Residental Solar 12.8 kw system outputting 9.96 kw

[keymaster]

**Update**

Thank you all for the advice and consultation. I spent a bit of time arguing on the phone with the solar company. The sales person was not fully educated on solar and kept disagreeing that this would solve the issue but they agreed to install the 2 inverters per the contract. The replacement of the 10k inverter with 2 7600 watt inverters was completed yesterday. Today my system output 12.3kw at the peak around noon.

To avoid mistakes like mine, understanding the initial design is important, but monitoring the installation and validating the right equipment is being installed is critical.

For those who asked about this being a single string as pictured in the monitoring app. The monitoring app shows it as one string, but there are actually 3 strings wired. The app shows a single string for an inverter no matter how many strings actually exist. With the 2 inverters it now shows 2 strings. There are still 3 strings, 2 connected to the lead inverter and 1 connected to the secondary inverter.

** Thank you again for the input, knowledge and education.**

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. I thought with a 12.8 kw system I would see higher production during mid day. I called the solar company and they said this was completely normal behavior for a 12.8 kw system.

To me (untrained but logical thought process) there should be some variation from 10 to noon as the sun rises and a gradual decline in the afternoon. Constant unvaried output of 9.96 kw from 10 am to sometime in the afternoon seems to be a limitation of the system somewhere. I thought likely the inverter is undersized but the solar company swears this is normal behavior. To me the graph should peak as the sun is highest overhead and gradually decline. (adjusting for angle and orientation)

Am I crazy here or missing something? System is 32 of the 400 watt q-cell panels with Solar Edge SE 100000h inverter grid tied.

 

[sunshine_eggo]

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. I thought with a 12.8 kw system I would see higher production during mid day. I called the solar company and they said this was completely normal behavior for a 12.8 kw system.

To me (untrained but logical thought process) there should be some variation from 10 to noon as the sun rises and a gradual decline in the afternoon. Constant unvaried output of 9.96 kw from 10 am to sometime in the afternoon seems to be a limitation of the system somewhere. I thought likely the inverter is undersized but the solar company swears this is normal behavior. To me the graph should peak as the sun is highest overhead and gradually decline. (adjusting for angle and orientation)

Am I crazy here or missing something? System is 32 of the 400 watt q-cell panels with Solar Edge SE 100000h inverter grid tied.

You have put 12,800W of PV on a 10,000W inverter. Looks good to me.

 

[keymaster]

so the inverter is undersized? the solar company designed the system.

 

[sunshine_eggo]

so the inverter is undersized? the solar company designed the system.

No. PV rarely puts out rated power. If you got a 12800W inverter, you'd be complaining you only get 10-11kW in great sun.

 

[Quattrohead]

You were sold 12.8kw of panels and a 10kw inverter, they should have explained better what to expect.
It is called over panelling. Nothing is actually wrong with the system.

 

[keymaster]

Good point, but I just checked my design documents and contract. The contract specifies 2 - SE7600H-US inverters for my setup. That would allow up to 15,200 watts of power from my array to be processed. They put the wrong inverter in my system, not too many panels. I know not to expect 12.8 kW constantly especially as the panels age, we covered all that in the design phase. That said, I paid for two inverters and 2 strings. They put in a single string and a 10k inverter instead.

I called my sales guy and he is working on the issue. The solar company subs all the installs out, I am assuming they did the substitution without permission as I didn't sign any change agreements.

 

[Lt.Dan]

I've heard of many nightmares of people going through Solar "Brokers". My co worker had to have almost the entire system redone on his house.

 

[sunshine_eggo]

Good point, but I just checked my design documents and contract. The contract specifies 2 - SE7600H-US inverters for my setup. That would allow up to 15,200 watts of power from my array to be processed. They put the wrong inverter in my system, not too many panels. I know not to expect 12.8 kW constantly especially as the panels age, we covered all that in the design phase. That said, I paid for two inverters and 2 strings. They put in a single string and a 10k inverter instead.

I called my sales guy and he is working on the issue. The solar company subs all the installs out, I am assuming they did the substitution without permission as I didn't sign any change agreements.

Go get 'em!

 

[keymaster]

Just want to clarify, am I correct in all this? I am guessing it's cheaper to provide one slightly larger inverter 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?

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.

 

[Quattrohead]

You might have someone else's system
There is a 10kw system size limit before you go to the next teer, so maybe the installer kept you under that limit for your connection agreement to the power company.

 

[kendive]

No. PV rarely puts out rated power. If you got a 12800W inverter, you'd be complaining you only get 10-11kW in great sun.

