Bifacial Solar Fence

[mburke6]

Hi, I'm new here and this is my first post. I've poked around a bit and haven't quite found an answer to a question I have. Mainly is there a such a thing as a 12kW grid-tied inverter that will take a high current 48Vdc input from a solar array?

I'm speculating about contemplating on building a 200' fence that will enclose an area in my back yard. The fence panels would be large bifacial modules mounted vertically and long-ways. I've found modules that are around 8' in length and nearly 4' in width and these would be mounted vertically between posts about 2 feet above the ground. There would be 22 panels in the fence and each panel is 48VoC and 17 short circuit amps.

I am hoping to get opinions and thoughts on wiring these panels in parallel to create two 48v, 6kW.

1. The primary power side of the panels will be facing in all four compass directions, depending on where it is located in the fence. I want the wiring side of the panels to be facing inside the enclosed area.
2. Every panel will be in sunlight 90% of the time, but every panel will experience some shading throughout the day.
3. The panels will be mounted low, so I'm worried about exceeding 48 volts for safety reasons.
4. Is there a 6kW to 12kW inverter out there that will accept a 40-48 volt input?
5. Is this fence just an all-around bad idea?

I've attached a sketch I made showing the fence.

 

[Brucey]

Pretty much every inverter/charge controller I've seen requires at least 5V over the battery voltage to start, and some of the AIOs seem to have a minimum voltage in the 100-120V region.

 

[Bop]

I can't think of any- for the reason that the cabling costs would likely exceed the cost of the panels...
22 panels at 17A is 370A, and with a total wiring run of 200ft- assuming you cut the arrays in half and run 100ft total distance on each, to keep a 3% voltage drop over 100ft/30m (I work in metric lol) you need some pretty heavy cables...
Each array is 187A at a nominal 48v, and with a 30m run to keep a 3% power loss from voltage drop, the minimum cable size needed is a scary 185mm^2 cable (scary for the wallet that is)- with 2 separate arrays, thats 120m needed


My conversion chart doesn't even go up to that in AWG...- we are talking some seriously industrial cables here...


It's bigger than 300AWG cable, and locally, although 185mm^2 cable is available, it is $$$ (so much so that of the half dozen distributors here in all of Australia- they don't list a price- call for a quote...) going from experience- you are talking $50-$60Au a metre plus which would be over $7000 Au- minimum...
Locally, a 10kw system using conventional panels would set you back about a grand less- for everything... installed on a rooftop even... (9.9kw fully installed $6200)
That's a LOT of money- just for the cables alone...

 

[Dooug]

You will need to do some more panels in Series. Parrallelling that many panels is a wiring night mare...

 

[mburke6]

Thanks for the replies! I knew the cable requirements were going to be tough. I have some ideas on how I would wire such a thing though.

My primary concern with this fence idea is safety. I'm wondering if a high current 48Vdc system is safer than a lower current high voltage DC system, or an AC system using micro inverters. For instance, if the neighbor backed into the fence with the car and I end up with live wires on the ground. I feel that anything above 48v would require more hardened cable infrastructure to make it safe, probably burial. Am I wrong here? Would high current 48Vdc have less safety concerns as say a lower current 300Vdc system?

Instead of wiring a group of 11 panels in parallel, what if I grouped them in parallel groups of 3-4? Then bring each group all the way around the fence to a common corner and terminate in a junction box. I'm probably using the same amount of copper, but perhaps at less cost. At the common point I would have 6 groups of parallel panels at 48v. At that point I parallel the 6 groups to get my high current 48v system.

 

[Bop]

Thanks for the replies! I knew the cable requirements were going to be tough. I have some ideas on how I would wire such a thing though.

My primary concern with this fence idea is safety. I'm wondering if a high current 48Vdc system is safer than a lower current high voltage DC system, or an AC system using micro inverters. For instance, if the neighbor backed into the fence with the car and I end up with live wires on the ground. I feel that anything above 48v would require more hardened cable infrastructure to make it safe, probably burial. Am I wrong here? Would high current 48Vdc have less safety concerns as say a lower current 300Vdc system?

Instead of wiring a group of 11 panels in parallel, what if I grouped them in parallel groups of 3-4? Then bring each group all the way around the fence to a common corner and terminate in a junction box. I'm probably using the same amount of copper, but perhaps at less cost. At the common point I would have 6 groups of parallel panels at 48v. At that point I parallel the 6 groups to get my high current 48v system.

