• How large would the intermediary battery need to be?
• What voltage should a system like this run on?
• Do I need any other parts other than solar controller, battery, inverter?
• Is there any off the shelf system that could handle this, either partially or completely (and that is not outrageously overpowered or expensive!)

10-20 kWh capacity minimum (ideal would be at least 2 times thesize of the tesla battery), Also depends on where you are located ,how much driving per day you do . number of hours of sunshine (usable sunshine) per day you get. The 2100w solar system is too small to keep up with the charging. 2100 x 5hours max production is just 10 kW a 21000w system is 105 kW
How often you want to charge the car ? The assumption is that you would charge during the day for a solar charge system to work. But if you up the size of the battery bank to 160 kWh storage capacity and only use 20 kW per day that gives you 7-8 charges you could use the car during the day charge it at night.
51.2-51.8v 16s LiFePO⁴ 14s NMC, any of the 3.6-3.8v nominal lithium cells. these voltages work with most 48v lead acid based inverters
There are inverters that take higher voltages.
A bms is required for all lithium based ESS
Tesla powerwall, LG RESU, There are many most have a high price. DIY for large systems one of the best resources around for DIY powerwalls is Second Life Storage & Solar
later floyd

 

The 2100w solar system is too small to keep up with the charging. 2100 x 5hours max production is just 10 kW a 21000w system is 105 kW

That's really confusing when you don't use the right units of measure for power and energy. This was presumably supposed to be:

The 2100 W solar system is too small to keep up with the charging. 2100 W x 5 hours per day max production is just 10 kWh per day, a 21000 W system is 105 kWh per day​

How often you want to charge the car ? The assumption is that you would charge during the day for a solar charge system to work. But if you up the size of the battery bank to 160 kWh storage capacity and only use 20 kW per day that gives you 7-8 charges you could use the car during the day charge it at night.

Good point, but again one of the units was mangled:

But if you up the size of the battery bank to 160 kWh storage capacity and only use 20 kWh per day that gives you 7-8 charges you could use the car during the day charge it at night.​

 

If the car is home every day, and if the car's battery capacity is high enough that you don't need to worry about charging it every day, then the intermediate battery at worst only need to store one day of solar generation, to be transferred to the car after the end of the day. As floydr noted, that might be 10 kWh. If you want to use the solar system to power anything else off-grid, I would think that you would want about that much energy storage anyway.

 

Yep, with only 2100w of solar, this is a waste of time and money. It'll take well over a week for the panels to output enough energy to fully charge your tesla. You'll probably want a system that is at least 8000w.

 

If the solar system can deliver - for instance - about 10 kWh per day, that's enough to drive the car at least 50 kilometres per day in reasonable conditions. If that meets the owner's needs (whether it is 50 km each day, or a 200 km trip every four days, or whatever), then the system will work.

Seasonal variations will be the big problem, with winter both greatly reducing energy production and substantially increasing energy demand (for the same distance driven).

 

What is ~2100 W peak ? Is that your total wattage of the PV array, your calculated estimate based on the geographic multiplier ?

 

So as mentioned, this is going to be a slow way to charge a car, but I am going to assume that you know this, and your intention is to use the big battery pack of the car to basically do opportunity charging, and not try and rely on a 2kw array to completely fill your battery every day.

If you were connected to a grid, I would agree that this was going to be more hassle than it was worth, but if you want to charge off-grid, then the situation is a bit different, as there are not really a lot of other options.

The part I am not sure on is if you can tell the EVSE or the onboard charger to only deliver/accept a certain amount of current. With my Jerry-rigged truck, I can just tell it to charge at whatever level I want it to, and then set that at just below what my panels can produce. If that is possible with your setup, then you should be able to just size the inverter to be able to deliver your peak power, and put in battery with enough capacity to run the charger for like maybe an hour? Just enough to give you a bit of buffer for clouds or whatnot. It will likely mean you have to babysit it while it is charging, but it should work just fine.

