Residental Solar 12.8 kw system outputting 9.96 kw

[Mike 134]

Just want to clarify, am I correct in all this? I am guessing it's cheaper to provide one slightly larger inverter Yes it's cheaper they likely put $1000 in their pocket. and a single string vs. actually building out what I paid for?

Isn't it better to have 2 strings with separate inverters for my 12.8 kW system? That configuration runs the inverters at less than 100%, spreads the load to two devices with some overhead. This also should provide basic redundancy if one inverter or string dies the other still produces power? Yes

right now I am running the single inverter (at 100% according to the monitor) and it's having to shunt the excess current to heat is my assumption.

Would love anyones professional opinion and thanks for the education.

See comments in red Plus you start clipping early in the day looks to be about 4 hours clipped you lose maybe 6-8KWhs? and depending on your rate might add up to some serious coin. I have attached my bell curve for comparison (7.2KW size) The second one was a cold day so I peaked at more than rated size.

 

[zanydroid]

Is there a production guarantee? If there is you can maybe negotiate against that -- would they rather pay you on the production guarantee, or upgrade your equipment up front. Maybe I'm cynical but I assume these solar installers will not last that long overall, so I'd always rather take an up front compensation vs an amortized over time one.

Clipping in April seems... premature. It'll just get worse by the summer.

 

[zanydroid]

mediation or arbitration clause looks like and how to complain to your state licensing board

Oh, also knowing those options if things really went south made me feel much better psychologically whenever I had to deal with BS over e-mail or phone calls.

Document early and often.

 

[keymaster]

That is another issue. Do you have specifics? Did they list a larger inverter and give you a smaller one? Did they give you less panels than what you paid for. Was there a change related to your power company or your main service panel bus size?

the contract calls for 32 - 400 watt panels. Those were installed. the contract calls for 2 SE7600H-US inverters. Those were not installed. The contract calls for 2 strings, only one was installed. the contract is very specific about part numbers and configuration.

It was just not installed as contracted. The solar company uses a 3rd party to install but the contract doesn't say anything about that.

 

[keymaster]

Oh, also knowing those options if things really went south made me feel much better psychologically whenever I had to deal with BS over e-mail or phone calls.

Document early and often.

The contract has a hard arbitration clause and I am required to notify in writing. Also their remedy is to fix or replace any defects within 14 days according to the contract after being notified. Otherwise I can take it to arbitration.

I am going to send them a registered letter tomorrow. The solar company is the one I have a contract with, there is 0 mention of 3rd parties doing the install in the contract.

 

[zanydroid]

Hmm, in that case you should easily be able to escalate if there is pushback.

Not clear what support you still need us to help with. Yeah, two strings is strictly more flexible and better than one. Both for redundancy and for updating your architecture in the future. EG there's another thread here where someone's having trouble AC coupling, and it would be easier with readily accessible 2 string instead of single string (in their case they were going to look into splitting the string themselves at the combiner. Which is better than rewiring everything but still kind of sucks to have to do).

 

[Ampster]

the contract calls for 32 - 400 watt panels. Those were installed. the contract calls for 2 SE7600H-US inverters. Those were not installed. The contract calls for 2 strings, only one was installed. the contract is very specific about part numbers and configuration.

Then you have a good case unless there was a reason from the builiding department or the utility to limit the project to kW. The solar company might use that as an explanation if that was the case. Typically that would be done with a change order even if they considered it beyond their control (per force majuere clause). The fact that they sub contracted out the install sounds like they did not use appropriate oversight. Was there any paperwork from the utility or building department? Have you paid in full?

 

[keymaster]

Hmm, in that case you should easily be able to escalate if there is pushback.

Not clear what support you still need from the forum. Yeah, two strings is strictly more flexible and better than one. Both for redundancy and for updating your architecture in the future. EG there's another thread here where someone's having trouble AC coupling, and it would be easier with readily accessible 2 string instead of single string (in their case they were going to look into splitting the string themselves at the combiner. Which is better than rewiring everything but still kind of sucks to have to do).

I think I have everything I need at this point. I appreciate everyone's input. I will post after I get it resolved just to close the loop if anyone is interested.

I think this should be a cautionary tale to anyone working with these solar companies. They did a great job designing and explaining the system and how it should work upfront.

The installer put something different in, and they tried to BS me and say it was functioning as designed. I guess in a way it was, I am getting 9.96 kw out of a 10k inverter, but they sold me something different and I paid a premium for something I didn't receive..

 

[keymaster]

See comments in red Plus you start clipping early in the day looks to be about 4 hours clipped you lose maybe 6-8KWhs? and depending on your rate might add up to some serious coin. I have attached my bell curve for comparison (7.2KW size) The second one was a cold day so I peaked at more than rated size.

100% what I expected to see in my graph, peak production at mid-day. I hit peak at 10 and in NY electric is currently .16 per kwh, soon to be .20 if the proposed rate hike goes into effect. I am likely losing a couple of dollars a day in production because they didn't install what I paid for.

 

[zanydroid]

Glad to help

I think this should be a cautionary tale to anyone working with these solar companies. They did a great job designing and explaining the system and how it should work upfront.

