MPPT (or whatever) to use 4 series small panels as "charger" for 14s EIG NMC battery

amberwolf

amberwolf

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Now *I* have a question; I know just enough to know it's possible, but not exactly how:

I picked up four PV panels at goodwill for about $33, my guess is they're worth about that, at best, but I missed out on the last ones I saw there, figured if I can't use these I can resell them. None are visibly cracked, etc. They do "work"; was already after sunset but light enough sky when I got home to test open-circuit voltage. By the time I got done feeding the dogs it was dark so I parked the trike under the new LED yard light, put the panels across the top of the canopy, and hooked them up in series to a 48vdc computer fan, but not enough power to run it, dropped to about 4v at the input to the fan. Was actually surprised they generated even that much power.

Three of them look like the ones I've seen in the "harbor freight" 3-panel 50w kit; each has it's diode box on the back with wires and ring terminals. All three labels are damaged/old, so I had to concatenate the info below from what I could read off of each of them, so stuff could be missing or wrong. Pics of all the labels are attached.
Maximum Power Pmax 15w +/-5w
Rated Voltage Vmp 17.5v
Rated Current Imp 0.86A
Open Circuit Voltage Voc 23.5v
Short Circuit Current Isc 1.15A
(unreadable) AM1.5.10000W/M2

The fourth is a Kyocera KC40T from 2006, it has diode in a box on the back and seems to also have a diode box on the panel:
At 47C (probably closer to what it would run at here in Phoenix, vs the 25C rating it also shows), it's a 30w panel, Vpmax 15.3v, Ipmax 1.97A, Voc and Isc are not given. 1000Wm2, AM1.5
At 25C it's a 43W panel, 17.4v, 2.48A, 21.7V, 2.65A. 800Wm2, AM1.5
Max system voltage 600v, series fuse 6A, mass 4.5kg


Now, the point is I'd *like* to run them all in series with an MPPT or whatever, that would let me connect them to the trike batteries, so that whatever power does come in from them can be pushed into the batteries. The SB Cruiser presently uses a 14s2p "52v" 40Ah NMC EIG pack, and my charger on the trike puts them up to 57.7v max.

I'm assuming whatever is used would have to be an adjustable-voltage output boost/buck type, with adustable-current limiting output like a charger (or one of those would have to be added on the output of the MPPT/whatever is used).


It's probably impractical, not worth doing on the trike itself. But figured I'd look into it, since the trike does use a lot of power, and much of the time I'm going places it's near the middle of the day (or completely at night), so while riding and parked outside it might get a little bit of extra charge.

I'm sure the panels weigh as much in total as just adding another 14s1p (20ah) to the pack, along with the MPPT or whatever is used to convert panel to battery voltage...but the panels can go on top of the canopy, and the battery would have to go in the cargo/seatbox, which hasn't really got the room.


So, anyway....ideas? Thoughts?




.
 

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I don't have a lot of experience with the low voltage panels, but from memory anything around the 12 V range is usually managed by a PWM charge controller. 24 V and up will likely use an MPPT charge controller.
Also, once you move past 24 V it's not camping gear country any more.
 
Genasun makes MPPT boost controllers, not sure of the top voltage output.

No need to serial connect unlike panels I think would hurt efficiency, and definitely any little shadow would derate production way too much.

I'm guessing you know you're filling a 44gal drum through a drinking straw. . .
 
If you put three of the panels in series you could feed output directly to your 14s battery as long as you have a BMS or other method of protecting the battery from overcharge. You could also connect them through a switch and only feed current to the battery while you are riding.
 
No BMS; haven't needed one for anything. Charger takes care of HVC, and controllers (and CA) take care of LVC.

But with teh solar, there wouldn't be an HVC if directly connected. :/

So I will need something to take care of that (in the highly unlikely event it sits in the sun long enough to actually get that much charge), and an MPPT is the "best" option that I know of (but I've no experience, only what I've read here on ES over the years, really).


There's no point in just having it charge while I ride, as almost all my rides are only minutes long, a half hour at most, these days. But it may sit in teh sun for two or three hours while I'm at my destination, and that might get me 100wh (maybe). (at work it sits inside, so it wouldn't get much from the overhead lights ;) ).


Power is pretty reliable around here these days, and rarely goes out at all, much less for long enough to need some sort of solar charger or backup bank, so I don't really "need" these at all, much less at home stationary (where they might do more good--I've considered setting them up to charge batteries to run yard lighting, rather than running wiring out to that lighting from the house).



