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Old 02-10-2021, 03:47 PM   #1
Mini-Skoolie
 
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310w Panels

So I found a guy north of me that orders and sells panels. He has 310w panels for $120 each. Brand new. I exchanged some text messages with him and it all seems to be on the up-and-up, but am I missing something or is there something I should be aware of?

His listing on Craigslist (I can't link it here since my PC blocks CL...thanks employer...) says they are Rec Solar 310 panels with a 21yr warranty. The warranty will be void when they are installed on a vehicle, but I don't know if that's "normal" or not. They are listed with 4mm glass, 39" x 78", and weigh just under 60lbs.

Any input you think I should have would be greatly appreciated. My intention is to put 2 of them on my roof.

Thanks all!
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Old 02-10-2021, 07:45 PM   #2
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We use REC panels and they are quality stuff. We get ours from Northern Arizona Wind and Sun, in part because their prices are fair and in part because they're local to us and I used to work with some of the employees there. Here's a link to one of their REC panels, just so you can compare specs and price to what you're looking at.

https://www.solar-electric.com/rec-s...tt-module.html

Most manufacturers won't cover mobile installation just due to the vibration and potential for racking/twisting...but we've not had a panel failure in almost 6 years of doing this.
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Old 02-10-2021, 09:27 PM   #3
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For a panel of that size I would seriously consider making a support frame for each one to take the strain off the panel's own frame. I did that for my eight much smaller 255W 60-cell panels, so now I don't have to worry if the wind kicks up while I have them raised. Also, If I ever need to replace one, it's a simple 5-minute job to just loosen four nuts that hold the panel in its support frame and unplug its MC4 connector, and any other 60-cell panel will fit.

And don't forget how to clean them - they do get surprisingly dirty and dusty, and that will reduce their output noticeably. I put some water outlets up on the roof to make panel cleaning easy and safe.

John
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Old 02-10-2021, 09:37 PM   #4
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Originally Posted by Iceni John View Post
On a panel of that size I would seriously consider making a support frame for each one to take the strain off the panel's own frame. I did that for my eight much smaller 255W 60-cell panels, so now I don't have to worry if the wind kicks up while I have them raised. Also, If I ever need to replace one, it's a simple 5-minute job to just loosen four nuts that hold the panel in its support frame and unplug its MC4 connector, and any other 60-cell panel will fit.

And don't forget how to clean them - they will get surprisingly dirty and dusty, and that will reduce their output noticeably. I put some water outlets up on the roof to make panel cleaning easy and safe.

John
Thats awesome. Great idea. I may run a quick connect for water up there. Then I can also take outdoor showers 11 off the ground for all to see!

I was thinking of getting some angle stainless to attach to the panels to keep them down and also to use to put supports in so I can raise/angle as needed since Ill be in MN 90% of the time and flat mounted panels may not be ideal for me.
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Old 02-12-2021, 02:46 AM   #5
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Yes tilting can double output, depending how diligent you are moving them east to west

Just tilting south and otherwise leaving them during the day, maybe 50-70% more than flat.

What is their Voc rating?

Check out Victron SmartSolar, very flexible pricing model, can even do a separate MPPT SC per panel.

Check the delivered cost delta between the 75/15 and 100/20 units

I reckon in practical, Ah/day actual input to your bank you'd only harvest another 5-10% going to the bigger / pricier one.

Also compare to going to one big SC for all the panels at once, but there you will potentially lose a lot of Ah/day if there is any variation in insolation per panel, especially any partial shading, even dust or a few leaves can really affect the MPPT optimisation

why a 1:1 ratio is best.
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Old 02-12-2021, 11:40 AM   #6
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Yes tilting can double output, depending how diligent you are moving them east to west

Just tilting south and otherwise leaving them during the day, maybe 50-70% more than flat.

What is their Voc rating?

Check out Victron SmartSolar, very flexible pricing model, can even do a separate MPPT SC per panel.

Check the delivered cost delta between the 75/15 and 100/20 units

I reckon in practical, Ah/day actual input to your bank you'd only harvest another 5-10% going to the bigger / pricier one.

