles deceived me, it took considerably more effort to sand the steel than it did the wood, to the point where the top of one of the tables I made from wood and steel was sanded by hand and I sanded the steel using a belt sander.

Why do you think we coat drill bits meant for high speed use with diamond?

The diamond is a hell of a lot harder than the metal, even a carbide, and will cut through the work material faster.

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#24 2019-07-18 16:47:40

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 18,282

Re: Ultra thin PV film

With any good solar cell panels that we will use on Mars we will need an equally good quality battery to go with them. The Musk powerwall and new powerwall2 have some new nearly the same capability from some other vendors. see musk topic....

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#25 2019-07-18 17:51:09

kbd512
Moderator
Registered: 2015-01-02
Posts: 3,316

Re: Ultra thin PV film

SpaceNut,

I would suggest that a battery with a broader operating / charging temperature range (something that can actually take a charge at lower temperatures, rather than just putting something on the sticker that says it operates at a given temperature without expressing what the real performance would be at the extreme ends of the operating temperature range), that is not prone to exploding or rupturing when shorted, is probably a better idea.

FIAMM SoNick battery for Energy Storage Systems - FIAMM ST523 620 V 22.5 kWh

The SONICK Battery by FIAMM

Yes, it's heavier than Lithium-ion.  It weighs 564lbs.  However, look at the cycle life at 80% DoD and notice how little volume it occupies.  Each ORU is 430lbs and the thermal regulation ("heater") plate is ~85lbs.

FIAMM ST523
Weight: 564lbs
Dimensions: 24.6" W x 40.2" L x 16" H
Capacity: 22.5kWh
Containment: Completely sealed

Aerojet-Rocketdyne ISS ORU
Weight: 435lbs (ORU) 85lbs (adapter plate); 520lbs (total)
Dimensions: 37" W x 41" L x 21" H
Adapter Plate: 36" W x 41" L x 15" H
Capacity: 15kWh
Containment: Open to preclude a cell rupture from destroying the other cells in the pack

ISS Lithium-ion ORU Test Data:

International Space Station Lithium-Ion Battery Status

Lithium-ion can work without catastrophic events from single cells, but it won't look much like a Tesla Power Wall when you're done and will definitely weigh quite a bit more:

Design Guidelines for Safe, High Performing Li-ion Batteries with 18650 cells

Assessment of International Space Station (ISS) Lithium-ion Battery Thermal Runaway (TR)

International Space Station Lithium-Ion Battery

ISS Thermal Management Systems:

Active Thermal Control System (ATCS) Overview

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