Still end up with the same overall copper, and you are increasing the amount of cables needed significantly- you are now up into the hundreds of metres of cables needed- still an expensive amount of wiring...(and still need to fnd a gridtie inverter that will work with that low an input- I can't think of any off the top of my head)

Here, ground based panels are acceptable, but the wiring has to be 'enclosed' ie all cables and junctions must be fully enclosed in conduit, and junctions in a sealed box requiring tools to access and marked with warning labels
So having 'heavy' support posts at the junction of each panels terminating point (ie a strong steel post concreted into the ground) with the cable run up the post in conduit and with a junction box with all cabling in conduit going underground to the next 'support post' would be acceptable (different places have different rules, so check what is acceptable there)

To minimise these 'connection points' it would be best to have the panels 'top to top' ie the end with the connections goes to a post, and the next panel is 'reversed' so its connections go to the same post and junction box- the next post has no wiring and no junction box, the next post again has two sets of connections going into one junction box and so on...

Here in Oz again, this would need a certified installer/electrician to sign off on the design and do the actual installation- this here is mandatory for all gridtied systems, no DIY allowed, other places are more lax about this

 

[mburke6]

Here in Oz again

I appreciative your taking time to discuss this with me. Sometimes we have to start in a place of fantasy and wishful thinking and engineer our way back to reality. It's sounding like, as a privacy fence in a residential setting, this is a fairly impractical idea, especially as a DIY project.

Now I'm off to watch the big American style football match at my sister's place.

 

[Bop]

I appreciative your taking time to discuss this with me. Sometimes we have to start in a place of fantasy and wishful thinking and engineer our way back to reality. It's sounding like, as a privacy fence in a residential setting, this is a fairly impractical idea, especially as a DIY project.

Now I'm off to watch the big American style football match at my sister's place.

Using panels as a privacy fence wouldn't be that impractical (although having bifacials may be an issue if the neighbours don't like the look on their side of course) but the low voltage system simply isn't a goer for practical reasons (it could be done, but only at a LOT of $$$)
A HV one could be practical- it becomes just a 'slightly different' ground mount- which are usually pretty easy to get done- just have to meet the rules in whatever place you happen to be in...

Here, a series string setup like that would be as easy to get set up as any other ground mount (ie no easily accessible wiring or connectors- all in conduit and junction boxes secured appropriately and bingo, no problems...)
This is one I did a while back- its running at several hundred volts, and is legal with all current Au design rules and regs- yours is just something like this 'tipped up on one edge and spread out'- sure it isn't the 'most efficient' way to use panels, but it would certainly work...

I sadly don't have a shot of the back- but all the cables (including from the panels output box to the juction boxes) were in conduit... A requirement here where 'panels are accessible' ie ground mounts- rooftop panels don't require that, but ground mounts do- for extra safety...

 

[skyking1]

I am pondering a bifacial solar fence oriented N-S with the primary side to the west. We tend to have morning clouds and then clearing in the PNW as the pattern for ~20% of the time.
I am thinking of a series system about 150' long, and run it 75' from each end to a housing in the middle for the inverters to cut cable runs to a minimum.
The house lot to the east is 8' lower than the bottom of the fence more or less. I don't expect shade from the structure to be a factor, but they may plant some trees. That is a bummer for series systems.
Perhaps micros are the way?

 

[Brucey]

150 feet long, how many panels?

 

[hwy17]

That's a really terrible orientation. Is the fence of significant useful value for the sake of being a fence?

 

[skyking1]

That's a really terrible orientation. Is the fence of significant useful value for the sake of being a fence?

yes it is. There is housing development to the East, and my own lovely trees and natural scaping to the west and north.
Perhaps I could do rows of panels like / / / / and stagger it with another row.
That's an idea.

 

[hwy17]

yes it is. There is housing development to the East, and my own lovely trees and natural scaping to the west and north.
Perhaps I could do rows of panels like / / / / and stagger it with another row.
That's an idea.

Would 45 degree tilt and array still running north south do anything helpful for you?

 

[skyking1]

Sure that is what I was crudely depicting with the / / /
We are spitballing at the moment. I will have some rooftop on the new house with the required RSD, but now I'm entertaining building out some ground mounts when we know what the needs will really be. It is so much easier without RSD and building inspection.
This new home development is going to be a slow roll. I plan on having a tax credit for several years to come
The neat thing about that fence location, is the north end if it may be my 400A service and meter, and two 200A ranch panels. Those panels have pass through lugs and 4 breaker spaces each. One goes to the house and the other to a future shop.
Talk about easy grid tie