Double solar system hookup.

[KJRitchie]

Originally Posted by BoldAdventure

You can if all the specs match.

What specs? When I look at specs from 100w panels offered by various popular companies:
AMSolar:
Here are the SF 100 panels
Pmax = 100 watts @ maximum power

Vmpp = 18.0 volts @ maximum power point
Impp = 5.55 amps @ maximum power point

Voc = 21.6 volts @ open circuit
Isc = 5.93 amps @ short circuit

Here are the GS100 panels
Pmax = 100 watts @ maximum power

Vmpp = 17.7 volts @ maximum power point
Impp = 5.7 amps @ maximum power point

Voc = 21.2 volts @ open circuit
Isc = 6.10 amps @ short circuit

Length = 40.8" (1037mm)
Width = 20.7" (527mm)
Depth = 1.38" (35mm)
Weight = 14.5 lbs. (6.6kg)

Here is the popular Renogy 100w panel
Built-in Components
Renogy 100 Watt Monocrystalline Solar Panel IP65 Rated waterproof junction box
Panel Leads (Pair): 12AWG IP67 Rated waterproof MC4 connectors

Specifications
Maximum Power: 100W Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 18.9V Open-Circuit Voltage (Voc): 22.5V
Optimum Operating Current (Imp): 5.29A Short-Circuit Current (Isc): 5.75A
Weight: 16.5lbs Dimensions: 47 X 21.3 X 1.4 In

Grape Solar 100w panel:
Characteristic Details
Max System Voltage 1000 V
Max Peak Power Pmax
100 W (0%, +6%)
Maximum Power Point Voltage Vmpp
18.0 V
Maximum Power Point Current Impp
5.56 A
Open Circuit Voltage Voc
21.9 V
Short Circuit Current Isc
6.13 A
Module Efficiency (%)
14.63%
Temperature Coefficient of Voc
(-0.32% /ºC)
Temperature Coefficient of Isc
(0.04% /ºC)
Temperature Coefficient of Pmax
(-0.45% /ºC)

Are they all incompatible with each other?

Thanks

Kelvin

[lewster]

Kelvin,

You need to match the MPPT voltage figures (Vmppt) as closely as possible across all panels to be effective when using an MPPT controller. A difference of more than 0.2VDC in panel output voltage will confuse the MPPT function.

If you want to use panels with a greater voltage differential, stay with a PWM controller. In any event, I would not use any panel in a PWM system that has more than a 0.5VDC differential.


Lew Farber
RVIA/RVDA Nationally Certified Master Tech
ABYC Certified Master Marine Electrician
Master Tech Energy Systems, Inc.
AM Solar Certified Installation Center*AMS Lithium Batteries
Lifeline AGM Batteries**Magnum Inverters
541-490-6357

[dznf0g]

Lewster,

If your MPPT controller has only one set of panel inputs from the panels and two panels are paralleled upstream from the controller...and they have more than .2 V difference in Vmp, how does that "confuse" the controller?

My understanding is the the two different voltages will result in the lower Vmp panel "dragging" down the combined Vmp of the system somewhere lower than the higher panel.

Example: (numbers pulled out of the air):

Panel 1 - 18.9Vmp
Panel 2 - 17.9Vmp

They are paralleled upstream from single controller posts

Observed Vmp of system 18.2Vmp.

How does that confuse the controller? I know there would be some loss of MPPT efficiency as system voltage has been dragged down.

[rodsterinfl]

I am going to mount 2 100W panels on the roof and have them wired thru a controller. Would it be possible to prewire a recepticle that is wired thru the controller and have the recepticle easily accessible on the outside of the A/S so that you can just plug in a suitcase solar array? That way you can just plug in the extra solar panels or not as needed? Tom

That is exactly what I did plus one. Last summer I planned a system to meet my needs- a triad setup with three controllers and it works fine. At first I was told you cannot have more than one controller. Then I had an appointment call with two different solar peeps- one a solar engineer. One of them was from GoPower; any who, I was told that it would be fine as long as the charge "rates/cutoffs" were similar. They are so it works for me. I have the 100w suitcase, a 50w single panel for battery/storage and a 150w roof unit. It is true that that one particular may cut off at a certain point BUT it would be doing that anyway and read the battery charge as complete. I have sat and watched the suitcase charge monitor and it reads the battery voltage while the other panels are charging without issue. It also cuts off when I plug in the trailer to power which makes sense. I added pigtail connectors on the side of my battery box for quick connect/disconnect. This week I am returning the flexible panel to Renogy for a different option as it is not charging but that is another issue. I may get the 60w suitcase instead of another panel to have to temporarily mount. Still deciding. I would steer clear of the flexible panels.

