Solar output goes down on sunny vs overcast days as displayed on Sol-Ark 5K? Need advice

[Dhalbmaier]

I have a new (8) panel array on a pergola, Trina Vertex S 390 watt panels. I am controlling it with a Sol-Ark 5k inverter which I like the features on. Since I turned the system on in November I get lower power generation numbers on sunny days vs overcast days by a lot, like 70% less. I have been online with Sol-Ark and had them login to my system to check settings and they have no explanation. Checked each panel with volt and amp meter and they are all the same, not sure they are correct but are generating the same output. My array has some shading from tree branches now that sun is low in the sky, I'm in Minnesota. Could the contrast from sun to shaded areas on the panels on sunny days cause the inverter MPPT or the panels shade optimization features to shut down power generation. Somethings wrong and I need help figuring it out. Could not find anything useful on general internet search so I'm turning to the experts here. Thank you.

Power calculations based on Trina Vertex S 390 watt PV panel specifications
String voltage: 8 panels x 33.8 (Vpmax) = 270.4V
String wattage: 270.4 x 12.34 (Ipmax) = 3,337 watts (per string)
Maximum string voltage: 8 x 40.8 (Voc) x 1.25 = 408 Volts
Maximum Current: 13.08 (Ic) x 1.25 (Irradiance) x 1.25 (NEC) = 20.44 Amps

 

[SunDave]

Hi Dhalbmaier,
You may have to break your problem down into pieces and take a look at it. There are ways to check with half the panels at a time, etc. to determine if there is a problem with each half. Before you do that though, check the simple stuff. For example, are your batteries full? If so, and not grid tied, your inverter will automatically limit the incoming wattage to match loads, but no more.

One other item. Not sure which 5k model you have, so input your Sol-ark model and panel specs into this calculator. Sounds like you have a good handle on the specs, but your panel spec sheet will have each category, including the temp coefficients. Don't forget to input a suitable minimum temp for Minnesota.

Solar Panel Sizing 4.6

www.sol-ark.com

I could be that you just have a panel with slightly too high of amperage for your model. I have never experienced with the unit will do with over amperage. My 15k says it is "self limiting" but what that means is not entirely clear.

 

[crossy]

Exactly which inverter do you have?
What's the maximum input voltage permitted?

 

[LydMekk]

The 5kW model has 425V as a MPPT max. Panels should not exceed 8 in series per string as the voltage would be too high.
Installing panels flat on a pergola is nice for summer conditions but now in winter the sun is at an low angle and your panels will not produce their max. Far from it.

 

[Dhalbmaier]

Hi Dhalbmaier,
You may have to break your problem down into pieces and take a look at it. There are ways to check with half the panels at a time, etc. to determine if there is a problem with each half. Before you do that though, check the simple stuff. For example, are your batteries full? If so, and not grid tied, your inverter will automatically limit the incoming wattage to match loads, but no more.

One other item. Not sure which 5k model you have, so input your Sol-ark model and panel specs into this calculator. Sounds like you have a good handle on the specs, but your panel spec sheet will have each category, including the temp coefficients. Don't forget to input a suitable minimum temp for Minnesota.

Solar Panel Sizing 4.6

www.sol-ark.com

I could be that you just have a panel with slightly too high of amperage for your model. I have never experienced with the unit will do with over amperage. My 15k says it is "self limiting" but what that means is not entirely clear.

Thanks for the advice, my system is grid tied so I know I am not exceeding the wattage required. For example I can see my usage maybe 50% higher than input at a given time. I can also see the panel wattage input to inverter as shown on Sol-Ark screen go DOWN when the sun comes out from behind a cloud. I have the -5k-1P-N inverter. Sol-Ark says the panel array is fine and sized correctly, I'll check the numbers on the calculator you sent.

 

[Dhalbmaier]

The 5kW model has 425V as a MPPT max. Panels should not exceed 8 in series per string as the voltage would be too high.
Installing panels flat on a pergola is nice for summer conditions but now in winter the sun is at an low angle and your panels will not produce their max. Far from it.

Thanks, Max input voltage is 408V from the array so I should be OK. Sol-Ark said the panels specs are fine also. The Pergola does have a 20 degree angle for the panels, so while not optimum still OK for my location. Either way this does not explain a 60% reduction in power generated on a sunny day vs overcast day one day apart.... Jan. 31 vs Feb. 1 for example.

 

[Dhalbmaier]

Exactly which inverter do you have?
What's the maximum input voltage permitted?

I have the Sol-Ark 5K-1P-N, the specs for the inverter align with the application from my calculation and those from Sol-Ark as well.

 

[Dhalbmaier]

Hi Dhalbmaier,
You may have to break your problem down into pieces and take a look at it. There are ways to check with half the panels at a time, etc. to determine if there is a problem with each half. Before you do that though, check the simple stuff. For example, are your batteries full? If so, and not grid tied, your inverter will automatically limit the incoming wattage to match loads, but no more.

One other item. Not sure which 5k model you have, so input your Sol-ark model and panel specs into this calculator. Sounds like you have a good handle on the specs, but your panel spec sheet will have each category, including the temp coefficients. Don't forget to input a suitable minimum temp for Minnesota.

Solar Panel Sizing 4.6

www.sol-ark.com

I could be that you just have a panel with slightly too high of amperage for your model. I have never experienced with the unit will do with over amperage. My 15k says it is "self limiting" but what that means is not entirely clear.

