Ideal xfmr(s) for connecting 480/277Y inverters (60kW total) to 12470/7200 grid

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jaggedben

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If the SI is not monitoring the current, you might be able to use an external ATS?

That would sort of just turn the SI into an ordinary UPS, which would either defeat the purpose somewhat, or call for re-configuring some other part of the system (i.e. no longer having four tripowers).

I do believe that the SMA Multicluster is designed to allow other configurations besides 3 SIs per Tripower. Not really sure about details though, and I believe you'd still have the silliness of converting everything to 280/120. The SMA rep who said it was possible probably didn't realize that the OP was talking about 480V inverters.
 
I don't think you can connect all the Tripowers on the AC side of the SI's.

But if the power coming from the Tripowers is going:
A. Out to the grid
or
B. In to the main load panel

Wouldn't this edited drawing work?
Is there any reason that you would *have* to use Sunny Islands?
It doesn't seem 100% necessary when there isn't any PV going through them.

http://1drv.ms/1d8tndN

Or something like page 2 here?
http://www.morningstarcorp.com/wp-content/uploads/2014/05/MSC-Diagrams-TS-MPPT-600V-150520-09-MG.pdf
 
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GoldDigger

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But if the power coming from the Tripowers is going:
A. Out to the grid
or
B. In to the main load panel

Wouldn't this edited drawing work?
Is there any reason that you would *have* to use Sunny Islands?
It doesn't seem 100% necessary when there isn't any PV going through them.

http://1drv.ms/1d8tndN
I think that the original thread topic took a turn near the end to consider what would be needed for the tripowers to produce local power during a grid outage.
Using the SIs and batteries just for time shifting storage is not economically feasible with current batteries.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
But if the power coming from the Tripowers is going:
A. Out to the grid
or
B. In to the main load panel

Wouldn't this edited drawing work?
Is there any reason that you would *have* to use Sunny Islands?
It doesn't seem 100% necessary when there isn't any PV going through them.
If you want the system to be able to run offgrid, i.e., when the grid is down, you must have batteries and battery compatible inverters*. Tripowers are not battery compatible. Sunny Islands are battery compatible, but they are not PV compatible.

*An exception is the SMA split phase transformerless inverters with the emergency power outlet that will function when the grid is down and the sun is shining, but that outlet will only supply up to 1500W at 120V, subject to the limit of how much sunlight there is.
 

jaggedben

Senior Member
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Solar and Energy Storage Installer
But if the power coming from the Tripowers is going:
A. Out to the grid
or
B. In to the main load panel

Wouldn't this edited drawing work?

It would work in the sense that you would have some back up supply for critical loads if the utility power went out. It would not work for keeping the building powered if the outage was long and the batteries drained. It would also not work for time-storage shifting. Like GoldDigger I fail to see the point of it.

Is there any reason that you would *have* to use Sunny Islands?

No, and in that setup if you used a Sunny Island you would be paying for features that you wouldn't be using. Again, what you've got in that drawing could be any ordinary UPS, for backing up only critical loads.


That is intended for a much smaller residential system. At most you'd transfer a couple strings of your huge PV system. Looks like it requires a lot of manual control. At least you'd have the option for recharging batteries with PV power in case of a long outage. Again, you could only power critical loads.

Sunny Islands are battery compatible, but they are not PV compatible.

I don't think you meant that last part exactly as you said it.
 

jaggedben

Senior Member
Location
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Solar and Energy Storage Installer
I think that the original thread topic took a turn near the end to consider what would be needed for the tripowers to produce local power during a grid outage. ...

Yes, although if he really wants local power during an outage then a different choice of inverters is probably warranted, which would change many other aspects of the design.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I don't think you meant that last part exactly as you said it.
You cannot connect PV modules to a Sunny Island* and you cannot connect batteries to an SMA Tripower. Isn't that what I said?

*You can, however, connect PV modules through a charge controller to batteries and then connect the batteries to a Sunny Island.
 
If you want the system to be able to run offgrid, i.e., when the grid is down, you must have batteries and battery compatible inverters*. Tripowers are not battery compatible. Sunny Islands are battery compatible, but they are not PV compatible.

There are these new ones.
So two of these, the 8.0 model, would have maximum input of 100A (50A each) at 240V, and are rated to put out 6000w/26A each at 240V.
They wouldn't know the difference between power coming from the Tripowers and power coming from the grid.

