Overcast day, 400 watt MPPT system is making less power than 50 watt panel with PWM

[iwasforcedtopickausername]

Hi everyone,

I have two solar systems at the moment.

One is 4x 100 watt mono Renogy solar panels in series, with maybe 90~ feet of 4 gauge aluminium wire going into a Renogy 60A MPPT charge controller. It's feeding a 100AH SOK 12V battery. I'm getting something like 0.1A with it. And the battery is not charged -- I turned on a load and the power did not go up. Panel voltages are in the 40-50V range. On a sunny day, usually about 88V and I've seen it pull well over 200 watts on a sunny day, not even in the summer.

Another is 1x 50 watt mono Renogy panel with the 20 foot long aluminum (10? gauge) cables it comes with. It's feeding a 10A rated Renogy PWM charge controller. With a load on it, it was saying 0.2 amps coming in. It's feeding an old flooded lead acid car battery (just for powering lights in the barn).

Both arrays are roughly at a 45 degree angle.

It's very overcast and sleeting outside right now.

Could anyone suggest why the 400 watt system is making about half the power, under similar circumstances? I know MPPTs get less efficient when the voltage is way above the battery voltage, but I'd still expect to be making at least twice the power of the 50 watt setup, even with losses. I know the MPPT controller also has more idle current draw (I think 2 watts), so that may be part of it, but I don't think it's the full story.

Appreciate any insights you can offer.

Thank you!

 

[sunshine_eggo]

Have you confirmed performance of the individual 100W panels?

I would attach a single panel to the MPPT and verify that all 4 perform equally.

 

[740GLE]

4 connections vs 1 connection?

A bad connection can show as decent voltage but low current. Why are you using aluminum conductors? What does of connectors/connections are you using?

On sunny days how does the 400w system output?

 

[Mattb4]

You would have to give watts from both solar arrays to compare. Plus how you obtain the readings.

 

[TorC]

Ah, are you looking at input amps from panels, or output to battery? If the former, you've probably got twice the real power on your MPPT. Line loss is likely not very relevant at the very low currents involved here unless you have a faulty connection.

 

[iwasforcedtopickausername]

Interesting idea to try a single panel at a time. I'm using aluminium because it's what I had around. And 4 gauge aluminium should be equivalent to 7 gauge copper, right? I don't have any 6 or 8 gauge copper around. Could've maybe done a long run of 10 gauge, but kind of costly, and this wire was here ready to go.

It's just the 4 gauge aluminium wire for almost the entire run, plugging into the pigtails off the panels. The end of the aluminum wire on the panel end has MC4 pigtails spliced into it. Those splices could be suspect, but I have recently seen far higher wattage.

On sunny days this setup has done much better, so I'm not suspecting connections, but I can tinker with it and try to see.

Watts wise, this is like 1 watt on the 400 watt system vs 2 watts on the 50 watt system.

 

[iwasforcedtopickausername]

Ah, are you looking at input amps from panels, or output to battery? If the former, you've probably got twice the real power on your MPPT. Line loss is likely not very relevant at the very low currents involved here unless you have a faulty connection.

Input amps from the panels. If the battery wasn't drawing, I through on a load. I'm just reading it off the solar charge controller.

 

[TorC]

Big system: 48V*.1A=4.8W. Small: 12V*.2A=2.4W. I don't have Renology on my list from when I was picking, but I have idle draw ranging from <1W for Outback FM-80 to <4W for Magnum PT-100. Attempting an MPPT search is likely to take noticeably more power than that.

 

[iwasforcedtopickausername]

Big system: 48V*.1A=4.8W. Small: 12V*.2A=2.4W. I don't have Renology on my list from when I was picking, but I have idle draw ranging from <1W for Outback FM-80 to <4W for Magnum PT-100. Attempting an MPPT search is likely to take noticeably more power than that.

This is all 12V, though. That's quite a range in the idle current between those charge controllers.

 

[TorC]

This is all 12V, though.

You told me you were giving input from panel numbers, which, for the larger system, you said in your OP was running 40-50V.

