PWM VS MPPT TROPICS

[s/v Jedi]

Originally Posted by ChuckSK

Observe that the voltage at MPP dropped from 35 volts to 27 volts.

Pfffff.... That is not a voltage drop, that is a change in impedance.

[ChuckSK]

Originally Posted by s/v Jedi

Forgot: an easy way to check if your panel has a blocking diodeis directly attaching to a battery; if the battery get charged during the day but discharges into the panel at night, you have no blocking diode. This is how it was 30 years ago.

Now, I know for sure that my Shell/Siemens panels have blocking diodes and I'm sure somebody will come up in this thread to tell us if the Kyocera 130's have one. I'm pretty sure they do since the last 30 years...

The Kyoceras do not have blocking diodes. What difference would it make in any case since the blocking diodes would be conducting.

[ChuckSK]

Originally Posted by s/v Jedi

Pfffff.... That is not a voltage drop, that is a change in impedance.

I never mentioned a voltage drop. That was your comment.

[s/v Jedi]

There:

Originally Posted by ChuckSK

Because a shaded panel in one series string will pull down the voltage in the parallel unshaded series string, thereby causing a double loss, it would be better to use a separate controller for each string.

Chuck

[ChuckSK]

As I was saying, using a separate controller for each series string reduces shading losses.

[s/v Jedi]

Okay, I think I understand what you mean: with the partial shading, the MPP is at a lower voltage. That is very different from shaded panels pulling the voltage down of unshaded panels, which wouldn't happen: the open array voltage will be that of the highest voltage output string in the array.

But when you load it you will only get 50% output power for the highest voltages because the shaded string is below that voltage. The controller needs to lower the input impedance so that a bigger current pulls the voltage down enough so that the partially shaded string gets to play again. This is the intended operation.

Is this a test you did yourself? How many strings of cells are in each panel? and how sure are you that only one cell was shaded? I think you have two bypass diodes?

About blocking diode: I see that they are omitted because they are not needed anymore. I'm opening up the connection boxes on my panels so will check if I really don't have them as I see absolutely no discharge current at all. I did not know they had perfected this backfeed problem that good in 2003/2004 which is the manufacture date of my panels.

[s/v Jedi]

Oh wait, I recognize the screendumps I think... this is an emulation with Spice?

[s/v Jedi]

Hmmmmm... This made me search for the graphs of my panels and the difference is bigger than I expected, comparable to the Kyocera panels.

So I'm gonna change plans and will wire all six panels in series for a lovely open array voltage of 130V

My controller can take 150V max. So that should be okay. I will wire it so that I can quickly change between 1x6 and 3x2 so that I could do some testing later. Right now I am still at 6x1 and I see about 2.5kWh days, which would be way below the theoretical 3.75kWh that I should be able to make (5kWh per m2 for early March, northern hemispere). My 6 panels is 0.75m2.

Oh I can hardly wait to finish this project and see the amps flowing

BTW, my panels are the old Shell SM110-12p and have 3 bypass diodes: one for each 36-cell string plus one for the whole panel.

[sailinglegend]

Originally Posted by s/v Jedi

....BTW, my panels are the old Shell SM110-12p and have 3 bypass diodes: one for each 36-cell string plus one for the whole panel.

My search of the net to get to the bottom of this has come to the same conclusion. This is the first time anybody on this thread has mentioned a bypass diode for the whole panel. It doesn't matter if modern panels have bypass diodes - Kyocera I think have 8, my Solara have 2 - they are needed to minimise the shading problem from the 36 individual cells within the panel. But if I wire my two panels in series I need extra bypass diodes across each panel of the correct voltage and current rating. As we are all going though a regulator, blocking diodes are not needed.

For a very simple explanation of both types of diodes, with diagrams, go to:
Blocking and By-Pass Diodes Used in Solar Panels

If you have 5 or 6 panels then series may be better because of the smaller cable size that can be used, but you have to engineer them properly with the right low-volt drop bypass diodes.

It seems a pity nobody else has bothered to do tests on their panels over the weekend. As someone else said "just connect them in parallel and go cruising."

[Sumner]

Originally Posted by sailinglegend

...It seems a pity nobody else has bothered to do tests on their panels over the weekend. As someone else said "just connect them in parallel and go cruising."

