DIY 11.7kw ground based grid tied system questions?

Hedges

I See Electromagnetic Fields!
Inverter can probably be programmed for a maximum wattage to stay under 80% of whatever breaker you do install; power output could be clipped during peak hours of days with best sun.

PV array if divided for multiple orientations can spread kWh over more hours with lower peak kW. e.g. some at 10:00 AM sun and some at 4:00 PM sun, 6 hours or 90 degrees apart, should reduce peak to about 0.7x as much.

Plan for where you might add battery backup. It can serve as UPS for a critical loads panel, and can backfeed main panel through an interlocked breaker adjacent to main breaker.
 

MarkSolar

Solar Enthusiast
If your PV needs 60A breaker, that backfed breaker plus main breaker of the panel it goes to are supposed to be no greater than 120% of panel busbar rating. I say each breaker could be 100% of busbar rating for a total of 200%, so long as located at opposite ends of busbar, and nothing bad would happen. The current from two sources subtracts, doesn't add. But NEC doesn't permit that, out of fear PV breaker will later get relocated next to main breaker so the current then adds.
Please explain why you say the current from two sources subtracts. Suppose I have 300A worth of circuit breakers in a 200A panel with a 200A main breaker and a 100A breaker at the bottom of the panel for the solar backfeed. If all 300A circuit breakers in the panel draw their full power, you could have 300A flowing on a 200A bus, couldn't you?
 

Hedges

I See Electromagnetic Fields!
At no point in the cross section is there 300A flowing.
200A can flow from main breaker, and exit through branch circuit breakers.
100A could flow from backfed breaker at other end of panel, and exit through branch circuit breakers.
At some point in the busbar, current drops off to zero.

If you stuffed two, 125A branch breakers facing left and right, then 250A total would come from the ends and split to the two breakers. That's the most extreme case. But other than at that one point of intersection, 200A is the max current. No problem overheating the busbar.

Think of what a suspension bridge looks like. That would represent a graph of current flow vs. position.

Enron did this once, claimed power was flowing from California to Nevada, and from Nevada to California in the same wire. Several times back and forth and there was too much power for the wire, so pay to reserve more capacity somewhere from them.
 

SteinVT

New Member
Thanks everyone for this discussion. It has been very enlightening. I find I have to read and reread at least three times to approach comprehension. I am a mechanical engineer by training that has been playing in the digital world for many years, so this shown me how little I really knew about the analog power world. And in the process, gained much respect.

Back to the project, I have decided to do the right thing and replace the main panel with a 200a version (225a busbars). I want to install another mini-split and will eventually be wanting a charger for an electric car. Might as well bite the bullet and do it right. - Mark
 

MarkSolar

Solar Enthusiast
At no point in the cross section is there 300A flowing.
200A can flow from main breaker, and exit through branch circuit breakers.
100A could flow from backfed breaker at other end of panel, and exit through branch circuit breakers.
At some point in the busbar, current drops off to zero.

If you stuffed two, 125A branch breakers facing left and right, then 250A total would come from the ends and split to the two breakers. That's the most extreme case. But other than at that one point of intersection, 200A is the max current. No problem overheating the busbar.

Think of what a suspension bridge looks like. That would represent a graph of current flow vs. position.

Enron did this once, claimed power was flowing from California to Nevada, and from Nevada to California in the same wire. Several times back and forth and there was too much power for the wire, so pay to reserve more capacity somewhere from them.
That is so beautifully simple it's hard to believe it can be true. When I think about current flow I think about wave mechanics and superposition. I have to go off and think about this some more.
 

Hedges

I See Electromagnetic Fields!
Back to the project, I have decided to do the right thing and replace the main panel with a 200a version (225a busbars). I want to install another mini-split and will eventually be wanting a charger for an electric car. Might as well bite the bullet and do it right. - Mark

Plan for where to install a battery inverter in the future, for grid-backup.
It's nice to be able to run A/C and everything else while the sun shines.

Your Enphase inverters probably do frequency-watts and can be controlled with frequency-shift by the battery inverter.
Enphase offers a product, also Schneider, Outback, SMA, probably others.

