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New Solar Panel Install - Questions

tap1936

Member
Jul 11, 2020
8
0
central NJ
This is an amazing forum, learnt a lot by reading through here but still have questions!

I have been spec'ed with a 12.24KW system with annual production of 11605 KWh

1. The inverter they have specified is a SE11400H-US. Is that enough without clipping or should I request two inverters?
2. The only document I see in my account is a customer layout. They did a site assessment before drawing this layout. They did send me some drawings to send my HOA but I have not had to sign anything and they have gone to the permitting step. Am I missing something here?
3. The tech drawing they sent for my HOA approval has a optimizer spec sheet, does that mean they will install optimizers on all my panels or only some of them? I will have shade.

I am sure I will have more questions, so thank you for your patience in answering!

RS
 

BrettS

Active Member
Mar 28, 2017
2,128
2,537
Orlando, FL
1. The inverter they have specified is a SE11400H-US. Is that enough without clipping or should I request two inverters?

You should be fine with that inverter, especially if all the panels are not facing the same direction. As the sun moves across the sky different panels will be getting different amounts of sun and it’s unlikely that you’ll be producing more than 11.4kW at any given time. If there is any clipping because of the cloud edge effect it will be very minimal.

2. The only document I see in my account is a customer layout. They did a site assessment before drawing this layout. They did send me some drawings to send my HOA but I have not had to sign anything and they have gone to the permitting step. Am I missing something here?

I think that’s normal. You can call and ask them to email you the electrical diagrams if you want to see them.

3. The tech drawing they sent for my HOA approval has a optimizer spec sheet, does that mean they will install optimizers on all my panels or only some of them? I will have shade.

You’ll get optimizers on all your panels.
 

tap1936

Member
Jul 11, 2020
8
0
central NJ
Thanks, @BrettS . The panels do face the same direction all in the back of the roof. Please see attached layout.

Is it generally better to have multiple inverters vs one?

Thanks!
 

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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
10,286
11,624
Riverside Co. CA
Thanks, @BrettS . The panels do face the same direction all in the back of the roof. Please see attached layout.

Is it generally better to have multiple inverters vs one?

Thanks!

Thats a technical answer that I dont have the answer to, but in general, its perfectly normal and expected that your inverter rating does not = the sum total of the panel ratings. even though all of your panels face the same general direction, you said yourself "I will have shade" so its unlikely all of your panels will be max producing at all times.

Sizing the system so there is NEVER any clipping means sometimes upsizing something for a very rare occurrence, if it clips a few days a year, thats not a big deal. The size of your system vs expected production tells me that its unlikely that you have tons and tons of "cloudless sunny days" where you would lose a bunch of power even if it does clip, which I think is unlikely based on inverter size to system size.

With all that being said, YOU are the customer, and if you want to ensure "my system will never, ever clip at peak production" tell them that, and if they have to upsize the inverter for that, they likely would, and charge you accordingly.

Also, maybe its just me, but I personally would never consider having another solar install without having powerwalls, having recently added powerwalls to my pre existing solar install. You dont mention them, but one thing to keep in mind is, if you have solar on your home, and have a power outage, it will not power your home during the outage without some sort of battery storage on premises.
 

Akikiki

A'-Lo-HA ! y'all
Nov 26, 2012
6,475
4,558
Kaneohe, HI
This is an amazing forum, learnt a lot by reading through here but still have questions!

2. The only document I see in my account is a customer layout. They did a site assessment before drawing this layout. They did send me some drawings to send my HOA but I have not had to sign anything and they have gone to the permitting step. Am I missing something here?
RS
If your HOA is only as good as mine, they know very little about solar. They will take what you give me, look at them, try to find someone to explain them, and something wrong with the forms, pass them around to several Board members, and if perfect decide to decide (yes, like that), then vote at the next Board meeting. Your sense of urgency is not theirs. All the while your PV contractor is moving forward quickly (already submitted the permit). Your HOA is about to become the delay. I hope not for you. Be prepared.
 

gpez

Member
Apr 25, 2019
720
587
USA
Clipping is not always a bad thing - there are economic reasons to undersize the inverter(s) relative to your panels and it's all about the ROI. If your budget is fixed it likely (and maybe counterintuitively) makes sense to oversize your panels relative to your inverter(s).

Inverter clipping: How to maximize solar project value

Then again if money is no object and your goal is to crank out as many watthours as you can then you'll likely want to prevent clipping.

Also, maybe its just me, but I personally would never consider having another solar install without having powerwalls, having recently added powerwalls to my pre existing solar install. You dont mention them, but one thing to keep in mind is, if you have solar on your home, and have a power outage, it will not power your home during the outage without some sort of battery storage on premises.