That's quite a range in the idle current between those charge controllers.

Different controllers are designed to different specs. I suspect if you actually look at some of the tier 2-3 Chinesium it's worse yet.

 

[MichaelK]

I turned on a load and the power did not go up. Panel voltages are in the 40-50V range. On a sunny day, usually about 88V and I've seen it pull well over 200 watts on a sunny day, not even in the summer.

I think this is a big clue as to what is the problem. Most of Renogy's panels have a Vmp of 18-20V, so four in series should be 72-80V. That 88V comment might be the panels Voc voltage. Even in low light, panel voltage does not drop much. I'd expect amperage to drop drastically, but not voltage.

The fact that it's Aluminum wire suggests to me that it might be Aluminum oxide corrosion that is limiting the flow of power. IWFTPAUN, did you polish the wire ends to bare Al metal before making the connections? Did you add anti-corrosion paste to the connections to prevent oxide development?

In addition to the individual panel tested mentioned above, I would test the resistance of each and every Al connection. I'm willing to bet that your problem is actually high resistance because of oxide formation.

 

[Checkthisout]

Hi everyone,

I have two solar systems at the moment.

One is 4x 100 watt mono Renogy solar panels in series, with maybe 90~ feet of 4 gauge aluminium wire going into a Renogy 60A MPPT charge controller. It's feeding a 100AH SOK 12V battery. I'm getting something like 0.1A with it. And the battery is not charged -- I turned on a load and the power did not go up. Panel voltages are in the 40-50V range. On a sunny day, usually about 88V and I've seen it pull well over 200 watts on a sunny day, not even in the summer.

Another is 1x 50 watt mono Renogy panel with the 20 foot long aluminum (10? gauge) cables it comes with. It's feeding a 10A rated Renogy PWM charge controller. With a load on it, it was saying 0.2 amps coming in. It's feeding an old flooded lead acid car battery (just for powering lights in the barn).

It looks like you're looking at panel amps on both systems even though they have drastically different array voltages.

Please verify the simultaneous WATTAGE output of both systems or tell us what is being input in amps to the battery since both systems are 12 volt.

 

[400bird]

It's so overcast you are getting 1 and 2 watts from your two arrays? I wouldn't be wasting time on that.

The bigger MPPT has real electronics inside and does switching to convert you 80v to 12 volts. This costs efficiency and had idle power use.

The little PMW just shorts the panel to the 12v battery. Very little energy required to do that so less idle energy use. Also significantly less efficient at other times, but I guess there are benefits ?‍

Also, in some posts you say the power is coming in, which I read as coming in from PV. Then in other posts you say this is battery power. Either way, it was dart and overcast, solar isn't magic.

 

[acdoctor]

If your connection are good and you are not getting enough light to produce VMP I wouldn’t bother with it until you do.
Until you have VMP you don’t have enough wattage to be meaningful. Your SCC may be consuming half of the tiny amount that is being produced.

 

[Checkthisout]

If your connection are good and you are not getting enough light to produce VMP I wouldn’t bother with it until you do.
Until you have VMP you don’t have enough wattage to be meaningful. Your SCC may be consuming half of the tiny amount that is being produced.

He hasn't confirmed whether or not he's looking at panel amps or battery amps.

He's already setting himself up for error by not using watts when comparing the two systems.

 

[iwasforcedtopickausername]

It was 1 watt into the battery from the 400 watt system and 2 watts into the battery on the 50 watt system.

I think I can connect my aluminum wire ends tomorrow and test the resistance across the setup. I can also get my volt meter and check each panel to see if they are in the ballpark.

I'm also curious to hook up another charge controller next to it. The Renogy MPPT charge controller got confused and held the panel voltage down to 13.1V once. I switched the panels on and off again and it went back up to around 50V and 0.1 or 0.2 amps into the battey.

 

[Checkthisout]

N

 

[Checkthisout]

At 1 or 2 watts, that's well within the margin of error for the measuring equipment.

You're wasting your time being curious.

Your time will better spent doing door dash and putting the money you make towards a wind turbine or backup generator. ?