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.

[NinerBikes]

Thank you ktmrfs... I am moving up fast on the learning curve with your very thorough lab results, as best as the equipment can measure.

As for your PWM and adding cable length once past the controller... One would look at the quality of the connections / size surface areas of the connections, dielectric grease treat them, and the gauge of the wire and the length of the run for additional resistance/voltage loss, as well as connections/oxidation at the battery terminals, due to acidic gases at the battery charging site, in the case of lead/acid vented batteries.

Keep the runs short for cable, the cable fat, and use the best connections you can, within budget, to keep the resistance losses down and your voltage up. No idea how much amperage is lost, but DC current is not kind to it on longer runs... it's why all high voltage long distance high tensions wires are run in A/C, not D/C.

Wish I would have taken more engineering courses in college, both electrical and mechanical, but I had some hard times with Acronyms, greek letters and advanced formulas.

Most important "trick" learned for efficiency is the dart with a suction cup or good old duct tape and a roll of empty toilet paper as a sight tube to optimize angle of panels.

Any one that would like to direct me to PWM threads, losses, and parallel panels and how to minimize losses, it would be greatly appreciated.

Two days ago, I was a complete newbie, and the threads read like Greek on panel brands and how the whole thread went sideways.

Yesterday I was down at Solar Blvd, a 70 mile drive to get some hands on visuals for some sort of portable system... with an idea to upgrade batteries in a bit. Watts is nice, amps are great too, but it takes enough voltage to overcome battery resistance to charge effectively. That 90% charge figure, while dry camping, done enough times, is just not enough... you need to get to 100%. So a 6 amp charger, a quiet Honda Gennie, and popping the covers and looking for bubbles is the acid test for 100% charge. And to think I knew this as a Power Train Technician my first year in college at Sears Automotive testing Die Hard Batteries, doing load tests on them... 600 amps and 10 seconds with voltage not to drop below 9.6V.

Look for the bubbles... and keep distilled water handy, and you should be good to go.

Also agree with you... I drive a long ways with trailer in tow to go fly fishing, so fly tying and fishing comes first, I can dink around with the trailer and electrical charging devices all I want once back home, fishing time is prime time, if my calculations and investment in solar panels are off a bit, the Honda Gennie can always take up the slack. Not afraid to over charge just a bit, boil off some water, and replenish with distilled, just don't make a habit of doing it too frequently. Battery life is short, price is low amortized over 3, 4, 5 or 6 years.

[westend]

Thanks for your experiments and posting. I know this took quite a bit of time and was more for the benefit of others.
I'll try to get up some type of meaningful numbers with my own smallish stationary system when time allows. I have the SS-MPPT-15 and Morningstar communications adaptor so, if I can get an understanding of MSView, the data should be easier to log and display.

Reading between the lines of how you use solar and your usage, along with the equipment you have, it seems like the purchase of a bigger +200w panel might fill in your power requirements quite well. I guess that would depend on how many modules you want to deploy and if you deem it worth the effort and expense.

Thanks, again for your efforts, there is very little real world data that is at the level of what you've done, and available.

[mena661]

Great work!!

[JiminDenver]

ktmrfs wrote:

JiminDenver wrote:
Great write up

I'll try to run the same types of test this weekend.

sea level far north vs. mile high and south two noticeably different test conditions, anxious to see the results.

We shall see what the brown cloud is like. Some days i can barely see the mountains.

[ktmrfs]

JiminDenver wrote:
Great write up

I'll try to run the same types of test this weekend.

sea level far north vs. mile high and south two noticeably different test conditions, anxious to see the results.

[JiminDenver]

Great write up

I'll try to run the same types of test this weekend.

[ktmrfs]

Post #11, summary and THE END!

Final thoughts

Hopefully this somewhat long and verbose post of various experiments is of value and helps provide some insight and answers to some of the questions posed regarding use of a solar panel with an MPPT controller.

It certainly will help me get maximum power and maximum battery charge into my batteries when we go camping next summer. This last summer I was clearly doing some things that were NOT helping get maximum charge into the batteries.

First, I was ignoring cable power loss until my last trip and using long cables and parallel configuration. One of those “currents to low, it won’t be a problem”. On our last trip I did a series connection and thought I was seeing better performance, but while camping wasn’t going to spend time doing an experiment. Fishing was higher on the list.

