Inverter Upsize Help

[cr0ntab]

Hey All,

I recently got a 10.89 kW DC solar array installed on my home and it consists of the following:

33x 330W Panasonic VBHN330SA16
1x SolarEdge SE7600H-US
2x Tesla Powerwall 2

The array is split into two strings, east side of the roof and west side of the roof.

I didn't have a full years worth of electrical usage data so I did my best to estimate my usage. I got close but I undershot.

We're using a bit more in the summer time than I had expected and it basically ate up my extra "budget" that I had planned for an electric car down the line.

On top of that the installer didn't really explain the consequences (AC output clipping) of using the 7.6 kW inverter with the 10.89 kW array, so I didn't know that I wouldn't get my whole output until everything was said and done.

I wish I would've known this before we did everything, but so be it, very expensive mistake on my part.

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I was thinking of upsizing the inverter to reduce the clipping losses.

This would involve upgrading the 7,600W inverter to a 11,400W inverter (SE11400H-US)

From the pricing I can find online this would be about ~$2120 for the inverter. I plan to do the installation myself.

This option would also allow for me to add additional panels down the line to my array to help offset my consumption if the upgrade doesn't cover it. As I understand it the 10kW+ inverters have inputs for 3 strings.

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Based off of the spec sheet for the inverter (attached) I would need to upgrade the backfeed breaker from 40A to 60A (47.5A * 1.25 = ~60)

I would also need to upgrade the existing #8 wire from the inverter to the panel to #6 to handle the increased amperage.

I don't think I have to do any derating of the main breakers based off of this math:

Main Panel

225A * 1.2 = 270A
270A - 200A = 70A backfeed max

70A > 60A from inverter

Sub Panel

225A * 1.2 = 270A
270A - 125A = 145A backfeed max

145A > 60A from inverter

If I do have to de-rate things the disconnect in the main panel is field replaceable so I could go down to something like a QOM2175VH, which is rated at 175A.

Lastly, I've attached a copy of the existing electrical diagram and associated wire sizes.

[J.P.M.]

Don't know if anyone ever told you, but it's pretty unlikely that any PV array will produce it's D.C. size as output. If it does, it will be only occasionally and for short periods. You will never see (33 panels) * (330w/panel) = 10,890 W D.C. output for several reasons, mostly but not entirely orientation related.

Depending on your location, you might see some clipping w/a 7.6 kW inverter, but the excess array output might be so small relative to the inverter capacity that it won't be worth spending the extra $$ and effort. In 92026, south facing max. hourly output is 933 w/D.C. kW, while max. combined E-W max. hourly output/D.C. 5 kW ea. and combined is 889 W. Both those values are for 1 hr./yr. All other hours are less.

Before you buy more equipment, run PVWatts for each orientation, use the hourly output option and sum the results. Sift the data for max. hourly values. The current inverter you have may well be fit for purpose in terms of capacity.

[cr0ntab]

Thanks for the reply!

So I ran the numbers with my array configuration:

https://docs.google.com/spreadsheets...it?usp=sharing

There are multiple tabs in the sheet:

Raw PVWatts Output
nw_array_hourly
sw_array_hourly

Aggregated hourly output from both arrays
total_array_hourly

And a filtered view of the hours in the year where the AC output is > 7600W which would mean I'm clipping

It looks like I'm only clipping ~99 kWh/yr

So that's good and bad:

Good in that I'm not leaving much energy on the table

Bad in that I do actually need to add more panels which means more $$$$

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So being that I need to add more panels which would be more cost effective?

Option 1
Adding a second inverter to handle the additional generation

Option 2
Getting a single larger inverter (say 11,400W inverter) and connecting 3 strings to a single inverter using a similar oversizing factor of ~1.43 or less

[ButchDeal]

Do you own this system or is it a PPA/lease?
Why are you skipping over the next sized inverter up which is the SE10000h?
you have a fairly large array now for residential, why do you need more power?
What area is the install?
how are the powerwalls configured? Load shedding/shifting or just backup?

[J.P.M.]

--------------------------

So being that I need to add more panels which would be more cost effective?

Option 1
Adding a second inverter to handle the additional generation

Option 2
Getting a single larger inverter (say 11,400W inverter) and connecting 3 strings to a single inverter using a similar oversizing factor of ~1.43 or less

Depending on the goals you have for the project, there are other options.

Assuming one goal of the exercise is to reduce the long term cost of providing electricity to a residence:

1.) Rather than simply replacing an entire annual electrical load, one (and a more cost effective) of those options is to reduce the load. Beyond providing for the basics, not using a commodity, or using less of it, is almost always cheaper than getting more of it.