AC input (PV array, grid or MC-Box)
Maximum AC input current 50 A
Rated current / maximum output current (peak) 26 A / 120 A
http://www.sma-america.com/products...d-self-consumption.html#Technical-Data-137064

It would work in the sense that you would have some back up supply for critical loads if the utility power went out. It would not work for keeping the building powered if the outage was long and the batteries drained. It would also not work for time-storage shifting.

Aren't the first two just a matter of how many amps of storage you have? And if you check out that link, those 8.0 models are supposedly great for time shifting.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
There are these new ones.
So two of these, the 8.0 model, would have maximum input of 100A (50A each) at 240V, and are rated to put out 6000w/26A each at 240V.
They wouldn't know the difference between power coming from the Tripowers and power coming from the grid.
Sunny Islands can tell the difference because the PV inverters connect to one AC connection and the grid connects to the other. Also, if this new Sunny Island is 240V split phase (I haven't seen one), how do you plan to interface it with the 480V three phase output of the Tripower inverters?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
You cannot connect PV modules to a Sunny Island* and you cannot connect batteries to an SMA Tripower. Isn't that what I said?

*You can, however, connect PV modules through a charge controller to batteries and then connect the batteries to a Sunny Island.

You said 'not PV compatible', which I didn't think was accurate. But the point is now clarified for anyone reading. (I know you and I both know this.)
 

GoldDigger

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Sunny Islands can tell the difference because the PV inverters connect to one AC connection and the grid connects to the other. Also, if this new Sunny Island is 240V split phase (I haven't seen one), how do you plan to interface it with the 480V three phase output of the Tripower inverters?

And what makes the SI/SB combination unique AFAIK, is that as the SI sees its output approach zero (SBs are meeting entire local load including battery charging) it can modulate the SB output (not just on/off as with other AC coupling schemes) by increasing the frequency above nominal.
Otherwise the excess power from the SBs would have nowhere to go. Either the load voltage would rise, increasing the power consumption or the battery inverter would be forced to shut down.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Aren't the first two just a matter of how many amps of storage you have? And if you check out that link, those 8.0 models are supposedly great for time shifting.

My point was that you are ignoring the option of having the PV recharge the batteries if the grid is out. Personally, if I was paying for both battery backup and for solar I would want them to work together when the power went out. Especially if I was paying extra for inverters (the Sunny Islands) that have that capability. Or, alternatively, I'd give up on having them work together if there was a ton of money to be saved by choosing cheaper equipment for the storage function. There are companies which are developing that market for demand management that have much more scalable products, probably cheaper, too.

And yes, I guess you can do time shifting with those. I mispoke. But I have yet to see how that's economical for anyone except maybe some large industrial customers. Give it five years and that may change.
 
You cannot connect PV modules to a Sunny Island* and you cannot connect batteries to an SMA Tripower. Isn't that what I said?

Am I missing something here?
The Tripowers are connected to a line side junction box which goes to grid or load.
The Islands are connected to the load side of the main service box.
There's a 480/277 to 120/240 xfmr between the junction box and main service box.

So how are the TPs and SIs connected?

If the grid goes down, the Tripowers will run the load (which includes charging batteries), or shut down if there's no load and batteries are full?

The wiring of the "load area" is currently 120/240. So the 120/240 xfmr would be supplying the 120V load, and using the two lines of 120V to make 240V for the SIs.

And what makes the SI/SB combination unique AFAIK, is that as the SI sees its output approach zero (SBs are meeting entire local load including battery charging) it can modulate the SB output (not just on/off as with other AC coupling schemes) by increasing the frequency above nominal.

Right? Like...what he said? Except decreasing is also an option?

My point was that you are ignoring the option of having the PV recharge the batteries if the grid is out. Personally, if I was paying for both battery backup and for solar I would want them to work together when the power went out. But I have yet to see how that's economical for anyone except maybe some large industrial customers. Give it five years and that may change.

I think the Islands could even go between the Tripowers' AC combiner panel and the line side junction box, but that would be pointless because you'd need 480 to 240V xfmr just for the Islands and then another to go back up to 480 for the grid.
I think that's what you're saying about using other equipment- just get a 480V to 48V charge controller between F and G in the diagram (F= PV meter, G=disconnect), and then a 48V to 120/240 inverter to run the load. Maybe?