I have gotten rated power out of my solar system but only when it's a perfect situation. I also have Enphase and my inverters are rated higher that the panels. I designed my system. I would not let any of these solar companies do that. LOL

Not sure why the Signature is not showing up... But here it is

9,360 Watt Enphase 26 REC Alpha Series 360 Black Panels with the IQ7A Inverters. IQ Combiner 3.
(2) 10T Batteries / (2) IQ load Controllers / IQ Controller 2 (Smart Switch)
Micro-Air Easy Start on the HVAC.
Blog - https://diysolarforum.com/threads/enphase-iq-battery-enphase-ensemble-installation.52354/

 

[Ampster]

I DC to AC ratio of 1.28 to one is not unusual. Your output will always be limited by the 10 kW size of your inverter.

 

[Quattrohead]

it's having to shunt the excess current to heat is my assumption.

No, it just ignores it.

 

[keymaster]

You might have someone else's system
There is a 10kw system size limit before you go to the next teer, so maybe the installer kept you under that limit for your connection agreement to the power company.

Maybe, but they charged me for the larger inverts and dual strings. They failed to refund anything on that part of the deal. Also forgot to mention that they were not installing the system I contracted for.

 

[Ampster]

I am guessing it's cheaper to provide one slightly larger inverter and a single string vs. actually building out what I paid for?

Yes it is but you paid for and received a 12.8 kW system. What is important is the area under the curve not the imaginary amount above the flat top of the curve. Did they give you an annual production estimate. If not go to PV Watts and enter your system with that 1.28 to 1 DC ratio and see what it says. Then enter one with a 1.1 to 1 and see if there is much different. That would have been an 11 kW system with the same inverter.

 

[Ampster]

Also forgot to mention that they were not installing the system I contracted for.

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?

 

[zanydroid]

Now if they caught an issue like going to the next tier with POCO or requiring main breaker derate / panel upgrades etc, and they saved you real costs from that, IMO you have much less room to ask for compensation.

It's SolarEdge so munging it all onto one string isn't that bad efficiency wise (due to the panel level MPPT on the optimizers), though you have all the eggs in one basket.

Inverters are rated at 100% usually, maybe splitting across two would help if there is temperature derate (which there often is).

Is there a larger SE than 10K? Can SE split a single string across two inverters? If they use MPPT to implement fixed voltage strings then this is easier than with a standard variable voltage strings. Thinking to what would be a cheaper modification than splitting the strings, if it comes to that.

 

[sunshine_eggo]

Just want to clarify, am I correct in all this?

Likely yes.

I am guessing it's cheaper to provide one slightly larger inverter and a single string vs. actually building out what I paid for?

Likely yes.

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?

Those are logical arguments.

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.

Conceptually:
Panels under load convert 20% of the sun that hits them into electricity and 80% into heat.
Panels sitting there in the sun doing nothing convert 100% of the sun that hits them into heat.

The inverter is a load to the panels, and it just pulls what it needs from the panels. The panels simply convert the amount of solar NOT being converted to electricity to heat, e.g., 18% and 82%.

Would love anyones professional opinion and thanks for the education.

Not a pro, but you didn't get what you paid for. Given the two choices, for the same price, I would choose the two inverter option.

Note that re-doing the installation is going to be a huge pain for them - pretty much starting over with additional hardware required. IMHO, they are going to push back hard. I would accept a 35% refund as an alternative.

 

[Ampster]

you didn't get what you paid for. Given the two choices, for the same price, I would choose the two inverter option.

I see in earlier post he was supposed to get two 7.6 kW inverters. I asked and did not get specifics. It is unclear what the contractual panel size was other than two strings which is a given with two inverters. Hopefully those details were in writing and form the basis of the contract. The design document may or may not be part of the contract. I am not a pro either but 50 years in business gives me a fundemental understanding of contract law.

 

[zanydroid]

Note that re-doing the installation is going to be a huge pain for them - pretty much starting over with additional hardware required. IMHO, they are going to push back hard. I would accept a 35% refund as an alternative.

I feel like pushing for or settling for 11.4 kW inverter is the past of least resistance that will also address the situation if the contract is written in a way to allow for substitutions that achieve the performance requirements (assuming two inverter functional redundancy requirement is not written there).

If the contractor pushes back a lot you can also look into what the mediation or arbitration clause looks like and how to complain to your state licensing board. For my dispute I kept that in my back pocket, the listed arbitrator wasn't that expensive and anyway the contractor was on the hook for paying for it. But that's my specific contract.