If you cannot throttle down the amount of current, then you would likely need to increase the size of the array and inverter to handle whatever the charger is rated for. I dont really know anything about real electric car chargers, basically you need to recreate whatever sort of circuit it needs, have enough panels to run that load, and enough batteries to pick up the slack for a little while. Also, as mentioned, you will need plenty of time to babysit it. But, you get the satisfaction of knowing you can charge up your car in the event of a zombie apocalypse. The self-driving feature will be nice when you want to hang out of the window and fire your machine gun with both hands.

 

The part I am not sure on is if you can tell the EVSE or the onboard charger to only deliver/accept a certain amount of current.

An AC EVSE is just a smart on/off switch - it can't control current except to shut it off entirely, and to tell the vehicle how much is available; the onboard charger controls the charging rate. The good part of this is that the onboard charger should stay within what the EVSE says is available, within the limits of the J1772 protocol presumably used.

 

I brought it up in another similar thread, but folks can also take a look at this :

SUNNY BOY-US

The Sunny Boy-US features Secure Power Supply, which now delivers up to 2,000 W of opportunity power when the grid goes down and the sun is shining. Installation has never been easier thanks to SMA’s Installation Assistant, direct access via smartphone, and integrated DC disconnect. Independent input channels, each with OptiTrac™ Global Peak MPP tracking, mean hundreds of stringing configurations while solving the challenges of complex roofs and shading. Through innovative improvements, the Sunny Boy US helps you decrease costs throughout all stages of the project cycle.

So basically it may be possible to build a charging setup that will operate opportunistically without a battery altogether. It may not work as well, but it will be a lot easier / cheaper to build.

 

I have no idea where subutai is in Sweden, but insolation in most of southern Sweden is over 1000 kWh per year, per kW of array capacity. So a 2100 W array should yield over 2100 kWh per year, or 5.7 kWh per day (the 10 kW estimate would not be valid as a year-round average). As noted above, with the entire country at least 55° latitude, the seasonal variation is huge.

This is a trend (should display for two complete years of 2020 and 2021, but tweak the sliders if it doesn't) for a commercial solar farm in southern Alberta, a bit further south than the southern tip of Sweden: Brooks Solar
The large-scale pattern of output shows the changing length of day; the day-to-day variations within that are due to weather. If you zoom right into to a good day you can see that output goes right up to the rated 15 MW capacity, but of course only at mid-day in clear weather. The annual output of this facility has been about 21 GWh per year, or about the 1400 kWh per kW of array capacity expected in its location, but a mid-summer month produces several times as much energy as a mid-winter month.

 

https://iea-pvps.org/wp-content/uploads/2021/10/National-Survey-Report-of-PV-Power-Applications-in-Sweden-2020.pdf

 

Thank you for all the brilliant replies. I know the system is quite small, but as @brian_ has pointed out, with 5 solar hours I estimate to be able to drive at least 50 km per day in the summer charging only off solar. I have already considered the size of the solar system and the implications for how many kilometers that will get me, but I appreciate everyone chiming in to confirm my calculations.

For some context, and yes I know I am crazy, but I am planning to make this system entirely portable. The plan is to drive south one summer and challenge myself to see how far south I can get using only solar that I bring with me. I know it's ridiculous, but people have done crazier things . And also, solar radiation average per year only counts if the system is stationary, right? The main purpose of my system is to be used during the summer, when even Sweden gets a lot of solar radiation.

This is also why I considered the Jackery 1500 because it's reasonably packaged and portable. A powerwall or such a massive 8 kWh+ system is not an option (and way out of my budget). And as some have pointed out, the solar will only output ~ 8 kWh in a day at most. So really what I'm getting at is I'm trying to estimate the lower limits of a battery system. If the battery fills up that's fine, I will take that opportunity to charge the car. I know it's very unpractical, but that's fundamentally what makes this a challenge!

