Answering some solar panel with MPPT controller ?

[ktmrfs]

Here is some real world data on solar panels when used with a MPPT controller to answer some question I, BFL and others have.
This report is focused on the questions we had regarding solar panel use with MPPT controllers.

AND FOR THOSE WHO MAY WANT TO START A MPPT VS. PWM CONTROLLER DISCUSSION PLEASE DO NOT TURN THIS INTO ANOTHER MPPT VS. PWM DISCUSSION, FLAME ETC. IF YOU WANT TO CUSS OR DISCUSS PWM VS. MPPT CONTROLLERS GO START ANOTHER THREAD.

OK, now to the questions I was looking to answer for:

1)BFL’s question; “Can you look for a peak in Voc or Isc to determine optimum panel orientation?”

2)Can one predict accurately output power by measuring MPPT input voltage and panel output current?

3)In late fall at high latitudes what % of nominal power can I expect to get from the panel under optimal light?

4)Can one predict power loss between the panel and controller and predict the effect on output power (charging current and watts) with reasonable accuracy?

5)If one knows the resistance and current between the panel and controller can one predict the power to the battery with Series vs. parallel panels and longer or higher resistance paths between the panel and controller? (really an expansion of the above question)

6)Can one measure Temperature effects on Panel output power?

7)What is typical MPPT controller efficiency, or for this paper, the efficiency of a Morningstar sunsaver 15 MPPT controller operating in the 130 W region???

8)What if I just lay the panels flat, how far from peak power will I be?

9)With series connected panels what is the effect of shading on one of the panels?

10)Since I also have another trailer with PWM controller and use the same portable panels with this trailer, I was curious what effect a long (90ft) run between the panels and PWM controller has when used with a PWM controller. In this case I don’t have the choice of going series connected panels, that’s counterproductive. So staying with parallel connected panels is the only choice. Can I predict the results?

Rather than one LONG……. Post, I will break the post into sections. The next section is focused on assumptions, test conditions, test equipment, and test methodologies.

Then there are individual posts for each of the 10 questions.

And for those reading now, please delay any responses till you see a “That’s All folks” in my last post so my posts can be in sequence uninterrupted. I should have them all posted within an hour.

[ktmrfs]

NinerBikes wrote:

ktmrfs wrote:
Post #10

10)
This is for the case of resistance between the panel and controller. The effects of a long run with PWM controller between the controller and battery bank is not part of this investigation. That experiment is “left as an exercise to the reader”. Any volunteers???

How would this vary between MPPT and PWM, assuming same input voltage and same input amperage coming out of the devices to the battery? Obviously, the thicker the wire and shorter the run, being DC current, the lower the losses of watts/voltage and amperage. This is of concern if you use long runs of wire between portable solar cells and your batteries, I would assume?

As you noted, "short and fat wins over long and skinny every time."

However there are several things that come into play that could have different consequences on MPPT vs. PWM with a higher resistance between the controller and battery.

I gave it signficant thought, and really couldn't remotely convince myself what the effects would be on each system, so rather than speculate, I left it as "an exercise to the reader".

similar to some of the textbooks I had in college where MOST answers were in the back. the ones without an answer often said. "left as an excercise to the student" I quickly figured out that the prof that wrote the book didn't give the grad student solving the problems the solution, and the grad student finally gave up trying to solve the problem and "left it as an excercise to the student".


If anyone has some actual comparison data, or even data for increased resistance effects between the controller and battery for EITHER controller type, please post.

[ktmrfs]

harold1946 wrote:
My question is how were you able to maintain 70 degrees panel temperature throughout the testing?

ambient was 70 as noted in the setup. Panel temp was 115F ish by time everything was set up and stayed in that range throughout the test. See more info on the post about temperature effects.

[BFL13]

harold1946 wrote:
My question is how were you able to maintain 70 degrees panel temperature throughout the testing?

He said 70F was ambient throughout and panels heated up right away so presume also maintained steady temp at 28C above ambient as he reported.

In my recent test of a panel, taking it out from the cool temp garage, it showed 37v Voc immediately, as rated, but very quickly that dropped to 36v as panel heated up. You could feel the glass was now warmer than it was at first. Happened fast.

[harold1946]

My question is how were you able to maintain 70 degrees panel temperature throughout the testing?

[NinerBikes]

ktmrfs wrote:
Post #10

10)
This is for the case of resistance between the panel and controller. The effects of a long run with PWM controller between the controller and battery bank is not part of this investigation. That experiment is “left as an exercise to the reader”. Any volunteers???

