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hvon11 avatar image
hvon11 asked

MPPT 100/30 not delivering rated amps

I have two 200 Watt Hitec panels in parallel connected to a Victron 100/30 MPPT controller. The panel surfaces are clean and have a clear sky view. Between 11am and 1PM my peak power production is only 260 Watts, ~19 Amps and ~13.44 volts on the battery side of the controller. I am configured for Lithium battery specs as per Victron and the battery manufacturer. Why is the wattage not closer to 400? Victron app shows the PV array at 17 to 18 volts and current 14 -15 amps. I have a separate 30AMP charger that when I shut down the solar and use it, it delivers ~30Amps. Thanks for taking time on this.

MPPT Controllers
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hvon11 avatar image hvon11 commented ·

Thanks for all the help. I tested cable resistance and panel short circuit currents; all normal. I set up panels in series configuration and still wattage is peaking out at 277W. The charge current appears to be more consistent (less fluctuations) in series. I was sent this calculator

https://www.victronenergy.com/mppt-calculator

It shows a potential to produce 1900Watt/Day in June in my location. Yesterday I produced just under that at 1500W but I started the series setup at 11AM. So all is good.

Thanks -Hans

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nickdb avatar image
nickdb answered ·

At best you get 2/3 of the panel rating assuming decent orientation and cover, this gets worse with high temps.

That works out to 264W on a typical day.

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hvon11 avatar image hvon11 commented ·
I was expecting closer to specified power at peak sun with direct orientation. I am getting 2/3 as you indicate. I will do some testing today as well as series panel configuration. If all I get is 2/3 I will consider adding a third panel. Thanks for the help, Hans
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nickdb avatar image nickdb ♦♦ hvon11 commented ·
That’s unrealistic. Quoted specs are at “ideal” conditions. Reality differs. Your yield is normal.
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hvon11 avatar image
hvon11 answered ·

Hmmm. Found the below on SolarReviews website. Which means I’m getting about 10% less than possible max. Hmmm. And if I assume a 10% loss due to surface panel temp rise then I am about spot on. Hmmm. Will do more testing today and series config.

“400-watt panel will only produce 400 watts of power under these ideal conditions. Unfortunately, your roof isn't a lab, so your panel will usually be outputting less power than 400 watts. In the real world, a 400 W panel will typically produce closer to 300 W of power.”

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Alexandra avatar image Alexandra ♦ commented ·
Yep, welcome to the disappointment side of solar.

Panel temps test and rated at 25°C

1000w/m also will hardly ever see. And if you do your panels certainly not likely to stay at 25°C. Especially if they are flat.

Note also most manufacturers want about 10cm under the panels for ventilation and cooling (junction boxes fail from trapped heat) and not flat again for ventilation reasons.

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neptuneuk avatar image
neptuneuk answered ·

HI @hvon11@msn.com ,

What are the Impp and Vmpp values from the technical specification label which should be affixed to the reverse side of the panels.

What make and model of panels are you using?

What is the make and model of the 'other' controller you mentioned... Was it supplied as part of a bundle with the panels?

Also check out the manual for the SmartSolar MPPT 100/30: https://www.victronenergy.com/media/pg/Manual_SmartSolar_MPPT_100-30__100-50/en/operation.html

I'd draw your attention to the following taken from the above manual:

The solar charger will commence battery charging as soon as the PV voltage is 5V higher than the battery voltage. For charging to continue, the PV voltage must remain at least 1V higher than the battery voltage.

You stated that you PV array voltage is 17-18v, and your battery bank voltage is 13.44v, this would mean your PV array needs to get to 18.44v to enable the SS MPPT 100/30 to enter it's initial bulk charging cycle from it's off state.

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kevgermany avatar image kevgermany ♦♦ commented ·
I read it that the 13.44V is max output Voltage after charging has started.

And that the 30A charger is not solar.


