Optimizing PV Array for MPP LV-MK 3048 48V

[ptanner]

First time system builder here and want to bounce a few things off the group if I may. I wired up the following setup a few weeks ago:

- 1x MPP LV-MK 3048 all-in one
- 12x HQST 100W 12V monocrystalline panel wired in 6S2P configuration, 6 panels in each series and 2 series in parallel.
- 2x 24V 100ah Ampere Time wired in parallel

In optimal conditions under heavy load I'm pulling maximum about 780-790 watts or about 65% of the rated panel output. I live in Southern California and I've tested on multiple days, multiple times per day and I'm convinced that this is not because I'm not getting optimal conditions.

I'm reading about 100-110 volts input at the inverter and my clamp meter shows 10.2 amps coming in on the PV wires to the inverter. It shows very similar readings at the roof. I was expecting around 11-12 amps based on the ratings of the panels so I'm not sure if that indicates a problem at the panels or not. I tested each panel individually and it seemed to be producing to specifications.

My question is whether my 6S2P configuration could be problematic for a 48V system. My battery wants to be charged at 57.6V and I have that set in the configuration for the inverter, could it be a problem that the 100-110 volts I'm giving the inverter (which falls within their 60V - 115V MPPT voltage range specified in the manual) is not optimal and I'm losing power because of it?

I was considering re-wiring to 4S3P but I don't want to go through the hassle if it doesn't have any logic as to why it might work better.

Should I be concerned that I'm reading about 10.2 amps on the cables coming off the roof which seems to be less than I expected based on the specs of the panels?

Any tips on where to go from here to improve my situation?

 

[iamrich]

110v x 10.2a = 1122w which is 94% of ideal conditions (ie: laboratory). How long are your feed wires from the panels to the charge controller and what gauge are they?

Also this may be an obvious question, but do you have demand for 1200wh? Your charge controller will not push more power than there is demand for.

 

[ptanner]

Thanks for the reply. The 780 watts I quoted is what is showing up on the inverter screen for the PV input wattage. I have 12 gauge cables going about 60 feet from panels to the inverter. The voltage is read on the inverter screen and the amps are measuring about 10.1 amps at the cables right before entering the inverter (I have a disconnect installed).

As far as demand, I'm running a hair dryer as a test and the demand spikes to about 1.5KW when it's on and the PV input still caps around 780 watts on the inverter screen.

 

[Lt.Dan]

If its 110v and 10.2 amps at the inverter, then there is something wrong with the inverter, not the panels.

Either check out your settings and see if you have a max charge wattage or some other setting that could be limiting it. If not, it may be a faulty unit.

 

[ptanner]

Thanks for helping me out on this. I will go through each of the settings again sometime this week and see if I can find anything else. I spent an hour running through the manual again today and tinkering with things without much luck. I also went through the sample settings that Will posted on his site.

My only thought was that maybe the input voltage was too high but as long as it's within the MPPT range they quote of 60-115Vdc it should be fine right? Optimal charging voltage according to my battery manual is 57.6V

 

[Lt.Dan]

You cant really have too high of a PV Input Voltage, so long as it is below the max VOC. The MPPT Range you are referring to is just the "Optimal" range. Notice how the manual also states that it can start charging when PV is above 34v? That is well below the 60-115v range.

 

[TJ King]

You cant really have too high of a PV Input Voltage, so long as it is below the max VOC. The MPPT Range you are referring to is just the "Optimal" range. Notice how the manual also states that it can start charging when PV is above 34v? That is well below the 60-115v range.

Im trying to figure out the meaning of "PV Array MPPT voltage range". In my manual for my LV 2424 msd it says "30~80vdc". The 30 is normal type font and the 80vdc is grey font for some reason. It says "Maximum PV Array Open circuit voltage" is 145v. My Solar panel array shows 104v open circuit on the voltmeter. What happens between 80 and 145? Is it the sub 80v area you are referring to as "optimal". Ive been presented with the above graphic from another manual that shows 115v as the high end of the range. What does this term mean?

 

[Lt.Dan]

Im trying to figure out the meaning of "PV Array MPPT voltage range". In my manual for my LV 2424 msd it says "30~80vdc". The 30 is normal type font and the 80vdc is grey font for some reason. It says "Maximum PV Array Open circuit voltage" is 145v. My Solar panel array shows 104v open circuit on the voltmeter. What happens between 80 and 145? Is it the sub 80v area you are referring to as "optimal". Ive been presented with the above graphic from another manual that shows 115v as the high end of the range. What does this term mean?

I realize now that my post above (post #6), is incorrect as I misread the bit where it says minimum battery voltage is 30v, not PV voltage.

In your case, you VOC is 104v, well below the recommended 145VOC. When connected to the inverter, the PV input voltage will drop considerably, more than likely below the 80vDC. Even if it was above 80v, I don't see there being a way to damage the SCC. I could understand the 30v to 80v DC being the "optimum" range, like you suggested.

 

[TJ King]

I realize now that my post above (post #6), is incorrect as I misread the bit where it says minimum battery voltage is 30v, not PV voltage.

In your case, you VOC is 104v, well below the recommended 145VOC. When connected to the inverter, the PV input voltage will drop considerably, more than likely below the 80vDC. Even if it was above 80v, I don't see there being a way to damage the SCC. I could understand the 30v to 80v DC being the "optimum" range, like you suggested.

Thanks for taking the time to respond. I’m still confused about my manual and what this 30v-80v term means. I hope it didn’t seem like I was suggesting it was an optimum range. I still remain ignorant about what that range is. Thanks again

 

[iamrich]

I have no data to back this up, but I would be a nickel to a donut that the manufacturer puts that range so that you will shoot for something inside it. For instance, my 250w panels run at about 33v usually. I see anywhere from 80-104vdc depending on the day. Logic would say that if I am seeing 104v from three panels (35v per panel), that I could squeeze one more in there (35x4=140v) and still be under the 145v limit. The problem comes when the panel goes open circuit early in the morning and I get 37.6v per panel x4 which allows puff the magic dragon to come out of my inverter (150.5v). If for some odd reason the temperature gets down to 6°F like it did last year in a freak storm, that number is even higher.

If you keep the panel max voltage (lower of the two numbers (not VOC)) inside the suggested range, no matter what happens (open circuit, blizzard, second sun pops up, etc.) you are not going to exceed that max 145v number.

 

[TJ King]

I have no data to back this up, but I would be a nickel to a donut that the manufacturer puts that range so that you will shoot for something inside it. For instance, my 250w panels run at about 33v usually. I see anywhere from 80-104vdc depending on the day. Logic would say that if I am seeing 104v from three panels (35v per panel), that I could squeeze one more in there (35x4=140v) and still be under the 145v limit. The problem comes when the panel goes open circuit early in the morning and I get 37.6v per panel x4 which allows puff the magic dragon to come out of my inverter (150.5v). If for some odd reason the temperature gets down to 6°F like it did last year in a freak storm, that number is even higher.

If you keep the panel max voltage (lower of the two numbers (not VOC)) inside the suggested range, no matter what happens (open circuit, blizzard, second sun pops up, etc.) you are not going to exceed that max 145v number.

Is the 104v open circuit on your voltmeter or is that on the LV2424 display? My 240 panels, 3 in series, put out 104v on voltmeter open circuit, but on 2424 display the range from 80 -90. The range listed in the manual is 30-80v. And yes, Max limit listed, prior to moment of damage is 145v.