@cricketo I'm not entirely familiar with the language, but as far as I understand, peak is what the solar system puts out at noon. It's probably redundant language. I plan on building a system with 12x175W panels if that's more clear!

@OR-Carl The Tesla on-board charger is able to limit how much current it draws from the grid. I have no idea how it works, but the range is between 4 A and 16 A on the European grid. That's why I estimate the min inverter output to be around ~1200W.

 

You already have a big battery in the Tesla, how many kWh?

That 50km,you think uses how many kWh?

the Jackery 1500 is how many Wh?

price per kWh?

8kWh is not a big battery for this use case?

Where are you carrying the 12 panels?

Are you planning to deploy them by the side of the road in a spot with no trees?

 

You already have a big battery in the Tesla, how many kWh?

That 50km,you think uses how many kWh?

the Jackery 1500 is how many Wh?

price per kWh?

8kWh is not a big battery for this use case?

Where are you carrying the 12 panels?

Are you planning to deploy them by the side of the road in a spot with no trees?

The Model 3 LR has about 68 kWh of usable battery. If I avoid driving at highway speeds, I think I can get consumption down to 140 Wh/km, so 50 km would require ~7 kWh (+charging losses) or about 10% of the usable battery. In theory I could park the car in an open space and set up the solar and let it charge for a week no problem. Then I could drive up to 350 km in one go.

Jackery 1500 - it's in the name. It's a 1500 Wh battery. Price per kWh? Not sure what this question means so please clarify! In terms of 8 kWh storage I think it's overkill, since the battery would just be a buffer between intermittent/unpredictable solar and the car's battery. I doubt the battery would ever get close to full if I do this challenge. Capacity is not the limiting factor for a portable system, charging rate is.

How to carry the panels is a solvable problem. I have plenty of ideas but nothing set in stone. I'd preferably park somewhere with no shade for charging yes Thanks for all your questions!

 

I like a challenge ( why else would I be building an Ev) good luck on the challenge. When I first responded I assumed that this was a stationary set up my bad. Since it is a portable system build a system like @cricketo suggests could work. Solar panels to an off grid solar pure sine wave inverter 230v eliminate the battery. https://www.amazon.com/s?k=300+watt+solar+panel+flexible a couple of the 1200w kits , an offgrid/hybrid 2.4-3 kW pure sine wave 230v solar inverter to AC EVSE. if necessary put a small 2 kw LiFePO battery in the system. The flexible solar panels 300 watt are 1.2m x .5m x 2.5mm + junction box 2kg . There should be room in a model 3 for 8 300w flexible solar panels.
This is for one summer? Not a multi year summer project. From what I have read the flexible panels have problems lasting for very long. Good luck
Later floyd

 

Really appreciate your responses! I'll try to address each one.

I like a challenge ( why else would I be building an Ev) good luck on the challenge. When I first responded I assumed that this was a stationary set up my bad. Since it is a portable system build a system like @cricketo suggests could work. Solar panels to an off grid solar pure sine wave inverter 230v eliminate the battery. Amazon.com : 300 watt solar panel flexible a couple of the 1200w kits , an offgrid/hybrid 2.4-3 kW pure sine wave 230v solar inverter to AC EVSE. if necessary put a small 2 kw LiFePO battery in the system. The flexible solar panels 300 watt are 1.2m x .5m x 2.5mm + junction box 2kg . There should be room in a model 3 for 8 300w flexible solar panels.
This is for one summer? Not a multi year summer project. From what I have read the flexible panels have problems lasting for very long. Good luck
Later floyd

I think unfortunately a battery is a must unless I want to modify the car. The car will not accept charge at a lower power than ~1 kW so if I want to be able to use the solar power even when the output from solar is less than 1 kW, a battery is a must. I'll probably build a smaller prototype this summer and then reuse parts for a larger system next year. Sucks to hear that flexible panels lose power so quickly, but I don't think rigid panels are an option when going portable. Cheers.

