Finally, the start of my 25kw Ground Mount grid-tie system

MarkSolar

Solar Enthusiast
That kind of sucks. You do all the planning and then they tell you what you needed to know in the first place.
 

live4soccer7

Solar Enthusiast
Agreed. I'd be more mad if this was something I did for a living, but I've learned so much in the process so far that I would never count that as a loss by any means. Ya win some and ya lose some. haha.
 

Hedges

I See Electromagnetic Fields!
Well.... the initial assessment from the utility company is a no go based on the transformer that feeds my home and my neighbor's. I am checking to see the max allowable size and also what it would cost to have them upgrade it.

A bit disappointing, but what can one do. Updates to follow as I receive them.

Export limited system, to not exceed 25kW or whatever max backfeed, even while it generates additional AC watts for your loads.

Batteries/inverters for peak production shaving, in conjunction with export limit. (may not be cost effective depending on batteries)

Multiple orientation PV arrays, can be about 1.4x inverter capacity without clipping, produces for more hours.
 

live4soccer7

Solar Enthusiast
Update, FINALLY!

I spoke with the utility company this week and they have the estimate to upgrade the transformer here. It is currently a 25kVA transformer and they will charge me $1700 to upgrade to a 50kVA unit. They said they will approve my system once that is upgraded. They have no problems with the size or design.

That is very reasonable compared to the cost of the system, so I think I am moving forward!!!!!!!!!!!!!!!!!!!

The next step here, and I have a couple questions for you all, is to solidify the array size for the fronius 15k units (3) and also get engineered plans for the ground mount system at 45* instead of the original 30-35. I'll be calling victor engineering, who does the plans for sunmodo, to talk with them to see what it would cost to get the sunmodo engineered for 45* and stamped plans. Once I have that then I can submit for permitting with the county. Once that is done (electrical permit should be easy) then I am ready to start buying components!!!

Is there a better ground mount system out there that would be configurable to 45* without additional engineering?

Here is a concern of mine regarding the array size. I am looking at the Hyundai bifacial panels (450W without the bifacial effect). 450 * 16 * 2 = 14,700W per fronius unit. If I said they could produce an additional 25% at peak production then that would equate to exactly 18kw, which is the absolute max that the fronius units are spec'd for on the PV side.

One, panels may only produce max wattage on the frontside for a few hours a day at best. Two when they are producing max then the sun should have much less of an effect on the back side due to the nature of where the sun is positioned to get that max production. I'm thinking that there is not anything to worry about in regards to providing too much power to the fronius units. Any thoughts on this????
 

Hedges

I See Electromagnetic Fields!
Was only 100A at 240V? Now you get 200A.
Should still not be at all excessive in terms of fault current (main breakers typically rated 22kA)

Ground mount, I used Unirack ULA. Don't think it has any particular angle limits, but I could be wrong.
User-supplied 2" pipe or conduit for vertical and horizontal sections.
Vendor-supplied square aluminum tubes for diagonals. (Those might get greater force from wind if steep. They also take forces from earthquake.)

Extra current available from PV shouldn't be a problem.
Inverters may have reverse-polarity diodes (which only get used if PV connected backwards). Those have a current limit.
MPPT algorithm cycles current up and down.
Just stay under Isc limit in spec.
 

live4soccer7

Solar Enthusiast
@Hedges

It's the high voltage coming into the property. Theoretic power is 25kVA before it is stepped down to 120v. They were requiring it to be 50kVA for the system.

I think I looked at unirac's ULA, but I'll take another gander here in a minute.

If I did a west facing array (probably 32 panels), any input on angle?

I'll check out the numbers for the specs you mentioned on the fronius.
 

Hedges

I See Electromagnetic Fields!
If due West, that may significantly reduce annual kWh with a steep tilt. If closer to flat, then might produce more.
What it would be good for is maximizing late in the day time of use. I have about 20% of my panels aimed almost West and 45 degree angle for that reason. $0.50/kWh 4:00 PM to 9:00 PM, $0.15/kWh before 3:00 PM.

More like South West would produce more year round.
My original arrays were aimed at 2:00 PM sun, about 40 degree angle. That was from when Noon to 6:00 PM was peak time.

You just have to use an insolation calculator, find the monthly and annual output of each orientation you're planning and add them together.
Multiple angles will let you use more panels, produce considerably (~ 40%) more kWh for a given maximum kW instantaneous output.
 