I looked up Genasun
https://genasun.eu/collections/genasun-lithium-mppts
https://cdn.shopify.com/s/files/1/0062/2959/0114/files/Genasun_GVB-8_Datasheet-ETL-2018.pdf?5193887046331177433
but as I expected, they're out of my price range, especially for a "whimsy" project. (already blew my budget for a while on the Honda-IMA-Lebowski project: https://endless-sphere.com/forums/viewtopic.php?f=30&t=105711 )
Looks like typical prices are somewhere around $170-$200 for the "56.8v" version of the lithium boost MPPT. Been a little tough searching cuz half the stuff I find is only the lead-acid versions (even if it comes up in a search only for lithium versions, excluding the lead-acid).

I can't find this one
https://genasun.eu/collections/genasun-lithium-mppts/products/genasun-gvb-8-lithium-50-59-9v-custom-voltage-mppt
so I assume it's only available directly from Genasun, and set by them to the voltage you specify, rather than an adjustable one? (which is what i'd prefer).
 
There just isn't a big enough market to make things competitive above 24V.

Victron's SmartSolar little 75/15 at 12 / 24V, serial connect for discharging.

Or boost convert the output separately, get an adjustable HVC specifically for this, cut off the SC from the panel inputs.

Actual output for a 100W panel figure maybe 3-400 Wh from all day in ideal conditions. Tilt angle helps.
 
I have one of those Victron Smart Solar controllers on my camper charging a large 6 s battery bank. I down convert to 12v for the camper circuits and use a 24v inverter for AC applications. It works very well and I love being able to monitor it with my cell phone via Bluetooth.
In Amberwolf’s situation if he can come up with a high voltage cut off, the resistance of the batteries themselves will keep the output of three panels (~51 to ~60 volts) pretty much in line with the maximum power point without the expense of a charge controller. And since he has the panels he should at least try it.
It is fun to have the bragging rights to say that your transportation is powered by the sun.
 
After coming home early from work today (sick with something intestinal), I did go ahead and try it, at midday. I'd used alligator clip test leads to connect the panels together previously, but for this test I bolted the ring terminals of the three identical panels together, and then bolted a pair of anderson PP45s to the outer +/- leads to be able to plug into the charger port (in place of the built-in charger).

Open-circuit, the 3 panels are about 60v at that time, full sun exposure. (56v before wiping the dog slobber spatters off of them, accumulated in the time since bringing them home and starting this thread :roll: )

The Kyocera panel outputs about 20v open circuit, so I gave it a shot to see if it might power up the 48v fan--and it does, dropping down to about 18v, running the fan at roughly half-speed or a bit less. I left the fan angled to blow on the backs of the panels, which are laid across the top of the open-frame area behind the canopy on the trike.

Connected to the battery, the three panel set drops down to the battery voltage itself, about 52v at that time. Current is only 0.56A, so that's about 30w, which is about what I would expect from these. Since I've used about 14Ah since the last time I charged the trike, it's not going to charge up enough before sunset to worry about, so I left it going and went to lay down for a while. Still feel pretty bad after a nap, so not getting back up yet, but i can at least post about it.


So I can use them like this, until eventually I decide what to do....but I'm not likely to build a mounting for them on the trike for a while. Got too much else to do with the HIL controllers project first, and then the rear wheel/dropouts/frame upgrade.
 
I hope you are feeling better today.
I kind of expected more than .56 amps at 52 volts but I’m used to working with larger panels. I guess every little bit helps but you have proved that it wouldn’t be worth spending a couple hundred dollars on a charge controller.
 
Actually feeling worse today....but the panels are only rated for 0.86A anyway, according to what I could read of the labels (as noted in a previous post), so I wasnt' expecting much current, especially with a half-charged battery.

The Kyocera is rated much higher, nearly 2A...but I only have one of those. If they were all that type, it'd be great.


If it werent' about 80v opencircuit, I'd be tempted to connect all four panels in series and see what the charge rate is, but if anything went wrong, somehow disconnecting the battery (whcih shouldn't be possible, but...murphy), it would blow up my motor controllers. :/ I'd have to setup a separate battery (which I have) and put the spare CA on that, to see what I get.