Interesting! I see it is more of a "The Martian" situation than "Mad Max", but I think the basic idea seems valid. I suggest you do some experiements to see how low you can actually get the consumption to go by driving slower so you have an idea of what to expect. There is probably a sweet spot between reducing drag and not having a bunch of angry cars behind you as you putter along. At least most of Sweden is flat, so you wont have to worry too much about hills. You dont happen to live in Dalarna, do you?

Flexible solar panels would save a lot of space and weight, and they do wear out after a couple of seasons. I have some that I think are maybe 4 years old, and they dropped to about 50% output. That Jackery power unit seems like it would likely work, but you could also put something like it together yourself and have more flexibility to do repairs and or upgrades.

Your basic components should include a battery, an inverter, a charge controller and some sort of meter. You would be wise to think about how you are going to rack your solar panels too. I am currently running my shop with a solar panel propped up on buckets, but it does not give optimal results, to say the least. A 2000W array will be fairly large. To get the most sun, tracking the sun would help, which will be easier if you are not having to fiddle with a dozen panels leaning against rocks and things 😀 . Also, MC4 connectors are sort of a hassle to undo, and it might be worth thinking about swapping them for some other suitably sized quick connector.

You're absolutely on point Carl. I'm not in a hurry at all, so hypermiling isn't necessary even though I lose efficiency to drag when going faster. I think targeting something like ~70 km/h (45 mph) is reasonable, even though the Model 3 has best mileage around ~45 km/h (~30 mph).

After looking at some other portable setups, I agree that something like the Jackery could work, but it is indeed a bit expensive. DIYing the system sounds like a better solution for sure for the exact reasons you gave.

For sure a lot of thought is going into how to rack the solar panels. I have been thinking a lot about weight, stability, reliability, and being able to angle the panels for best efficiency, especially since the sun is far down on the sky even in summer this far up north. I found the system at Tier 4 Solar to be pretty much state of the art in terms of these criteria, but obviously I would need even more portability.

I suspect that will not provide 2100W peak at noon. That is just the nameplate capacity, but that's where the the geographic multiplier comes in, which basically takes the latitude into account. For example for Oregon, which is significantly further South, 0.8 is used. So if I wanted 2100W of peak output I'd actually need a 2500W worth of panels. Though to be honest I don't know if they take the angle into account - typically stationary systems are installed at 30 degrees, which is sort of an average angle for year round operation. My optimal summer angle would be about 20 degrees I believe.

Either way, I do have some experience with the mobile solar systems too, and I would say even 2kW will be quite a pain to position at an optimal angle and without shading

Thanks for the advice about geographic multiplier. I've been trying to find such a number so that really helps me with estimating charging times etc. I think a smaller prototype will also be really helpful in that regard.

I have been doing some research into battery systems, and as far as I can tell, LiFePo4 batteries generally limit the input power to about half of the output power. Maybe this is for overheating protection? But it seems like if I want a battery to be able to receive 2000W from the solar panels, I would need at minimum something like a 250 - 300 Ah 12V battery (3000-3600Wh). Please correct me if I am wrong.

 

Interesting! I see it is more of a "The Martian" situation than "Mad Max", but I think the basic idea seems valid. I suggest you do some experiements to see how low you can actually get the consumption to go by driving slower so you have an idea of what to expect. There is probably a sweet spot between reducing drag and not having a bunch of angry cars behind you as you putter along. At least most of Sweden is flat, so you wont have to worry too much about hills. You dont happen to live in Dalarna, do you?

Flexible solar panels would save a lot of space and weight, and they do wear out after a couple of seasons. I have some that I think are maybe 4 years old, and they dropped to about 50% output. That Jackery power unit seems like it would likely work, but you could also put something like it together yourself and have more flexibility to do repairs and or upgrades.