MarkSolar

Solar Enthusiast
The next step here, and I have a couple questions for you all, is to solidify the array size for the fronius 15k units (3) and also get engineered plans for the ground mount system at 45* instead of the original 30-35. I'll be calling victor engineering, who does the plans for sunmodo, to talk with them to see what it would cost to get the sunmodo engineered for 45* and stamped plans. Once I have that then I can submit for permitting with the county. Once that is done (electrical permit should be easy) then I am ready to start buying components!!!

Is there a better ground mount system out there that would be configurable to 45* without additional engineering?
I looked at the same thing when I did mine. One mechanical issue with the Sunmodo was that the length of the uprights only allows up to 35deg, if you want to go higher you'd need longer uprights. Not sure they have them available. The other option is to lower the front edge right down to the ground, but we get a lot of snow so didn't want to do that. I found a few engineering papers that showed stress difference between 35 and 45deg, it was really large. As I recall it was about 5 times larger for some of the bending stresses. So you need to either use larger pipes, or add the appropriate diagonal bracing.
Here is a concern of mine regarding the array size. I am looking at the Hyundai bifacial panels (450W without the bifacial effect). 450 * 16 * 2 = 14,700W per fronius unit. If I said they could produce an additional 25% at peak production then that would equate to exactly 18kw, which is the absolute max that the fronius units are spec'd for on the PV side.

One, panels may only produce max wattage on the frontside for a few hours a day at best. Two when they are producing max then the sun should have much less of an effect on the back side due to the nature of where the sun is positioned to get that max production. I'm thinking that there is not anything to worry about in regards to providing too much power to the fronius units. Any thoughts on this????
Fronius data sheet for 15kW model shows recommended input range of 12-18kW, don't see a problem. On the best days so far I've gotten 83% of the rated output of my panels. We haven't had any cold weather yet so that might go up slightly, but I'd be surprised if you ever see more than 85-90% of the rated output in the real world.
 

wattmatters

Solar Addict
I spoke with the utility company this week and they have the estimate to upgrade the transformer here. It is currently a 25kVA transformer and they will charge me $1700 to upgrade to a 50kVA unit. They said they will approve my system once that is upgraded. They have no problems with the size or design.
That's a bargain.

When the local grid company here made me an offer I couldn't refuse to upgrade the local transformer the estimated cost was between $30-50k. I did refuse it though but I had to accept reduced connect limits (32A per phase).

Here is a concern of mine regarding the array size. I am looking at the Hyundai bifacial panels (450W without the bifacial effect). 450 * 16 * 2 = 14,700W per fronius unit. If I said they could produce an additional 25% at peak production then that would equate to exactly 18kw, which is the absolute max that the fronius units are spec'd for on the PV side.
It won't be an issue. The recommended PV input wattage range for the 15kW Primo is 12kW to 18kW but that doesn't mean you can't have more than that. Indeed it would likely cope with 20kW provided the MPPT voltage limits were not exceeded.

Just remember you have two MPPTs with different current capacities. When an array(s) is generating enough power to reach an MPPT's current capacity, the inverter will simply clip the current.

The only array input limit you really need to be concerned about is the short circuit voltage.

Given the angle of the dangle you are talking about, I very much doubt you'll see much over 15kW.
 

live4soccer7

Solar Enthusiast
I believe our average is between 40-50", but it tends to melt rather quickly in between snowfalls. I have a sub compact tractor with a blower on it, so it wouldn't be too terrible if I had to clear snow once or twice a year in front of the panels.
 

live4soccer7

Solar Enthusiast
@Hedges

I'll likely be using the unirac ULA system. Do you recommend the pro series clamps or just the standard ones? I input into their generating with both and it is about $1000 price difference on my system build.

Well.... The sunmodo system seems to be way cheaper because it includes the pipe that is used as well. I have sent off BOMs to CEDgreentech and hopefully I will have more information on THEIR pricing for this stuff. I think it will end up being very clear which one will be cheaper. I think I will know Monday.

The cheapest I could find 2" SCH40 pipe was $5700 for 800', which is what was spec'd. Then I would have to take it to get galvanized as well.

I'm anxiously awaiting the numbers on these systems because it is mainly the last major aspect of the system.
 
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