So for now, this at least proves they *could* be used to get me a bit more range, if I happened to be stuck somewhere without access to an outlet, in the middle of the day, and needed to get to someplace that did have an outlet, to then charge enough get home. ;)


But I expect the extra aero drag and the extra weight would cause enough extra power usage, over the 30 miles+ that it would take to empty my battery, to more than negate the amount of charge i could get out of the panels.


A few more stats; current dropped down to less than a third of an amp by late afternoon / evening, and by near-sunset was negligible but still positive, in the hundredths of an amp. Re-angling the panels perpendicular to the sun didn't even bring it back up to a tenth of an amp, but did increase it several times what it was with them still pointing nearly straight up on top of the trike. Voltage on the battery didn't change enough for me to notice, still 52.something, the entire time.

(the trike itself uses about 0.08a continuously while turned on, which is necessary for the charge port to connect to the battery. If I were to actually mount these on the trike, I'd have to create a separate charge path for them with it's own switch and monitoring device (or use the solar firmware for the CAv3, and lose the preset switch, and have to rewire where the CA gets it's power so it can be powered from either source, via diodes)).


The three identical panels weigh a little more than 10 pounds each, so about 31 pounds to get this tiny amount of extra charge. Much much better weight ratio to just add another 40Ah pack, which is only another few pounds (if there was room). The kyocera is what it says on the back, a little more than 4kg, about 9 pounds. If I could trade the three identical ones for three more of these kyoceras, I'd do that. ;) They'd fit better on (or as) the trike canopy, too. :lol:


Some pics, of the panels laid on top of the trike as I used them yesterday, and of the fan powered by the Kyocera panel, and of Kirin and Jelly being bored and trading places (Yogi was smart enough to just stay inside out of the heat).
 

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amberwolf said:
Maximum Power Pmax 15w +/-5w
...
(unreadable) AM1.5.10000W/M2
Click to expand...

It's +/- 5% (+/-5W would be huge on a 15W panel). The unreadable part is "Standard Test Conditions" or STC and refers to the conditions at which all the voltage and current are measured. They're temperature and irradiance dependent, respectively, so the printed values are only valid at 25°C cell temperature and 1000 watts per square meter irradiance. The 1.5 "Air Mass" of atmosphere is only relevant for the parts of the light spectrum which are filtered out by the atmosphere and can safely be ignored for our terrestrial purposes.

When designing traditional residential PV systems, we need to know the absolute highest voltage the panels will produce and the lowest MPP voltage. The first is to ensure we don't over-voltage the inverter and the second is to ensure the inverter doesn't shut down on a hot day due to low input voltage. We calculate these values using the temperature coefficient of voltage which is typically found on the datasheet. Here's a good resource which explains the details.

These appear to be thin film panels so we can estimate using a similar-looking thin film panel I randomly found online (PDF datasheet). The temp. voltage coeff. is -0.31%. The record coldest temp for Phoenix, AZ is -8°C which is 25-(-8) = 33°C below STC so our absolute maximum Voc would be 23.5*(1-33*(-0.0031)) = 25.9V per panel or 77.7V for 3 in series. Using 0°C as the low temp gives us 76Voc. Battery resistance will bring this down some but I don't think I would directly connect these panels to a lithium battery without some sort of HVC protection.

The lowest Voc will occur on the hottest day which is 50°C record ambient temp plus 30°C for the cells heating up so 3*23.5*(1+(80-25)*(-0.0031)) = 58.5Voc.. so the good news is that the voltage should be high enough on a hot day to fully charge your battery.


amberwolf said:
I'm assuming whatever is used would have to be an adjustable-voltage output boost/buck type, with adustable-current limiting output like a charger (or one of those would have to be added on the output of the MPPT/whatever is used).
Click to expand...

I've never come across a commercially available boost/buck solar charge controller. They seems to always be one or the other although you may find a non-solar-specific boost/buck converter would work well enough for your needs even without MPPT.

You can find solar boost converters on eBay for as little as US$40-45 including shipping. Grin Tech sells the black one. The green model on eBay has some weird quirks like shutting down when a cloud passes overhead and not resuming charging when the sun comes out again but it's just a default setting you can change, according to some YouTube videos I've watched. The Genasuns I use will not charge if the PV input is higher than battery voltage so I have to make sure that my highest PV Voc is lower than my battery's lowest voltage. If these Chinese controllers have the same behavior, you could connect your 3 panels in parallel with the trade-off that you lose a little efficiency from the charge controller due to the lower input voltage.

