diy solar

diy solar

Grid tied electrical diagram review

6 awg is good for 60A fuse (I use it for 70A)
10 awg is good for 30A.

If more than 3 current-carrying conductors in cable or conduit, then there is derating to lower current allowed.
Also if in hotter than normal environment.

Hot "Line" wires count as current-carrying. Ground does not, and neutral in split-phase 120/240V does not.

Because 10 awg has 40A ampacity (although no larger than 30A fuse allowed), even though you have 4 hot wires going to two inverters, the derating still allows 30A fuse.

Your drawing shows two separate 30A disconnects (fused?) after the breaker panel with 30A breakers.
Utility may want a visible-blade disconnect, to be absolutely certain power source is isolated.
But do they require a single switch, rather than two separate ones? I don't know.
Mine has a single switch, branching to multiple breakers downstream.
You could put a single switch before the sub-panel. Which of course means any loads there would be shut off at the same time.
Or a single 2-pole breaker in the panel, feeding a 60A switch, and multiple branches of fuses/breakers downstream (like I did.)


Hedges, Could you comment on the attached electrical schematic?
 

Attachments

  • Electrical diagram 2x6kwr6.jpg
    Electrical diagram 2x6kwr6.jpg
    157.4 KB · Views: 24
Azimuth 270 degrees - due West?
If that's the roof orientation you have available - usually somewhat South will produce more.

Tilt 14 degrees
Shallow for a roof.
If your location was latitude 14 degrees, then this tilt and due South might be optimum.
It is flat enough that orientation hardly matters. It catches the sun well when overhead.

PV wire #10
Ampacity 30A (really 40A, but we are supposed to operate no higher than 30A)
30A / 1.56 = 19.2A Isc max
Probably heavier than required for one PV string, 12 awg would work up to 12.8A Isc.
Less IR drop.

6kW inverter / 240V = 25A
25A / 0.8 = 31.25; OCP and wire ampacity should be greater than that.
10 awg to be fused at 30A. Next larger gauge and fuse would be better.

2 x 25A / 0.8 = 62.5
8 awg would be good for 55A, so 6 awg seems appropriate (presently blank on drawing).
60A OCP doesn't quite meet requirement of continuous current being no more than 80%

Programming inverter for 5760W could be a way to properly use 30A and 60A OCP, if it is a concern.
Are PV panel orientations set by roof angle? If they could be tilted differently, one string at a different angle from other would reduce peak production so not clipped by inverter limit.

But, if PV array is 12.9 kW (STC), under typical temperature conditions would peak at PTC production about 85% or 90% of that, so programming inverter lower won't usually lose anything. Maybe you can argue OCP isn't operated with continuous current above 80% on account of PV array size.

You posted "360W", drawing says "365W"

"Patio cover frame" for ground connection.
That by itself wouldn't be adequate ground to PV panel frames per NEC.
Either a lug connected to each frame (set-screw lets ground wire be unhooked to remove panel without interrupting ground to remaining panels),
or "WEEB" connections electrically bond mounting rails together as grounding electrical conductor, and bond panels to rails.


I thought there might be a limit to amperage allowed with supply-side tap, but haven't found anything that says so. Seems to me loads could be connected so it draws 60A plus main panel 200A for 260A from utility feeder, which might exceed its ampacity.

I like to over-panel an inverter, with PV strings of multiple angles for more kWh total while not clipping excess kW. Your panel Voc and Isc together with inverter may or may not allow that.

Inverter max 550V, 12.5A Imp, 16A Isc
What is record cold temperature for your location? 550V/9 = 61.1 max voltage per panel
61.1V/1.16 = 52.7Voc max panel spec allowed (using a conservative temperature adjustment)

"Open circuit voltage 47.66"
Good enough, don't need more accurate temperature coefficient and cold temperature.

"Short circuit current 10.08A"
Within limit. Can't put another PV string in parallel (unless inverter allowed paralleling its two MPPT inputs, for 3 strings into two inputs.)

"Disconnect amp rating" in drawing is blank.


Overall looks like it works, just max current seems close to ampacity/OCP and grounding to panel frames should be done correctly.
 
