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Joined: May 2010
Posts: 5
D
New Member
Currently I am looking at a 10KW solar install. The plan is to install 2 string inverters (5KW ea.) at the house 350ft away from the panels. This would involve 4 DC circuits at about 355V each. Full load current would be about 8 amps. I plan on using 8 runs of 1/0 RW90 cable (4runs x 2 wires/cct) I figure this would be about a 3.5% volt drop. Additionally this would all go in one 4 inch PVC conduit underground. I have never installed DC circuits of this high voltage before, does anyone have any thoughts or considerations on this setup and on working with high voltage DC circuits?

Joined: Jun 2004
Posts: 1,273
T
Member
Use only one inverter...

Getting twins to co-operate is unnecessarily tricky.



Tesla
Joined: May 2010
Posts: 5
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New Member
What is tricky about it? Still possible I assume? I have done several grid-tied parallel type systems with micro inverters but not a string inverter yet.

Joined: Jun 2004
Posts: 1,273
T
Member
Talk to the manufacturer's tech rep...

Ordinarily you have issues of TIMING.

DC to AC conversion in this electronic age uses switching circuits and the math of Fourier transforms to synthetically build up 60 Hz ( or 50 Hz ) power.

If there is ANY timing difference between your paralleled systems then you're in for some harmonics.

Enjoy!


Tesla
Joined: Jul 2004
Posts: 9,689
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The way I understand it...

These grid tie things do not put out anything until they see the grid, then they lock onto it. Timing should be right in lock step after the first cycle or so.


Greg Fretwell
Joined: May 2005
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Greg's right about not getting any AC output until there's a live grid, but the DC from the panels is there anytime that there's light falling on the panels. Watch what wires you touch and you should be fine.


Ghost307
Joined: Jul 2004
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This sort of gets back to the desire for a disconnect right at the collector. I am just not sure what the best method might be. Maybe just a small encapsulated relay as part of each collector with an "enable" line.


Greg Fretwell
Joined: Nov 2005
Posts: 141
C
Member
I haven't posted for a long time now, but I must comment on the collector panels.

Even the 15 watt suckers can give you a nasty jolt when they are are unloaded. They put out a bunch of volts in direct sunlight at the terminals that can knock you off the roof at the terminals. - I know- I just went through that this week and would up connecting - very stupidly - with the unloaded output with the "tame" voltage from the sunlight panels. I damn near got knocked off the roof by the jolt I got.

"Green is good" for now, but and a big BUT, be careful with these so called "docile" panels.

BTW - anyone have any hints on how to earth these things and isolate them from a grid tie system?


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