I put together a solar setup on our TT when we bought it new. I went with 2 x 140 watt 12V nominal panels in parallel and a PWM controller. Panel specs:Max Power: 140WpOpen Circuit Voltage (Voc): 21.0VShort Circuit Current (Isc): 8.40AMaximum Power Voltage (Vmp): 17.0VMaximum Power Current (Imp): 8.00AThere are quite a few MPPT controllers out there now that aren't terribly expensive (under $200). I have contemplated swapping the PWM controller to an MPPT as a way to squeeze some more potential bulk charging amps out of the panels without having to do anything else besides swapping controllers. I know there are some benefits for running panels in series to double the voltage and cut down on wire gauge needs. But my panels are already in parallel with fat wiring from junction box to controller (4 gauge). It seems to me that the math for potential max charging amps works out the same whether my panels are in parallel or series. Is that correct?

Note that with two 12v panels in series you have to add their Voc to the controller which has a Voc limit. So yours would be 42 Voc.The older Eco-Worthy 20a controllers work great but have a Voc limit of only 42. Newer ones are 50 but they have the same model number and appearance. Other more expensive MPPT controllers can be 60 or 100 Voc limit or more. Read the specs.I have tried two 12v panels in parallel and in series on an MPPT controller (Tracer) and it makes no difference in amps to the battery in good light. Supposedly in low light you get more when in series because of the bigger voltage spread between array and battery. No real way to tell if you are getting that or not while camping.If you get shade on one panel in parallel you still get the amps from the other panel, but in series it kills both panels. Depends on where you are parked.You will get a trivial improvement in amps to the battery by swapping your existing set-up for an MPPT set-up. I took lots of comparison measurements and posted the results last year and the year before. But if you don't believe that, it is your money! :)

You did comparisons for MPPT vs PWM, or series vs parallel with MPPT? My estimate would be I could maybe get an additional 5 amps out of my setup if batteries were low and the sun was just right with MPPT vs my PWM. Not really enough to make me want to do it right now. But it also seems like an easy way to optimize my existing system.

I compared PWM with MPPT in the past, and found they come out fairly close because with MPPT you have the buck converter in it, which uses the input POWER which is reduced by the panel heating up in the sun which reduces the voltage component in the power.The PWM controller just passes through the AMPs which are not reduced by panel heating (they go up a little in fact)You can still get a little more from the MPPT at times, but it is trivial for RV camping. This summer I had a different solar set-up and got to play with three 100w panels and an MPPT controller. I tried series vs parallel with them and got the same amps either way when there was no shade on any panel. I was not able to run a comparison of series vs parallel in low light. In low light there are hardly any amps anyway, so there is not much to be gained with a small array from that I figure, even if it is better in series then.BTW, I got this 20a controller when it looked like I would have two 100w panels, but then I got a third so I should have bought the 30a version for an extra 20 bucks. Mistake!!! :(The 20a version is not limited to 20a as such but has a 260w input limit, which has the same effect. So my 300w array was acting as a 260w array. But now I got to play the "over-panelling" card when the array woukld only be collecting under 260w anyway, and that was when the third panel got to do some good. I should still have chosen the 30a version though.http://www.wegosolar.com/products.php?product=EPS%252dMPPT%252d20-EPSolar-20-Amp-12%7B47%7D24V-MPPT-Solar-Charge-Controller

Thanks BFL13. Good input and makes feel less insecure about my less-than-optimized solar setup. :-)

Strange that they say they're 140 W panels, when 8.00 A x 17.0 V = 136 watts.But, looking at the numbers, compare that 136 W to what one panel would be putting out charging the battery with PWM. 8.4 A x 13.8 V = 116 W would be a reasonable average working number (12V panels generally put out the short circuit current until you get to around 15V). Making the unreasonable assumption that MPPT is 100% efficient, you'd gain 20 W x 2 panels = 40 W total.But, for the $200 and time spent upgrading to MPPT, you could easily add another 100 W (80 W effective) or more on the roof, if you have space and controller capacity.edit:redid the math slightly

SOLAR - Switch from PWM to MPPT, series vs parallel matter?

26 Replies

BFL13
Explorer II
Sep 14, 2016
It is true that with the buck converter, MPPT controllers do better on "same" voltage for panel and battery than when bucking from higher. PWM is always 12-12 or 24-24. MPPT is also 12-12 or 24-24, but is often 24-12 or more.

