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Scotty11

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Reply with quote  #1 
Planning 80 panel system...1 installer says single inverter as good sun, no shade...another says micro inverters on each panel.
Who leans which way?
Regards, Scotty

stmbtwle

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Reply with quote  #2 

If all your solar panels are in one plane AND there is no shade issue, a single inverter is fine.

If you are putting panels on more than one plane of your roof, you'll need a separate inverter for each plane, as different areas may put out different voltages.

If shading is an issue, you need micro-inverters.

Another consideration:  Micro inverters put out 240AC and each inverter is grid-tied. If the grid is cut they all go down and the array could be considered "safe".   The series DC strings of panels to a single inverter can put out 400-600 volts DC and even if the inverter is shut down, as far as I know the DC strings remain "hot" and potentially lethal. 

Then there's the capability of microinverters to tell you if there is a problem with a single panel. Also if an inverter or panel fails, it only affects that one unit. 

Micro inverters are easier to expand, as each panel/inverter is a separate entity.  With a series inverter, once you reach the limit of the inverter you can go no further without buying another inverter ($$$). (You could however install a separate array with micro-inverters.)

My system (2009) is a string system with a single inverter and it works fine, however if I had it to do over again, I'd go the micro-inverter route, for the reasons above.

Article on the subject here: http://energyinformative.org/are-solar-micro-inverters-better-than-central-inverters/

Not sure how the costs add up; you'll have to do the math.


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Scotty11

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Reply with quote  #3 
You mentioned micro inverters put out 240AC and grid tied. Does this mean they can tie into the grid without going to the 400 amp service? I ask as the panel box is 300' from the solar panels, whereas the power line from the street passes alongside the solar panels on it's way to the 400 amp.
If going 300' to the panel box, I've heard it suggested to go 550V DC or 480V AC. I wonder if micro inverters can do that.
Regards, Scotty
stmbtwle

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Reply with quote  #4 

First, I'm NOT an expert.  These are just my thoughts on your dilemma.

The inverters (micro or central) don't know or care where they are connected.  If they sense the appropriate voltage/cycles in the line they will match that and feed back the power.  That's what they're designed to do. 

I can see why tying into the service line would be attractive, BUT:

Will the utility even LET you do that?

Where is your power meter?  Is it near the 400a service panel or is it near the street?  If you connect your system "before" the meter, there will be no way for the utility to measure the output of your system.  The inverter will still feed it back to the utility but you WON'T get credit for it, nor will it show up on your meter as a reduction in consumption.

Options:

A: If the meter is near the service panel, what you might be able to do is get the utility to move your power meter to a position near the array, and install a new "splitter" panel that services both the array and the existing 400a panel.  If the meter is near the street you might not have to move it but you'll still need the switch panel.  This would keep your wiring run relatively short.

B: I don't know of inverters that output 480v (contact the mfgr), but there are transformers that could step the inverter output up to 480v.  You'd need two, one to step the voltage up, and another to step it back down to 240v, and then of course the separate high-voltage line. Unless you ALREADY have 480v, it might not be worth it.

C: The 550VDC option may be the simplest and most efficient, but you'll still have to run those long high-voltage wires, and from a personal standpoint I'd avoid it if I could (just me).

Again, I'm not an expert, but if it were me I think I'd talk to the utility company about option A.  You'd have your choice of central or micro-inverters, and your wiring runs will be shorter, and you can avoid the high voltage circuits. 

Also contact your local authority about codes, they vary from place to place. You'd be really ticked if you built your system and the inspector made you change it.


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Scotty11

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Reply with quote  #5 
Good info...lots to think about. I'll post here on how it turns out.
Regards, Scotty
sundug

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Reply with quote  #6 
These may help, just ask if you have any questions. Doug



http://www.builditsolar.com/Projects/PV/DougEnphase/DougEnphase.htm

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stmbtwle

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Reply with quote  #7 
Scotty: If you're still considering 480v, these folks have a 480v, 20kw inverter for you:
http://www.wholesalesolar.com/9994954/solaredge/inverters/solaredge-se20000us-480-inverter

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
tacman7

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Reply with quote  #8 
The video helped me, I didn't understand that the inverters are the real working part.
Everything else (besides the backwards running meter) is just junction boxes.

I think.

I don't have micro inverters and I loose most of my power 2-3 pm.


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