Since there are two MPPT controllers on the Sol-Ark inverter I was thing about connecting four (4) panels in series to MPPT1 and four (4) to MPPT2 to see what happens. This however, requires some new wiring it would only be an experiment so I'd like to try other avenues first. I did switch the panel input connection between MPPT1 and MPPT2 with no change noted.

 

[SunDave]

Since there are two MPPT controllers on the Sol-Ark inverter I was thing about connecting four (4) panels in series to MPPT1 and four (4) to MPPT2 to see what happens. This however, requires some new wiring it would only be an experiment so I'd like to try other avenues first. I did switch the panel input connection between MPPT1 and MPPT2 with no change noted.

Just an idea here. Is it possible to check if the array is wired backwards? Meaning the + and - of the solar input is swapped? There are solder points just above the MPPT inputs. If you are confident with a mulit-meter, you could check the reading at the terminals and make sure it shows a positive number at those terminals when your meter is correctly on the + and - points.

That is an odd situation. I'm surprised the sol-ark support didn't have more ideas to test. Maybe they could take another run at it if you call in and get a different tech.

 

[Dhalbmaier]

Just an idea here. Is it possible to check if the array is wired backwards? Meaning the + and - of the solar input is swapped? There are solder points just above the MPPT inputs. If you are confident with a mulit-meter, you could check the reading at the terminals and make sure it shows a positive number at those terminals when your meter is correctly on the + and - points.

That is an odd situation. I'm surprised the sol-ark support didn't have more ideas to test. Maybe they could take another run at it if you call in and get a different tech.

Yeah, I like trying a different technician idea. I did check the polarity right away at the inverter and on the panels just to make sure that the panels weren't labeled wrong. I agree it is strange, thank you for your thoughts / help.

 

[Hedges]

I think you've only told us 70% reduction, without telling us how many watts.
Maybe, slightly overcast with glowing clouds as light source provides more power than direct sun at oblique angle.

"some shading", can you provide a photo? Shade on a single cell absolutely kills power output from that section of 20 ~ 24 cells. Much shade, or enough to drop voltage below MPPT, would kill production. But overcast would provide uniform illumination, albeit reduced.

What is voltage range for your MPPT, and what voltage is the array producing? What current?

 

[Doggydogworld]

Shading is the first thing I'd suspect. A little bit of shading in the right spots can kill production. All panels in series have the same current, so if shading slashes your current on one panel it will pull them all down. Panels have bypass diodes to reduce/prevent this effect, but they can't fix every situation.

Overcast days have less total light, but it's more omni-directional so you don't get the shading issue.

 

[Dhalbmaier]

I think you've only told us 70% reduction, without telling us how many watts.
Maybe, slightly overcast with glowing clouds as light source provides more power than direct sun at oblique angle.

"some shading", can you provide a photo? Shade on a single cell absolutely kills power output from that section of 20 ~ 24 cells. Much shade, or enough to drop voltage below MPPT, would kill production. But overcast would provide uniform illumination, albeit reduced.

What is voltage range for your MPPT, and what voltage is the array producing? What current?

Thank you for the comments.....Ok, I will take a picture of the panels on an overcast vs cloudless day at the same time of day and record the Voltage and Watts. The Sol-Ark panel calculator for the panels I have says I can have (11) on each MPPT circuit of the inverter. There are two MPPT circuits on the 5K-1P-N inverter. The highest voltage I have seen is around 300 V. Not sure what the max. watts are....I'll check.

Today I generated 2.3Kwh of power from my 3.16 Kw array with mostly overcast and occasional breaks in the clouds. Hourly power generation graph on inverter shows this exactly with variations by hour. Yesterday, completely overcast all day generated 2.6Kwh of power with the expected hourly power generation graph that smoothly ramps and declines with daylight hours. Five days ago complete sunshine all day generated .7Kwh of power with uniformly low output all day almost no variation by the hour of day. Array faces due South, I am at 45 degrees in Minneapolis/St Paul MN area.

 

[Dhalbmaier]

Shading is the first thing I'd suspect. A little bit of shading in the right spots can kill production. All panels in series have the same current, so if shading slashes your current on one panel it will pull them all down. Panels have bypass diodes to reduce/prevent this effect, but they can't fix every situation.

Overcast days have less total light, but it's more omni-directional so you don't get the shading issue.

Thanks, Please see my reply to Hedges on the Kwh's of power generated. If it is shading then the Trina Vertex S panels and the MPPT are doing a poor job of mitigating this situation. I thought the zone/cell control in the panels would perform better. As the sun's horizon raises with the seasonal change my shading will be greatly reduced/eliminated. I turned my system on in November 2023. Seems to me it's more than shading but, I am no expert.

 

[zanydroid]

I thought the zone/cell control in the panels would perform better.

This sounds like your mental model of what is possible is disconnected from how it works in reality.

If you have full cut panels you will lose 1/3 of production if you have hard shade anywhere on the 1/3 of panel covered by the same bypass diode. No optimizers or MPPT will recover it.

 

[zanydroid]

Photos please of the shading pattern.

 

[Hedges]

But an MPPT can do worse, and half-cut panels could really trick it.
Also, if shade drops voltage below minimum MPPT, output drops off rapidly.

Need to see the shade, and the data sheets & array series/parallel configuration.

 

[zanydroid]

Also, if shade drops voltage below minimum MPPT, output drops off rapidly.

LOL, forgot about that.

 

[Hedges]

How could I forget?
When one of several SWR 2500U inverters failed, I rewired from 4x 24s to 3x 16s2p.
Worked fine in full sun, but one or 2 panels shaded and power dropped off a cliff.