When I did my 24v battery with 24v panel test, one thing that came out was the 60 cell panel was able to raise the 24v battery bank to 30v max (like 15v with 12s) so it was able to do a recharge ok, but would be unable to do an equalize if you ever wanted to do that.

With 36 cell 12v panels in series, two is 72 cells, which ought to beat the single 60 cell when trying to do equalize level voltages on a 24v bank. There are 72 cell singles, but 60 cells are very common.

My Eco-Worthy 20 amper at 42Voc input limit would be over limit with two 12s in series at 21.9 each, but my Tracer can do 90-100 Voc so there is another factor to consider if you are looking at your options. A single 24 can be less money than two 12s though.

The Eco-W has adjustable voltage settings while the Tracer has a fixed charging profile (which is a good one for many situations) unless you spend more for the adjustment gizmos.

Lots of factors to consider with solar.
red31
Explorer
Sep 14, 2016
mike-s wrote:
red31 wrote:
look at the efficiency curves near the end of whatever controller ya might get.

higher input v (series) yields a lower efficiency.
That's only MPPT. For a PWM controller the limit on controller efficiency is the Rds(on) of whatever MOSFET they chose to use.

well the OP is asking about mppt (parallel vs series), charts in manuals show the difference and how the performance varies over a range of power input.
mike-s
Explorer
Sep 14, 2016
BFL13 wrote:

Compare MS manual here Figure 9 para 4.3
...
with LS Manual Figure 4-1, para 4.2 here
That's what you call an "exact same manual?" Looks more like EP took a drawing and two paragraphs of text from MS instead of getting more poor translations done. And, the similarities end quickly. After those two paragraphs it's back to Chinglish.

(and the products themselves are very obviously completely different)
Boon_Docker
Explorer III
Sep 14, 2016
x2 on the Tracer MPPT controller. Have been using one for 5 years now and would highly recommend it.
BFL13
Explorer II
Sep 14, 2016
hedge wrote:
well I've read both manuals and they are nothing alike so no idea what you're talking about there. the EpSolar manual is full of Chingrish and a few pages long... the Morningstar manual is a book.

Morningstar manual

EP Solar Manual

I must be missing something because I see no similarity in the manuals.

Compare MS manual here Figure 9 para 4.3

http://www.morningstarcorp.com/wp-content/uploads/2014/02/SSMPPT.IOM_.EN_.03-4-131.pdf

with LS Manual Figure 4-1, para 4.2 here

http://www.epsolarpv.de/support/downloads/item/ls1024rpls1524rpls2024rp-manual.html
ewarnerusa
Nomad
Sep 14, 2016
My PWM controller is a Morningstar Tristar 45. It has a lot of features and I think works well. I too designed initially for expansion but found that after upgrading to 2x6V GC batteries that I didn't need any more solar to meet our needs. But some of these 40A MPPT controllers on Amazon have temperature compensation and are fully programmable as well for under $200. Thus the temptation...
hedge
Explorer
Sep 14, 2016
well I've read both manuals and they are nothing alike so no idea what you're talking about there. the EpSolar manual is full of Chingrish and a few pages long... the Morningstar manual is a book.

Morningstar manual

EP Solar Manual

I must be missing something because I see no similarity in the manuals.
BFL13
Explorer II
Sep 14, 2016
Since Morningstar and EP Solar (Chinese) have the exact same user manuals obviously written by the same guy word for word and using the same pictures and diagrams, how can you be sure that " Morning Star" is any different from "Land Star" (one of EP Solar's products)???

Never mind the Star Ferry between Victoria and Kowloon in Hong Kong :)

BTW I have been using EP Solar controllers PWM (LandStar) and MPPT (Tracer) now for a while and think they are great. Very solidly built and good charging profiles.
hedge
Explorer
Sep 14, 2016
ewarnerusa: I think I have the same disease, my system is working fine with my Trace 30W Mppt controller but for some reason it bugged me that it was a chinese controller.

I then was going to get a Morningstar PWM which would have worked fine in my setup but having already spent money twice on a controller I decided to go all the way and get the Morningstar MPPT. I have a truck camper with limited space on the roof so I really can't add any more panels than the 3 100's I have now.

I guess I'm trying to future proof a bit as this controller will be removed if I change RV's. This stuff becomes addictive lol, I guess as long as the important bills are paid this is kind of my hobby so I don't mind spending a bit on it.
mike-s
Explorer
Sep 14, 2016
ewarnerusa wrote:
No room for more batteries. And I don't even really have a need for faster charging. I just thought it might be cool to squeeze some more amps out of the panels i already have.
It's your money. Spend it however you want.