2.) A second option is to not change anything. If the NPV over your long term time frame of the extra electricity generating in the upsizing is less than the NPV of the cost of the upsizing, then, at this point, and from a long term perspective, doing nothing will be more cost effective than doing anything.

[cr0ntab]

Do you own this system or is it a PPA/lease?

I own this system.

Why are you skipping over the next sized inverter up which is the SE10000h?

Honestly because I'm a little bitter about the whole clipping thing. If I'm going to upgrade I'd rather just go to the size that would give me a little more breathing room if need be. It's a $200 difference between the 10k and the 11.4k

you have a fairly large array now for residential, why do you need more power?

We live in a hot area and I work from home, so I find myself running the AC much more than I predicted which is using more power than I predicted. I had originally sized the system to have a bit of extra power left over for an electric car but the A/C usage is eating all of that buffer.

I didn't have a year's worth of utility bills when I got the system installed, but I knew I wanted solar so I just made my best guess and targeted that size for the install.

What area is the install?

Not sure if you mean geographic or what, but I'm located in Corona, CA

The two strings are located on the roof, 99* and 279* azimuth. I didn't measure the pitch of the roof but I think it's a 20* tilt.

how are the powerwalls configured? Load shedding/shifting or just backup?

Load shifting and backup level at 30%

[cr0ntab]

Depending on the goals you have for the project, there are other options.

Assuming one goal of the exercise is to reduce the long term cost of providing electricity to a residence:

1.) Rather than simply replacing an entire annual electrical load, one (and a more cost effective) of those options is to reduce the load. Beyond providing for the basics, not using a commodity, or using less of it, is almost always cheaper than getting more of it.

2.) A second option is to not change anything. If the NPV over your long term time frame of the extra electricity generating in the upsizing is less than the NPV of the cost of the upsizing, then, at this point, and from a long term perspective, doing nothing will be more cost effective than doing anything.

The biggest line item on my electric usage is by far my air conditioning. It's pretty hot in my area and I work from home so I found myself running the AC more than I anticipated.

The house has a single 5 ton 13 SEER unit.

To use less power I suppose I could go down the route of replacing it with something more efficient, but I think that would cost more than just adding more solar?

[ButchDeal]

I own this system.

Great so you legally can alter it.

Honestly because I'm a little bitter about the whole clipping thing. If I'm going to upgrade I'd rather just go to the size that would give me a little more breathing room if need be. It's a $200 difference between the 10k and the 11.4k

I doubt you have much clipping now. You can look at the solaredge production graphs and see how much of the curve is flat at the top.

We live in a hot area and I work from home, so I find myself running the AC much more than I predicted which is using more power than I predicted. I had originally sized the system to have a bit of extra power left over for an electric car but the A/C usage is eating all of that buffer.

I didn't have a year's worth of utility bills when I got the system installed, but I knew I wanted solar so I just made my best guess and targeted that size for the install.

You might find that you would get better return on your further investment with improvements to the insulation in the home and or higher efficiency A/C

Not sure if you mean geographic or what, but I'm located in Corona, CA

The two strings are located on the roof, 99* and 279* azimuth. I didn't measure the pitch of the roof but I think it's a 20* tilt.

Are there any shadows now? can you post a good clear days graph from the solaredge monitoring or set it up to go to pvoutput.org?
Also are in on Corona Water & Power as the utility?
It looks like they have a tiered utility plan which has Tier 1 = $0.12, Tier 2 = *0.14, Tier 3 = $0.23, and Tier 4 = $0.32

Avoiding tier 3 and for is the most bank for buck on solar installs,
the solar costs to avoid Tier 1 and 2 have the lowest return on investment....

https://www.coronaca.gov/home/showdocument?id=2238

Load shifting and backup level at 30%

Do you have Time of Use billing? Corona Water & Power doesn't list such a plan for residential.

[ButchDeal]

The biggest line item on my electric usage is by far my air conditioning. It's pretty hot in my area and I work from home so I found myself running the AC more than I anticipated.

The house has a single 5 ton 13 SEER unit.

To use less power I suppose I could go down the route of replacing it with something more efficient, but I think that would cost more than just adding more solar?

uh definitely. that is a base end unit. You could try adding a high efficiency mini split to just the primary area you use during the day or replace the entire system with something at least in the high teens.

https://kobiecomplete.com/cool-tips/seer-savings-calculator/

[J.P.M.]

The biggest line item on my electric usage is by far my air conditioning. It's pretty hot in my area and I work from home so I found myself running the AC more than I anticipated.