Come to think of it, the Vmp of the Kyocera panel is close enough that you could connect all 4 panels in parallel to the same boost charge controller. At $45, this is your best bang for your buck?

These cheaper Chinese boost controllers are not waterproof and they have a loud fan but several of The Sun Trip participants, including Justin, have used these with some success so I think they're worth a look. Unlike the Genasuns, the output voltage is user-adjustable.


amberwolf said:
Now, if I had one good panel the size of the top of the trike (roughly eight feet long by just under three feet wide ), that could produce 200-300w, at something like 60v (or just under) open-circuit (ideally 58v so it could literally never overcharge), I could direct-connect the panel to the battery and just leave it that way, and it would just get any energy available, whenever there was any, and it might be worth carrying around, at around 4A or so charge current.

I poked around a teeny bit, and found nothing at that voltage for that wattage of panel, but I did find several in that wattage range that would physically fit in the space available, and weigh around 40lbs (so no more than the four I have now, but much better efficiency). The closest stuff I found was about 40v-45v....
Click to expand...

Based on the 40 lbs (18 kg), it sounds like you were looking at traditional panels made with glass and an aluminum frame. These can be found for around US$0.80/watt new but there are some deals out there for used panels. Here's a listing in Gilbert, AZ: $35 for a 270W panel. Freight shipping will cost a fortune but maybe the seller would agree to local pickup? The panel voltage would need a boost converter but maybe it's worth it at this panel price? Oh, wait, that one is 61 lbs. Ooof. How about this 250W, 41 lb panel for $50 from the same seller?

At around US$2/watt, you can find semi-flexible panels which weigh only around 10 lbs for the same 250 watts but we're in a different budget category there.

If you're committed to doing this without a charge controller, you'll want to string together enough cells to give you 58Voc on a hot day. Most of the used panels out there appear to be polycrystaline types so using -0.34%/°C Voc temperature coefficient and 0.62Voc/cell from this datasheet gives us 58/((1-(80-25)*0.0034)*0.62) or 115 cells. Rounding up, this would be two 60-cell panels in series which is much bigger than what you're looking for (and you'd still need HVC protection).
 
PS: A 250 watt solar panel in Phoenix, Arizona with 90% charge controller efficiency and 10% shading losses would average the following watt-hours per day. (source)

Phoenix-250w-panel.png

You guys get some serious sun. There's a reason the U.S. Global Horizontal Irradiance map looks like this:

US-GHI.jpg
 
Thank you very much for the detailed reply! :)

I'm a bit under the weather and overwhelmed with projects (not unusual) and the dayjob, so will get back to this with questions once I digest the info you've provided. :)


solarEbike said:
amberwolf said:
Maximum Power Pmax 15w +/-5w
...
(unreadable) AM1.5.10000W/M2
Click to expand...

It's +/- 5% (+/-5W would be huge on a 15W panel). The unreadable part is "Standard Test Conditions" or STC and refers to the conditions at which all the voltage and current are measured. They're temperature and irradiance dependent, respectively, so the printed values are only valid at 25°C cell temperature and 1000 watts per square meter irradiance. The 1.5 "Air Mass" of atmosphere is only relevant for the parts of the light spectrum which are filtered out by the atmosphere and can safely be ignored for our terrestrial purposes.

When designing traditional residential PV systems, we need to know the absolute highest voltage the panels will produce and the lowest MPP voltage. The first is to ensure we don't over-voltage the inverter and the second is to ensure the inverter doesn't shut down on a hot day due to low input voltage. We calculate these values using the temperature coefficient of voltage which is typically found on the datasheet. Here's a good resource which explains the details.

These appear to be thin film panels so we can estimate using a similar-looking thin film panel I randomly found online (PDF datasheet). The temp. voltage coeff. is -0.31%. The record coldest temp for Phoenix, AZ is -8°C which is 25-(-8) = 33°C below STC so our absolute maximum Voc would be 23.5*(1-33*(-0.0031)) = 25.9V per panel or 77.7V for 3 in series. Using 0°C as the low temp gives us 76Voc. Battery resistance will bring this down some but I don't think I would directly connect these panels to a lithium battery without some sort of HVC protection.