Second, I really wasn’t paying a lot of attention to panel orientation. Mostly a “this looks about right”. Given that in the same time I could get optimal orientation, why not.

Since we don’t have enough solar, and DW likes to occasionally use the hair dryer, microwave etc. along with the furnace in the fall or fans in the summer, we seldom can use just solar to get the batteries charged. I typically recover between 50% and 80% of the power used the previous day. Keeps us from running the generator more than once/wk. But that also means the batteries can take ALL the current the panels can deliver. So minimizing losses is important for us,.

For those who can get to full charge before the end of the day, bits of additional power loss may not be nearly as big an issue but might let you get to full charge earlier in the day.

And I'd like to give thanks to those who were asking questions about solar and MPPT controllers. Trying to answer those questions was certainly valuable for my solar use cases, and a good brain excercise for a retired engineer.

[ktmrfs]

Post #10

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. Can I predict the results?

I've updated this post with some "before and after" data I forgot to include initially. MPPT parallel output current before the swap and after the swap. Just to check that conditions were similar to the day before and that solar conditions didn't likely change much during the test. Also to verify that I was operating the panels near Imp. Since I thought the biggest influence of changing resistance would occur with the PWM controler operating between Imp and Isc. No point in swapping controllers if I wasn't near Imp for panel current.
Thanks to BFL for bringing this to my attention.

OK, I’ll start with the last part first. Can I predict how cable run length (or more accurately additional resistance) will affect the current when used with a PWM controller? Qualitatively yes, quantitatively NO. Assuming the panel is operating near or above Imp, additional wire resistance will cause the panel voltage to rise up on the VI curve, and in the area of interest, increasing voltage will cause a slight decrease in current. How much? That’s the hard part. It’s highly non linear. My guess is not near as much as with an MPPT controller.

Test method. As quick as I could, I swapped out the MPPT controller for the PWM controller. Time to swap was about 10 minutes. In this case series connected panels make absolutely no sense, your throwing away current; all I’d get would be 4.5A or so. No reason to even do that test with a PWM controller.
Since a PWM controller is not a power converter more like a voltage controlled current source, I didn’t bother measuring voltages, just battery current.

Test:
parallel connected panels with MPPT controller and very short interconnect as a baseline comparison to previous days test.
Battery current: 10.4A (trimetric)
Parallel connected panel with PWM controller and very short interconnect.
Battery current: 9.5A (Trimetric)

Parallel connected panel with 90ft of cable BETWEEN the panel and PWM controller.
Battery current 9.0A (Trimetric)

parallel connnected panels with MPPT controller and very short interconnect
Battery current 10.3A (Trimetric)

solar conditions likely stable "enough" during the tests.

Conclusion:
First, test conditions are "close enough" to the day before that I was operating under similar conditions and the panel output is near Imp, something I wanted to see for the PWM data.

With panels in parallel, 90ft cables and the MPPT controller I saw a drop of almost 1.1A from optimal configuration of very short cable.

Under similar test conditions with PWM the drop was about half, 0.5A.

The % drop was 5.3% for the PWM case, 10% for the MPPT case with parallel cables. The effect of additional cable resistance between the solar panel and PWM controller clearly is not as significant with a PWM controller as it is with a MPPT controller, at least when the PWM controller is operating between Imp and Isc. I suspect if the PWM controller is operating at or below Imp, the drop would be even less noticeable.

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???

[ktmrfs]

Post #9


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

I forgot about this question in my initial test list, so I wasn’t able to run an experiment till October 16th about 10AM PDT. Rather than looking at detailed power out, I concentrated on what the effect was on battery charging current.

My expectation was that the charging current would drop roughly in half, maybe a little more than 50%.

So with both panels in the direct sun, adjusted the best I could, I checked charging current, 9.4A. Then I moved one panel into the shade between two trailers. Looked at the panel current, it was 4.1A with both panels in direct sun and stayed at 4.1A even with one panel in the shade.
Just what I expected. Current should remain basically the same, voltage would drop.

