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560WP Solar panel low voltage on open circuit

mmm1998

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Aug 10, 2022
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Hi,

For a project at home i bought one 560WP solar panel from the brand Resun. I am trying to test the output of the panel by measuring the open circuit voltage.
I got the panel in full exposure in the sun (no clouds) and got about 46.2V.
Can you guys help me read the datasheet correctly? I think i'm doing something wrong since i'm not even getting close to the given 50.05V on the datasheet (in STC).
I included the datasheet in attachments. Thank you so much!

ps. I dont have a resistor to test the power output.
 

Attachments

  • RS8I-M FULL BLACK.pdf
    901.6 KB · Views: 15
Your panel is delivering real close to NOCT open cell voltage of 46.92 from the data sheet you posted. Looks like it is right in spec.
 
Your panel is delivering real close to NOCT open cell voltage of 46.92 from the data sheet you posted. Looks like it is right in spec.
Yes I figured, but i'm might missing some experience here.
On a open voltage of 46.92V it delivers 424WP. Am I correct?

Resun is advertising this panel delivering 560WP.

Thanks!
 
Yes I figured, but i'm might missing some experience here.
On a open voltage of 46.92V it delivers 424WP. Am I correct?

Resun is advertising this panel delivering 560WP.

Thanks!
Edit: deleted.
 
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Yes I figured, but i'm might missing some experience here.
On a open voltage of 46.92V it delivers 424WP. Am I correct?

Resun is advertising this panel delivering 560WP.

Thanks!
Most all panels are rated at STC though real world numbers would say to use NOCT. Your panel manufacturer is being a lot more honest to give both ratings.

BTW. Size your SCC based on STC numbers for the panel.
 
It is not necessary to use a load resistor to load test a panel. Use a DVM in amps mode directly connected across the panel. Do not connect the ammeter across the panel when in full sun as there will be a big arc created when you essentially short out the panel into the DVM possibly damaging the connectors on the panel. Shade the panel with a tarp or whatever then connect DVM in amps mode, then remove panel cover. THIS WILL NOT be maximum power but will give you an indication of panel power.

Just my opinion.....these panels are made of left over half cells and are not in the “top tier” quality is suspect
 
Yes I figured, but i'm might missing some experience here.
On a open voltage of 46.92V it delivers 424WP. Am I correct?

Resun is advertising this panel delivering 560WP.

Thanks!

Realistically you only get 75% of the rating which will be 420w in your case. Panels are rated at the factory with "Standard Test Conditions" that you'll rarely ever achieve in real life.
 
So you guys are saying the STC numbers are not achievable at all? I actually bought these panels according to the given numbers. I cant believe it actually,
 
So you guys are saying the STC numbers are not achievable at all? I actually bought these panels according to the given numbers. I cant believe it actually,

Solar panels are rated at one temperature ( 77F ) and irradiance level ( 1000 watt meter squared which is the strength of sunlight ) know as STC

The environment varies great amounts in temperature and irradiance, for example dawn and dusk isn't the same as high noon.

Panel voltages go DOWN with temperature and current goes UP with temperature but about 1/10 that of voltage in change.

Also panels only convert ~20% of that sunlight to electricity, the rests is absorbed by the panel as heat, typically panels run ~50 degrees hotter than the ambient temperature. Wind will help reduce this, hence why ground mounts are typically cooler running that roof mounts.

So what you may think is "full" sun, usually isn't, the panels run hot and have lower voltage hence, the power output in typical conditions are lower than the STC test standard.

No different than EPA rating "standard" of vehicles when road conditions like snow, high winds or driving over the test speed reduces mpg.
 
Yes I figured, but i'm might missing some experience here.
On a open voltage of 46.92V it delivers 424WP. Am I correct?

Resun is advertising this panel delivering 560WP.

Thanks!
The panel doesn't source current at open circuit voltage.
 
It is not necessary to use a load resistor to load test a panel. Use a DVM in amps mode directly connected across the panel. Do not connect the ammeter across the panel when in full sun as there will be a big arc created when you essentially short out the panel into the DVM possibly damaging the connectors on the panel. Shade the panel with a tarp or whatever then connect DVM in amps mode, then remove panel cover. THIS WILL NOT be maximum power but will give you an indication of panel power.

Just my opinion.....these panels are made of left over half cells and are not in the “top tier” quality is suspect
Most meters can't measure much more than 10A. May need a clamp on meter and just create a dead short across the panel and measure the short circuit current that way
 
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