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Inverter size when maximum system is 11.56 kW (34 panels)

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nwdiver

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But that's different than saying that Tesla can make $1,000 less profit if they size the inverter to allow maximum production.

Well.... if you don't like saving money on a more economic system you can always spend ~30% more with another installer and get fewer kWh/yr. :)

Given the prices Tesla is charging I'm not sure there IS a profit yet. I wouldn't be surprised of they're at or below cost to increase market share.
 
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Southpasfan

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Well.... if you don't like saving money on a more economic system you can always spend ~30% more with another installer and get fewer kWh/yr. :)

Given the prices Tesla is charging I'm not sure there IS a profit yet. I wouldn't be surprised of they're at or below cost to increase market share.
Not only do I like Tesla as a company, I love it. I just think that one huge problem with getting large adoption of solar and ESS is that people seem to be buying one product but in reality everyone is buying a slightly or largely different product.

So one has to accept, ans calculate, all the variables as to your own location and own roof and what your utility charges.

I don’t know, it just seems wrong, or poor marketing, or poor design to sell a system that you (here Tesla) knows will under perform. I would say charge a slight premium for the southern US if they need to, but don’t sell systems they know will clip on any significant way.
 

nwdiver

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I don’t know, it just seems wrong, or poor marketing, or poor design to sell a system that you (here Tesla) knows will under perform. I would say charge a slight premium for the southern US if they need to, but don’t sell systems they know will clip on any significant way.

???? They don't. For the ~5th time it's cost benefit. If $1 invested in more inverter yields fewer additional watt-hours/yr than $1 invested in more panels.... you put the $ in more panels. Numbers. It's not like they're selling 10kW systems on 3.8kW inverters....

Even a system oversized by 50% loses <5% to saturation. I don't think 5% is 'significant'.
 

wwhitney

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Nov 2, 2017
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Berkeley, CA
Clipping = wasting panel capacity
Not clipping = wasting inverter capacity

You want to balance the wastes to be economical.

Another example:

You have a certain base system in mind, and decide you want to spend a little more for a little more energy production. Your base system will have some clipping, and the cost of bumping up the inverter to the next size increment is the same as the cost of adding, say 3 panels. Which is the better choice?

If you've maxed out your inverter as far as DC input capacity, obviously you have to bump up the inverter. Otherwise, the only question is how does the extra energy the 3 more panels will produce during morning/evening (when there's currently no clipping) compare to the extra energy the larger inverter will produce around noon (when there's currently clipping), over the course of the year.

That's it.

Cheers, Wayne
 
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h2ofun

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Aug 11, 2020
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auburn, ca
???? They don't. For the ~5th time it's cost benefit. If $1 invested in more inverter yields fewer additional watt-hours/yr than $1 invested in more panels.... you put the $ in more panels. Numbers. It's not like they're selling 10kW systems on 3.8kW inverters....

Even a system oversized by 50% loses <5% to saturation. I don't think 5% is 'significant'.
When I got the largest inverter for the same price as a smaller, seems easy to decide what to do :)
 
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Southpasfan

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Well, unfortunately people forget that if an inverter doesn't clip, the duration of that 3.8kW will be shorter duration time wise than if the system had a 1.5 ratio, and clipped. Clipping increases time duration for that 3.8kW, hence many hours of 3.8 kWh of energy generation.

Here is the image of that clipped inverter from one of the link above with a long duration of max energy production. Yes, counter intuitive perhaps but it is the case:

I’m not talking about a day or five where there is slight clipping for an hour.
The attached photo in the post above shows power sitting on 9kwh from Nine am to Five pm! On days like yesterday my system blasts through 9kwh and hits 12-13 from 11 to 1 that’s 10 kWh at least in one day! If you have 60 days of that it’s 600 per year or 12,000 lost over the life of the system or $4k! If it was $1k for the larger inverter it’s a no brainer.
If my system had this profile today it would be like 150 days of clipping!! The poster seemed to argue that “efficiency” somehow makes up for that degree of loss which makes no sense. Your system produces a net of 9kw when the sun allows. A smaller inverter cannot increase the radiation.
 