Went back in and looked at the trimetric. Now you quickly can see the tracking effect of a MPPT controller. It was seeing probably about 30V @4A or so, and now it is down to about 15V @ 4A, but the conversion algorithm is based on 30V. Trimetric showed charging current less than an amp. HOLD ON, actually I expected something like that until the controller did another search. So I watched. After what seem like an eternity, but really was only a minute or so I could watch the controller doing a search. Interesting, charge current would go up several amps, bounce up and down, and then go up again, bounce around, go up repeat, and in about 30 seconds was up to 4.4A. So a drop of slightly more than 50%. So then I went back out and placed the panel in the sun to verify current. Went in and watched. Current 4.4A, and again after a minute or so the search started, went down to about 2A and then started climbing and settled in a 9.4A. But then we have those pesky wispy clouds messing stuff up today.

Conclusion:
Shading panels in series reduces current by the % of panel shaded related to total panel area.

But it also takes a some time for the MPPT controller to search and find the new Max Power point.

Hum.... wonder what happens when clouds are sporadic and the panel quickly and constantly going in and out of shade. can the controller track fast enough, or does it get appiplexy and give up and not do a decent job of tracking max power point???

Another "I'll leave it to the reader" to investigate!!

[ktmrfs]

Post #8

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

For this experiment I just laid the panels horizontally and look at output current vs. the optimal angle I was at. Then, not believing the results I went back to initial configuration, verified currents, and repeated. And repeated. Why??? Well, in my case at high latitude, and fall, output current with the panels horizontal went from 10A to get this 5.1A!!!! Wow, sure glad my panels aren’t mounted flat on the roof!!

Conclusion:
At least at high latitude in the fall, DO NOT lay the panels flat if you can avoid it. You will take a big hit in power output. In my case close to 50% At least place the panels at an angle equal to the latitude. Of course with the sun higher (in the summertime) and at lower latitude I wouldn’t expect as big a drop. But then in late winter it could get even worse at this latitude.

[ktmrfs]

Post #7

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???


Measuring (Or attempting to Measure) converter efficiency:
While Morningstar claims 98% efficiency, and my various calculations varied all over from about 98% to over 100%. All I can say is that my measurement equipment kept me from getting any efficiency numbers I can believe in. The Morningstar data sheet shows typical efficiency at 125W output power of 96%.

Conclusion:
I don’t have accurate enough measurement equipment or stable enough solar source to reliably and accurately calculate converter efficiency. However the data suggest that converter efficiency is likely in the 95-98% range consistent with the Morningstar claims.

[ktmrfs]

Post #6

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

Our ambient temp remained about 70F during the whole test. If there is a temperature effect, the thermal time constant on the panels is short enough that by the time the panels were set up and ready for charging measurements, they had reached equilibrium Using an IR thermometer I measured the panel front and back temperatures. Readings were consistently in the 115F range. That’s a 45F (28C) rise.

Conclusion: Predicting or monitoring temperature effects on a panel certainly is not trivial, and could end up being an exercise in futility. Solar power is changing during the day so to separate out changes in solar power vs. changes in ambient would be tough. And then even if you know the effect, not a lot you can do about it anyway. However, panel temperatures will rise noticeably especially in clear sunshine. And most panels are spec’d at 25C (72F), certainly below typical actual panel temperatures.

[ktmrfs]

Post #5

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)

So with a MPPT controller, how does a long extension cord (cable power loss) affect the output power? In my case the 90ft of cable has an R=0.015 calculated, so using this number, I calculated the expected output power loss for a series and parallel panel configuration.
At Imp (4.5A) I calculated the power loss to be 3W (1/4A) for series connected panels and 12 W (1A) for parallel connected panels. However, for this measurement I repeated the calculation using actual measured panel current.

For series, cable power loss is I^2R, or V*I or V^2/R. To satisfy Salvo I’ll use V*I to calculate the power loss. R=0.15ohms, I= 4.4A, therefore the voltage drop across the cable would be 4.4A*0.15ohms=0.660V. Therefore the power loss in the cable would be V*I= 0.660*4.4=2.90watts. The expected drop in output current (charging current) would be about 2.90W/13V= 0.2A. Not much, worth the loss if I can get the panels in the sun.

For parallel configuration, same calculations, but I am now estimated to be 8.8A. Therefore voltage drop= 8.8*0.15=1.32V, power loss = 1.32*8.8=11.6W. Or about 11.6/13=0.9 A. Ugg…

Note that the parallel case with double the current has 4x the power loss, not double the power loss. (11.6W vs. 2.9W)

So now with the panels and cable ready for quick changes, I checked the input and output conditions once more, everything consistent with the initial measurements, and then added 90ft of my extension cord and redid the measurements for series and parallel configurations.