Not just you! I'm totally sold on PV + battery too. The technology on both sides can only get better and make it more compelling in the future too. :)
 
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jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
10,286
11,624
Riverside Co. CA
If your HOA is only as good as mine, they know very little about solar. They will take what you give me, look at them, try to find someone to explain them, and something wrong with the forms, pass them around to several Board members, and if perfect decide to decide (yes, like that), then vote at the next Board meeting. Your sense of urgency is not theirs. All the while your PV contractor is moving forward quickly (already submitted the permit). Your HOA is about to become the delay. I hope not for you. Be prepared.

I am not an HOA detractor like some are, because it depends on how aggressive they are, but with that being said...

You speak #BIGTRUTHS here, lol. It was super annoying with my HOA and solar back in 2015 / 2016... even though they can not deny you solar. From the time I submitted my plans to them, to the time I got approval, was like 3 months. I got tired of waiting and pushed ahead with the install because I didnt want to lose the install date. I submitted in december of 2015, and they didnt mail me the approval till march 15th of 2016, and I not only had been installed by that time, but also had PTO by then.
 
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tap1936

Member
Jul 11, 2020
8
0
central NJ
Great information here, thanks everyone!

@jjrandorin - I hear you regarding the inverters. I do not believe I will have clipping (possibly in summer) but maybe for a couple of hours. I was thinking also if the single point of failure is one inverter whether having two would offset that.
While I would like Powerwalls, might have to do that later as a separate project. Buying this system so dont want to layout more cash.

@Akikiki - Regarding HOA approval already got that within one day! My HOA was formed in the nineties so there were no rules regarding solar then, so by default approval is given especially since my panels are in the back. Though some houses here do have solar in the front.

Further question more as an education and I am sorry if I am repeating common questions:
1. Size of the system = 12.24KW - is that DC power? Because I notice that the inverter has input power and out power of different numbers, output would be lower than input due to losses.
2. How does 12.24KW translate to 11605KWh est. annual production? Is it related to efficiency?
3. How accurate is PVWatts? There I get an est. annual production of 13000KWh
2. Does having two inverters make the system inherently less efficient in its overall output?
3. Considering the PVWatts number above, would that make a difference in the clipping?

Sorry, if these are really basic questions, trying to understand better before I sign off!!
Thanks!
 

BrettS

Active Member
Mar 28, 2017
2,128
2,537
Orlando, FL
1. Size of the system = 12.24KW - is that DC power? Because I notice that the inverter has input power and out power of different numbers, output would be lower than input due to losses.

12.24kW is DC power. A number of inverters do allow more DC input than AC output, primarily because you are unlikely to get the full amount of DC input due to shading and panel orientation and such. If you have so much DC input at a given time that it exceeds the AC output capacity then there will be clipping.

The advantage of an inverter that allows more DC input than AC output is that it allows for a less expensive inverter and a bigger DC system. Clipping, if it happens, would only happen for a short time in the afternoon, but during the rest of the day you would be able to take advantage of that larger DC system and generate more power overall.

2. How does 12.24KW translate to 11605KWh est. annual production? Is it related to efficiency?
It doesn’t directly translate. A 12.24kW system that is oriented north will have a much lower annual production rate than a 12.24kW system oriented south. The angle of the panels will also affect the annual production numbers as well as any shading, not to mention weather. Annual production is simply an educated guess based on panel orientation, panel angle, your location and weather patterns, etc.

3. How accurate is PVWatts? There I get an est. annual production of 13000KWh
As I said above, annual production numbers are little more than an educated guess. Different calculators weight things differently, so they will all come up with slightly different numbers. In my experience Tesla tends to estimate on the conservative side, it I wouldn’t be surprised if your numbers are closer to the PVWatts numbers, but there’s really no way to know for sure until you’ve had your system for a year.

2. Does having two inverters make the system inherently less efficient in its overall output?
As long as the two smaller inverters have the same efficiency as the one larger one, then no. Efficiency would be the same. Two smaller inverters are likely to be more expensive than one larger one, not only because of the cost of the inverters, but there would also need to be additional electrical connections, breakers, and possibly even an additional panel.