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nwdiver

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I’m not talking about a day or five where there is slight clipping for an hour.
The attached photo in the post above shows power sitting on 9kwh from Nine am to Five pm! On days like yesterday my system blasts through 9kwh and hits 12-13 from 11 to 1 that’s 10 kWh at least in one day! If you have 60 days of that it’s 600 per year or 12,000 lost over the life of the system or $4k! If it was $1k for the larger inverter it’s a no brainer.
If my system had this profile today it would be like 150 days of clipping!! The poster seemed to argue that “efficiency” somehow makes up for that degree of loss which makes no sense. Your system produces a net of 9kw when the sun allows. A smaller inverter cannot increase the radiation.

It's really hard to determine saturation losses from eyeballing a days production. It looks a lot worse than it really is.

This is oversized by 50%;


Screen Shot 2021-03-13 at 12.28.27 PM.png


But annual losses last year were only ~4%. (Only string A cuts back when the inverter is saturated)

Screen Shot 2021-03-13 at 12.29.21 PM.png
 
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h2ofun

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Aug 11, 2020
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auburn, ca
It's really hard to determine saturation losses from eyeballing a days production. It looks a lot worse than it really is.

This is oversized by 50%;


View attachment 644134

But annual losses last year are only ~4%. (Only string A cuts back when the inverter is saturated)

View attachment 644135
Does it just not come down to how much money folks want to spend? Meaning, one can get a much higher wattage panel, but it is a lot more money.
Is it worth it? And can get a larger inverter if one wants to spend more money, but is it worth it? One can get a lot more powerwalls spending lots more money, but is it worth it. Some folks make decisions on pure dollars and cents. Others make it on emotion. There is no one right answer I assume?
 

nwdiver

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Feb 17, 2013
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Does it just not come down to how much money folks want to spend?

.... sure.... if all you care about is kWh with no regard for cost then proper design really doesn't matter. ;)

Plenty of $5/w installers still kicking around more than willing to take advantage of... er... I mean entertain peoples emotions.
 

nwdiver

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Feb 17, 2013
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I agreed until the end. Why is proper design only what you think it should be? Again, for some its cost. For some its no clipping. For some its ......

Proper system design is the most kWh/yr for the least $. 'No clipping' is incredibly arbitrary. 'No Clipping' ever? So should the proper ratio be 0.8 so that even when output surges due to cloud edge effect nothing is wasted? Is clipping ok for 1 hour 1 day a year when it's cool and windy? Why not just use math? If $ spent on more inverter increases kWh/yr more than $ spent on more panels...... then spend the $ on more inverter.... numbers.

If one $12k system produces 10MWh/yr with no inverter saturation but another $12k system produces 11MWh/yr with inverter saturation.... you'd prefer the 1st to.... 'feel better'?
 

h2ofun

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Aug 11, 2020
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auburn, ca
Proper system design is the most kWh/yr for the least $. 'No clipping' is incredibly arbitrary. 'No Clipping' ever? So should the proper ratio be 0.8 so that even when output surges due to cloud edge effect nothing is wasted? Is clipping ok for 1 hour 1 day a year when it's cool and windy? Why not just use math? If $ spent on more inverter increases kWh/yr more than $ spent on more panels...... then spend the $ on more inverter.... numbers.
I tried
 

h2ofun

Active Member
Aug 11, 2020
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auburn, ca
So what's the right amount of 'clipping'? I've seen 7kW 'clip' on a 8kW inverter. Rare but it happens. Is that acceptable?
My only point I am trying to make is everyone has a right to the opinion, hot button, etc. I am not saying you have an option that makes total sense.
But as example, IMO, buying a EV at the moment is a total waste of money. I expect you totally disagree with me and will give all the global warming stuff to back up your opinion. I do not believe in global warming either. :)

All I am asking is why does it seem to you for others to have different values, needs and spend their money different. You give one option which is great. But why no be open minded that others may have different needs than yours?
 

nwdiver

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Feb 17, 2013
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My only point I am trying to make is everyone has a right to the opinion, hot button, etc. I am not saying you have an option that makes total sense.
But as example, IMO, buying a EV at the moment is a total waste of money. I expect you totally disagree with me and will give all the global warming stuff to back up your opinion. I do not believe in global warming either. :)

All I am asking is why does it seem to you for others to have different values, needs and spend their money different. You give one option which is great. But why no be open minded that others may have different needs than yours?