Your basic components should include a battery, an inverter, a charge controller and some sort of meter. You would be wise to think about how you are going to rack your solar panels too. I am currently running my shop with a solar panel propped up on buckets, but it does not give optimal results, to say the least. A 2000W array will be fairly large. To get the most sun, tracking the sun would help, which will be easier if you are not having to fiddle with a dozen panels leaning against rocks and things 😀 . Also, MC4 connectors are sort of a hassle to undo, and it might be worth thinking about swapping them for some other suitably sized quick connector.

 

12x175W

I suspect that will not provide 2100W peak at noon. That is just the nameplate capacity, but that's where the the geographic multiplier comes in, which basically takes the latitude into account. For example for Oregon, which is significantly further South, 0.8 is used. So if I wanted 2100W of peak output I'd actually need a 2500W worth of panels. Though to be honest I don't know if they take the angle into account - typically stationary systems are installed at 30 degrees, which is sort of an average angle for year round operation. My optimal summer angle would be about 20 degrees I believe.

Either way, I do have some experience with the mobile solar systems too, and I would say even 2kW will be quite a pain to position at an optimal angle and without shading

 

I think the battery is going to be an integral part, if nothing else to buffer the voltage for the inverter. If this was a conventional off-grid system, I would say go with lithium, and size it so that the battery can accept the full charge current ... However, this is not really a conventional system. The idea is that all the power that comes in, goes right back out again, so even if 2000w is being generated (and others are right to point out that actual output will not be the same as nameplate output) then 2000w will be going out the inverter, and the charge current that the battery will see will be essentially zero. Of course if the inverter were to shut off for any reason, suddenly the battery is going to get full current. A charge controller with adjustable setpoints should be able to handle that fairly well. By setting a pretty low max voltage, a sudden rush of current would push the battery voltage to "full" and the controller would pare back current to maintain the float voltage. Disabling the absorb charge might be a good call.

Honestly, I would be inclined to think that 2x12v flooded lead batteries in series might be just the ticket. They would not even really need to be deep cycles. I would agree that 12v would be too many amps - but 48 seems like overkill. 24v should be plenty to handle 2kw of array, and lead acids are pretty tolerant of abusive charging. I looked at the specs for those spiral-cell batteries, which claims it has no max charge rate as long as the voltage is held to 15.6v and the temperature does not exceed 50C. Lead would add a bit of dead weight, but are also cheap - so they could be rode hard and then scrapped without breaking the bank.

 

I would agree that 12v would be too many amps - but 48 seems like overkill.

Here is a datasheet comparing some 230v inverters https://www.outbackpower.com/downloads/documents/inverter_chargers/fxr_vfxr_e/FXR_E_specsheet.pdf
surprisingly to me efficiency differences between input voltages aren't very dramatic, but this is certainly a quality brand too. Either way, one needs to remember to subtract at least 10% from the DC->AC conversion when sizing the system.

 

Thanks again for insightful replies. It's certainly an unconventional setup. Did not know that the current could be limited at the charge controller, that's really good to know. Cricketo, regarding oversizing the array, I don't think it's an option for a portable setup. I'd much rather make sure to push every watt out of the solar panels than not be able to use them if they deliver less than 1 kW (which if we are reasonable, will be probably 80-90% of the day this far up north).

I will consider lead batteries if the budget requires it, but since the setup is both charging and discharging the batteries, I assume this will essentially "extend" what counts as a full cycle so I'm not too worried about wearing them out. Even a 200Ah LFP battery costs less than $1000 as far as I can tell which is reasonable considering the cost for the PV.

I'm definitely a rookie regarding voltage pros/cons so I appreciate the input. If I go with 24v instead but the panels are 12v, I assume I would need to combine parallel and series (2s6p if that's the correct language?). I've heard connecting solar panels in series could limit the output if one of the panels is covered though? Should this be a concern in that case?

