Confusing the MPPT controller

[JiminDenver]

Here I go with my ignorant self again, seeing something and thinking I can figure it out. 😉

When I first got my original panels I talked to quite a few people including Mark at Rogue saying to run then on his 30a MPPT controller. I had told him they were different wattage as well as type but that didn't concern him at all. With all of my driveway test I realized that they never matched up in any way in any light. The 220w mono will gain a higher Voc in bright light than the 230w poly, but in low light it crashes while the poly still produces. Reading that somehow the controller tweaks the array made me think that the different voltages would have a adverse affect. I have never tried them together but I did know that I would have matching panels to mount.

Move forward to this spring when I got the Morningstar TS-MPPT-60 and did test adding the 230w poly into the three 250w polys as a mixed panel test. The 230w wasn't a match but it was of the same type and reacted to different light like the rest. What I saw was less output than I would have expected from the 970w total or even four 230w meaning that the whole array was being controlled by the low panel. Either should have easily maxed out the controller but the best I saw was 58 amps, close but no cigar. Looking at the grafts I saw that the array was providing over 800w at times but the controller was only using a portion of it and not much more than the three 250w panels could produce themselves.

Since my MegaWatt died I took advantage of needing to hook up something at home and ran the 230w schott poly and the 220w Canadiansolar mono together in series on the TS-MPPT-60. I set them out around 10 am in bright sun with a decent tilt/angle. The 220w had a Voc of 23.8v, to 230w 24.5v. When I hooked them in series I got 68v which would follow the concept of the lower panel controlling the voltage.

Now I know in parallel the 220w puts out 12a and the 230w puts out 15a here in Denver. In series they were maxing out at 23.8a which again would follow the concept of the 220w limiting the 230w.

What was interesting is the display on the controller was jumping up and down by a watt and a bit of a amp. It was doing it when the batteries were in absorb and close to what the 230w could do on its own so I unhooked the 220w and ran the 230w alone. As soon as I did that the watts and amps production settled to a solid amount.

So with like types the controller knows the watts are there but doesn't use them even though the load calls for it. With mixed types the controller seems to be having trouble settling. I'll have to set up the test again and do a log to see if the Vmp is changing that fast too meaning the controller can't find a sweet spot.

I know boring stuff, crude observations, probably way off base. Just posting what I see.

[BFL13]

Not sure if this is related or helps any, but I have this data so might as well use it!

The controller adjusts Vmp to suit circumstances. If things are getting tight as in the following example, where it had to raise Vmp as "overhead" shrank, then I suppose mixed panels would make it tighter/more critical?

In this case, the 60 cell panel ran out of "overhead" on a 24v battery bank when it got Vbatt to 30v, but the neat thing is to watch the Vmp climb. (Or maybe the controller ran out of Vmp it could go up to while in MPPT?--panel voltage would go to 35v or whatever once in Float)

THE TEST
The bank was full, in Float (as set) at 14.4v as 12v bank, so knocked that down with microwave on inverter for three minutes, disconnected solar, put batts in 24v mode, connected solar controller but not array yet, and set Absorb to 31v (max setting) and Float to 29v (max setting) By now battery holding at 25.6v ready to start, so connected array

I measured Vmp at the controller array terminals and took battery voltage and amps from the controller's display. I did not note the times. Controller was in Bulk and doing MPPT-- So here is how it went with Vmp, V batt, Amps, output watts

29.0, 26.3, 6.0
29.8, 27.4, 5.01, 138
30.1, 27.7, 3.52
30.4, 28.7, 4.64
30.4, 29.3, 4.81, 142
30.7, 29.9, 4.66
31.0, 30.2, 4.52
31.1, 30.3, 4.04, 137

It stayed at 30.3 saw 30.4 but fell back to 30.3 again so stuck there, still; showing Bulk ( not yet to the 31v Vabs setting)

The key seems to be the MPPT finds an ever higher Vmp as Vbatt gets higher, so the amps keep coming.

[grizzzman]

NinerBikes wrote:
Is it any easier just going with 12V panels in parallel, and just using a PWM charge controller, asks the Captain of The Simple Minds?

I know, not as cost effective, $ per watt, but hey, the output is consistent, even if you mix and match brands of panels?

This one of the reasons i went PWM. My system will expand as needed over
next few years. This way i dont need to worry about mismatched panels.

[NinerBikes]

Is it any easier just going with 12V panels in parallel, and just using a PWM charge controller, asks the Captain of The Simple Minds?

I know, not as cost effective, $ per watt, but hey, the output is consistent, even if you mix and match brands of panels?

[MrWizard]

many things to consider, parallel verses series, PWM vs MPPT

MPPT with series panels is the most critical and least forgiving
for max performance everything Must match

PWM with parallel is the most forgiving, little variations in VOC or imp are not as detrimental as everything contributes the best it can

like BLF and his multiple Vector battery chargers

[JiminDenver]

I never have set up and tested the three 250w panels to see how well they match up. Luckily the controller hasn't had any issues running just them.

Going over the different test I have realize there is another affect that can be seen with the controller being confused. I would have the four mixed panels out and when it went from cloudy to sunny the controller didn't kick up the output. A few times it eventually did after a few minutes, a few times I had to disconnect the array and allow the controller to go to sleep. It would start producing the expected amps when it came back on line. Normally the controllers respond to changes in light instantly.

[MEXICOWANDERER]

Yep. Same here. Did not realize how deep into algorithims (fuzzy logic) newer MPPT controllers have waded. Need same same panels. Best would be to cherry pick from a large stack. Same exact OCV and "I" short circuited. Absolutely exact.

