It’s often stated that PWM performs better than MPPT up to 10% at higher temperatures which is a statement that’s largely out of context and basically incorrect. For anything other than for simple solar arrays the performance of the two controllers is the same. I certainly agree that if you only only consider the panel temperature coefficients panel voltage goes down with increasing temperature and vice versa. The current changes but by by a much smaller percentage. I guess this is the source of the misinformation. Increasing temperature moves the maximum power point down (less power) and to the left (less voltage) and the IR curve also shifts to the left. This results in decreasing power available for charging and at both lower temperatures and higher temperatures MPPT has the advantage. IN 2014 when I was gearing up for solar I didn’t fully understand the issue which is explained in the “Victron White Paper Which solar charge controller: PWM or MPPT?”. If interested the document is not long or deeply technical. EnjoyClick here: https://www.victronenergy.com/blog/2014/07/21/which-solar-charge-controller-pwm-or-mppt/Then just under the Victron controller picture click on the link to download the pdf file.

Interesting article. “The MPPT controller will harvest more power from the solar array. The performance advantage is substantial (10% to 40%) when the solar cell temperature is low (below 45°C...”I don't camp much when the temp exceeds 113 degrees F for me or my panels.

No idea who often claims that.It is a fact that panel heating lowers the panel voltage so that typically, you lose 10% of the power because voltage which drops with heat is such a big component of watts compared with amps which go up a bit with heat. So you lose watts for using MPPT which has a buck converter that uses watts in and watts out.Meanwhile PWM gets the prevailing panel amps to the battery up to and sometimes over the Isc value no matter what the panel heating is. So for instance with my three 100w panels aimed at high sun each panel rated 6.3 Isc, I got 18.6 amps to the battery with PWM as seen on the Trimetric.Nostalgic photo--those three are now on top of the Class C in sig.Swapped out the PWM real quick, no change in the sky, for the MPPT controller set to 12-12, no change in wiring and Ta Da! 18.x amps not even 19. So same amps. I did all kinds of measurements of temperature with my IR gun and tried different things with different panels and measured it all, did all kinds of math with the temp coefficients . I reported a lot of that on here back then. Most of my notes from then are now gone.Anyway despite those studies that showed (one was Dutch ISTR) that what I was seeing was impossible, I got what I got. Everyone is invited to go out there and do the same thing, swapping controllers, etc, and see what you get. I have now got a mix of MPPT and PWM controllers in parallel set to the same voltage on my roof arrays and they all behave adding their amps to the right amounts (as expected by me) so I do not have a dog in this race anymore. I will stick with what I saw with my own eyes for real, never mind what I am supposed to see according to the MPPT enthusiasts, Dutch or not :) .Note--I do not have the controller efficiencies for my PWM and MPPTs. the wiring was good for 12v and both controllers were 12-12. Panel temps taken on the back of the tilted panels aimed at the sun showed variations in temp with location on the panel--not the same everywhere, but more to where the sun was and up higher too. So panel temp must be taken as some sort of average and the voltage of each cell is added to get panel voltage remember. Anyway, it was all good fun playing scientist and seeing what was really going on.

the full white paper is informative although I believe biased as one can see in the graph fig 15 (chapter 7). The problem is their comparison includes series connected panels for MPPT! Well additional voltage above batt from somewhere!"Let us now assume that the MPPT controller is connected to a solar array with sufficient cells in series to achieve an MPPT voltage several volts higher than the highest battery voltage."Full white paperIt is hot here! All I need to do is look at fig 15 and see that PWM is above the 90% line in the temps of concern. The MPPT line should mimic PWM when Vmp is less than batt voltage as seen in chapter 5. Vmp drops with heat!"Most MPPT controllers cannot transform a lower voltage to a higher voltage, as that’s not what they are made for. If the MPPT voltage Vm becomes lower than Vbat, they will therefore operate like a PWM controller, connecting the panel directly to the battery."to me the 90% line represents the bucking eff. With regular controller limiting power in abs and float it just don't matter much then you go series (wiring. light and heat) and ya need MPPT.