[AWCHIEF]

I have a couple of 25 year old no name brand (the labels fell off years ago) flexable panels that as I recall are around 35 watts that I picked up in Georgetown, Bahamas. They still put out about 2.5 Amps in direct sun light. I used them and the 75 watt panel on my boat full timing down island for years. I realize that opinions differ here but I know plenty of boat folks that swear by flexable panels and have never had any problems with them.
By the way, I talked to Renogy yesterday about my crazy idea. They said using the two controllers the way I had in mind was a bad idea. They did have a couple of suggestions as to how to add an additional panel to the suitcase. But did not recommend using the old 75 watt panel.

[dznf0g]

So, I have been googling the voltage difference between panels discussed above and am unable to find anything definitive. Relative to parallel hookups of arrays, they all seem to say the panels should have "similar" voltages, but do not define "similar". They then go on to discuss issues with 17 Vmp and 24 Vmp panels. I know Lewster likes the .2V difference as a bogie, but I wonder if that is the "perfect world" spec and if "similar" carries a larger V difference for discussion. All say the the system voltage will be dropped to the lowest panel (array) in the parallel system.

Has anyone seen discussion (links please) as to one array being at 17.9 Vmp and one at 18.9 Vmp, for example? Is that "Similar"?

[AWCHIEF]

Sure would be nice if someone would come out with a book like this for us complete solar deficients.

[lewster]

Originally Posted by dznf0g

So, I have been googling the voltage difference between panels discussed above and am unable to find anything definitive. Relative to parallel hookups of arrays, they all seem to say the panels should have "similar" voltages, but do not define "similar". They then go on to discuss issues with 17 Vmp and 24 Vmp panels. I know Lewster likes the .2V difference as a bogie, but I wonder if that is the "perfect world" spec and if "similar" carries a larger V difference for discussion. All say the the system voltage will be dropped to the lowest panel (array) in the parallel system.

Has anyone seen discussion (links please) as to one array being at 17.9 Vmp and one at 18.9 Vmp, for example? Is that "Similar"?

Here is the 'least technical explanation' of how MPPT works in the real world: http://www.blueskyenergyinc.com/uplo...at_is_MPPT.pdf

This is on the Blue Sky Energy web site. Since the maximum power point voltage is the determining basis for 'solar boost' from the controller to the batteries, anything over a small differential will cause the MPPT function to operate more like a PWM unit, or will fixate on the lower Vmpp voltage panel and you will loose the advantage of the higher output panel(s). Output also depends on the specific algorithm that is used for the MPPT sampling: some use a rather slow sampling ( a minute or two) while others sample at several times a second.

This has always been the mantra at AM Solar, and I would expect that they have conducted real world testing (as they do with all of their offerings) before arriving at a position statement.

While some may be tolerant of lower panel output to your batteries, most of the folks that I work for expect to achieve the maximum output from their systems. After all, that's why they hire me. This is why I'll stick with my 0.2VDC differential…..no guess work and I know it works as designed!

[dznf0g]

I just found a couple of references which say that panels should be no more than 10% different in Vmp. With an MPPT controller, max efficiency will be affected, as it will sense a voltage between the two panel voltages. Some controllers work better than others with the variation of Vmp.

[lewster]

Originally Posted by dznf0g

I just found a couple of references which say that panels should be no more than 10% different in Vmp. With an MPPT controller, max efficiency will be affected, as it will sense a voltage between the two panel voltages. Some controllers work better than others with the variation of Vmp.

Kind'a what I said….no? I still don't go for the 10% but as with anything else….YMMV!!

[AWCHIEF]

More power! Been projecting (sp) today. Swapped the controllers out and added the 75 watt to the suit case panels. With full early afternoon sun output was around 9.5 Amps at 14 volts. Up from 6 amp with the Renogy panels only. Not quite as much as I hoped but a nice improvement at zero cost. What is next on the agenda? Not sure. As soon as I win the lottery I plan on getting a full system installed. Until that day happens I think what I have will work just fine for my limited needs. The local power company has nothing to fear from me.

