question,, which is better when looking at solar panels.??

[carl2591]

Higher voltage, ie.. 24 vs 12 or max amps they can produce.

example: I am looking at a panel rated at 195 watt, 24vdc that produces 5.38 amps and another one that is 160 watts, 12vdc that produces 9.8 amps max.

one panel the 195 watt cost $195. the 160 watt cost $300 and is a bit smaller.

not sure how to see the differences in which is the better panel. higher volts or higher amps.

[JiminDenver]

Should someone else feel like pushing the Voc just to see what happens, let us know. 🙂

[Salvo]

Where is that stated. That link says exceeding 150V may damage controller.

smkettner wrote:
Morningstar does actually protect itself from high panel voltage.
The issue is that you get no power while in protection mode.

http://www.morningstarcorp.com/wp-content/uploads/2014/02/TSMPPTdsEng.pdf

[time2roll]

Deleted

I misread the high voltage protection 😞

Actually the controller starts to derate long before even 145 volts. See graph in the operators manual.

Best to follow the original plan and string calculation with the 72 cell panels and keep the panels in parallel.

For 3 in series it is best to stick with 60 cell panels.

[JiminDenver]

Over paneling is one thing and even sanctioned by Morningstar. I don't personally believe it's good for the controller as it can get hot enough without stressing it.

Pushing the Voc limits is not a good idea. I've watched the Voc on a panel jump 5 volts on cold day. I've seen reports of someone driving over a 12,000 ft pass on a cold day when the sun peaked out. Cold, cloud effect, elevation and pop goes the controller.

[MEXICOWANDERER]

These fine calculations cutting specifications with a scalpel are somewhat of a pipe dream. One cumulus laden sky will "cloud edge" the E=MC2 precision right into oblivion. If you folks haven't seen the effects of cloud edging and razor thin the capacity margins god help you.

[time2roll]

Shipping will kill ya though so look for a local supplier with some surplus if you want to consider lower voltage 60 cell panels.

[carl2591]

size is some of the issue.. the 195s might not fit as it and teh 260s are even bigger.. will have to see for sure.

thanks

Almot wrote:
Where did 45.5 VOC at 25C come from? For panels he considers it's 36V at 77F. Barely comes to 42V at 19F.

In defense of parallel living 🙂 - if (IF) 3*195W can be wired in parallel with #8 cable, this is a good news because #8 MC4 cables exist and don't cost too much. There will still be parallel connectors but no rooftop box. But this still requires MPPT controller, because feeding 36V into PWM doesn't make sense.

OP - here is a curveball for you. Buy TS MPPT 45, #10 cable and 3*260W panels $234 each in series. String calculator shows max 104 Voc at 19F.
Total 780W and only $100 more than your planned 3*195W.

60-70% of time it will work as 600W, in the morning/evening/overcast/winter etc. (Your planned 3*195W would work as 400W in those periods). At peak sun the controller will clip the output down to 45A/600W. Or man up and get TS MPPT 60 😉

[pianotuna]

smkettner wrote:
Oh good now we are fighting over $6 :R

(this was my point from the start)

X2

[Almot]

Where did 45.5 VOC at 25C come from? For panels he considers it's 36V at 77F. Barely comes to 42V at 19F.

In defense of parallel living 🙂 - if (IF) 3*195W can be wired in parallel with #8 cable, this is a good news because #8 MC4 cables exist and don't cost too much. There will still be parallel connectors but no rooftop box. But this still requires MPPT controller, because feeding 36V into PWM doesn't make sense.

OP - here is a curveball for you. Buy TS MPPT 45, #10 cable and 3*260W panels $234 each in series. String calculator shows max 104 Voc at 19F.
Total 780W and only $100 more than your planned 3*195W.

60-70% of time it will work as 600W, in the morning/evening/overcast/winter etc. (Your planned 3*195W would work as 400W in those periods). At peak sun the controller will clip the output down to 45A/600W. Or man up and get TS MPPT 60 😉

[Salvo]

If you put the 3 panels in series you may not outperform pwm during low sun angles. Look at the efficiency curves in the manual. At low solar output the controller efficiency is not very good. Efficiency is better when panels are in parallel.

I don't understand why you want to pursue a series configuration. The 150V max rating is not to be taken lightly. 150V is the switching FET breakdown voltage. You never even want to get close to that limit.

At 25C the panel has an open circuit voltage of 45.5V. Voc temperature coefficient is -0.159V/C. At 19F, or -7.2C the open circuit voltage is:

Voc = 45.5V + (0.159 * (25C + 7.2C)) = 50.62V

3 panels will bring you 1.86V over the 150V absolute max limit.

Do what you want, but no respectable engineer will sign off on that. 19F isn't even that cold. You don't have to be camping. The trailer could be parked somewhere.

carl2591 wrote:

My main purpose of this post was not to find the cheapest way to do this install. I want to do the best with a budget in mind and using the most cost effective products of quality, like morningstar products.

I know there are other good lower cost products but when you read post of folks that do a lot of solar like my friend handy bob solar, you learn what is a good quality product at a good price and will do the best job for your batteries.

In reading the morningstar white paper on the difference between MPPT PWM on lower watts and voltage system the PWM is the best choice. On higher voltage systems the MPPT will out perform more often with lower sun angles.

[time2roll]

Oh good now we are fighting over $6 :R

(this was my point from the start)

[Salvo]

I hope you're kidding! A pack of wire lugs is about $6. A nut and bolt to hold them together, under $1.



Attitude is everything.

smkettner wrote:

Even the parallel connectors will cost that much.

[Almot]

carl2591 wrote:

I do understand about the wire size and estimate only needing less than 10 ga which is most of the MC4 stuff. so the loss will be less than 1%

Yes, - if you run 3*195W in series. Then you have to buy MPPT, 'cause PWM won't work. TS MPPT 45 is "officially" rated 600W, but 3*230 or 3*235 "flat" will work as well, as long as you don't exceed Voc. Note that standard unit comes with LED indicators only. Display is extra.

Most MC4 extension cables are #10, some are #12 and some are #8. For 3*235W in series you will need #10.

Edit - PS:

when I put a low temp of 19­°F in the string calculator, "they" came up with voltage at 50.52vdc which is over by 1.56volts when connected in series.

Not sure how you got this 50.52. Check that you're using the right controller and right panel voltages. Your panel is not there but Grape 235W is close, and at 19F it comes to 41.55V. This is 125V for 3 panels in series. TS MPPT 45 should be alright - even with 3*235W.

[Almot]

Salvo wrote:
Instead of guessing, let's look at what's needed.

The panel under discussion is 195W, Imp = 5.38A, Vmp = 36.2V. Three panels in parallel

Sorry. I was thinking 4*12V, namely 4*150 or 4*160 in parallel, since the OP main objective appeared to be the low cost and those were the cheapest.

Salvo wrote:
The OP wants to buy the cheapest panels on earth, yet you want him to purchase a $60 combiner box??? When a substitute box can be gotten for under $5?

No. I "don't want" them to purchase $$ combiner box, but they "will have to", if they go for PWM and parallel wiring :)... And the substitute is not $5, but $5 +terminals + some elbow grease to put it together. And $5 is a PVC from Home Depot that doesn't look like up to prolonged UV and heat exposure.