600W Solar - Getting 420W Max

Sorry about that! It was just more about the watts you will see being less than panel watts rating, but got carried away there. (You are very polite! :) )

OP here, I am thank full for all the help I get from you guys. At time, it helps me a lot, however some times you get into your own world over some things that I have no clue on what you are talking about, and some time I don't think it has to do with a persons original post or question. I hope I don't get on wrong side of you guys as I find some of your information very helpful. Thanks everyone. I am very happy with my 600Watt system and my PWM controller. If I was going with higher voltage panels I would have gone with MPPT system, however cost wise for me, I thought this was the way to go. Thanks Gary

Salvo, you ignored that I could not get Isc from the 60 cell panel doing 24-24 so I didn't get as many amps as I should have compared with 12v 36s.

So you just can't use the Iscs in proportion to compare. If you could, I would have been getting 9 amps (like 18)with the PWM instead of 8 amps (like 16) with the MPPT, but they were even at 8.

I don't know why the panel Isc (disconnected) was 9.2 amps (rated 9.0) but the controller only saw about 8 amps. With 36 cell 12v panels it sees the rated Isc doing 12-12.

The MPPT controller also saw 8 with 24-24 instead of 9 as usual with 24-12.

That makes it look like the lower "overhead" with the 60 on 24s put the amps farther to the right on the IV curve (so at a lower amount)?

EDIT- the 255w 60 with 9 Isc only drops to about 8.8 at 26v, but the 310w 72 stays at 9 way higher in battv, but 8.8 is still not much down like at the 8 in question, so IV curve can't be the real story I guess.

That would not affect MPPT output amps (which are based on output watts) but would affect the PWM which just does the actual amps never mind the watts.

the 24-12 MPPT amps with 60 cells were the same as the 12-12 PWM 72 cells would have been at Isc. I think the 60 cell and 72 cell amps with MPPT would be the same having the same watts.

The curiosity is how the 24v 60 cell panel Isc is higher in proportion than 72s but Salvo explained that earlier. It is just that you can't get at all of them :(

I didn't have to account for heat. I compared two pwm systems. One system has 36 cells & 12V battery the other 50 cells & 24V battery. If the panels have exact same wattage, the 50-cell panel outputs 20% more power.

Your conclusion has little to do with mppt vs. pwm. It's a 36-cell vs. 50-cell issue.

BFL13 wrote:
Salvo, check out my EDIT above (we cross-posted). In your comparison I think you did not account for the heat loss when using MPPT, which does not apply to the PWM getting Isc.

Salvo, check out my EDIT above (we cross-posted). In your comparison I think you did not account for the heat loss when using MPPT, which does not apply to the PWM getting Isc.

That just goes to show your pwm is quite a bit worse.

Let's look at some real life numbers. We'll compare a 60-cell 24V battery pwm system to a 36-cell 12V battery pwm system.

Sharp 224W, 60-cell: Isc = 8.33A
Kyrocera 140W, 36-cell: Isc = 8.68A

To make things equal, we'll scale the 224W panel down to 140W to get an equivalent Isc.

Isc_60cell = 8.33A * (140W / 224W) = 5.20 A

Now we can calculate how many watts each system outputs.

12V system: P = 13V * 8.68A = 112.84W

24V system: P = 26V * 5.20A = 135.2W

The 24V system outputs 1 - 135.2/112.8 = 20% more power. That's the same 20% advantage I calculated in my previous post.

BFL13 wrote:
The 60 cell "amps advantage" didn't happen in real life though.

The 60 cell "amps advantage" didn't happen in real life though.

I expected to get panel Isc by using PWM but instead of 9 amps I got 8 amps with both the MPPT and PWM controllers in 24-24. Amps would not go higher at full insolation. I suppose that has to do with the 60 vs 72 cell business, but it didn't affect the comparison.

If I had 72 cells, the voltage would be higher but the amps lower on the same 255w. So I should get the full Isc, but that Isc would be less, so I figure it is a wash. A watt is a watt.

(The 60 vs 72 did show up in terms of "overhead" when I could not get the 24v batts higher than 30v (like 15v on 12v) but that is not an MPPT vs PWM thing--neither could get the batts higher.)