[dznf0g]

Originally Posted by lewster

Kind'a what I said….no? I still don't go for the 10% but as with anything else….YMMV!!

Yes, I was just struggling with the .2V statement. I'd wager that two panels from the same manufacturer and model might vary that much, due to build variation.

I'm going to try with mine and see. I have one at 17.9 Vmp and one at 18.9 Vmp. I think I'll go ahead and install a marine cutoff switch on the rooftop one...if for no other reason than battery removal, service etc. Then, If I do see an issue when using the suitcase, while the trailer is in the forest, I can switch the rooftop off and just plug in the suitcase.

[KJRitchie]

Brings up another issue PWM vs MPPT. Bogart Engineering has this explanation for PWM vs MPPT.

http://bogartengineering.com/support/faq

With my projected project of 2 100w 12v panels on the roof which would be used most of the time then adding my 200 Watt (2 100w 12v panel) Zamp suitcase for times when the roof is partially shaded, I would think PWM controller would be sufficient and more cost effective. Trimetric 2030 monitor and paired with the SC 2030.

Kelvin

[BoldAdventure]

Originally Posted by KJRitchie

Brings up another issue PWM vs MPPT. Bogart Engineering has this explanation for PWM vs MPPT.

http://bogartengineering.com/support/faq

With my projected project of 2 100w 12v panels on the roof which would be used most of the time then adding my 200 Watt (2 100w 12v panel) Zamp suitcase for times when the roof is partially shaded, I would think PWM controller would be sufficient and more cost effective. Trimetric 2030 monitor and paired with the SC 2030.

Kelvin

I've read that, and he pretty much accuses Blue Sky of lying in their 30% claims, yet I see that all the time from mine. Also his claims about ideal situations. Mhem. Reads like counter-marketing to me to explain away short comings.

[lewster]

I don't really understand where Bogart is coming from on this. Is he then the ONLY ONE in the entire solar industry that feels this way.

Look at any quality MPPT solar charge controller on the market like:
• Blue Sky
• Morningstar
• Magnum
• Victron
• Outback
• Midnight Solar

They all are not blowing smoke, as Bogart suggests! I think he has been hanging around with Angry Bob (sorry, that's Solar Bob now!).

[AWCHIEF]

Sounds like Bogart is just trying to push the product brands he sells. Normal marketing practice, every retailer does it.

[rodsterinfl]

Rich (dznf0g) pretty much explained all it. Friend here has a Renogy suitcase, same one you have with a 300 watt Renogy kit on the roof. He kept finding that the roof controller was still charging but the suitcase kept reading as full. Basically the systems were mismatched.

So I helped him bypass the PWM on the back of the suitcase, and we wired it with a SAE plug into the one controller for the roof solar. Works better that way.

What kind of controller for his roof does he have?

[BoldAdventure]

Originally Posted by rodsterinfl

What kind of controller for his roof does he have?

Whatever that 40amp one is that comes with the Renogy kit.

[rodsterinfl]

When I bought my small system the gentleman told me that for what I was doing the PVM would be just fine that loss would be negligible. I already knew about the difference but followed his advice. At optimum power have a 3.3V loss on my system using the PVM or just under 20% or about 63 watts in a perfect scenario. What the advice told me is that you never get that perfect anyway so it is, in actuality less of a loss. Here is a good non technical description of PWM versus MPPT and what the difference is really all about:

https://www.victronenergy.com/blog/2...r-pwm-or-mppt/

It is the same principle the electric company uses to step down electricity to homes. I do understand that with a MPPT it is advantageous to go with higher voltage- 24V panels and in doing so the wiring size requirement is less AND you get more power as it has that extra voltage to step down to AMPS per se. It just depends on how much you want to spend.

[rodsterinfl]

Just read two more write-ups including the Bogart one above.

Question, when WOULD a PWM controller be a better choice?

It is obvious that the companies make them and sell em. The write-ups say "for smaller systems" so what is smaller? To me, when looking at the stories on the websites where they are hooking up 10 panels etc. That is big. So, is a three panel system small? Just sayin.