Selling home, solar inspection issue with VOC measurement.

[J.P.M.]

None of us is as good as all of us.

Hmmm ??? Where have I heard that ?. Seems to have the ring of truth to it. Take a victory lap. Just don't get cocky.

[max2k]

....

Looks like I'm late to the party- great work, sensij .

Since OP seems to have resolved his problem I might continue hijacking his thread with remotely relevant data. Today I tried to collect actual Voc values along with Vmp, Imp and time of the day and here they are. Please note I had clouds passing over which caused wild swings of power. On top of that my trip time to take Voc reading was about 1 minute while clouds could change things in seconds so I may have few outliers there. Nonetheless I think these 2 graphs have some value as they show Voc actually has 2 max points- one in the morning and one in the evening. The morning one is 'helped' by thermal lag of ambient temp, roof, etc while the same lag prevents irradiation to have higher impact in the evening. The messy one 'Voc vs Power' shows Voc depends on irradiance below 20% of the max power. In the transitional zone between 20% and 30% both temperature and irradiation have impact and above that- solely temperature. The mess was caused by thermal inertia- after cloud came over and dropped the power it also allowed cells to cool so when it passed and irradiation sharply returned back to its expected level Voc was often higher for few minutes due to lower temp at the time.

Along the way I learned that my array peaked at 7,000+ W and stayed there for few minutes between clouds so I think LG panels provide good ratio: 7,000 / 7,320 approx 0.95.

I also found that SMA inverter as probably all of them out there is constantly 'hunting' for MPP as a result Vmp readings partially reflect that process and not true Vmp of the panels.

This also left me still wondering what is the practical value of measuring Voc to begin with besides fitting within voltage ratings? VocVmpPower_Time.png
Voc_Power.png

[azdave]

The house I'm buying in Arizona has solar on it too, fully owned, not a lease, and I believe it will be grandfathered into the old program.

Glad things worked out on the old panels.

Is the new house under SRP or APS utility? I'm with SRP and I know my contract from late 2014 is grandfathered to the service address for 20 years and it automatically transfers to any new owner.

SRP contracts entered into before Dec 8th 2014 are far better deal than those that came after. The only thing I wish were different is that my SRP annual true-up date is April 30th so I only get wholesale credit ($62) for the 2369 kWh I banked last winter and spring. These days, I think new contract SRP RE customers get settled up at the end of each month so you can't bank over long periods.

[jschner]

Glad things worked out on the old panels.

Is the new house under SRP or APS utility? I'm with SRP and I know my contract from late 2014 is grandfathered to the service address for 20 years and it automatically transfers to any new owner.

SRP contracts entered into before Dec 8th 2014 are far better deal than those that came after. The only thing I wish were different is that my SRP annual true-up date is April 30th so I only get wholesale credit ($62) for the 2369 kWh I banked last winter and spring. These days, I think new contract SRP RE customers get settled up at the end of each month so you can't bank over long periods.

The house will be with APS. I'm totally new with APS and not sure what will happen or what plans they had in the past or future. I see a lot of people say the future plans do not pencil out for new installs. I hope whatever plan this system is under is a good one. I'm trying to get utility bills from homeowner to get an idea of what to expect. Homeowner says the bills range from $20 to $100 during the year. The inspection of the house is on Tuesday and I will look the solar over and see what more I can find out. I might just have to have a solar inspector check the string VOC on it.

[J.P.M.]

The house will be with APS. I'm totally new with APS and not sure what will happen or what plans they had in the past or future. I see a lot of people say the future plans do not pencil out for new installs. I hope whatever plan this system is under is a good one. I'm trying to get utility bills from homeowner to get an idea of what to expect. Homeowner says the bills range from $20 to $100 during the year. The inspection of the house is on Tuesday and I will look the solar over and see what more I can find out. I might just have to have a solar inspector check the string VOC on it.

Hopefully, a different inspector than the other one.

I'd be interested in what the findings may be. There's a lot more to system health than open circuit Voltage, starting with the integrity of the roof penetrations.

[max2k]

The house will be with APS. I'm totally new with APS and not sure what will happen or what plans they had in the past or future. I see a lot of people say the future plans do not pencil out for new installs. I hope whatever plan this system is under is a good one. I'm trying to get utility bills from homeowner to get an idea of what to expect. Homeowner says the bills range from $20 to $100 during the year. The inspection of the house is on Tuesday and I will look the solar over and see what more I can find out. I might just have to have a solar inspector check the string VOC on it.

On electrical side of the system Voc would be the least of my worries if at all. Looking at this thread alone is a good illustration of how difficult it is to interpret its value. Why not ask for recent total kWh generated by the system? This is the actual value you're getting and I'd make sure it exists. Besides that I'd check how install was done overall and if there's any transferable warranties exist on its components.

In my mind solar has multiple aspects: financial (lease, owned, etc), electrical (kWh production, overall code complaint install), mechanical (roof, rails), maintenance (did it required repairs and what kind) and I'd like to get info on all of them. Voc wouldn't even be on my list .

[sensij]

On electrical side of the system Voc would be the least of my worries if at all. Looking at this thread alone is a good illustration of how difficult it is to interpret its value. Why not ask for recent total kWh generated by the system? This is the actual value you're getting and I'd make sure it exists. Besides that I'd check how install was done overall and if there's any transferable warranties exist on its components.

In my mind solar has multiple aspects: financial (lease, owned, etc), electrical (kWh production, overall code complaint install), mechanical (roof, rails), maintenance (did it required repairs and what kind) and I'd like to get info on all of them. Voc wouldn't even be on my list .

Agreed! That the electrician chose to measure Voc at all is hard to understand, when much better measures are available.

[AzRoute66]

Just knowing how much Voc has been a pain in the butt to him, the notion that he wants an 'inspector' to do the measurement, and the winky-smiley emoji, I suspect that Voc will be the last thing he looks at - UNLESS he is a out and out troublemaker looking for purchasing leverage from the uninformed. There is an evil part of me that would like that.

[Ian S]

The house will be with APS. I'm totally new with APS and not sure what will happen or what plans they had in the past or future. I see a lot of people say the future plans do not pencil out for new installs. I hope whatever plan this system is under is a good one. I'm trying to get utility bills from homeowner to get an idea of what to expect. Homeowner says the bills range from $20 to $100 during the year. The inspection of the house is on Tuesday and I will look the solar over and see what more I can find out. I might just have to have a solar inspector check the string VOC on it.

You will be grandfathered but its being a fairly recent install, I think you will have a flat fee surcharge (insignificant IIRC) that older installs didn't have. You will likely be on either the standard rate or the noon to 7PM T.O.U. plan. Which one is better for you depends on your usage and size of system vis a vis your consumption. I have not looked recently so I don't know whether you have any newer plans from which to to choose. Welcome to the Valley of the Sun aka "heatstroke heaven!"