Series connection with 90ft of cable.
Vmpptin=30.5V (TX3DMM)
Impptin=4.5A (DCM330)
MPPT power in= 30.5*4.5=137W
Vbat=13.39 (TX3DMM)
Ibat=10.1A (Trimetric)
Power to the battery =13.39*10.1=135.2

Conclusion:
Measurement uncertainty and repeatability is probably compromising results. Couple that with possible slight variation in solar radiation. Trying to resolve a 3 watt change with a shift in time is suspect. About all I can conclude is that observed results are consistent with the calculated analysis, a few % change in output power and that with the low current and low resistance, the extension cord isn’t making a noticeable (to me at least) change in available power to the batteries.


Parallel connection with 90ft of cable
Vmpptin=14.60V (TX3DMM)
Impptin=8.3A (DM330)
MPPT power in=14.60*8.3=121W
Vbat= 13.50V (TX3DMM)
Ibat=9.0A
Power to battery= 121.5W

Output power dropped about 12 Watts compared to earlier measurements, and output current by about 1.1A. When I quickly unhooked the cable and configured in series with short cable, output current jumped right back up to 10A. I then quickly when back to 90 ft of cable and current dropped again to 9.1A So, while a change of a few watts is hard to observe, bigger expected changes are consistent with actual measured results.

Conclusion:
1)If you have an estimate of panel output current and cable resistance you can do a reasonable accurate estimate of cable power loss and estimate loss of output current.

2)Even with what one would often consider low current, (8A) and low resistance (0.15ohm) noticeable charge current and charging power loss in watts can occur. Most noticeable with portable panels with long runs. If I can increase charging current by .75A -1.0A by going series vs. parallel, why wouldn’t I??

3)If you’re looking at power losses in a few watts range and even in the 10W range, unless you have very constant and clear skies, and measurement equipment with high resolution, it could be very hard to verify the expected results.

In any event, doing a power loss calculation for your setup certainly makes sense.

Now for those who might say, “Well, a 100ft run to a portable panel is really not a realistic user situation anyway”. What I will say is for ME, it IS. When we dry camp, often it is in the trees, and if I set panels close to the trailer, to get decent sun they need to be moved very often, sometimes every hour or so, and still only gives me sun for 6 hours.
If I can get 50-100 ft away I can get the panels in direct sun from sunup to sundown, and not need to move them, that’s what we do.

And if I can do it with very minimal power loss with a series configuration so much the better.
Kinda like having your cake and eating it to!

[ktmrfs]

Post #4

2)Can one predict accurately output power by measuring MPPT input voltage and panel output current?
3)In late fall at high latitudes how much power can I expect to get from the panel under optimal light?

I configured the panels in series with the shortest connection path to the controller possible and started taking measurements. With the panels in series I was able to measure panel output current with the DMM. In my case, there is not an easy way to measure the output voltage of the panel easily other than at the MPPT controller input. And its panel input power vs. output power we care about anyway. Vout (and battery voltage) measured with the DMM at the controller output terminals. With the configuration I have, the voltage drop between the controller out and battery terminals is only a few millivolts for the currents of interest. So rather than using the trimetric voltmeter with 0.1V resolution, I choose to use the Tek TX3 DMM with 1mv resolution. Battery current measured with the Trimetric with its 0.1A resolution.

So here are results for series connected panels:

Vmppt in= 30.74V (TX3DMM)
Impptin= 4.442A (TX3DMM)
Panel output power= 30.74V*4.442A= 136.5W
Vbat= 13.36 (TX3DMM)
Ibat= 10.3A (Trimetric)
Controller output power = 13.16*10.3= 135.5
Controller efficiency = 135.5/136.5=99% I don’t think SO! I suspect that the trimetric current resolution of 0.1A and trimetric accuracy is the issue. 10.2A for current yields 97% efficiency. So even 0.1A error is significant here.
And the 135W panel output power seems (at least to me) reasonable given the latitude and time of year. 135W is 83% of rated.

I repeated the measurements for parallel connected panels. In theory with a very short low resistance interconnect results should match very closely a series connection.

In the case of parallel panels I could not use the TX3DMM to measure current, but had to resort to the clamp on current probe, an unwelcome but unavoidable additional variable.

