First Solar Installation - What went wrong? Please solve the Enigma

[AgroVenturesPeru]

This is my first solar installation, but I'm working with a technician. It's a 4s4p array. The first 3 strings are with 4 400W Mono PERC panels in series, and the last string is composed of 4 410W Mono PERC panels in series. The STC of both panels is almost exactly the same, and some knowledgeable members on this forum even took a look at their spec sheets on another thread, and confirmed that they are fine together.

We completed the installation a couple days ago, and then fired it up about 2pm. It was cloudy and overcast. The array got up to about 1800W, and then it rained the rest of the afternoon, and production dropped off considerably.

The roof angle is oriented to the sun at about 10-11am.

Today, the sun was out for a while during that time. However, the highest output (Pmax) throughout the day was recorded as 1035W, with a total yield of 1.2kwh. That's considerably worse than yesterday, even though the environmental conditions were considerably better.

I'm very worried about this.

The voltage produced seems to indicate that 4 panels have been wired successfully in series, but it's almost like the paralleling did not work or something, because ohms law indicates that only 5.4 amps entered the MPPT during pmax today.

I'll try uploading a couple photos in my next post. We have a couple multimeters on hand, so we can check things out tomorrow.

I have a Victron Smart Solar 250/100 Tr ve Can.
Unlikely, but maybe these MPPTs limit the solar production based on the state of charge of the battery bank? I was under the assumption that the MPPT is simply measuring the raw electricity being produced by the PV modules + combiner box.

 

[AgroVenturesPeru]

The second image shows the string box when I received it from the distributor for 4s3p.

The last photo shows the box after upgrading the same box for 4s4p. The photo was taken prior to the installation, so since then the output pos/negative 6mm^2 cables were installed as well as the ground wire.

The wires were all crimped with ferrules using a ferrule crimper, and heat shrunk sleeves placed. The connections were all solid and tight.

 

[AgroVenturesPeru]

I think I remember something about the MC4 connectors saying, "do not disconnect under load". Does that mean I need to shut off my batteries and inverter before poking our multimeter probes into the mc4 terminals during the day tomorrow? The idle load when running the touch screen, bluetooth, Inverter, etc. is about 50W according to what the CerboGX senses from the batteries.

 

[Diysolar123]

if you have no load, well, no current is going to move...where and how are you testing you solar production; do you have a couple of, everyones favorite, resistive heaters plugged in?

 

[Bud Martin]

Do you have Clamp on DC Amp meter to check the current of each PV string?

 

[AgroVenturesPeru]

I guessed the problem was that I didn't discharge the batteries very much, so they topped off every morning early, and the MPPT didn't need to produce anything. I didnt realize the MPPT displays only the electricity it harnesses. I'm assuming my theory is correct at this point, because I discharged the batteries overnight to 23% capacity, and this morning I acheived a reading of 5000W, which would suggest all strings are functioning properly.

 

[Jordi]

Hi Agroman, so your installation is off-grid?

I have the same phenomenon here. I have a 100W panel with a 250Wh battery off-grid which means that in one day I would normally reach full charge. When this happens; besides reading the full charge voltage on the charge regulator (14,4V), I see that the voltage received from the panels gets much higher than the battery voltage (18-19V). Also current oscillates around lows (one fourth of max.). When I plug in a load and the battery voltage goes down, then the panel produces again at full capacity.

So out of curiosity, what are you going to do with your system to avoid wasting production capacity?

 

[wattmatters]

I was under the assumption that the MPPT is simply measuring the raw electricity being produced by the PV modules + combiner box.

There is no "raw electricity". If there is no load to feed, then the panels will produce zero output. If there is only a light load, then that's all the panels will supply.

Only exception to that is for grid tied arrays where the grid effectively becomes an unlimited load (think of it like a ginormous battery) which will take whatever is thrown at it, or at least up to whatever export power limit has been set in the inverter.

 

[svetz]

That's some nice craftsmanship in those photos! Well done! I guessed the problem was that I didn't discharge the batteries very much... Don't feel bad, you've a lifetime of experiences saying something is broken if you turn it on and nothing is coming out. Great job diagnosing it! The roof angle is oriented to the sun at about 10-11am.... Today, the sun was out for a while during that time. However, the highest output (Pmax) throughout the day was recorded as 1035W, with a total yield of 1.2kwh. Don't expect 1600 watts from four 400W panels. Peru is in winter so the sun is fairly low now. It sounds like you have east rather than north facing panels... so picking Ica at random a solar calculator shows an insolation of about 4, so 1600 x 4 = 6.4 kWh/d is about the best you should expect now (minus battery and inverter efficiencies).

Hope that helps and good luck!

 

[Jennifer]

Are you running both parallel strings through the single MPPT 250/100? Have you tried running each of the strings separately through that MPPT to log the number and see if the results are what you'd expect from just the individual series strings? If separately they perform, you may have to add a second MPPT (split them up) I have the same 250/100 so am curious how this gets resolved.

Jen