[brulaz]

JiminDenver wrote:

...
For me it's understanding what would have been had I followed the advice I was given three years ago. I would consider the person that owns the company that developed three MPPT controllers and discusses them in depth to be more than just some person. My mistake I guess. Lol

When I added another parallel panel I followed your advice and this advice from the Rogue manual:

Although the individual PV modules of an array need not necessarily be of the same make or model, you will
achieve better tracking performance from an array in which all of the modules have the same maximum
power point (V mp ). This is best accomplished by choosing modules of the same make and model. Even if
modules are not identical, be sure that they each have the same number of cells. While it is possible to wire
modules together with varying numbers of cells, this will degrade the output of the entire array.

So I matched mono to mono, # and config of cells, and got within a few tenths of a volt Vmp. It wasn't easy to find the right panel, but I got lucky and only paid Can$1 per watt.

But haven't had the sun or loads to really challenge the array yet. So ...

[westend]

My hope is the info is useful to someone with mixed panels like I had. It might also help someone wanting to expand and not able to find a match to their original panel.

Exactly my situation and I do appreciate your posts on the experimentation.

[JiminDenver]

What's too bad is I had to sell the 245w mono's to get the new controller. The one side by side I did with one of those and the 250w poly had both at 35 Voc. The result probably would have been the same as the 250w has a slightly higher Isc and it's controller had a bit of advantage in output. Each controller ran at a different Vmp even though they were on a shared load.

My hope is the info is useful to someone with mixed panels like I had. It might also help someone wanting to expand and not able to find a match to their original panel. The options are to add a new panel/smaller controller and run them in parallel with the old system and milking both for all you can. Add a new panel matched up as well as possible with a big controller to run both, just maybe not as optimal as it could be. I've done both of the above as well as the last option which is spend the cash to have matching panels that the big controller would be able to run and not be confused.

For me it's understanding what would have been had I followed the advice I was given three years ago. I would consider the person that owns the company that developed three MPPT controllers and discusses them in depth to be more than just some person. My mistake I guess. Lol

[MrWizard]

if have a corresponding set of amp numbers
match them up side by side
i think you will see matching changes
the load cannot be consistently maintained because the voltage and current cannot be consistent using panels with different specs in series

[westend]

Part of the issues may be the type of MPPT controller being used and the differential outputs from the panels. Most newer controllers use a sophisticated algorithm and "Incremental Conductance" for stepping in the controller to reach the MPPT. The older "Perturb and Observe" models would probably have less of an issue with the mixed panels. Jim may have the IC model but is introducing his own perturbation with the mixed panels.

Article on MPPT implementation

[JiminDenver]

Generally I feel I have been lucky to have had as many different panels as I have and be able to run the odd ball test. You can see do this or that but not often why. Most people don't use a program to see the second by second operation of the controller either.

To the controllers credit, even in it's confusion it was able to deliver the total amps I would expect out of a pair of the weaker panel. Push come to shove the pair still deliver more than either panel alone in bright light. In low light it's better to run the poly by itself.

Looking at a log of the 220w and 230w in parallel earlier this year I can see the same rise and fall of the array voltage and current. This time the pair did produce close to the expected 27a.

So the controller will function and the output should be predictable if not perfect. Matching panels will always be the best choice.

Now if I had to run those two panels and found that running them together was bad for a single controller, I would run them with a pair of Eco-W just as I will run the 230w as a portable if needed. The Isc exceeds ratings here at altitude but that's nothing compared to what a MPPT controller can do with the excess voltage.

[grizzzman]

JiminDenver wrote:
Actually if you read the first part of my OP, the experts didn't know and suggested I run them on the Rogue 30a MPPT, even the owner. Come to think of it I haven't seen anyone post proof that the controller can lose the ability to settle on it's values or use the full potential output of the array. The concept of the weaker panel limiting is accepted, not the confused controller.

You took the word of a person that is NOT a panel expert plain and simple.

[Golden_HVAC]

When you are wiring a bunch of panels in series, then they need to be the same amperage rating, and probably the same brand, and voltage rating as well.

If you wanted to run them in parallel, then you could wire anything together, as long as the open circuit voltage is within 0.5 volts. But as you tested for yourself, those two styles of panels have different voltages under the same conditions. . So no do not pair them up.

It is not that expensive to buy it's own 20 amp controller for the oddball panel. Get a PWM controller, they are about $35. You might not get 'every' watt possible, but you will be surprised that it will put out it's rated amperage in Denver. Besides I do not thing your MPPT controller will be putting out 50 amps all that often, because the battery bank can only accept about 50 amps for a short time. Unless you are running an electric refrigerator on a big inverter, then you can consume all the power that all the panels can make.

So the 4th panel will only be needed when the batteries are really low. A 20 amp controller is only about $20 - 35 with shipping at this website.

AliExpress.com This is a company that lists many manufactures products, and then holds your money in escrow until you write in that the order has been received, and you are happy with it. If you do not write them within 60 days to extend the order time, they pay the seller. If you are not happy, you can open a protest, and they will work with you, and refund if required.

I bought some 24 LED 5050 Panel lights there, and replaced most of the bulbs in my motorhome with LED panels that are pretty bright. I even used my old pair of 45 watt panels on my buddy's home, with about 10 of the $1 panel LED's to light up his home at night. The controller that I bought has a light output that comes on after solar production stops, and will stay on all night, or for an adjustable number of hours.

Good luck,

Fred.