July 2, 20179 yr Good day guys, I have a 6kw solar array. 2 Axpert mks 5KVA running in parallel 6 strings of 4 panels (Renesola Virtus II 250W) String output under load 110V 5A 3kw east & 3kw west On a normal roof tilt. I would like to know what your maximum PV output is this time of year. Between 11:00-13:00 I get about 3000W. it seems to be a bit low, I know i am pushing the MPPT to its maximum voltage. Any recommendations ?
July 2, 20179 yr 35 minutes ago, Jako said: Any recommendations ? Hi Jako Welcome Fortunately your system seems not to be running optimally. 4 panels in series should be over the 145V DC even at STC. At 0oC you could expect a Voc 160V DC. Your are not pushing the MPPT to its maximum - you could be in the territory beyond its rated maximum. With a East -West orientation I would expect maybe 4000W. You may find your MPPT doing odd things due to you being close/over the Voc max. I would have 8 strings of 3 to be within the MPPT's sweet spot <115V DC steer clear of the 145V DC Voc max. It just takes one cold bright day and for your MPPT to recalculate the power point and you will be in trouble. Chris
July 2, 20179 yr 5 minutes ago, Jako said: Thank you I will fix this ASAP Here is a cheat I submitted your details to MIdnite Solar sizing tool. and this is the output. Rensola.pdf
July 2, 20179 yr 11 minutes ago, Jako said: I see the VOC 149.6 That is at 25°C at 0°C it is 160.8V DC.
July 2, 20179 yr Author Ok , so this will affect the MPPT charger ? Will 3 panel strings work better than 4 panel series strings or are you scared the MPPT wil burn. I did the 3 panel cheat & it seems to be better siuted for the MPPT range. Is it better to run the MPPT at the highest point or lowest point ? What %output difference do you normally expect from winter to summer ? Rensola 3x8 strings.pdf
July 2, 20179 yr On 3 kW I experience about a 5kWh drop in winter from 17kWh in summer to 11-12 kWh in winter. Yes I recommend 3 panel strings for 60 cell panels because I am "scared the MPPT will burn". MPPT will sort itself out so long as within the MPPT range.
July 3, 20179 yr What you must remember is PV production is dependant on load. If you suspect that your PV production is low, switch a heater or some other large load on so that one can see what one's PV is capable of at that time of day.
July 3, 20179 yr 19 hours ago, Jako said: Is it better to run the MPPT at the highest point or lowest point ? Depends on the design of the buck converter component. The precise choice of capacitor and inductor usually depend on 1) maximum allowed current ripple, 2) maximum allowed voltage riple, 3) output current capability, 4) input vs output voltage ratio, 5) operating frequency, which in turn is limited by the output rating and "skin effect". So plugging all those into a calculator usually yields a "window" within which things are optimal, and thankfully Voltronic was nice enough to tell people what theirs is :-) That is, keep it around 100V, for best results.
July 3, 20179 yr How are the 2 inverterts and 2 PV arrays wired? Does your inverter have a single MPPT or a dual MPPT?
July 3, 20179 yr 2 hours ago, SilverNodashi said: How are the 2 inverterts and 2 PV arrays wired? Does your inverter have a single MPPT or a dual MPPT? Two single MPPT Axperts in parallel, each with separate array but sharing a single battery bank.
July 3, 20179 yr Author Jip, I loaded the inverter with about 5KW, the total load from the 6KW panels only supplied about 2985W. The axpert is set to suppy "max solar power = charging + connected load" Interestingly today in centurion I got about an average of 1000-1500W from the panels. It was overcast for the whole day. This output seems to be quite good for the conditions. but on a sunny day it is quite a different story. As pilotfish mentioned, two axperts in parallel, each with its single mppt connected to 3KW PV. Sharing a single battery bank.
July 4, 20179 yr 6 hours ago, Jako said: As pilotfish mentioned, two axperts in parallel, each with its single mppt connected to 3KW PV. Sharing a single battery bank At midday is there any difference between your two strings?
July 4, 20179 yr 12 hours ago, Jako said: Jip, I loaded the inverter with about 5KW, the total load from the 6KW panels only supplied about 2985W. The axpert is set to suppy "max solar power = charging + connected load" Interestingly today in centurion I got about an average of 1000-1500W from the panels. It was overcast for the whole day. This output seems to be quite good for the conditions. but on a sunny day it is quite a different story. As pilotfish mentioned, two axperts in parallel, each with its single mppt connected to 3KW PV. Sharing a single battery bank. Are you grid tie or off grid?