The lowest Voc will occur on the hottest day which is 50°C record ambient temp plus 30°C for the cells heating up so 3*23.5*(1+(80-25)*(-0.0031)) = 58.5Voc.. so the good news is that the voltage should be high enough on a hot day to fully charge your battery.


amberwolf said:
I'm assuming whatever is used would have to be an adjustable-voltage output boost/buck type, with adustable-current limiting output like a charger (or one of those would have to be added on the output of the MPPT/whatever is used).
Click to expand...

I've never come across a commercially available boost/buck solar charge controller. They seems to always be one or the other although you may find a non-solar-specific boost/buck converter would work well enough for your needs even without MPPT.

You can find solar boost converters on eBay for as little as US$40-45 including shipping. Grin Tech sells the black one. The green model on eBay has some weird quirks like shutting down when a cloud passes overhead and not resuming charging when the sun comes out again but it's just a default setting you can change, according to some YouTube videos I've watched. The Genasuns I use will not charge if the PV input is higher than battery voltage so I have to make sure that my highest PV Voc is lower than my battery's lowest voltage. If these Chinese controllers have the same behavior, you could connect your 3 panels in parallel with the trade-off that you lose a little efficiency from the charge controller due to the lower input voltage.

Come to think of it, the Vmp of the Kyocera panel is close enough that you could connect all 4 panels in parallel to the same boost charge controller. At $45, this is your best bang for your buck?

These cheaper Chinese boost controllers are not waterproof and they have a loud fan but several of The Sun Trip participants, including Justin, have used these with some success so I think they're worth a look. Unlike the Genasuns, the output voltage is user-adjustable.


amberwolf said:
Now, if I had one good panel the size of the top of the trike (roughly eight feet long by just under three feet wide ), that could produce 200-300w, at something like 60v (or just under) open-circuit (ideally 58v so it could literally never overcharge), I could direct-connect the panel to the battery and just leave it that way, and it would just get any energy available, whenever there was any, and it might be worth carrying around, at around 4A or so charge current.

I poked around a teeny bit, and found nothing at that voltage for that wattage of panel, but I did find several in that wattage range that would physically fit in the space available, and weigh around 40lbs (so no more than the four I have now, but much better efficiency). The closest stuff I found was about 40v-45v....
Click to expand...

Based on the 40 lbs (18 kg), it sounds like you were looking at traditional panels made with glass and an aluminum frame. These can be found for around US$0.80/watt new but there are some deals out there for used panels. Here's a listing in Gilbert, AZ: $35 for a 270W panel. Freight shipping will cost a fortune but maybe the seller would agree to local pickup? The panel voltage would need a boost converter but maybe it's worth it at this panel price? Oh, wait, that one is 61 lbs. Ooof. How about this 250W, 41 lb panel for $50 from the same seller?

At around US$2/watt, you can find semi-flexible panels which weigh only around 10 lbs for the same 250 watts but we're in a different budget category there.

If you're committed to doing this without a charge controller, you'll want to string together enough cells to give you 58Voc on a hot day. Most of the used panels out there appear to be polycrystaline types so using -0.34%/°C Voc temperature coefficient and 0.62Voc/cell from this datasheet gives us 58/((1-(80-25)*0.0034)*0.62) or 115 cells. Rounding up, this would be two 60-cell panels in series which is much bigger than what you're looking for (and you'd still need HVC protection).
Click to expand...

 
Hope you feel better soon.

Upon further reflection, it occurred to me that my explanation makes it difficult to see the bigger picture. This chart might help make it clearer why the voltage range of these (or any other) solar panels is unsuitable for direct connection to a lithium battery. The Vmp is always too low to deliver maximum power to your battery and the Voc is always too high to connect safely, hence the need for DC-DC converters.

Screen Shot 2020-05-18 at 10.28.30 AM.pngspreadsheet
 
Thanks--that helps; I see the issue.

But these particular panels aren't really worth the weight of carrying them on the trike (at least, not the generic (possibly harbor-freight) ones, that I have three of).


I poked around at the links, and SantanSolar is about 45-50ish miles away by trike depending on route, which puts them within range without recharging if I used three of my 40Ah packs (the one built in, plus two more strapped down in the cargo area), though it would be an all-day trip at around 15mph average (call it 4 hours there and 4 back, plus however long to look at and pickup and strapdown panel(s)).

They have some deals that if I were to be making a small solar system for the house seem good, though some of the lower price stuff on ebay is listed as "white label", and they say those have "snail trails that don't affect power output", but they look like cracks in teh cells to me, which would seem to *have* to affect power output.