Also compare to going to one big SC for all the panels at once, but there you will potentially lose a lot of Ah/day if there is any variation in insolation per panel, especially any partial shading, even dust or a few leaves can really affect the MPPT optimisation

why a 1:1 ratio is best.
According to the manufacturer label on the back of the panels the VOC is 45.8V. I was thinking of getting the Renogy DCC50S which combines MPPT and DC-DC charger. It's a 50a charger that will max 25a solar and 25a alternator when driving but will allow for up to the full 50a when on solar alone. Am I going to have overkill on the panels with that device? I'm still deciding on battery but I'll either buy a 200ah LiFePO or build a 280ah.
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Old 02-12-2021, 07:40 PM   #7
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Nothing wrong with overkill.

But no, I would be very surprised if anything by Renogy got within even being in the same league as Victron

you would be sacrificing **a lot** of conversion efficiency, not as bad as not tilting, but maybe like going back to PWM.

The 75/15 model will be fine if the 100/20 is too pricey.

As a DCDC for alternator the Renogy might be fine, Sterling is the way I'd go though for adjustability, Renogy has canned switches only. Plus build quality, service availability. . .
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Old 02-13-2021, 03:37 PM   #8
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Originally Posted by john61ct View Post
Nothing wrong with overkill.

But no, I would be very surprised if anything by Renogy got within even being in the same league as Victron

you would be sacrificing **a lot** of conversion efficiency, not as bad as not tilting, but maybe like going back to PWM.

The 75/15 model will be fine if the 100/20 is too pricey.

As a DCDC for alternator the Renogy might be fine, Sterling is the way I'd go though for adjustability, Renogy has canned switches only. Plus build quality, service availability. . .
So I picked up the Mobile Solar Power book written by Will Prowse and have a question on your MPPT recommendation. You recommend the Victron 75/15 or 100/20. In the book, hes recommending that you take your wattage output of your panels and divide it by your bank voltage to arrive at the recommended controller amperage output. For me, with 310w panels, that would be at least a 40a charger. Am I understanding that correctly?
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Old 02-13-2021, 06:39 PM   #9
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First off, you will see far less than the theoretical wattage rating 99.9% of the time, nearly impossible in real life conditions.

So say 280W, between 18 and 20A but only in rare peak conditions.

You don't use the nominal voltage but the SC charge setpoint

12V nominal, that is often close to 15V, for LFP I use 13.8V.

Don't know how you got 40?

31012=25.8

Technically as I said buy the 20A SC if the price difference is not so much, say under $50 delivered? Or if you're flush and getting every last bit of energy out is your top priority.

IRL between the 15A and 20A your overall energy per day may increase from say 90 to 100Ah, but only in super optimal insolation conditions, cold bright sunny and 90 panel angle,

On average days no increase at all. . .
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Old 02-14-2021, 10:11 AM   #10
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Quote:
Originally Posted by john61ct View Post
First off, you will see far less than the theoretical wattage rating 99.9% of the time, nearly impossible in real life conditions.

So say 280W, between 18 and 20A but only in rare peak conditions.

You don't use the nominal voltage but the SC charge setpoint

12V nominal, that is often close to 15V, for LFP I use 13.8V.

Don't know how you got 40?

31012=25.8

Technically as I said buy the 20A SC if the price difference is not so much, say under $50 delivered? Or if you're flush and getting every last bit of energy out is your top priority.

IRL between the 15A and 20A your overall energy per day may increase from say 90 to 100Ah, but only in super optimal insolation conditions, cold bright sunny and 90 panel angle,

On average days no increase at all. . .
Got it. I was just posting based on what I read. Still trying to get all of this. Ill probably go with the Victron parts (separate MPPT and DC-DC) vs the Renogy. I like the Bluetooth integration and they seem to be the most recommended. Its a little more $, but not prohibitively so and I want to do this right.
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Old 02-14-2021, 04:40 PM   #11
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I found a local guy that was selling a few lightly used 315W panels, Hyundai. I was replacing two defunct panels from a fallen tree, and decided I might as well as double up from 3050W to 6200W. Holy cow the frames of these things are beefy! Industrial panels are no joke! ( Left: Hyundai panel, Right: Trina panel )
side_diff_01_25%.jpghyundai_label_02_25%.jpgsize_diff_03_25%.jpg
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Old 02-14-2021, 05:34 PM   #12
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Pretty good deal,, though, you may find an even better one here @ SantanSolar
https://store.santansolar.com/produc...ef=errolprowse
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Old 02-14-2021, 05:59 PM   #13
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This site has 310w panels for $99- @ SignatureSolar