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hvon11 avatar image hvon11 commented ·

Neptuneuk- The panels are Hightec 200 Watt Impp is 9,50A Vmpp 21.052V. The other controller is Sterling B2B 30A charger. Not a bundle, home built by me. My third RV solar setup. Yes, read manual, the 5V delta is achieved at start, as Amps increase, panel voltage drops to 17-18V range but always satisfying the 1V delta requirement. The controller behaves correctly; Bulk to Absorption (14.6V) then 2 hours to Float 13.6V. I just never get more than 260 Watts from the solar configuration. I did measure the Amps each panel was making using a clamp on meter, the Amps were evenly split so each panel was producing 50% of the total. My PV wires are 10AWG x 10’, connectors and combiners are the usual bayonet solar connectors. Thanks for your help. Hans

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neptuneuk avatar image neptuneuk hvon11 commented ·
Great comprehensive answer.

As mentioned by @kevgermany suggested, series may be the best configuration in your setup going forward regardless of the issue you are experiencing now.

Do check for higher than expected resistance at any point in your installation, very possibly a bad crimp or possibly damaged cable.


You have ruled out any form of shading?

You have taken account of the external temperature and panel face temperature and their possible effects on charging resistance?

The other thing is, there is, at least in the UK high humidity at the moment, this can affect the solar radiance penetration, so what looks like a great day, isn't delivering the energy you may think as all that solar energy is defracted by all that pesky water in the atmosphere.

Where are you located?

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kevgermany avatar image
kevgermany answered ·

Check for high resistance between all components.

Also makes sure the MPPT is running the latest software

But you probably need to wire the panels in series, not parallel.

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hvon11 avatar image hvon11 commented ·
Kevgermany- I will check resistance today, I used good PV wire and connectors but possibly a bad crimp is hiding there (would be on the roof if anywhere). Was also planning to test with panels in series as well. Thanks for help. Hans
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klim8skeptic avatar image
klim8skeptic answered ·

@hvon11@msn.com Given the physical size of the panel 1480 x 670 I would think it is more likely to be a 170w panel.

Nothing new about people inflating solar panel specs....

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hvon11 avatar image hvon11 commented ·
Even so I think I should get upwards of 340 Watts if performing at capacity. Appreciate your input. Hans
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neptuneuk avatar image
neptuneuk answered ·

OK, so dealing with your figures @hvon11@msn.com and the quoted panel specs for your solar panels.

The panel Impp you quote is 9.5A and you have two in parallel = 19A. This is the absolute maximum Impp output of your two panels in absolutely ideal conditions.

You stated in your original post:

"~19 Amps and ~13.44 volts on the battery side of the controller."
And
"PV array at 17 to 18 volts and current 14 -15 amps."

So the maths......

If we take the voltage from the array to be 17.5v and the incoming current to be 14.5 A.

By driving down the output voltage via the MPPT we increase the output current.

So incoming Vi = 17.5V. Incoming Ai = 14.5A

Reported outgoing (Battery) voltage Vo = 13.44V, outgoing Va = 19A.

Our power factor (Pf): 17.5Vi/13.44Vo = 1.302

Now Ai x Pf = (14.5 x 1.302) = Ao 18.879 (18.8A) - (our MPPT is being 99% efficient)

You can see the Victron 100/30 is demonstrably supplying the expected Ao given the supply Vi and Ai.

Ao x Vo (18.88 * 13.44) = 253.74W

The question that maybe needs answering and maybe should be directed to the panel supplier is why the Vmpp is below the specification for the panels, in what are reported to be ideal conditions? However using your figures they are performing at just under 85% of their absolute ideal maximum, which IMHO is acceptable.

At their rated maximum output, Panel Impp (9.5 x 2) x Vmpp @ 21.052 = 19x21.052 = 399.99w

The Victron 100/30 is constrained by physics......

Have you measured the Vo and Ao at the panel (panel tails) with good quality test apparatus?

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hvon11 avatar image hvon11 commented ·
I agree with all your math. I did measure Ao at panels on roof, individually and after combiner and that matched with MPPT Victron App displayed values. Did not measure Vo as both MPPT and Shunt displayed identical. Agree with you on asking panel supplier and did submit same yesterday to them. I do suspect the panels but need to verify wiring first. I don’t agree that I am getting 85% of performance. Wouldn't that mean i should see ~340 Watts peak? Thanks again for your help. Hans
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neptuneuk avatar image neptuneuk hvon11 commented ·

Hi,

I'll get to the 85% later, but first.

