Inverter Sizing Opinions Needed

[Jtt777]

I happened to notice after install my inverters are sized for a maximum of 10,400 kW but my theoretical panel capacity is 11,340 kW.

It is pretty close but slightly undersized. I've been reading about pro / cons of under or over sizing. What are opinions on this design. It is a design that is in NJ and is facing southwest with little shading on the roof. The two inverters split up half of the 36 panels.

If they chose the next bigger inverter size, it would be able to take 13,200 kW, so somewhat oversized. I should add that I have no plans to add more panels.

Expected production is around 13 kWh per year.

Thoughts?

 

[nyprepper]

Absolutely, Yes, you should go with the 2 x 6600w inverters (13.2kw).

I'm curious as to why the production estimates on your system seem so low. I am in your general area and have a 6.6kw PV, like yours, southwest facing and partially shaded, and my production estimate from Tesla was 11.5kWh per year. I've only had the system for 7 months but I think i'm going to reach that number.

Also- again with regards to the inverter sizing, i have a 7.6kw inverter tied to my 6.6kw PV. On occasion I have seen production as high as 7.4kw coming from the array.

 

[Jtt777]

They already installed the inverter how do I flag it as a poor design and make them swap out the inverter?

 

[nyprepper]

Was the specific model/size of the inverters explicitly stated in your contract or system design documents?

 

[Dan123]

Thoughts?

That's totally fine. You are unlikely to see any clipping with this setup.

For your reference, Solaria makes an AC panel (built-in inverter). The panel is rated 355 watt, and the inverter is rated for 290 watt continuous output

 

[ortizla96]

as Dan123 noted -- clipping should not be much of an issue. If you did not already account for this, it is important to distinguish between the DC kW rating of your solar system and the AC kW rating of the inverters that are delivering the useful energy. For your reference, efficiently designed commercial solar systems (MW scale and larger) typically oversize the solar system by 30% --- 1.3 MWp,dc with 1.0 MWp,ac inverters

 

[SoundDaTrumpet]

I calculated about $50 of loss credits clipping with my system, and asked & received for the $50 back in a gift card. I'm 37 deg N latitude with a system half the size as the OP. My theory AC to inverter AC is 1.05. @Jtt777 is 1.09. New Jersey is at 40deg N latitude. Fast forward 3 years, I had planned to add 1kW more panels, and same installer wants extra to replace with larger inverter as an $1500 option. They did follow manufacturer guidelines for under sizing, but never plan for the future. This cost them future sales, but fortunately Tesla systems came down drastically last week, and may just elect to add a separate smallest possible system with them.

 

[Jtt777]

Was the specific model/size of the inverters explicitly stated in your contract or system design documents?

I didn't see any specifics quoted in the design. I see that they are now using SolarEdge optimizers... I didn't get one. What decides if you get one or not?

 

[Jtt777]

I calculated about $50 of loss credits clipping with my system, and asked & received for the $50 back in a gift card. I'm 37 deg N latitude with a system half the size as the OP. My theory AC to inverter AC is 1.05. @Jtt777 is 1.09. New Jersey is at 40deg N latitude. Fast forward 3 years, I had planned to add 1kW more panels, and same installer wants extra to replace with larger inverter as an $1500 option. They did follow manufacturer guidelines for under sizing, but never plan for the future. This cost them future sales, but fortunately Tesla systems came down drastically last week, and may just elect to add a separate smallest possible system with them.

Great. I am going to keep things as is the more i read. Looks like there is also an efficiency credit to some amount of clipping and if I get there, I actually fit within that positive efficiency. Thanks all!!

 

[m3-pw2]

I have 12.4kw system with a 10kw inverter.
I asked the engineer why the inverter is smaller when they were designing it.
They said that the system will only reach the inverter maximum capacity a small fraction of the time. But the benefit is that the smaller inverter will do better when production is very small. Look at the inverter spec. There should be a graph that shows how it performs at different levels. Larger inverter has reduced performance at lower power generation which can impact your generated power. Think about it. The only time you will produce full capacity is in perfect condition of clear skies, not very hot day, and panels perfectly aligned with the sun. And that's would be a 30 minutes window for a few days in the year. Mornings and evenings, winter days, cloudy days, production is not that high and having a smaller inverter optimizes those times.

 

[harry]

There's another point to be thought about. Panel rated capacity is like OEM's gas mileage ratings. Very few, if any, panels will produce their rated capacity. California has a list of hundreds of panel brands that they tested, and they have a table which shows the rated versus the actual maximum production. Our 245W panels, for example, actually will produce only 238W. The other comments concerning the amount of time you'll see maximum production are also cogent, but in your case you'll never see the label capacity.

 

[Dan123]

There's another point to be thought about. Panel rated capacity is like OEM's gas mileage ratings. Very few, if any, panels will produce their rated capacity. .

Panels also degrade over time, so clipping will be reduced as the panels age.