EDIT--example 72 cell 310w vs 60 cell 255w(mine) -both CanSolar
Vmp- 36.4/30.2
Imp- 8.52/8.43
Voc- 44.9/37.4
Isc- 9.08/9.0

So compare getting Isc with 310w worth of 36 cell 12v panels vs MPPT with that 72cell 310w panel.

PWM- 310/130 x 8.2 = 19.55 amps (like 9.8 at 24v)
MPPT -310w minus 8.6% for heat (20C above 25C-- 45C) = 310-26.7 = 283.3w minus 2% line loss to controller 5.7w = 277.6w input minus 5% controller loss 13.9w = 263.7w output. ---at 26 battV, 263.7/26 = 10.14 amps

So it is 10.1 vs 9.8 using 2% line loss and 5% controller loss for the MPPT (does not affect the PWM) If I picked 3% line loss and 6% controller loss it would be 283.3-8.5 = 274.8 - 16.5 = 258w/26 = 9.9a vs 9.8 amps.

So now what if it were warmer out like when it was 25C and panel was 51C? Now panel heat loss is 51-25 = 26 x 0.43 = 11.2% (34.7w) instead of that 8.6%.

So now 310-34.7= 275.3 minus line loss (use 2% again, why not?) 5.5w = 269.8 minus controller loss (5% again, why not?) 13.5w = 256.3/26 = 9.85 amps vs 9.55 amps--Drat! Should have used 3% for line loss :)

No, I call that cheating. You changed the ground rules. It's not an apples to apples comparison.

Some very smart people determined you need 36 cells to configure a 12V panel. If you have a 24V battery then you need 72 cells.

I believe your "24V panel" has only 60 cells. It is not a 24V panel, it's more like a 20V panel.

What does that mean? Since panel power does not change, if voltage goes down by 20% then current must go up by 20%. In other words, the "24V panel" has larger cells that produce more current.

You are giving the pwm configuration a 20% advantage from the get-go and then concluding pwm is better.

Your test and conclusion is one of smoke and mirrors.

BFL13 wrote:


And that was all "apples to apples"--same panel, same wires, same batts , same day and time of day.

Salvo wrote:
Let's be clear. PWM never has an advantage. It will always lag MPPT in performance. When comparing apples to apples, under normal operating conditions, mppt will have a 5 to 10% advantage.

JiminDenver wrote:

PWM advantage when it is hot is mid day when most of our systems are in float or close to it and again, there isn't much advantage there.

Never say never. :)

Actual results with 255w panel same wiring, same batts just swapping controllers. 25C ambient, 51C panel (IR on back of tilted up panel)
Panel rated Isc 9.0, actual Isc at the time was 9.2 so insolation was STC or better.

Standard PWM (12-12) would get 255/130 x 8.2 = 16a but not possible to measure 12-12 PWM with 24v panel. I was able to measure 24-24 PWM by putting the batts in 24v mode.

Results (mode, battv, output amps, output watts)

24-12 MPPT 13.0v, 15.85a, 206w
24-24 MPPT 27.0v, 7.95a (like 15.9a), 215w
24-24 PWM 27.0v, 7.99a (like 16.0a), 216w

So call the 24-24s equal. The 24-12 MPPT was also equal to the expected 12-12 PWM as calculated at 16a. So really, it was 16a for every situation 12v batt or 24v batts.

And that was all "apples to apples"--same panel, same wires, same batts , same day and time of day.

I do agree that often, the 12-12 MPPT does a little better than 12-12 PWM as Salvo measured in his test a while back and as I have also seen. But as seen above, it is not always so. Never say never!

JiminDenver wrote:

CT_WANDERER wrote:
OP here, I am running with a Morningstar TS45 PWM controller.

You may see a improvement with a TS-MPPT-45 but it comes at a cost. The question is are your needs being met?

Yes I am happy with my system, I was trying to get an idea if this is what I should expect, or if I should see more? The 420 was peak. I am happy with seeing the 87 to 197AH days recorded on the Morningstar control panel. In 35 days I only had to use the converter four night(cloudy or raining days) to bring my batteries back up.

I guess the only way I will see higher watts would be to tilt the panels.