Solar panel low output

SeriousTree

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Jun 20, 2022
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Hello, I'm left scratching my head at the numbers. Am I mathing correctly? 35v x 8a = 227w? Shouldn't it be like 280 watts? I tested the solar panel at the leads and I'm getting good voltage, even with 40ft extension cables, the numbers are still good. I'm using a Cen-Tech basic clamp meter for testing.
Here is what I'm working with:

Growatt 3000lvm 24p
Bigbattery 24v Mule, 3Kw
40ft 12awg extension cables
(1) TrinaSolar 390w 144cell:
Imp 9.64a
Vmp 40.5v
Isc 10.08a
Voc 49.7v
Mono, 12awg wire

Panel lays almost flat (10°), I thoroughly inspected panel for snail trails, corrosion at the connections between solar cells, nada. Panel is good.
My concern is I'm not getting enough watts to power my little a/C unit which uses about 400watts (measured with a Kill-a-watt meter)
I expected to only ever get maybe 330 watts on a clear day at noon ish, but the most I've ever seen is 270watts on the display.

Any advice would be appreciated. BTW, first solar setup, and I'm new to this all.
 

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DThames

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Those amps are going into the battery. Try <battery voltage> * 8amps
 

rmaddy

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35v x 8a = 227w? Shouldn't it be like 280 watts?
It's 35V input from the panels. It's 8A output to the battery. Those are two unrelated numbers that you can't multiply together.

227W to the battery at 8A means you have a battery charge voltage of 28.375V. That seems about right for a 24V LiFePO₄ battery.

Of course this doesn't answer why you are not getting more wattage from the panel. It just explains the math of what you are seeing.
 

SeriousTree

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Jun 20, 2022
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Thank you for the speedy responses, I totally overlooked those things. So I'm actually getting low amps from the panel is what it sounds like, based on the voltage being 35v from the panel. Does that sound about right? Looks like I need to change the post title, that's the most inaccurate thing now lol
 

rmaddy

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227W / 35V = 6.5A from the panel. I wouldn't worry too much about the specific input voltage and amperage. Only getting 227W from a 390W panel is what matters. But there are many factors. Panel angle is a big one. But it is about the summer solstice. Power drops in the heat. What's the temperature where you are? The panel will be a lot hotter than that. You could easily lose 15% or more on a hot day.

Try angling the panel more directly into the sun and see how that helps.
 

SeriousTree

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Jun 20, 2022
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I'm on the west coast and have full sun, rarely any cloud cover. Temp today will be about 95F(78F currently). The panel sits almost flat on a patio overhang so I can grab more energy over the course of the day versus being angled directly towards the sun on an angled portion of the roof. But I will give it a shot tomorrow. Could a blown diode cause a drop in amps like this or would that also drop voltage? BTW, 264 watts @ 10:53am, that's almost the max it produces (~275w)
 

SeriousTree

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Jun 20, 2022
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Something else I noticed, the battery will pull 9amps with nothing running on the AC circuit. Does that look correct? Funny thing is with the inverter turned to the OFF position (AC circuit off, inverter still on) the pv voltage coming in will go down below the threshold of 30v and constantly restart until I turn the inverter on (AC circuit) with the circuit On, it's at 39v and doesn't restart ever, and battery is being charged.

I apologize if my n00bness causes anyone a headache.
 

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mikefitz

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You panel is most likely getting hot in the sun. Typically for every 10 degrees centigrade above 25 degrees you will lose almost 5% of panel power, as the voltage falls. Could be 15 to 20% loss
Measure the temperature with a IR gun.
Panel heat loss, 20%, + cable loss , 5%, + solar controller loss, 5%, drops the 390 to 280.

Mike
 
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SeriousTree

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Jun 20, 2022
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You panel is most likely getting hot in the sun. Typically for every 10 degrees centigrade above 25 degrees you will lose almost 5% of panel power, as the voltage falls.
Measure the temperature with a IR gun.
Panel loss + cable loss + solar controller loss
I'll measure with the IR gun around 2pm-3pm today to try and get a peak temp. I can understand the panel & cable loss, but does an inverter typically make your wattage pay tax before it hits the lcd display?
 

DThames

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Are the panels new? If used on a solar farm, often replace them when output is low 80% percent of rated, under good solar conditions.
 

SeriousTree

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Are the panels new? If used on a solar farm, often replace them when output is low 80% percent of rated, under good solar conditions.
Yes, to my knowledge it's new, purchased from IES. I did unfortunately reconnect the panel to my inverter after testing it, while the sun was shining. It took almost a minute for the inverter to start allowing power into the battery. But since it's only 1 panel operating at 35v and roughly 270 watts I doubt it fried anything...although I'm sure it wasn't a good idea in retrospect.

Also I've check each mc4 connector by unscrewing the plastic cap, pushing wire inwards and also slightly tugging to make sure it's securely connected. No dice.
 

