Should I change my solar panels from parallel to series?

[Pugwash69]

When I first set up my system, I had two 100W panels in parallel into a 20A PWM controller. I was under the impression PWM could only handle it this way.
I've recently replaced this with an MPPT controller and added a 3rd 100W panel, still wired in parallel.
I'm guessing that if my panels were pushing 100W each I'd probably be approaching the 20A limit on my controller, but it occurs to me also that I can now change my panels to be in series?
Having read an article about the whole thing and guess having the combined voltage of 3 panels would work better than combined amperage?

They are connected up currently with MC4 and branch connectors so it won't take long to jiggle them about. Not going to detonate my new charge controller am I?

 

[wildebus]

What is the maximum voltage of your MPPT Controller? That is probably the key question. 50V is quite a common limit and 3 x Panels would exceed that.
Also different controllers have different limits - some have a hard limit on the total power, others have an absolute limit on incoming current which should not be exceeded. some have the current limit (20A in your case) as an output current limit and anything above is thrown away.

FWIW, I changed my array of 4 100W panels from a Series/Parallel setup to all-series. I honestly have not seen any noticable difference by changing them.

 

[Pugwash69]

It's the Victron SmartSolar 100/20 so should be ok up to 100V from the solar?

 

[wildebus]

It's the Victron SmartSolar 100/20 so should be ok up to 100V from the solar?

That is good for upto 330W I think it is and anyway you want to wire it

 

[SquirrellCook]

I hope you don't mind me hijacking your post Pugwash, as this is along the lines of a post I was planning.
"So why can't I split my five panels into parallel and series"
I'm guessing that two panels would hold the voltage down of the three?
Would this heat one or all of the three panels?

So if I was intent on doing this I guess I could stop back feeding with "Blocking diodes" ?

Ok I give in and accept that even numbers of panels is the way to go.
But remembering the original discussion, what happens when one or more of my panels in series connection becomes shaded?
Do I end up in the odd number of panels scenario again?
If so can "Blocking Diodes" improve my panel voltage rather than it being held down by the shaded panels?

Makes you think.

 

[wildebus]

I don't know but my feeling is you would end up with less capacity?
Say each panel is a nominal 20V and 5A (100W)
put 60V sending 5A (3 in series) in parallel with 40V sending 5A (2 in Series) and what would you end up with? would it be 50V (average of 60V and 40V) sending 10A? or would it gravitate down to the lower voltage, so you just have 40V sending 10A?
Or 20V sending 15A (3 in Parallel) in series with 20V sending 10A (2 in Parallel). Would you end up with 40V and 12.5A, or 40V and just 10A?

An Interesting question

 

[SquirrellCook]

What drove me to consider this was after fitting two extra panels yesterday, was how are the others connected? After fitting the Victron mppt, I found an improvement by disconnecting one panel and doing a parallel series set up with four panels. As for how the panels were connected in relationship I never gave a second thought. Though as the months passed I noticed a directional improvement.
The first two panels mounted are about as optimum as I this possible. Foolishly the subsequent panels were mounted transvers between skylights.
It has a curved roof One skylight is smaller than the other and should allow some shadow clearance if I mount a panel each side as close to the edge of the roof as I dare.
Each side of the roof then become a 3 panel series string. So with wishful thinking most of the it should not be to hard to get at half the panels receiving some sunshine.

I'm guessing all solar panels are built with bypass diodes in them, so it would be hard to measure the panels internal resistance.
I've got no good panels to hand, but putting a suspect one face down it has approximately 25k ohms in one direction and into meg ohms the other way. I can't see this back feeding theory being a problem if shaded.

 

[wildebus]

There is meant to be an update imminently for the Victron Smart Solar Controllers for them to link together via the Bluetooth VE.Smart Networking to work effectively as a single controller. That mighy well be the best way to have 5 panels in an essentially series/parallel setup? would mean another pair of cables and of course the cost of another controller.

 

[SquirrellCook]

After torchlight wiring Murky now has 2 x 3 solar panels with the series sets running the length of one side of the roof. Some wiring anchoring still required, but it's good enough for test. Assuming the sun will pop out to say hello today..