These
https://www.ebay.com/itm/Used-270W-72-Cell-Polycrystalline-Solar-Panels-270-Watts-No-Vinyl/283875977866?hash=item421853aa8a%3Ag%3AzQwAAOSwRRVbtmmy&LH_ItemCondition=3000
*appear* to be the cheapest deal. They say "missing outside vinyl layer" but I'm not sure if that means they don't have the layer of protection on the surface against damage, or what, exactly.

Their specs are listed as
Rated Power: 270W
Open circuit voltage (VOC): 44.4 V
Max power voltage (VMP): 35.5 V
Short circuit current (ISC): 8.25 A
Max power current: 7.60 A
Power Tolerance 0/+3%
Maximum system voltage: 600V (UL)
Fuse Rating: 15 A
IP65 Junction Box w/ standard solar connectors
Frame: Anodized aluminum alloy
Weight: 61.7 lbs
Dimensions: 77 x 39.05 x 1.81 inch
Click to expand...
which as you pointed out means I'd have to use an MPPT on one to put it on the trike (as only one would fit, and not enough voltage for direct connection), but it would also provide perhaps twice the power as the 3 generics in the experimental "package" I started this thread with. ;) However, it's also twice the weight, and I could almost have another 80Ah (4kwh) of battery for that weight, tripling the size of the battery I have on there now.


I guess at this point, I'm probably better off not worrying about the panels on the trike itself, except maybe making a mount for them to put on there "for show" just to show that I *could* charge it from solar.

In the meantime, I may use the Kyocera panel to run a DIY "gable fan" just so I don't have to run regular AC power up to one, or remember to turn it on, etc--it'd automatically run as long as there's enough sun, whcih is generally when it's most needed anyway to vent the hot air from the attic.
 
amberwolf said:
But these particular panels aren't really worth the weight of carrying them on the trike (at least, not the generic (possibly harbor-freight) ones, that I have three of).
Click to expand...

Definitely not. Thin film is around half the efficiency of traditional crystalline silicon so twice the surface are and twice the weight for the same power, assuming both panels use glass. I figured these were just a starting point.

amberwolf said:
They have some deals that if I were to be making a small solar system for the house seem good, though some of the lower price stuff on ebay is listed as "white label", and they say those have "snail trails that don't affect power output", but they look like cracks in teh cells to me, which would seem to *have* to affect power output.

These https://www.ebay.com/itm/Used-270W-72-Cell-Polycrystalline-Solar-Panels-270-Watts-No-Vinyl/283875977866?hash=item421853aa8a%3Ag%3AzQwAAOSwRRVbtmmy&LH_ItemCondition=3000 *appear* to be the cheapest deal. They say "missing outside vinyl layer" but I'm not sure if that means they don't have the layer of protection on the surface against damage, or what, exactly.
Click to expand...

"Mfg labels have been removed" tells me these were possibly warranty claims or a factory recall. I've been involved in a couple of projects where panels were replaced under the power warranty. Those warranties don't cover cosmetic defects so I would expect some power loss due to aging and the cell cracks. At $35/panel, even if the 275 watt panel is down to 200 watts, that's still only $0.18/watt compared with $0.80 for a new panel. If you're thinking of getting the Chinese boost controller, I would consider getting that first and taking it with you to check the panel output before buying?

I'm not sure what the missing vinyl is referring to. Modern PV module backsheets use specialized plastics like Tedlar as a moisture barrier and are part of the laminated structure and would not normally be removable without destroying the panel. If longevity of the panel is important to you, this is a red flag.

amberwolf said:
... it would also provide perhaps twice the power as the 3 generics in the experimental "package" I started this thread with. ;) However, it's also twice the weight, and I could almost have another 80Ah (4kwh) of battery for that weight, tripling the size of the battery I have on there now.
Click to expand...

I though you were only getting 30W from the generics? This should provide significantly more than double, no? But 62 lbs is definitely too heavy. The 41 lb. 250 watt panel begins to compete with a 38 lb. 2kWh battery in Arizona in the summer months and a 10 lb. 250 watt semi-flex panel delivers significantly more daily Wh per pound than a battery which is charged once per day.

It's hard to beat a battery for compact size and rain-or-shine power delivery where grid charging is conveniently available. Solar is mostly a touring game.
 
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