DThames

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Yes, to my knowledge it's new, purchased from IES. I did unfortunately reconnect the panel to my inverter after testing it, while the sun was shining. It took almost a minute for the inverter to start allowing power into the battery. But since it's only 1 panel operating at 35v and roughly 270 watts I doubt it fried anything...although I'm sure it wasn't a good idea in retrospect.

Also I've check each mc4 connector by unscrewing the plastic cap, pushing wire inwards and also slightly tugging to make sure it's securely connected. No dice.
Most chargers need to be connected to the battery first, before the PV is connected. If the system is booted up and the battery connected, you can slam the PV to it however you desire. I have breakers right by my units and turn them off and on without regard to the PV conditions. They do take a minute or so (typically) to decide how to load the panel (MPPT stuff). Do understand that the charger develops a load to draw amps from the PV panels. No current flows until the charger provides the load. Think of how your microwave oven works. It is plugged in and connected to the AC power source of near unlimited power. But it is the timer and the power level setting of the oven, followed by the Start button that causes electric power to be used.....other than lighting the display and powering the internal controls. Most chargers are powered from the battery side, so connecting the battery first gives the system the power it needs to boot up and be able to carry out its programming.
 

SeriousTree

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Most chargers need to be connected to the battery first, before the PV is connected. If the system is booted up and the battery connected, you can slam the PV to it however you desire. I have breakers right by my units and turn them off and on without regard to the PV conditions. They do take a minute or so (typically) to decide how to load the panel (MPPT stuff). Do understand that the charger develops a load to draw amps from the PV panels. No current flows until the charger provides the load. Think of how your microwave oven works. It is plugged in and connected to the AC power source of near unlimited power. But it is the timer and the power level setting of the oven, followed by the Start button that causes electric power to be used.....other than lighting the display and powering the internal controls. Most chargers are powered from the battery side, so connecting the battery first gives the system the power it needs to boot up and be able to carry out its programming.
Thank you for that explanation, by 'developing a load' do you mean it connects the panels (35v) to the battery(~24v) and feeds it current? Like, it connects it internally and the higher volts pushes current into the discharged battery bringing up the voltage to nominally levels?
 

740GLE

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MPPT searched for the most optimized voltage to draw current from the panel, always looking to maximize watts out.

Honesty I don’t think you have anything wrong with your system you’ve just proven that real world numbers don’t reflect name plate ratings in ideal lab conditions.

With how cheap panels are why settle for just one? Buy 3 or 7 more and load up the Growwatt so you can run your AC.
 

SeriousTree

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MPPT searched for the most optimized voltage to draw current from the panel, always looking to maximize watts out.

Honesty I don’t think you have anything wrong with your system you’ve just proven that real world numbers don’t reflect name plate ratings in ideal lab conditions.

With how cheap panels are why settle for just one? Buy 3 or 7 more and load up the Growwatt so you can run your AC.
I believe you might be spot on. I'm going to try jumping to a 10 awg solar cable of 40ftand get rid of the 12 awg 50ft cable I have now and see how much of a difference it makes. If that makes a difference I'll end up cutting the 40ft 10 awg down to 30ft by routing them through a more direct way. I'm sure that will make a difference in the voltage drop (just recently learned about that) and thus wattage. I haven't checked solar panel temp yet, been too busy.

Also the diodes and the connections are sealed with a white sealant on each junction box on my panel, so I can't check the diodes. They recommend trashing the panel. At $165 I can't say that's a bad idea, hah.
 

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Ellcon123

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Don't forget the SCC efficiency. They state high % but that is ideal conditions. It will vary depending on the input vs output voltage.
 

SeriousTree

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Jun 20, 2022
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Don't forget the SCC efficiency. They state high % but that is ideal conditions. It will vary depending on the input vs output voltage.
Input can show up to 45v which I was definitely surprised to see, but I only ever see an average of 35v from my panel. Once I wire up the 10 awg cables on thursday/Friday I'll report my wattage.

Update: it just rained pretty good and cleaned off the dust, achieved a new world (my world) record of 285 watts @ 87F° ambient temp


Update to the update: it just pushed 336 watts. So it looks as if the very light dust played a significant role in power loss. I'm still rocking 12awg 50ft cables, so nothing has changed. Although I did unplug the battery from the inverter as well as the pv quick disconnects while there were thunderstorms. I'm assuming things will only improve once I install 10awg 40ft cables.
 
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SeriousTree

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Jun 20, 2022
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I do have 1 concern: is it possible for a solar panel to produce too much current under normal conditions?
 

Berseker

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US $56.29 50%OFF | EL400B/ EY800W Photovoltaic Panel Multimeter Auto/ Manual MPPT Detection Solar Panel LCD MPPT Tester Voltage Testing Tool

This tool could help, am tempted to buy it as my 10yr old renogys are underperforming.
55w from 3 x 250w panels, on a dull day, while 3 x 250w suntech is spitting out 180w
 
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