3. Considering the PVWatts number above, would that make a difference in the clipping?

Clipping will really be minimal. Say that your system could generate a full 12.24kW at peak times, but your inverter is limited to 11.4kW. In the real world there’s no way that your system would generate the full 12.24kW, but we’ll use that for the sake of argument. That peek time might be for an hour a day, so you would lose .84kWh a day (12.24kW - 11.4kW = .84kW over one hour = .84kWh). If that happened every day of the year (Which, again, it won’t, because of weather) the most you would lose over an entire year would be 306kWh. (.84kWh times 365 days a year = 306kWh). That’s less than 3% of Tesla’s annual production number. And like I said, that 306kWh number would be in absolute perfect conditions. In real world conditions, you will likely lose much less than 100kWh over a year due to clipping.
 
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Vines

Active Member
Jul 20, 2018
2,043
2,371
Silicon Valley, CA
Solar Equipment Lists

This shows the actual output in watts of panels in real world conditions. Look up your panels, multiply by the number of them, and then by inverter efficiency. I'll bet its under 11400 watts. Your DC/AC ratio is 1.07, totally reasonable. In fact I'd be comfortable throwing another 1-2 modules on that inverter.

Typically you will pay less for a single inverter, however a single if it does fail will take out all PV production. Since you aren't getting powerwalls its not a huge difference likely and I would go with the single, less stuff on the wall, and cheaper overall.

Clipping isn't your main concern imo, you are concerned with area under the curve, per dollar. If your dollars are not the concern, you can optimize for no clipping. Most people optimize for dollars.
 
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BrettS

Active Member
Mar 28, 2017
2,128
2,537
Orlando, FL
I thought the inverters are included in the cost of the shirt-sized installs.

Inverters are included, but the OP is saying that Tesla has designed his system to use one large inverter and he’s wondering if he can (or should) switch to two smaller ones instead. It may be possible to switch, but since two inverters would cost more it’s possible that if it can be done there may be an extra charge to make the switch.
 

Akikiki

A'-Lo-HA ! y'all
Nov 26, 2012
6,475
4,558
Kaneohe, HI
@Akikiki - Regarding HOA approval already got that within one day! My HOA was formed in the nineties so there were no rules regarding solar then, so by default approval is given especially since my panels are in the back. Though some houses here do have solar in the front.

One word. WOW !!

My HOA was formed in ’73. And over the years amended the rules never included PV. Then in 2008, I proposed adding the first PV panels. Caught them off guard. Tried to say no and discovered like @jjrandorin, that they could not. Now about 25% of our 300 units have PV and they still don’t want to approve more. In 2019, I removed all and updated inverters and PV to newer while we still had 65% in tax credits.
 

TheTalkingMule

Distributed Energy Enthusiast
Oct 20, 2012
7,227
27,691
Philadelphia, PA
I have a 6.6kW system and a 5kW inverter(same line as yours). I clip every sunny day from late Feb to November, but it's still up for debate whether or not I should've gone to a 6kW inverter. I'm losing out on maybe 120kWh a year net. Nothing.

There's value in having an inverter sized below your system capacity, it supposedly makes the whole system more efficient. As in, a 7kW inverter in my 6.6kW solar array would likely produce slightly less total kWh than a 6kW inverter.

11.4kw inverter on a 12.24kw array sounds just about perfect to me.
 
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SMAlset

Well-Known Member
Mar 4, 2017
9,178
9,905
SF Bay Area
Our single family home HOA was also very quick approving our solar project despite they had just had a quarterly board meeting. Architectural Change applications go through an Architectual committee instead of the board for approval and with covid SIP here the management company just emails the application and supporting docs to everyone on the committee. Our homeowners are pretty respectful of people’s time so unless some new issue to consider and discuss comes up they are pretty fast approving or not. A number of homes already have panels on their roofs either for pool heating or solar house usage so we weren’t inventing the wheel here.
 

Vines

Active Member
Jul 20, 2018
2,043
2,371
Silicon Valley, CA
I have a 6.6kW system and a 5kW inverter(same line as yours). I clip every sunny day from late Feb to November, but it's still up for debate whether or not I should've gone to a 6kW inverter. I'm losing out on maybe 120kWh a year net. Nothing.

There's value in having an inverter sized below your system capacity, it supposedly makes the whole system more efficient. As in, a 7kW inverter in my 6.6kW solar array would likely produce slightly less total kWh than a 6kW inverter.

11.4kw inverter on a 12.24kw array sounds just about perfect to me.

This is the right way to look at it. 120 kWh per year lost is worth about $50 (assuming super expensive $0.40 /kWh) per year. Compare that cost over the average life of an inverter (10-20 years) for the cost of the alternative and you can see what the change is really worth.

Most residential systems will be well served up to 1.15 DC/AC ratio (depending on module efficiency.) Commercial systems go even higher.
 
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