And- check THIS out!!
:eek:hmy:
(from April 2014)
On Wednesday, New York City?s Metropolitan Transit Authority (MTA), which suffered its own Sandy-related shutdown, announced one of the city?s biggest energy storage projects to date: a 400 kilowatt-hour array of CellCube vanadium redox flow batteries at its new facility at 2 Broadway in downtown Manhattan.
http://www.greentechmedia.com/artic...y-Brings-Energy-Storage-to-New-York-Citys-MTA
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Am I missing something here?
The Tripowers are connected to a line side junction box which goes to grid or load.
The Islands are connected to the load side of the main service box.
There's a 480/277 to 120/240 xfmr between the junction box and main service box.

So how are the TPs and SIs connected?

If the grid goes down, the Tripowers will run the load (which includes charging batteries), or shut down if there's no load and batteries are full?

The wiring of the "load area" is currently 120/240. So the 120/240 xfmr would be supplying the 120V load, and using the two lines of 120V to make 240V for the SIs.
The Tripowers will shut down when the grid goes down in that configuration. The SI has two AC connections - one to the MDP and grid and one to the protected loads panel. Only the connection to the protected loads panel stays energized when the grid goes down (dictated by UL1741 and physics), and any PV inverters that you want to keep running during a outage must be connected to the protected loads panel; their connection to the grid is through the Sunny Island. The Sunny Island is connected to the MDP through OCPD sized for its maximum current, which also limits the size of the PV inverter that you can connect through it to the MDP.

IMO something you should consider is how important it is for the PV to continue to run during a grid outage. PV is a strategic tool to lower your electric bill, while inverter backup for AC power is a tactical tool to get you through outages. The contribution to your customer's bottom line from PV running during outages is minuscule if outages are infrequent and/or of short duration, and it's expensive to build this capability into a system no matter how you go about it. In many (most?) cases it is not worth it. If a long outage is a concern, it will be much cheaper to wire a genset into the protected loads panel and run it during outages to power loads and charge batteries than it will be to get PV to fill that role. A generator is a voltage source (it delivers current on demand by the load it sees), so its size is not limited by the OCPD between the protected loads panel and the MDP.
 
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IMO something you should consider is how important it is for the PV to continue to run during a grid outage. ...The contribution to your customer's bottom line from PV running during outages is minuscule if outages are infrequent and/or of short duration

That's really the thing here- every single situation is different. You could say that most residential setups are similar, sure, but ya know?
The issues of concern with battery banks/grid tied are:
1. Power outage back up
2. Time/demand
3. You can theoretically spend less on the PV equipment and use that for the battery bank. For say net metering deals, you can use the batteries at night, and keep your bill at zero or below (meaning you get some $$ or credit)
4. Others?

How do you explain it in layman's term (meaning: to me)?
Having a battery bank....makes your PV system have an output when the sun is not up.
What can you do with that? Anything you want, really. It doesn't make sense to just have it for backup.
So...what do you want to do? Making your bill zero is one thing, and then getting reimbursed for the PV power is a whole other thing.
It seems sort of silly, if you want your bill to be zero, to put in a bunch of power during the day, and then...take it back out at night.

Why not...put as little in as possible?
You'd need less solar panels to do that with batteries than without.
I think.

The other "issue" is that none of these "pricing breakdowns" make a bit of sense.
$96,000??? For what where?
2.5 times as expensive as ... WHAT? :blink:
We're just supposed to be like "WHOA, 2.5 times as much, that stinks!"
But that's basically WRONG, and they aren't telling you how they got the wrong numbers, which is a bit...suspicious and makes me think that in fact, batteries ARE a good option!

That's some pricey power, given how infrequently the lights go out. The average US home loses power for just under 2 hours a year. Over the course of a nine-year lease that average homeowner would pay $277 for each hour the battery is running.

To some, that peace of mind may be worth it, though many who wanted that peace of mind bought a home backup generator long ago.

The price to go completely off the grid is even higher because that would require a rooftop solar system bigger than what is now usually installed, and at least two Powerwall batteries. That kind of system would cost $96,000 without subsidies, about 74 years of electric bills for an average US customer, calculates Bernstein Research's Wynne. Even assuming the cost of solar and batteries declines by 80 percent in the coming years and that it will be subsidized by clean-energy incentives, the system would still cost 2.5 times more than buying electricity from the grid, according to Wynne.