I also assume I would want to get two 100 Ah 12V batteries and wire them in series if I go with a 24V setup instead of a single 200 Ah 12V? If this is the case, would it be worth the trouble, what is the downside of pushing high current in low voltage?

 

Even a 200Ah LFP battery costs less than $1000 as far as I can tell which is reasonable considering the cost for the PV.

200Ah at what voltage ?

 

The downside to high amperage is how much copper you need to move it around. Charge controllers are also limited to how much current they can pass, so an 80amp unit can only handle 960 watts at 12v, but 1920 watts if you double the voltage to 24. At 48 volts, it would handle 3840W of output - but that is likely more array than you will want to haul around.

Lithium will give you a lot more output for the same nominal AH rating, since you can discharge it a lot deeper. However, they are a lot more delicate, so you would probably want to make sure you had enough capacity to handle your max solar output. It looks like a 24v 100AH battery should be okay with 100A charging current, which would be able to handle your proposed ~2kw array.

Ampere Time 24V 100AH LiFePO4 Deep Cycle Lithium Iron Phosphate Battery for RV 791755563703 | eBay

Automotive Grade Lithium Battery： Ampere Time lithium iron batteries have exceptional quality since they are manufactured by Automotive Grade LiFePO4 Cells with higher energy density, more stable performance & greater power. Highest-level safety based on UL Testing Certificate for the cell...

www.ebay.com

 

The downside to high amperage is how much copper you need to move it around. Charge controllers are also limited to how much current they can pass, so an 80amp unit can only handle 960 watts at 12v, but 1920 watts if you double the voltage to 24. At 48 volts, it would handle 3840W of output - but that is likely more array than you will want to haul around.

Lithium will give you a lot more output for the same nominal AH rating, since you can discharge it a lot deeper. However, they are a lot more delicate, so you would probably want to make sure you had enough capacity to handle your max solar output. It looks like a 24v 100AH battery should be okay with 100A charging current, which would be able to handle your proposed ~2kw array.

Ampere Time 24V 100AH LiFePO4 Deep Cycle Lithium Iron Phosphate Battery for RV 791755563703 | eBay

Automotive Grade Lithium Battery： Ampere Time lithium iron batteries have exceptional quality since they are manufactured by Automotive Grade LiFePO4 Cells with higher energy density, more stable performance & greater power. Highest-level safety based on UL Testing Certificate for the cell...

www.ebay.com

Brilliant. That's very enlightening. Definitely sounds like 24v is the best voltage to go with for the system.

200Ah at what voltage ?

Sorry. 12v battery. Most batteries I can find on Amazon or the like are 12v, but I guess there are 24v batteries and larger if one knows where to look!

I still wonder about the PV array, whether a 24v system means I would wire pairs in series to get 24v and whether that would affect the output in case one is covered? Or does this vary depending on the panel? Perhaps it's better to just look for 24v panels instead (if that's a thing)?

 

If he manages to harm himself with a 24v solar array I will laugh; but I would also encourage the OP to do as much research as possible on the subject. The shading thing, as pointed out can be a problem. If they were installed on a roof. Since they are going to be on the ground, on well designed, portable, adjustable stands (right?, you could just ... move it so the shaded cell gets full sun. If you are really concerned, bring an electric chainsaw.

12 volt panels are more common in the small sizes - I am not sure if I have seen a 24v version of a flexible panel - they might be out there. Running two 12v panels in series would work fine. They usually state the max series voltage - usually it is something crazy, like 600v. I would give some thought to finding a different connector, though, as plugging and unplugging a whole bunch of MC4 connectors every day is going to be annoying. Just make sure it is safe-ish. Also, I expect some pictures of your solar powered vacation for all this free advice 😀!

 

If he manages to harm himself with a 24v solar array I will laugh

230V AC isn't very funny - I've tried.

 

With good MPPT SCs the voltage of the panels can go much higher, get away from cheap chinese consumer toys up to the larger residential / industrial units.