July 5, 20179 yr Author Rewired the panels to 3panels x 6 strings, 3 EAST, 3 WEST Midday I got 1680W (slave) from the one inverter & 800W (Master) from the second inverter. Although it was overcast the difference is huge. The one inverter sees a input of 90V from the 3 strings & the other sees an input of 60v ? from the three strings. Something seems to be bad, I highly doubt it is the wiring. will double check in any case. Eskom is connected as backup.
July 5, 20179 yr 1680W is about right for a 20-30° roof tilt at this time of year for your array which is now 2250W That 800W 60V is problematic. Using the DC circuit breaker/disconnect isolate the PV feed. Once the panels are not under load isolate each string using the fuses in the combiner box. Switch back on and at least identify which string is problematic.
July 5, 20179 yr Author That is the next step. I normally isolate the PV arry with the isolator(DC), remove the fuses(DC), test the strings one by one for Voc. refuse one string, switch back isolator & see what the string gives me. It sould either be the inverter or pannel array ? I will give you feedback as soon as I tested it. One question, If the inverter has an issue. Can I connect the total of 2x6 strings (4500W) to a single inverter while the one is away? & one sets the max charging current as applicable to the battery ? This will give you max charging amps early in the day & give you a flat topped curve instead of a nice wave ?
July 10, 20179 yr Author Good day I had a faulty panel on one string that pulled the whole inverters PV input down. I was a bit "stout" & left the strings as is. 4 panels, 3strings. I was only charging the battery & house today. Please see the atached picture of the output. Question: I am using the windows ICC version. Notice the red voltage graph below. Is it normal to go coloring in like that or is it a function of the mppt & high volts running 4 panels in series ?
July 10, 20179 yr This is my curve for today. We were away and there was very little load.no real load. What you can see is the MPPT working hard at low light intensity levels and settling down during the middle of the day. What I think is happening in your graph is the MPPT is continuously having to backoff as it hits the 115V DC MPPT threshold. You have a beautiful bell curve but I think (as I have said before ) 4 x 60 cell panels in series is a stretch for the Axpert's SCC. I think you would produce more power with 8 strings of 3 panels.
July 10, 20179 yr 40 minutes ago, Chris Hobson said: What I think is happening in your graph is the MPPT is continuously having to backoff as it hits the 115V DC MPPT threshold. I agree. The reason it is coloured in like that is because it literally goes up and down so much that it colours-in the entire space. It's the kind of thing that happens when the plot-area is only 1000 pixels wide (for example) but you have 20000 data points to plot :-) I don't know if you can zoom in a little, but if you zoom in on a smaller area I bet you'll see a nice little see-saw going on, quite possible as Chris says because it has to back off repeatedly from moving outside the recommended voltage window.
July 11, 20179 yr Author Here is the snapshot up close The voltage stays quite stable at around a 110V
July 11, 20179 yr 25 minutes ago, Jako said: The voltage stays quite stable at around a 110V Mmmmh, assuming the measurement is done right, yes, it does look stable. But look at the ampere thing, that is way too close to a square wave, as if it continually bounces off some bad condition. Shot in the dark, compare PV-volts of MPPT1 to MPPT2? Do they perhaps follow each other exactly? (I have a theory but don't want to spit it out just yet). Also, I would not rule out voltage just yet. Perhaps the logging misses the high spike because it's intermittent.
July 11, 20179 yr Author Well there are only 1 mppt per inverter. Not two. But we have two inverters. Can ICC show the PV volts & amps of both inverters independantly ? Currently its flashing the one then the other every 3-4 seconds on mppt1, mppt2 is always 0. Can it be that the west side is the high amps & the east side the low amps at that time of day ? So early in the morning there is a huge difference, midd day no difference & late it goes to the difference in amps of east & west strings ?
July 11, 20179 yr 3 hours ago, Jako said: Well there are only 1 mppt per inverter. Not two. Can ICC show the volts & amps of both inverters independantly ? Currently its flashing the one then the other every 3-4 seconds. Can it be that the west side is the high amps & the east side the low amps at that time of day ? So early in the morning there is a huge difference, midd day no difference & late it goes to the difference in amps of east & west strings ? The graph says it is for MPPT 1. We will have to ask @Manie for help.
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