Yeah, I definitely agree with this. Unless you pay cadillac prices for an installer that's been around for 30 years (which some people I know go for) you have to really supervise the installation.

In my case, at least the rando installers changed the layout and inverter hardware in my favor...

OTOH, they messed up the torque specs on all electrical terminals, they left multiple panels disconnected, and they only installed half the clamps on some panels. And half of the time when they temporarily moved a panel to correct issues they messed up the clamps again...

 

[keymaster]

Then you have a good case unless there was a reason from the builiding department or the utility to limit the project to kW. The solar company might use that as an explanation if that was the case. Typically that would be done with a change order even if they considered it beyond their control (per force majuere clause). The fact that they sub contracted out the install sounds like they did not use appropriate oversight. Was there any paperwork from the utility or building department? Have you paid in full?

I paid in full at the time they turned on the system. There was nothing from the building permit dept or electric company. I think the reason the contract spells out the part numbers and configuration is because the solar company is giving that to the installers as a configuration / build sheet.

I did sign a configuration change doc a week before install because the Sil-Fab panels specified were not available and the QCell's were. They were the same configuration, watts, amps etc so I signed it. Even that document says 2 strings with 2 inverters and is specific about part numbers.

 

[svanand]

I had similar problem with the 8.4KW panels coupled with 7.8KW microinverters producing peak 6KW of power

However, Im noticing that now-a-days (spring), the output does reach 7.6KW, which leads me to believe the angle of the sun is matching the panel angle in spring and not so much in fall/winter
That said, there is some DC to AC conversion loss (typically 3-10%), hence the installers use a lower capacity inverter

Watch the output over the year. If you have homeassistant, you can add the forecast.solar addon and provide the angle, so it gives a good estimate

 

[Ampster]

I think I have everything I need at this point. I appreciate everyone's input. I will post after I get it resolved just to close the loop if anyone is interested.

Yes, it would be nice to know how it was resolved and a good lesson for other readers.

 

[wattmatters]

Just had solar installed at my house a few months ago by a local company. I have noticed something odd in the monitoring. Each day around 10 am I hit production of 9.96 kw. It stays there for a few hours and then starts declining as the sun goes down.

with Solar Edge SE 100000h inverter grid tied.

This is exactly how it will behave. A 10 kW inverter cannot output more than its rated capacity of 10 kW.

Over panelling is not only common, but good practice.

In your case if you paid for a system which should have had a larger inverter and PV system then you definitely have a case. There is always a chance you were quoted for a system would could not be installed (e.g. lack of roof space), regulatory limits etc.

But making changes without your permission is not good.

Isn't it better to have 2 strings with separate inverters for my 12.8 kW system?

A single large inverter will typically already have two MPPT inputs. Some have three. MPPT inputs may also be designed to accept parallel arrays.

Having more MPPT inputs that having mutliple inverters provide can be useful, especially with multi-faceted array design if the PV is on a complex rooftop.

But more inverters also means more cabling, more space taken up, more connections, and sometimes more challenging communications.

In some instances its desirable, such as when operating with an AC coupled battery system (e.g. Tesla Powerwall 2) which will have a limit on the size of the inverter/PV system it can control during grid outages (IOW to keep at least some of your PV online during a grid outage).

Good system design is a function of many parameters.

 

[Mike 134]

Over panelling is not only common, but good practice.

Please explain why it is a good practice other than saving a few $$ on a smaller inverter.

 

[wattmatters]

the contract calls for 32 - 400 watt panels. Those were installed. the contract calls for 2 SE7600H-US inverters. Those were not installed. The contract calls for 2 strings, only one was installed. the contract is very specific about part numbers and configuration.

It was just not installed as contracted. The solar company uses a 3rd party to install but the contract doesn't say anything about that.

I find it hard to believe only one string was installed. If that were the case your inverter would have let out the magic smoke by now.

It has a 480 V DC PV input limit. Not sure the exact model of panel you have but their Voc is likely to be ~ 37 V. 32 x 37 V = 1,184 V.

But frankly, 2 strings doesn't make sense either as that would still exceed the DC input limit.

 

[zanydroid]

Please explain why it is a good practice other than saving a few $$ on a smaller inverter.

I’m assuming this was asked in good faith…

Couple reasons. ROI/opportunity cost. The dollars might be better spent on more panels or other investments with better incremental ROI than another $100 on the inverter.

Avoid technical issues. You can avoid a panel replacement sometimes, NEC generally requires you to use AC nameplate. Chances POCO will need to upgrade your transformer goes up with bigger backfeed. Can hit AC coupling limit too.

If you are overpaneling via panels on different planes for different times of the day, the incremental ROI is probably minimal or zero, and you added all the technical liabilities.

 

[wattmatters]

Please explain why it is a good practice other than saving a few $$ on a smaller inverter.

Because in many locations there are limits on the grid-tied inverter capacity one is permitted to install. So you make the best use of it by over panelling.

 

[zanydroid]

But frankly, 2 strings doesn't make sense either as that would still exceed the DC input limit.

It’s SolarEdge with MPPT and DC converters on each panel.

 

[wattmatters]

It’s SolarEdge with MPPT and DC converters on each panel.

Ah, SolarEdge. Good point. It's OK kit but unnecessary complication IMO.