Yep I agree. I like to see less theory and more real life tests like you did, thanks.

Ours are in parallel on both boats and have worked fine so will stay with that,

Sum

[colemj]

Why do you demand the experiments be done now? Many of us have already done that and reported the results. See post #16 in this thread. And do a google search on this site for another thread where tests by several people were also done and reported.

While our test was not done "this weekend", it was a 6-week test averaging output from 3 weeks in each configuration. For us, there is definitely a 25% increase for our series/parallel configuration over a strictly parallel one.

Mark

[s/v Jedi]

It is because our results are not what they have or what they want. It's unfortunate that theory doesn't agree with their wish so it gets pushed aside as well

Originally Posted by colemj

Why do you demand the experiments be done now? Many of us have already done that and reported the results. See post #16 in this thread. And do a google search on this site for another thread where tests by several people were also done and reported.

While our test was not done "this weekend", it was a 6-week test averaging output from 3 weeks in each configuration. For us, there is definitely a 25% increase for our series/parallel configuration over a strictly parallel one.

Mark

[zeehag]

i use 4 panels rated at approx 3 amps each and iu use a pwm controller---seems to work just fine n dandy ..am in tropix, and i have 2 huge panels resting, as i call it--not in use. when i am in temperate zones with less sun, i use all 6 panels.
sorry, no math for ye. i am just totally happy with my set up..for now....another place i may use a different set up, as i have with each place i have rested, so far.

[Sumner]

Originally Posted by colemj

Why do you demand the experiments be done now? Many of us have already done that and reported the results. See post #16 in this thread. ...

I did see your results and thanked you for posting them. Other than those I haven't seen others post anything here and none that were done at the same time in different controlled shading as was posted.

I also don't think anyone is 'demanding the experiments be done now', I'm not for sure. I look at old data or links to it where they tested different configurations similar to what was done above.

Jedi where are your results with panels in both configurations near to the same time with the same simulated shade?

Our one array has similar 12 volt panels but different wattages. They will stay in parrallel. The other boat has 6 80 watt panels all the same that are in parallel now. After what Mark posted back on post 16, that I did read and thanks again Mark, I might try them in a series/parallel configuration. I guess if I do that there is no need to post the results as there is no further need of 'experiments' ,

Sum

[Pelagic]

Originally Posted by colemj

We have 4 Kyocera 120W panels (nominal 12V) feeding a Morninstar Tristar 60 MPPT controller. The panels are mounted on our bimini - 2 per side - and are wired so that two the two panels on each side are in series and the two sides are in parallel. In this configuration, there isn't any partial shading of a series string.

In the tropics, we have no measurable gain in daily output vs. our old PWM controller when all panels were wired in parallel. We see a 25% increase in output when the MPPT is used with the series/parallel panels. We don't really see higher peak amperages from the MPPT vs. the PWM, so the gain must be from getting more usable power from the morning and evening lower light periods.

Our controller uses 1.3-2.5W, as per the spec sheet. The heat sinks are warmish, but not anywhere near hot, during the highest output. The heat sinks on the previous Trace C40 PWM controller got hotter. I don't know how much power the old controller used.

We get no SSB interference at all on any band from it. Our old Trace C40 PWM controller used to cause high interferences on many bands.

Mark

Thanks to all for this Series/Parallel discussion in order to maximize the benefits of a MPPT controller.

Just a newbie on Solar but I suspect the best wiring solution is often dependent on the balance between the equipment and installation factors.

Colemj’s 4 x 120W Kyoceras each have a Voc of 21.5V
As Mark surmised... a drop in voltage in low light supported his Series solution to keep juice flowing into 12v battery bank? (float at about 13.8v??)

In my case my 4 x Sunpower E20/327W units each have Voc of... 64.9V (for a 24V House bank)
96 cells and specs say 3 bypass diodes
I am also using the Outback 80 amp with 150VDC Max


1.....Will the MPPT perform better if it is seeing 129.8Voc as opposed to 64.9V for 24V delivery?

Unlike Colemj….I will have partial shading.

2......If so is it still worth testing in 2 sets of series, while at Marina?
Or
3......Just set up with 4 in parallel as previously advised?

Thanks for your guidance..

http://global.sunpowercorp.com/cs/Sa...&ssbinary=true