Hedges, Thank you for such an in-depth answer. A little background info may help you understand the limitations.
The Azimuth and tilt are dictated by the patio cover structure design and are not optimum for power production but cannot be changed. See photo in a previous post. The panels are frameless Glass on glass, bifacial (see attached spec sheet), I ordered 360w (but actually received 365w STC) Because of the non optimum positioning I was using the STC ratings for output calculations rather than the BSTC rating of 412w.
If using the 412, each inverter may see a max of 7416w, Within its limit 8100W, but max output from the inverter is still only 27.2A, per inverter spec. Sizing the wire to 32.64A means 8AWG between the inverter and the breaker box, and use 35 or 40A breakers? Then use 6AWG from the Breaker box to a Fused disconnect, rated 75A ? with 70A fuses? Thanks for your help.
 

Attachments

  • BN72 Gen2 rev1.2 (3) (4).pdf
    539.9 KB · Views: 9
I guess glass frame changes grounding requirements a bit. If patio roof frame is metal, it should be grounded. If I was trying to look for trouble I would say any metal parts the panels contact should have a reliable ground (if glass breaks they could become electrified.

Yes, those gauges and OCP seem good.

Maybe at some angles the sun will hit patio and get some power from the backside. Likely when off-angle and the front isn't at 100%.


Will you want to add backup at some point? If those inverters do frequency-watts, could integrate with a battery inverter. Some considerations for how that is best accomplished while making sure you don't have connections that can overload utility drop.
 
Yes the glass panels are held in place by an aluminum base, cap and girt components that are attached to a grounding lug on each rafter. What size wire should I use for ground, 10AWG?

Initially, I didn't intend to have backup storage, and I'm not sure the Growatt min6000 tl-x has that capability. Attached is its installation manual.
 

Attachments

  • Growatt 2500-6000.pdf
    4.5 MB · Views: 10
Ground wire could be same as current carrying conductor.
For systems with OCP, NEC tables list smaller ground wire gauge, sufficient to trip the breaker/fuse. In that case doesn't need same ampacity because not carrying current indefinitely.
PV inverters typically have ground-fault detector.

I don't even find "1741" as in UL-1741 SA. No indication it does frequency-watts
A model with battery-optional would be nice.
 
I think they got it UL (ETL) after the spec sheet was published, see attached. On one end we have the ground wire attached to the panel frames, and the other end is connected to the ground from the service panel?
 

Attachments

  • UL_1741_For_MIN_3372.pdf
    165 KB · Views: 8
Hey Repman, I have been following along and am excited to see your project completed. Looking to diy my own here in the Tampa area and taking notes!
 
Hello TheDan, oddly enough I've just been to the Tampa Area (Treasure Island ) for a family reunion and am about to head back to Dallas to continue with my project. If you're interested, I will post more photos as the project progresses.
 
Looking forward to seeing the pictures. By the way, did you opt for the Growatt? The price and features make them very appealing.
 
Very clean layout, with PV panel frames lined up to wood frame.

How does rain drain? Spill between panels onto wood, or did you come up with a way to have it shed down to a gutter area?
 
First, love the solar awning. I currently have an aluminum awing on the pack porch, and I'm seriously considering putting 5kW of panels as it's a perfect fit.

Second, @Hedges, I'm stalking you, and I think this guy could benefit from your wisdom:

 
Very clean layout, with PV panel frames lined up to wood frame.

How does rain drain? Spill between panels onto wood, or did you come up with a way to have it shed down to a gutter area?
The frame is all aluminum, with weather stripping above and below the panels making a water tight seal.
 
That looks really nice, that would be a good advertisement for companies trying to sell solar systems to people. Why don't I see any wires or junction boxes on the bottom of those panels?
 
diagram fine, are you installing this in USA? Has your utility approved using growatt?
who has to approve the installation? Why do people have to consult utility companies for solar installation?
Can't you get your solar system connected off grid completely and disconnect utility or not to use them at all?
Or get a system with blackout protection that won't send power to the grid during an outage?
 
who has to approve the installation? Why do people have to consult utility companies for solar installation?
Can't you get your solar system connected off grid completely and disconnect utility or not to use them at all?
Or get a system with blackout protection that won't send power to the grid during an outage?

Please note the "grid-tied" aspect of this thread. Most advice will be in that context.

Yes, you can set it up as you describe; however, authorities having jurisdiction (AHJ) will require compliance with NEC codes even if no permit is required. NEC requires units be UL listed.
 
Back
Top