I think that's why we're disagreeing. You think opinion = fact. An opinion is not a fact. There's a difference between having an opinion and being wrong. If I say 2+2 = 5.... that's.... that's not an 'opinion'.... I'm wrong. If I say my $5 is worth more than your $7.... also not an opinion.

.... thinking your opinions are facts is also not an option ;) Because words.

If you want a $12k PV system that produces 10MWh/yr with no saturation over a $12k system that produces 11MWh/yr with saturation.... that's fine... you do you... but don't try to delude yourself into thinking it's rational. Inverter sizing is an engineering question.... not fine art. It's quantifiable.

... I also don't 'believe' in Global Warming any more than I 'believe' 2+2=4 or that the Earth orbits the sun... I accept them as verifiable, falsifiable facts of reality :)
 
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h2ofun

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Aug 11, 2020
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I think that's why we're disagreeing. You think opinion = fact. An opinion is not a fact. There's a difference between having an opinion and being wrong. If I say 2+2 = 5.... that's.... that's not an 'opinion'.... I'm wrong. If I say my $5 is worth more than your $7.... also not an opinion.

.... thinking your opinions are facts is also not an option ;) Because words.

If you want a $12k PV system that produces 10MWh/yr with no saturation over a $12k system that produces 11MWh/yr with saturation.... that's fine... you do you... but don't try to delude yourself into thinking it's rational. Inverter sizing is an engineering question.... not fine art. It's quantifiable.

... I also don't 'believe' in Global Warming any more than I 'believe' 2+2=4 or that the Earth orbits the sun... I accept them as verifiable, falsifiable facts of reality :)
You win. I NEVER said my opinion was fact.
 

nwdiver

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Feb 17, 2013
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You win. I NEVER said my opinion was fact.

You certainly drew a false equivalency....


I expect you totally disagree with me and will give all the global warming stuff to back up your opinion. I do not believe in global warming either. :)

CO2 is 40% higher, CO2 causes warming with radiative forcing... those ain't opinions :) If you're having trouble with the difference here's quick way to tell... is it falsifiable? Either CO2 is >40% higher or it's not.... there IS an answer. Either CO2 blocks IR or it doesn't... there IS an answer.

If it can be tested.... it's not an opinion. So the correct way to articulate your view is that you're wrong on global warming ;)

Same thing with inverter sizing. Unless your objective is a bell shaped production curve (Which in my OPINION is a weird objective) the most effective ratio is usually ~1.3 with current inverter and module prices. Testable, Measurable and Quantifiable. But.... that's only if your objective is more energy for less money.
 
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dareed1

Member
Jan 15, 2021
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Belmont, CA
As others have noted here, you will be clipping if you oversize your panels. I have the standard 8.16kW system with 7.6kW SE inverter. It's March and I'm already clipping. That's OK as I'm only 7% oversized and there's no 8.16kW inverter anyways.
Additionally, while pvwatts is good to get estimates, I find it inaccurate for my real world observations in this instance. Even if I enter in my system at 180 Azimuth, it doesn't show much clipping. Perhaps there are other parameters which need to be entered more accurately. Not sure.
Assuming you are in California Irvine, and all 24 panels face due south with a roof inclination of 27 degrees, you'll see the largest extent of clipping on about March 30. If you have a steeper roof at 32 degrees, the largest extent of clipping will be a couple of weeks earlier, and a few day later if the roof is 22 degrees. The clipping will last for about 90 minutes with about 4% loss of power generation during that time, or about 0.5 kWh. (Assumes clear day, utility voltage is at 240V, 95% system efficiency, etc.) The primary reason that clipping is strongest this time of year is solar insolation is somewhat counter-intuitively highest in December and lowest in June/July. Apparently there are more aerosols, etc in the atmosphere in the summer. A second effect is better solar panel efficiency when it is colder--0.36%/C for the Q-Peak Duo G6+ 340 panels, but I didn't include it in the above calculation.

Regarding PVWatts, it defaults to 86% efficiency which is way too low for a new installation. Also, it does an excellent job of finding the annual power production, but it does this by taking into account representative weather conditions, so it generally doesn't provide an estimate for clear days. At least you need to pick and choose the days which were assumed by PVWatts to be clear.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
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