Victron at the low end is fine with 60V, quickly gets up to 100V and higher

Gives the MPPT algorithm more headroom to optimise efficiency. Also, lets you have one SC per panel, much better handling of partial shade issues.

Makes no difference to the solar, if your storage backbone is 12, 24 or even 48V and no need for inefficient "boost" conversion.

The challenge is finding these panels nearby, you do not want to pay shipping.

Best is to stay in touch with pro installers in your area, they order by the pallet, end of the job may have leftovers to sell.

 

The semi-flex panels have a very short lifespan.

They are meant to be slightly flexed only at installation, onto a perfectly rigid (non flexing) substrate, e.g. a gently curved concrete building.

They cannot flex at all in use. They also require a heat sink below, often with a gap for airflow.

By the time you're done, the framed rigid glass panels are stronger and lighter.

The USA vendors have discontinued them in jurisdictions with better consumer protection regimes.

 

The semi-flex panels have a very short lifespan.

They are meant to be slightly flexed only at installation, onto a perfectly rigid (non flexing) substrate, e.g. a gently curved concrete building.

They cannot flex at all in use. They also require a heat sink below, often with a gap for airflow.

By the time you're done, the framed rigid glass panels are stronger and lighter.

Yes, all of this is true, with the possible exception of the heatsink, which I have never used on a flexible panel, but I have never mounted them flat on a surface either (nor is the OP suggesting this). For reference, the type I am talking about are these:

Amazon.com

The stock photo is wildly deceptive - they are much too stiff to be easily bent like depicted.

Anyway, despite all of this being true, none of it is really relevant to some sort of ground-mounted array of these panels. compare them to this panel:

Amazon.com

The flexible one weighs 4 lbs, and is .1 inches thick, the other one is 14 lbs and 1.4inches thick. Glass panels are going to weigh 280 lbs for a 2kw array, vs 80lbs for the flexible ones. You will also not be able to flex them at all as you have to stuff them into the trunk.

So stronger - yes - but I still think that the flexible panels are a better fit for the use criteria.

 

So long as you don't mind replacing them frequently.

And that is, even if mounted on rigid metal like 1/2" plate. The car body steel flexes too much, and the underside gets VERY hot.

Average 2-3 year lifespan would be optimistic in any mobile context.

 

No one is talking about wind as in nature

but the airstream flow from driving at speed.

Yes, if you are driving at say 20km those forces will be less.

But again, those fraudulently marketed "flex" panels stop working very quickly if they are allowed to flex AT ALL after being installed, and all of the scenarios you suggest are absolute non starters.

Unless you don't mind purchasing replacement units as a weekly consumable expense

Not very green.

You designing and building the framing / mounting required to let these panels last even a few months on average

will cost and weigh far more than just buying the standard rigid glass panels already including the required framing

So, if that latter style will not work for you, the project is not practical.

Maybe epoxying DIY cells to the vehicle skin directly, but again, not enough power production.

 

But again, those fraudulently marketed "flex" panels stop working very quickly if they are allowed to flex AT ALL after being installed, and all of the scenarios you suggest are absolute non starters.

Are you basing this on any actual first hand experience?

This just all sounds like the bitter rambling of an old curmudgeon to me. If you dont think this project is a worthy use of time, then go contribute your free advice somewhere else.

 

I reckon once you start talking about several fixed panels, Your probably better making a 'solar charge trailer' and towing that, rather than trying to get it on the roof of the car. It'll be too heavy for the racks and frame and it'll place all that weight up high, which will affect the center of gravity and wind drag while driving.

A trailer could easily be set up to have multiple panels fold out, 3 at least, maybe even 6 depending on the hinge design and folding mechanism.

You'll still have a drag penalty with a trailer, but Id expect it to be a lot lower than a bulky structure on a roofrack, But it has the bonus of only being there when its being towed. If your just getting around town, you don't need to tow it with you.