Why shouldn’t solar panels be tested before acceptance?

[ACH]

I don't know why a client would ask to have individual panels tested after installation. The initial power output obviously should be compared to what's expected, subject to things like weather (cloud cover) and time of year.

I was thinking before installation. Once it is installed it seems to me to be difficult to test.

 

[ACH]

I don't know why a client would ask to have individual panels tested after installation. The initial power output obviously should be compared to what's expected, subject to things like weather (cloud cover) and time of year.

I was thinking it is too late after it is installed to determine the bad panel.

 

[petersonra]

I was just thinking that if I am purchasing a 400W panel it should put out 400W or close to 400W.
It appears that this is not normally done so my expectations are probably unreasonable.

I'm not sure of 400 w panel will actually put out 400 Watts. The sun light has to be just perfect and at the exact right angle.

 

[Ravikumar]

I subcontracted a residential solar installation. I have never used solar before. I was expecting the new panels to be tested before accepting the installation. The solar contractor told me that testing the panels was never done and is not necessary. Is this correct?

Mostly not need. But before connecting in array, check Voltage. By checking PV module voltage you can find any damage in transportation

 

[pv_n00b]

I was just thinking that if I am purchasing a 400W panel it should put out 400W or close to 400W.
It appears that this is not normally done so my expectations are probably unreasonable.

That is a reasonable expectation. But it requires a lab to do the test. Few end users can flash test modules under STC. Putting a module in the sun and measuring the Voc and Isc will not tell us if it will produce the listed power on the data sheet. It will tell us if there is a gross defect in the module, so that is something. To make sure the modules are operating as stated the best thing is to buy from reputable manufacturers and monitor production to find gross defects.

 

[jaggedben]

I was just thinking that if I am purchasing a 400W panel it should put out 400W or close to 400W.

Nope, that's not really realistic. The rating is based on lab test conditions that approximate a perfectly clear sky, a direct angle of sun on the panel, and an unrealistically low temperature (because the panel doesn't heat up during the test like it does all day in the sun). So for a fixed orientation installation, you may only see 400W on a few days in May. Your milage may vary. There is also the issue of inverter sizing and DC/AC ratio.

It appears that this is not normally done so my expectations are probably unreasonable.

No, but what is normally done is some type of ongoing monitoring so that problems can be identified later. That allows you to compare monthly and annual production to what was predicted, and compare modules to one another (keeping in mind that shade and dirt can cause module to module differences that aren't the module's fault).

 

[ACH]

Thank you for all your comments. I now have a better understanding and I appreciate the help.

 

[GeorgeB]

With many systems which include individual panel monitoring, installed is trivial; the 81W is shaded by a vent at this time. Panels are "250W"

 

[pv_n00b]

And if your customer sees that one module is putting out only 81W while the rest are around 130 expect a call to complain that the module is defective.
I thought the companies with module level monitoring were offering an option for the installer to block the individual module output view for the owner and only provide a total output to stop calls caused by this kind of view? Did they ever implement that?

 

[GeorgeB]

And if your customer sees that one module is putting out only 81W while the rest are around 130 expect a call to complain that the module is defective.
I thought the companies with module level monitoring were offering an option for the installer to block the individual module output view for the owner and only provide a total output to stop calls caused by this kind of view? Did they ever implement that?

I don't know, but don't think so with Enphase Enlighten. I __DID__ recognize that I had shading, and had observed that 5 of my 17 would see shade from my house at some time of the day when talking to the contractor before signing. That was one reason I preferred individual vs string inverter(s). 3 of the 5 that see shading see significantly less at some time of the day.

My installation is far from optimal if I had no constraints; roof pitch is about 51 degrees helping winter production. but hurting summer; PVWatts guessed I'd see about a 3% (If I recall correctly' it was almost 7 years ago that I had it installed) below optimum purely from angle (I'm at about 35 degrees latitude, Greenville SC). Overall, I was an informed purchaser and consumer and am 100% satisfied with my system.

 

[tallgirl]

I was just thinking that if I am purchasing a 400W panel it should put out 400W or close to 400W.
It appears that this is not normally done so my expectations are probably unreasonable.

You'd have to have very specialized equipment to verify that a 400 watt panel is putting out 400 watt. That 400 watts is with the panel junction temperature at 25*C, 1 atmosphere, not cloudy, 1,000 watts per square meter direct normal irradiance.

 

[jaggedben]

And if your customer sees that one module is putting out only 81W while the rest are around 130 expect a call to complain that the module is defective.
I thought the companies with module level monitoring were offering an option for the installer to block the individual module output view for the owner and only provide a total output to stop calls caused by this kind of view? Did they ever implement that?

Enphase started charging the customer extra for panel level data a few years ago. Then they backtracked a little and started showing energy production (but not power, voltage etc.) per panel with the basic level monitoring. But I think their considerations had more to do with webserver bandwidth than customer complaints about module discrepancies. Most residential customers either don't care until their bill goes up, or they understand shading and other stuff once you explain it to them.

 

[tallgirl]

Enphase started charging the customer extra for panel level data a few years ago. Then they backtracked a little and started showing energy production (but not power, voltage etc.) per panel with the basic level monitoring. But I think their considerations had more to do with webserver bandwidth than customer complaints about module discrepancies. Most residential customers either don't care until their bill goes up, or they understand shading and other stuff once you explain it to them.

I worked for a manufacturer which did module-level monitoring - I wrote parts of the firmware for the microinverters, as well a big chunks of the data logger and some of the web portal. So far as I know, Enphase now owns everything I did.

The problem really was customers complaining. The great thing about micros is they help increase production in roofs with some shading. The bad thing about micros is shaded modules underproduce and then customers get upset.