How would this vary between MPPT and PWM, assuming same input voltage and same input amperage coming out of the devices to the battery? Obviously, the thicker the wire and shorter the run, being DC current, the lower the losses of watts/voltage and amperage. This is of concern if you use long runs of wire between portable solar cells and your batteries, I would assume?

[ktmrfs]

CA Traveler wrote:
The serial panel shading test could suggest that the panels have bypass diodes. Is that the case? Shading only 1 or 2 bypass cell areas would also be interesting.

Perhaps even more interesting would be a test with soft shading (like a tree) on 1 and 2 panels as compared to full sun. Past discussions suggest parallel panels with soft shading on one panel will outperform the same shading on serial panels. I.e. Soft shading on one serial panel restricts the output of both serial panels.

More ideas for more tests. And if I do more tests, I think I'll just use the MS SW for the controller.

[CA_Traveler]

The serial panel shading test could suggest that the panels have bypass diodes. Is that the case? Shading only 1 or 2 bypass cell areas would also be interesting.

Perhaps even more interesting would be a test with soft shading (like a tree) on 1 and 2 panels as compared to full sun. Past discussions suggest parallel panels with soft shading on one panel will outperform the same shading on serial panels. I.e. Soft shading on one serial panel restricts the output of both serial panels.

[KJINTF]

Always something to do ..........

I used the MSVIEW software to get the data for the many detailed grpahs I posted a few months back. Thinking the controllers efficiency was excessive I then used external test equipment for a few static measurements and obtained extremely close results. My conclusion is that the software is wonderful and lets the user easily get all the data they will ever need.

My tests were done by selecting all the variables (TS_MPPT 60) and a 2 second sample rate for about 10 to 15 minutes of data collection, while loading the controller with a several hundred watt load. The data confirmed most of my assumptions with only a few items that made me take a closer look see. This solar PV stuff is a lot of fun. Nice to see everyone does it differently and expects different functionality.

again thanks for posting your data
Looking forward to seeing other folks data

[ktmrfs]

KJINTF wrote:
Good read!

Individual PV systems and environmental conditions vary almost as much as each user’s expectations of their personal system

Do you have the MS adaptor that fits into the data port of your Sunsaver 15?
It's low cost and a nice thing to have laying around
PM - me if you want to borrow mine
My rig is put away for the winter

MSVIEW can be used to log a few dozen parameters of that nice little controller

KJINTF:

, yes I have the MS adapter and SW. In fact I used the adapter and SW to make a custom charging profile for the controller that I can switch over to when it fits.

Didn't really think about using the SW for collecting the data Good and Bad.

The Good is that w/o the SW I used commonly available tools and techniques that others could use to do similar measurements on their systems.

Bad is that with the SW it may have been quicker and let me output charts and graphs. And by using the SW I likely would have been able to get data that would give a better shot at determining controller efficiency.

It would be interesting with the SW to watch input voltage/current with big changes in conditions (quickly shading one panel) to actually graph how the controller searches for Vmp and Imp.

Ah.... now a few more experiments I can think of doing....

[ktmrfs]

red31 wrote:
Thanks for the effort and report.

I'm gonna guess these test where made on Oct 14, 2013 based on the data from U of O (Portland), click on chart recent data, then previous chart back to 10/14/13.

ktmrfs wrote:

And looks like in the fall at 46N latitude, I’m getting about 135 Watts from a nominal rated 160W panel, or about 85%. Sounds pretty reasonable to me, but would be interested to know what others are getting under similar conditions.

yes, the data was collected on Oct 14th and 15th, amazingly we had absolutely clear skies on the 14th, a few wispy clouds in the morning and evening on the 15th. And there also was NO noticeable haze either. Summer "clear" skies in portland start to get hazy after a few days due to pollution.

[red31]

Thanks for the effort and report.

I'm gonna guess these test where made on Oct 14, 2013 based on the data from U of O (Portland), click on chart recent data, then previous chart back to 10/14/13.

ktmrfs wrote:

And looks like in the fall at 46N latitude, I’m getting about 135 Watts from a nominal rated 160W panel, or about 85%. Sounds pretty reasonable to me, but would be interested to know what others are getting under similar conditions.

[DryCamper11]

Thanks for the report. I know how much work it takes to do something like this.

[KJINTF]

Good read!

Individual PV systems and environmental conditions vary almost as much as each user’s expectations of their personal system

Do you have the MS adaptor that fits into the data port of your Sunsaver 15?
It's low cost and a nice thing to have laying around
PM - me if you want to borrow mine
My rig is put away for the winter

MSVIEW can be used to log a few dozen parameters of that nice little controller

[ken_white]

ktmrfs, thanks for taking the time to try and sort out some of the nuances between systems.

[BFL13]

Lots to learn from there! Very clear report. Thanks very much for sharing this information.