The house has a single 5 ton 13 SEER unit.

To use less power I suppose I could go down the route of replacing it with something more efficient, but I think that would cost more than just adding more solar?

Before I did any of those things, to use less energy, I'd investigate the cost vs. benefits of tightening the house up. Throwing technology at a situation is one method, but it's usually the less cost effective option.

Your A/C unit is similar to mine in terms of COP and size. I too am in a relatively warm climate. My annual kWh use for A/C averages ~ 800 - 1,100 kWh/yr. depending on how hot the summer is on ~ 6,900 - 7,200 kWh/yr. usage for a 3,200 ft.^2 residence. Changing out to a higher COP unit would gain me ~ 200 kWh/yr. in lower use. Not worth it, at least not for me.

Button the house up and ventilate at night as much as possible.
Then adjust your heat tolerance up a degree F or two.
Adding a small amount of PV will be costly.
Comes down to how you want to adjust/think of your perceived comfort level for what cost.
Pay your money, take your choice.

[cr0ntab]

I doubt you have much clipping now. You can look at the solaredge production graphs and see how much of the curve is flat at the top.

I ran the numbers in the above linked spreadsheet, I do see clipping on the graphs but once plotted over the year it didn't amount to much.

Are there any shadows now? can you post a good clear days graph from the solaredge monitoring or set it up to go to pvoutput.org?
Also are in on Corona Water & Power as the utility?
It looks like they have a tiered utility plan which has Tier 1 = $0.12, Tier 2 = *0.14, Tier 3 = $0.23, and Tier 4 = $0.32

Avoiding tier 3 and for is the most bank for buck on solar installs,
the solar costs to avoid Tier 1 and 2 have the lowest return on investment....

https://www.coronaca.gov/home/showdocument?id=2238

Do you have Time of Use billing? Corona Water & Power doesn't list such a plan for residential.

There are some shadows on the east facing array due to a chimney.

I am on SCE power on a TOU plan under NEM 2.0

Peak $0.48/kwh
Shoulder $0.28/kwh
Off Peak $0.12/kwh

[discodanman45]

It is making me sick with the oversizing of inverters with no research being done on how much clipping will occur. I have had posts about this before, but I want to share an update with a summer graph with a day over 100 degrees. I have clipped almost every day with a 11.25 kW system with a E, W, S arrays on the 7600 inverter. Probably on average I have clipped 3 hours a day, maybe 4. I am even clipping with the horrible hazy skies because of the California fires and ash on my panels.

[discodanman45]

To the original poster, if you are clipping like myself I would contact Tesla and tell them that the clipping is not acceptable and what can they do to fix this issue. I would also leave negative feedback on yelp/google telling them about the clipping. I would also contact SolarEdge and ask them if this type of clipping is expected and if Tesla installed the system improperly. You will be taking years off the life of your inverter, so I hope you get the extended 25 year warranty.

[nomadh]

After having my system for 2 years and having radical changes in my usages and number of people at home I am finding I undershot and My system does great running a summer surplus except when I AC my house. And I still need to do some big work upgrading insulation. In the mean time I added a window AC. Its 400 watts vs my big 3500 watt system. It still costs me $30 a month for july/aug/sept hopefully -$30 jun/oct. Very comfortable for 90% of time in the house and sleeping well for cheap.
The only reason I havent insulated is I'm debating air sealing the attic. Air sealing takes the job from easy to a nightmare.

[J.P.M.]

After having my system for 2 years and having radical changes in my usages and number of people at home I am finding I undershot and My system does great running a summer surplus except when I AC my house. And I still need to do some big work upgrading insulation. In the mean time I added a window AC. Its 400 watts vs my big 3500 watt system. It still costs me $30 a month for july/aug/sept hopefully -$30 jun/oct. Very comfortable for 90% of time in the house and sleeping well for cheap.
The only reason I havent insulated is I'm debating air sealing the attic. Air sealing takes the job from easy to a nightmare.

Before you insulate, spend a few bucks on caulking and sealing devices, and a few hours paying some careful attention to details of were surfaces are supposed to, but don't quite meet. Seal before adding insulation. More bang for the buck.

BTW, seal the warm (cld) side of unheated spaces. For example, if an attic/crawal space is uninsulated, and intended to stay that way, first seal the ceiling in the area(s) below the uninsulated space (and REALLY seal it), and then insulate the interface between heated and unheated space. Sealing is necessary not only to reduce in/exfiltration losses/gains, but equally importantly (mostly for colder climates) to reduce the effects of condensation damage which is often not even known much less considered.