Lwiddis wrote:Interesting article. “The MPPT controller will harvest more power from the solar array. The performance advantage is substantial (10% to 40%) when the solar cell temperature is low (below 45°C...”I don't camp much when the temp exceeds 113 degrees F for me or my panels.Typically panel temp is about 20C above ambient, which I can confirm from my measurements. So when it is nice out at 25C, panel is 55C and down 10% in watts at around 50CI cannot understand the way they do panel specs at panel 25C which would mean ambient is just above freezing. Sort of weird.The MPPT guys all talk about power but PWM could care less about power--just the amps. So all that power being wasted by PWM is bogus, since you still get the rated Isc so the power does not matter.The main thing is that you need the buck converter in the MPPT to do 24-12 with 24v panels, which PWM controllers cannot do. They can do 12-12 or 24-24, while an MPPT can do either 24-12 or 12-12 or 24-24 so you have a choice between series and parallel with 12v panels.

Many panels have published NOTC.This test is @ 80% or 800 watts per square meter vs 1000.20C air blowing on the panel @ 20C.45C temps in these conditions! with a breeze and space behind the panel for air flow."Both conductive and convective heat transfer are significantly affected by the mounting conditions of the PV module. A rear surface which cannot exchange heat with the ambient (i.e., a covered rear surface such as that directly mounted on a roof with no air gap), will effectively have an infinite rear thermal resistance. Similarly, convection in these conditions is limited to the convection from the front of the module. Roof integrated mounting thus causes higher operating temperature, often increasing the temperature of the modules by 10°C."https://www.pveducation.org/pvcdrom/modules-and-arrays/nominal-operating-cell-temperature

Solar Controllers PWM MPPT Temperature Performance

Smileymaddog
Explorer
Jun 11, 2020
I found this video to be very helpful. Good luck and we love to talk to anyone about this. I have four 12v batteries on a 100watt panel in series and so far am impress what I can do.

https://youtu.be/kF_cVEYxj3E
BFL13
Explorer II
Jun 11, 2020
Vintage465 wrote:
All great info. Personally, I need the best charging when it's cold. I like to winter camp and the recharging in the morning when it's clear and cold is what I need. I think when It is hot thru the night I will have the fantastic fan on and the drain that it has will be overcome the following morning with the solar before it get's hot.

That is why they say to add up your rated Vocs in a series string and then x 1.25 for margin for when it is cold out. If you go over the controller's Voc limit, it fries--no second chances!
Vintage465
Nomad
Jun 12, 2020
BFL13 wrote:
Vintage465 wrote:
All great info. Personally, I need the best charging when it's cold. I like to winter camp and the recharging in the morning when it's clear and cold is what I need. I think when It is hot thru the night I will have the fantastic fan on and the drain that it has will be overcome the following morning with the solar before it get's hot.

That is why they say to add up your rated Vocs in a series string and then x 1.25 for margin for when it is cold out. If you go over the controller's Voc limit, it fries--no second chances!

I think I'm not in danger of exceeding my Voc's.........but I'd be more sure if I knew what Voc's are. Not real into acronyms here. I'm under the wattage, amps and voltage for what my controller is rated for. All panels in parallel.
BFL13
Explorer II
Jun 12, 2020
The specs for your controller will include a voltage limit. The voltage used for that limit is the open circuit voltage (Voc) of your panels added up if they are in series or for just one if they are in parallel.

Those panel spec Vocs are for 25C temperature (about 77F) and voltage goes up when it is colder than that. So they warn to allow more than rated Voc when camping in the cold so you don't hit that total Voc limit and fry your controller.
CA_Traveler
Explorer III
Jun 12, 2020
Voc Voltage Open Circuit
CA_Traveler
Explorer III
Jun 12, 2020
Morningstar has a calculator that will check your setup. On their website search String Calculator. If they don't have your panel you can enter it's specs. They only support their calculators and if you don't have one choose something like the MPPT 60. You'll get the information for the panels including Voc etc. With a non Morningstar controller the panel hookup information may not be correct but there is still a lot of good information.
CA_Traveler
Explorer III
Jun 12, 2020
Here you go: http://string-calculator.morningstarcorp.com/

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