With 225A main panel and 200A main breaker, you can have 70A branch breaker feeding through battery inverter to sub-panel with critical loads and GT PV. Those would continue running through a power failure (possibly with a brief dropout), given enough battery and PV.

However, if excessive protected loads drain battery so inverter shuts off, no AC means microinverters can't make power to recharge battery. Two solutions: Either a load-shed relay to disconnect loads (what I have), or additional DC coupled PV (supported by the other brand battery inverters, not by Enphase.)

So if you do this you might want to add a 3rd panel for protected loads on output of battery inverter, with only microinverters and maybe telecom equipment always powered. Relay from there to your existing sub-panel so it is backed up so long as batteries have charge (requires a "load-shed" signal to disconnect, which SMA provides but don't know about the others.)

A manual interlocked breaker in main panel would let you disconnect from grid and power it from inverter as well. (You'll want a way to observe when grid has returned so you can manually switch back.)
 

SteinVT

New Member
Here is an update on my project. It really has been a lot more work than I had imagined. Yet to do is dress the wires behind the array and add labels to the meter, disconnect switch and combiner. My plan is to call the power company tomorrow and see what happens. Appreciate any and all comments from you guys. Because of your help, I really feel I understand the what as well as the why that goes into a project such as this.

Lets start with the array itself.
IMG_1707.JPG
The two things that helped the most were the ground screws and a laser level.

Next the combiner box. Here I added a Midnight Solar SPD.
IMG_1892.JPG

From here the power goes through 225' of 1 1/2" PVC conduit on 2- #2 gauge Cu with #4 for ground to the garage. More conduit routes the wires to the other side of garage to the power meter located on the outer wall in a little enclosure. There was enough room, so I added the power meter socket and disconnect in the same enclosure.
IMG_1890.JPG

The power than routes through a flexible 1 1/4" PVC conduit to my new 225 amp main panel.
IMG_1891.JPG

Anything you guys see that the power company might not like, please speak up. I'll call tomorrow, but who knows when they will show up. Again thanks for your guidance and information to get me to this point. - Mark
 

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Hedges

I See Electromagnetic Fields!
At first I was going to ask if those were AC only breakers used for PV DC, or if they were DC rated.
But I see you use Enphase microinverters, so AC to the breaker panel.

What looks odd is that there aren't separate ground wires for each circuit. Just one insulated ground wire to surge arrestor and one bare copper ground wire, I guess to the array?
Is that the proper way for Enphase, 2-wire cables with no ground?

"Enphase micro converters and Enphase combiner box with IQ envoy"

I'm not clear what the four circuits are in the breaker box. Must be four groups of microinverters landing there?
 

SteinVT

New Member
The only connections to the micro inverters is the Q cable and ground through the structure. The Q cable just has the two legs of the 240v. The bare ground wire attaches to ground lugs on the panel structure.

Three of the four breakers are a simple way to combine the outputs of the three sub arrays. The Q cable will support a maximum of 13 micro-inverters, so I broke up the array into three sub arrays. Two sub arrays have 11 panels each and the third has 10. The forth breaker was just an easy way of attaching the SPD. Thanks for the comments - Mark
 

SteinVT

New Member
Just wanted to pass along that the array is alive and well and producing power since Tuesday morning. Having the power company stop by was almost a non-event. Nice guy who took about an half an hour to swap out my old meter and add the production meter.

I am impressed by the Enphase Envoy monitoring hardware and software. I opted to add the consumption option so have an idea on my use versus generation. First two days were sunny and yesterday cloudy, but I am still 50 kWh to the good. It will be fun to follow along as the season progresses.

Thanks again to everybody that helped along the way. Couldn't have done it without you. Now onto the my next project, a 1962 Airstream travel trailer that I will be adding 1.2kW of solar along with a bunch of batteries. - Mark
 

MarkSolar

Solar Enthusiast
Congrats, it's a nice feeling when the electrons start moving. We already had smart meters before I did my solar, so the only thing I had to do was send the utility pictures of the tag off the inverter. I think the only thing they care about is that I don't backfeed more than I said I would.
 
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