https://www.signaturesolar.us/catego...89000000543131

They also have 400w PERC 144 half- cells (perc's supposedly gets good power even when partially shaded) for $176 - best deal I've seen. Think I may spring for 4 of these this week...
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Old 02-14-2021, 07:09 PM   #14
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Pretty good deal,, though, you may find an even better one here @ SantanSolar
https://store.santansolar.com/produc...ef=errolprowse
The panels SanTan sells are great...and they're here in AZ. These are the ones, from that source, which "beginningfromthismorning.com" (Juan and Michelle) used on their coach conversion.
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Old 02-15-2021, 03:23 PM   #15
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@NovaTron

Thanks! Those are great sites to check out for an alternative. I may end up going that route.
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Old 03-02-2021, 07:41 PM   #16
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Originally Posted by john61ct View Post
First off, you will see far less than the theoretical wattage rating 99.9% of the time, nearly impossible in real life conditions.

So say 280W, between 18 and 20A but only in rare peak conditions.

You don't use the nominal voltage but the SC charge setpoint

12V nominal, that is often close to 15V, for LFP I use 13.8V.

Don't know how you got 40?

31012=25.8

Technically as I said buy the 20A SC if the price difference is not so much, say under $50 delivered? Or if you're flush and getting every last bit of energy out is your top priority.

IRL between the 15A and 20A your overall energy per day may increase from say 90 to 100Ah, but only in super optimal insolation conditions, cold bright sunny and 90 panel angle,

On average days no increase at all. . .
So after a few more weeks of reading, researching, etc... I've punched numbers into two different MPPT calculators. The one on Victron's site and one from Explorist.life. Both of them point me to the Victron 150/45. Now, as you stated, the likelihood of getting 99.9% efficiency is almost nill, but I don't want to risk damaging anything either.

If I left a little charging on the table, that wouldn't be the end of the world, but with 100v being the max VoC (on the 100 vs 150 lineup) and my panels maxing out at 91.8 (45.6 each panel), isn't that getting a little too close for comfort?
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Old 03-02-2021, 11:50 PM   #17
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Victron's MPPT are designed to not suffer any damage from being overpaneled far beyond the maximum amps and watts they can put out.

The Voltage yes, but even on a clear bright day at noon in **freezing** temps

the panel won't be going any significant percentage over that 92V

unless the panel is directly perpendicular to the sun, **and**

lots of reflections off snowy peaks are focused like a mirror on it.

IOW no, 10% cushion is fine
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Old 03-02-2021, 11:53 PM   #18
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Plus I would not be series-connecting them in the first place, both losing out on lots of MPPT efficiency by going more than one panel per SC

but **so** susceptible to the slightest bit of partial shading, a branch, dust, even a stray leaf could reduce total output by **a lot** hooked up in series.
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Old 03-02-2021, 11:56 PM   #19
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Quote:
Originally Posted by john61ct View Post
Victron's MPPT are designed to not suffer any damage from being overpaneled far beyond the maximum amps and watts they can put out.

The Voltage yes, but even on a clear bright day at noon in **freezing** temps

the panel won't be going any significant percentage over that 92V

unless the panel is directly perpendicular to the sun, **and**

lots of reflections off snowy peaks are focused like a mirror on it.

IOW no, 10% cushion is fine
10-4! Thanks. That helps a ton. Now, and not that money isn't a thing, but would you do the 100-20, 30, or 50 without $ being a consideration?
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Old 03-02-2021, 11:59 PM   #20
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Plus I would not be series-connecting them in the first place, both losing out on lots of MPPT efficiency by going more than one panel per SC

but **so** susceptible to the slightest bit of partial shading, a branch, dust, even a stray leaf could reduce total output by **a lot** hooked up in series.
Again, thank you! I would've had that as a question at some point. Parallel it is. My panels will be almost directly above the "garage" so wire length/gauge on the increased amperage won't be super prohibitive.
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