help with a solar issue while testing with multimeter

[alishac]

So I got a 300w 70.8v solar blanket thats etfe.

I cant test it using elejoy cause of the voltage so used a multimeter and victron solar controller.

The specs of it is:
300w
70.8 voc
60 vmp
5 imp
5.5 short circuit

So first with victron it shows 58 voltage - im guessing thats voc or is this vmp.. the reason I say it could be voc is I have hit 302w at 68v and in history I seen it hit over 74v. Issue is its saying 58v with about 3.1a - 180w.. thats with 10m 6mm2 high heat rated PV solar cable.. Based on vmp/amp for distance it states I can do 4mm2 for less then 1% drop.. Im using 6mm2 though.. Now thats with victron.. I then test with multimeter.. It tests at 71.5v with 3.7 at the panel not with the extended cable which should be 262.7w. Now I just did a test in the afternoon and with the 10m extended 6mm2 connected to panel and its saying 71.2v with 3.21a which should relay to 228.5w but victron is saying now 160w, 2.9a.. Whats happening.. Anyone know why victron is showing nearly half amount of watts and around 14 less volts?

 

[rodrick]

how long are your extensions could it be voltage drop, has this system been running and this problem has arose suddenly if so check all your connections also what is the current charge level of the battery maybe it’s not wanting more power can you put a load on the system and then check if you readings change

 

[alishac]

the extension is 10m or 32ft, I did a test with multimeter and it was testing same voltage and current with and without the extension.. the max on the blanket can charge is 25ah into battery, 5a current the victron is 100/30.. based on last year I tried it same month, about the same temp and also midday with 10m/32ft extension I got 301w 67v... The only change I have done since I connected the victron to my battery is I added another battery and made it parallel.. So unsure if thats something to do with it?

 

[mikefitz]

Whats happening

Your meter tests are measuring OC volts and SC current. The Victron is carrying out a maximum power search .



Mike

 

[alishac]

Your meter tests are measuring OC volts and SC current. The Victron is carrying out a maximum power search .

View attachment 173711

Mike

OK but what's that mean...cause it's not hitting 250w..it's hitting 170w or less..when I looked at victrons mttp calc and put the values in it said based off 58v at 35 Celsius I should get 20a to battery or 240w but I was getting 170w and 9a to battery at 35c

 

[alishac]

So it was cooler today but same issues.. So I did some more tests.. On the victron app it was saying 165w-170w, 58v-60v, 2.8a-3.1a Using mutlimeter from the anderson plug coming out the solar blanket it says 72.2v, 3.76a which should be 271.4w.. So I then test the 10m extension cable at the end.. it said same as where it was at the blanket anderson.. So then I put the multimeter to the controller PV screws it says the same as the app so a 10-12v drop and a few milli amps drop.. I mean even if it was same current and 72.2v it still would be more wattage... Anyway I then take out the PV wires and then test them and yet again they test the same as whats coming off the solar blanket so 72.2v, 3.76a...So I have zero clue why there is a 10-12v drop when its int he controller.. Ive yet to do a hard reset by taking out all the wires but if that doesnt work I'm guessing it means the controller is faulty

 

[mikefitz]

Look at the graph of typical solar panel power. When you measure volts, OC v, the current is zero, thus no power.
When you measure panel current , I sc there is no volts, thus power is zero. Multiplying the values together is pointless.
The MPPT.controler loads the panel and computes maximum power. This will be at lower volt and current than your meter tests .
The panel is a current source not a voltage source like a battery.
Your panel specification will identify the maximum power voltage and current values . These values will occur under ideal solar.

Perhaps read up on how a solar panel functions.

Mike

 

[alishac]

I see.. but so far for 2 days ive tested it and its showing the same volts, same current, same watts.. when I test another lower volt panel with elejoy it tests at its max watts "180w and max current".. plug that into victron and it drops to 122w, and 1-2a less current.. 98% effieciancy on victron as if.. But the thing is.. in october last year with same temps, same amount of extension cable I got 301w, 295w at 67v, 4.9a and yet this year 2 days in a day I can't get over 170w, 58v, 3.1a.. I never had this issue of having 10-12v loss at the controller last year.. The only thing I've changed since last year was add another battery and set it in parallel.

 

[mikefitz]

. in october last year with same temps, same amount of extension cable I got 301w, 295w at 67v, 4.9a and yet this year 2 days in a day I can't get over 170w, 58v, 3.1a..

Solar conditions may be different and your flexible panel is a year older. Flexible panels degrade

Panel specification is max power at 60 volts.
Something to be considered is the battery SOC. Try loading the battery and see if the Victron output increases .

 

[Supervstech]

Only way to know if conditions are the same is with an irradiance meter at the panel.
High clouds, dust or smoke in the air, dust on the panels, air temp... all contribute to panel output capabilities.
If the battery is full, or of there are resistance on the battery connections...

 

[alishac]

I'll do some more trouble shooting today. It's not a flexible panel it's a solar blanket. And I've only had it the sun for max 30 days in a year ,rest time it's been packed away so I doubt it's degraded. Max power maybe 60v but not sure if I said it but when I plug the mttp in on the victron app for about 1 second it hits 72v which is voc..also even though it maybe 60v I'd had it reach on the controller 73v so is it using vmp or voc..seems like it's using voc if it reaches 13v over max..but that's when I tested it last year.