Hi all,Victron, which makes high quality equipment, has charge controllers. At the end of an overview they give their description of the differences between PWM and MPPT. They do not support it with figures, but they don't get into any "hype" either.Charge Controller"PWMThe PWM charge controller is a good low cost solution for small systems, when solar cell temperature is moderate to high (between 45°C and 75°C).MPPTTo fully exploit the potential of the MPPT controller, the array voltage should be substantially higher than the battery voltage. The MPPT controller is the solution of choice for higher power systems because of the lowest overall system cost due to smaller cable cross sectional areas. The MPPT controller will also harvest substantially more power when the solar cell temperature is low (below 45°C), or very high (above 75°C), or when irradiance is very low."Here is a link to the "white paper" from Victron. It does have a lot more to say about the differences.Basically MPPT is better than PWM in low light because panels can be placed in series.White Paper MPPT or PWM

PT Thanks for the linkAlways nice to read this kind of stuff Every manufacturer has their unique spin

Hi KJ,The white paper goes into a lot more detail. I would rather pay for MPPT, but I probably can't afford a high amperage Victron controller.

IV and power curves :BComment: They use a 45C temp for their low light conclusion :hThe white paper supports free standing portables for those so inclined :C

Sort of what I have been seeing as previously posted a few times.However, the paper calls "performance" by the watts. This is bogus. Performance is in amps to the battery. Watts mean nothing to the battery. Amps charge the battery.So it is disguised how the PWM is "under-performing" in watts but doing just fine in amps to the battery.The other thing is that STC is 25C CELL temperature, not ambient. At 16C ambient, open back panel propped up, under the panel aiming the IR gun up at the white backing a foot away, I got 44C. At 25C ambient, I got 51C under the panel.Ambient would have to be near freezing to get panel at only 25C.So it is not made clear that most of your camping time is when ambient is between say 15C and 25C when panel temps are so high that PWM is nearly as good in watts as MPPT, and according to my results at 25C ambient/51C panel --ie, all summer! I got more amps to the battery with PWM than MPPT. This is hidden in that paper by only talking about watts. :(To repeat my 230w results for comparison I got:Ambient T, Cell T, MPPT Amps, PWM amps16C, 44C, 15.5, 14.525C, 51C, 13.5, 14.5

Hi,I would surprized to see a panel temperature much higher than 45 C (113 f) in low light conditions. Their definition of low light is 1/5 of STC test conditions or an irradiance of 200 compared to 1000.If you read the entire white paper you will find they say that between 45c and 75c that pwm and mppt perform more or less the same. Below and above those numbers MPPT has an edge. Since BFL13 has measured 51 C at an ambient of 25 c I'd not be surprized at all to see panel temperatures above 75 C when it is 40 C ambient. My interpretation of the reason for high temperatures is that pwm panel voltage may be below the 14.8 volts needed to complete the charging on a lead acid jar. That can not happen with MPPT because voltage drop is not going to be from 34 down to 14.8 EVER (maybe on Venus?).They are also of the opinion that with 12 volt batteries pwm for small wattage systems is probably the way to go. But with larger wattage (and amperage is of course higher) then MPPT comes into its own. They make both pwm and mppt controllers, so they have no reason for a bias to one type or the other. I don't think they are hiding anything.red31 wrote:IV and power curves :BComment: They use a 45C temp for their low light conclusion :hThe white paper supports free standing portables for those so inclined :C

mppt or pwm An opinion from Victron | Good Sam Community

MrWizard
Moderator
Dec 28, 2014
no temp doesn't affect the mppt controller
high temp reduces the output of the solar panel
reduced output means there is less power for the mppt to harvest
but it will produce just as much as the pwm controller NOT less
there is just less overhead to be harvested

Salvo wrote:
No, nothing significant is wasted. You forgot one key element to the equation: TEMPERATURE. It kills mppt performance. Go read that white paper again. It's very good.

The 36-cell panel was specifically designed for pwm use. Very little power is wasted at normal operating temperature. That's why there's only a 5 to 10% performance gain of mppt over pwm.

MrWizard wrote:

7amps at 14v is 98 watts, with out MPPT you loose the rest of the power, it is simply not converted... it is chopped off and eliminated... wasted ..not used

PWM is fine for panels with a 16v output, but wastes power on larger panels
BFL13
Explorer II
Dec 28, 2014
JiminDenver wrote:
I've never had my Schott poly 230w peak out at 13.5a no matter what the temperature. Maybe 14.5a once but generally it's a solid 15-16a depending on here or at altitude. The difference in peak on my 245w twins was 16.5a on a hot day vs 17.1a on a cold clear morning, both tracking. The Canadian solar 220w mono is a very solid 12a here unless you put it in freezing temps, then you get a extra 3/4a. I don't see a huge drop with heat (80-90s), just a bit of a rise from cold. (sub freezing)

I have been reading about solar air mass on Google. It is not just a question of altitude, but it could be that you would get better results at your locations at either 5,000 or 10,000 ft than where I got mine at the sea shore.
BFL13
Explorer II
Dec 28, 2014
Salvo wrote:
Without measuring the panel output power, your time was wasted writing all that. :S

BFL13 wrote:
A. 230w (two 115w) total Isc of 14.5a to battery, batt voltage 13.5 = 196w

230-196= 34w wasted or 34/230 = 14.8% wasted power with PWM all season

B. One 230w and MPPT 15.5a to battery, batt voltage 13.5 = 209w

230-209 = 21w wasted or 21/230 = 9% wasted power with MPPT at 16C ambient, 44C panel. (April)

C. 230w and MPPT 13.5a to battery, batt voltage 13.5 = 182w

230- 182 = 48w wasted or 41/230 = 21% wasted with MPPT at 25C ambient, 51C panel (July)

Salvo, I don't think so. It is not necessary to have exact figures to show that the panel does fewer watts than rated when hot. The definition of "wasted watts" may be at issue.