Voltage is not the main determinator of output current, that is 'insolation', basically how much energy in various wavelengths is striking the panel surface, to be converted to an electrical output (temperature is probably an equal determinant on the ability to output that energy based on electrical resistance). This is a nice simple explanation of insolation courtesy of BBC bitesize: https://www.bbc.co.uk/bitesize/guides/z24rr82/revision/1

Look at the amount absorbed by water vapour.... stuff you won't normally see, humidity will play a role in how much energy you can collect from a panel, even on what appears visually to be a sunny, clear day. (https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/humidity)

What all this starts to show is possibly the worst day for solar is a hot, sunny day, almost everything is working against us.......... Cool, bright days on the other hand.....

Some times in any system you'll see a reduced output voltage and increased current / high current. The physics at play are very complicated indeed and for the most part the simplified maths we use is sufficient. You can discover all of the physics and mathematics at play if you have the time and willingness to learn more. Google is your friend. I'm sure there are some on here who could educate us all on the matter.

As for the 85%:

Vo = 17.5v / Rated Ao 19A (you can potentially achieve 19A at any voltage, but 19A is your practical maximum, and in terms of energy harvesting we are mostly interested in the amps we can potentially harvest).

17.5v*19A = 332.50W

332.50W/400W = 83.125%

You were collecting just under 85% of the Immp your panels could potentially output.

By way of an example I've included an image of solar output from 1 of my panels. You will note that while the voltage remains fairly constant, amperage can fluctuate quite dramatically, and on some days arrives at the maximum Immp of the panel, despite the voltage remaining constant across most days, look to the 8th and 10th of May in particular as examples. The humidity was 80% and 60% respectively for Bristol/Lulsgate (https://www.weatheronline.co.uk/weather/maps/current?LANG=en&DATE=1715338800&CONT=ukuk&LAND=WES&KEY=WES&SORT=2&UD=0&INT=06&TYP=feuchte&ART=tabelle&RUBRIK=akt&R=310&CEL=C&SI=mph), and we all thought it was about getting a sunny day right?

Hope this helps.


screenshot-from-2024-06-20-20-00-44.png

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dc-marine avatar image
dc-marine answered ·

A good way to quickly test your panels is to measure open voltage and short circuit current under maximum exposure. First disconnect the panels and measure the voltage at each panel leads, which should be very close to the open circuit voltage on the specs. Then using a DC clamp meter around one of the leads, connect the positive and negative leads together and see if the short circuit current is anywhere near the rated one. It is safe to do so for a few seconds, but too long may heat up the cells so be ready to measure before connecting.


Also if you're in a very warm environment, the panels performance will be derated from the 25°C test conditions. Cooler climates generate higher output than warmer ones. For examples in the late spring early summer where mornings are cool but sun is up high, my 800w panel gives me upward of 1000w. The opposite would be true in a hot morning.

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hvon11 avatar image hvon11 commented ·
Interesting. I have tested open circuit voltage but was always afraid of damage to do a short circuit amp test. Thinking about it, I will try short circuit amp draw through a 30 amp breaker. If it trips I know I get at least 30 and if not, I can measure the actual. Good idea. Thanks for help. Hans
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dc-marine avatar image dc-marine hvon11 commented ·

Your panel short circuit current won’t be anywhere near 30a. When you short them, what happens is the generated power has to go somewhere, and that somewhere is heat. The cells can handle some heat so a bit, like a wire can get hot from too much current. As long as you don’t short it for minutes or hours, you’ll be fine. The panel is self-limiting, it cannot make more power than it can handle.

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hvon11 avatar image hvon11 dc-marine commented ·
That really helps me understand what happens when shorting the panel. Will give that a try today. Who ever designed the clamp on DC amp meter deserves an award. Thanks for your advice. Hans
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kevgermany avatar image
kevgermany answered ·

Just to add.

Some panels are marked with the temperature comp coefficient. Based on degrees deviation from 25C. Measuring the actual panel temp while doing the other readings will give a better picture. It's usually significantly higher than ambient.

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