The Tesla battery still has appeal, however, and that appeal could grow with regulatory changes that would enable owners to get more use out of their batteries.

http://www.autoblog.com/2015/05/21/what-do-you-really-get-for-7000-tesla-powerwall-home-battery/
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
How do you explain it in layman's term (meaning: to me)?
Having a battery bank....makes your PV system have an output when the sun is not up.
I believe that the correct way to think of it is as two separate systems - the PV system and the battery backup system. A PV system never has output when sunlight is not available. A battery system (when the batteries are charged) has output whenever it is needed. A PV system (a current source with its voltage clamped) produces the amount of power that the array captures from the available sunlight - no more, no less - and it has to go somewhere or the system shuts down*. A battery backup system (a voltage source) provides the amount of power that the loads demand. They are different tools for different tasks.

*An exception is the SI/SB system where the SI throttles back the SB when necessary to fit the demand, but there are specific ways that such a system must be designed and configured in order for it to function this way.
 
The SI has two AC connections - one to the MDP and grid and one to the protected loads panel. Only the connection to the protected loads panel stays energized when the grid goes down (dictated by UL1741 and physics), and any PV inverters that you want to keep running during a outage must be connected to the protected loads panel; their connection to the grid is through the Sunny Island.

Right. But!
First of all, what's going on here?
It's in German, that doesn't help.
It looks like the SI is only hooked up to ONE Of the 3 phases of the grid here. Huh?
http://www.sma-america.com/fileadmin/_migrated/pics/summenstrom_01.jpg

And then, never mind that- regarding your quote above-
If the MDP and grid are both getting power from the Tripowers, and the MDP includes the SIs, and then the grid goes down, the Tripowers will throttle down and supply the load instead of grid, won't they?
This goes with that link/pic above.
Although the Sunny Island is only connected to one line conductor, it automatically manages the total power. The energy meters work in a cumulative manner, so that the power from the individual line conductors is added up. The Sunny Island can then always feed in or draw as much energy as is needed in accordance with the sum total of all phases
. http://www.sma-america.com/products...ed-self-consumption.html#sthash.N6XDLcQN.dpuf
 

GoldDigger

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Location
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Right. But!
First of all, what's going on here?
It's in German, that doesn't help.
It looks like the SI is only hooked up to ONE Of the 3 phases of the grid here. Huh?
http://www.sma-america.com/fileadmin/_migrated/pics/summenstrom_01.jpg

And then, never mind that- regarding your quote above-
If the MDP and grid are both getting power from the Tripowers, and the MDP includes the SIs, and then the grid goes down, the Tripowers will throttle down and supply the load instead of grid, won't they?
This goes with that link/pic above.
Although the Sunny Island is only connected to one line conductor, it automatically manages the total power. The energy meters work in a cumulative manner, so that the power from the individual line conductors is added up. The Sunny Island can then always feed in or draw as much energy as is needed in accordance with the sum total of all phases
. http://www.sma-america.com/products...ed-self-consumption.html#sthash.N6XDLcQN.dpuf
That implies that the tripower can function on all three phases with only one "grid qualified" reference phase. This would have to bevatotslly different mode of operation from the normal grid tied modevin whichbesch phase follows the timing and voltage of its corresponding grid phase.
I have never heard any mention of this before, so I am skeptical or confused.
 
it has to go somewhere or the system shuts down*.

*An exception is the SI/SB system where the SI throttles back the SB when necessary to fit the demand, but there are specific ways that such a system must be designed and configured in order for it to function this way.

Ok- so in this "not line-side" diagram, it would go from SBs into the SIs and/or out to grid.
It would go in that setup at a point after the customer owned PV meter and before the MDP.
http://www.nationalgridus.com/non_html/dg_sample_1line_a.pdf

But then in this "line-side" diagram, the SIs would go...into the main breaker (busbar?) of the MDP, right? By that I mean "the single breaker that the other 4 breakers are attached to".
Because, the 480/277 from the SBs is going through a 480/277 to 120/240 xfmr on its way there.
So- in this second scenario, no "loss of grid" for the SBs, and no "PV connection" for the SIs?
https://www.nationalgridus.com/non_html/DG_sample_1line_B.pdf

Will the SBs not "throttle back" without SIs to "tell them to" or something? How would they even know the "grid went down" other than the output going from unlimited to being whatever the load is at that moment? If they're already taking care of the load AND the extra is going out to the grid...
Isn't the issue more that SBs don't interact with batteries than that they won't put out power when the grid is down? Like you said, there's a way to do it?

P.S.
I am skeptical or confused.

I don't know enough to be the first one, so I'm just confused! ;)
 
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