If the watts were never produced, were they "wasted" or just lost?

I do have the controller's output power as quoted above, so all I need is controller efficiency and there is the power at the controller intake. I also know that voltage is 29.3 at the panel and 29.0 at the controller for line loss. That voltage should be the Vmp selected by the controller at the time. Only thing not measured is Imp but it can be calculated from what is known.

If my controller is 93% efficient, much lower than its max efficiency, then when its output is 182w as seen in July, then input must have been 196w. (29.0 Vmp x 6.76 Imp)

Suppose I had a meter on Imp and it was indeed 6.76 while voltage at the controller's array terminals was 29.0. What more would that tell you than now? What more would you know if it were higher or lower other than give a different controller efficiency percentage?
Salvo
Explorer
Dec 28, 2014
Without measuring the panel output power, your time was wasted writing all that. :S

BFL13 wrote:
A. 230w (two 115w) total Isc of 14.5a to battery, batt voltage 13.5 = 196w

230-196= 34w wasted or 34/230 = 14.8% wasted power with PWM all season

B. One 230w and MPPT 15.5a to battery, batt voltage 13.5 = 209w

230-209 = 21w wasted or 21/230 = 9% wasted power with MPPT at 16C ambient, 44C panel. (April)

C. 230w and MPPT 13.5a to battery, batt voltage 13.5 = 182w

230- 182 = 48w wasted or 41/230 = 21% wasted with MPPT at 25C ambient, 51C panel (July)
JiminDenver
Explorer II
Dec 28, 2014
I've never had my Schott poly 230w peak out at 13.5a no matter what the temperature. Maybe 14.5a once but generally it's a solid 15-16a depending on here or at altitude. The difference in peak on my 245w twins was 16.5a on a hot day vs 17.1a on a cold clear morning, both tracking. The Canadian solar 220w mono is a very solid 12a here unless you put it in freezing temps, then you get a extra 3/4a. I don't see a huge drop with heat (80-90s), just a bit of a rise from cold. (sub freezing)
BFL13
Explorer II
Dec 28, 2014
A. 230w (two 115w) total Isc of 14.5a to battery, batt voltage 13.5 = 196w

230-196= 34w wasted or 34/230 = 14.8% wasted power with PWM all season

B. One 230w and MPPT 15.5a to battery, batt voltage 13.5 = 209w

230-209 = 21w wasted or 21/230 = 9% wasted power with MPPT at 16C ambient, 44C panel. (April)

C. 230w and MPPT 13.5a to battery, batt voltage 13.5 = 182w

230- 182 = 48w wasted or 41/230 = 21% wasted with MPPT at 25C ambient, 51C panel (July)
pianotuna
Nomad III
Dec 28, 2014
Hi SC,

Do you see any amps when getting 17 volts from moonlight?

Shadow Catcher wrote:

I was forced to buy an MPPW controller by my ignorance, I bought a 185W 66 cell high voltage panel intended for a residential grid tie system. that will typically put out 35V in shade, I have even seen it put out 17V under a full moon. Morningstar makes a good quality product and respond quickly to problems.
Salvo
Explorer
Dec 28, 2014
No, nothing significant is wasted. You forgot one key element to the equation: TEMPERATURE. It kills mppt performance. Go read that white paper again. It's very good.

The 36-cell panel was specifically designed for pwm use. Very little power is wasted at normal operating temperature. That's why there's only a 5 to 10% performance gain of mppt over pwm.

MrWizard wrote:

7amps at 14v is 98 watts, with out MPPT you loose the rest of the power, it is simply not converted... it is chopped off and eliminated... wasted ..not used

PWM is fine for panels with a 16v output, but wastes power on larger panels
Shadow_Catcher
Explorer
Dec 28, 2014
Morningstar has a similar white paper comparing MPPT and PMW controllers MPPT vs PMW

I was forced to buy an MPPW controller by my ignorance, I bought a 185W 66 cell high voltage panel intended for a residential grid tie system. that will typically put out 35V in shade, I have even seen it put out 17V under a full moon. Morningstar makes a good quality product and respond quickly to problems.
MrWizard
Moderator
Dec 27, 2014
Was asking why so many installations including the AM Solar installs use a MPPT controller as compared to the lower cost PWM controller for the parallel nominal 12Vdc array.

my take on this, Nominal is the word in question
140w has an ISC around 7amps because the voltage is 19v~22v (only need 14+ to charge the battery)
7amps at 14v is 98 watts, with out MPPT you loose the rest of the power, it is simply not converted... it is chopped off and eliminated... wasted ..not used

PWM is fine for panels with a 16v output, but wastes power on larger panels