And here are the results for parallel connected panels.
Vmpptin= 15.43V (TX3DMM)
Impptin= 8.8A (DCM330)
Panel output power = 15.43*8.4= 135.8W
Vbat= 13.30V (TX3)
Ibat= 10.3 (Trimetric)
Controller output power = 13.30*10.3= 136.99W
Controller efficiency= 137/135.8 >100%

NOTE: I’m nailed by two low resolution current measurement tools, the DCM330 and the trimetric. So efficiency measurement is meaningless. However, output power and current are close enough to “identical” to the short series configuration that I’ll call them equal, which is what one would expect.

I’m not going to “dry lab” the numbers to try to correct the efficiency.

Conclusion: yes, by measuring controller input voltage and current you can get pretty close on predicting output power. Close enough for me anyway.

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.

[ktmrfs]

Post #3

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

I’ve broke this into two conditions. One with the panels not connected to the controller and another with the panels connected to the controller supplying a load to the battery. Basically unloaded and loaded panel conditions.

Condition 1: NO LOAD CONNECTED TO THE PANEL!!!

With no load I measured Voc with the panel vertical and horizontal to see how much Voc varied. With the panel vertical Voc = 20.85V, Horizontal, Voc=20.52, and it peaked at 20.90 at an estimated 60 degrees. Humm….. Might work.

Then with the panel at best orientation by using Voc, I measured Isc to see if I was close to optimum. Isc= 4.94A, and further adjustment showed it was at or very close to optimum position. I couldn’t increase Isc, and much movement caused Isc to drop.

Repeating the alignment, starting by monitoring Isc, got me to essentially the same orientation.

And once connected to the controller, I wasn’t able to get any noticeable improvement in output power. But I only fussed around with it for a few minutes and decided it was “good enough” after all the optimum position is varying all day long.

Conclusion:
Maximizing Isc or Voc seems to get one “good enough” to optimum angle. At least it is “good enough” for me. However, Isc seems to be more sensitive to position than Voc.

Since optimum orientation changes continually during the day, I figured using either of these methods is probably good enough. Once you get max Voc or Max Isc, it’s up to the user to decide how to orient the panel angle to maximize power captured during the entire sunshine period if you choose a fixed angle.

Condition 2: PANELS UNDER LOAD.

This test was done on a different day and different time. 10AM PDT on October 16th, with a few wispy high clouds.

In this case, once the MPPT controller finds it peak power conditions, it will wait some period of time before searching again. I wondered how this might affect trying to find the optimal angle. Also, one the panels are connected to the MPPT controller, it is not easy for me and probably others, to monitor panel or MPPT voltage while adjusting the panel. So that leaves monitoring current.

So, with my panels connected in series via a short run I hooked my clamp on DC current probe onto one output lead and watched current as moved the panels from horizontal through vertical. I did see about 0.75A change in current, and when the current peaked it did so over a fairly narrow angle. I then repeated with the second panel. However, with panels in series what happens is the current is set by the panel with the highest output current, and the second panel will increase/decrease output voltage as it is moved. Good news/bad news. Good news is that the second panel would be expected to be in the same orientation as the first. Common sense. So with that as a starting point, I tried adjusting the second panel, then the first. Careful adjustments gave me about another 0.1A in peak current. But my final orientation was darn close to the optimal position with one panel.

Then I went in and looked at the trimetric. 9.1A. given the wispy clouds and early morning, not bad. I then waited a few minutes to see if the controller was able to get any more power once it did another search. A little later another 0.1A, but don’t know if that was the controller or a little more sun.

Conclusion:

I think it is easier to find optimal angle with unloaded panels, but it certainly is doable with loaded panels. So if in the AM you adjust for optimum, and later in the day want to adjust, using the clamp on meter to optimize current does seem to work and is a lot easier than asking DW to monitor the trimetric as you tilt the panels.!!

But WAIT there appears to be a better method:

One proposed by Jim Denver and expanded by CA Traveler.

Put some form of cylinder on the panel. When the sun is perpendicular to the panel (the optimum position), there should be no shadow. Jim Denver suggested a TP tube, CA Traveler a dart with a suction cup. I’ve got a spare Garmin suction cup mounting system I’m tempted to put a plastic tube on and use that. I tried a TP tube. Very quick, very accurate.

So after all those current/voltage measurements, SIMPLE is better, thanks Jim and CA Traveler!!