10.6KW bifacial off grid ground array powering multiple locations 500 feet away

AlaskanNoob

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Any recommendations on a transformer for taking the 230 volts from the Multiplus and stepping it up to some voltage, and ditto a recommendation for a transformer on the receiving end to step it back down?
 

AlaskanNoob

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Alright, so now something that suggests I did not need to double the cable length in the sizing calculator and therefore the cable needed will not be $30/ft ... This calculator asks for the "one-way" cable length and comes out to <3% voltage drop with a 1 AWG copper wire over 500 ft with 43 amps. If I double this one (which it says not to do) then I get the 4/0 gauge wire. So that makes me think the other calculator was also asking for one-way length and it did not need to be doubled?
 

AlaskanNoob

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Here is another calculator. One I've used for years, gives good info. https://www.southwire.com/calculator-vdrop

I'm not a professional, just a fellow Alaskan who has installed several off grid systems with solar and wind.

That makes you doubly more qualified to educate me if you're feeling charitable. We finally figured out getting a structure and storing stuff the bears can't destroy. Now we're ready for some electricity. Moving right up that Hierarchy of Needs!

That calculator is the first one we used. If I plug in the length of the cable (500 feet) then it shows we only need 1AWG wire instead of the $30/ft wire.
 
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AKvalleyguy

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Moving on up, Right On! I'll reread your basic layout and see if I can offer any suggestion, or questions. I don't mind tossing out what little I know about this stuff, I got my education in the early 2000's from books, online forums and doing what you are doing, hooking up wires and making stuff happen! Sounds like there are a lot of smart people on here for technical questions. I can certainly offer info on logistics for shipping equipment around if you haven't gotten that worked out yet.

If you got 4 hours sun today you must be a little further south of us or out here in a flatter area. I'm in the MatSu Valley close to Castle Mountain and the sun gets blocked by the hills for a few weeks late Dec early Jan.
 

AlaskanNoob

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Moving on up, Right On! I'll reread your basic layout and see if I can offer any suggestion, or questions. I don't mind tossing out what little I know about this stuff, I got my education in the early 2000's from books, online forums and doing what you are doing, hooking up wires and making stuff happen! Sounds like there are a lot of smart people on here for technical questions. I can certainly offer info on logistics for shipping equipment around if you haven't gotten that worked out yet.

If you got 4 hours sun today you must be a little further south of us or out here in a flatter area. I'm in the MatSu Valley close to Castle Mountain and the sun gets blocked by the hills for a few weeks late Dec early Jan.
Yeah, we're further south on the Kenai. Our cabin has terrain to the south though, so it doesn't see direct sun for three months or so. We're hoping this solar array will power a ground source heat pump for the cabin. I'm too lazy for all this firewood cutting.
 

AKvalleyguy

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Nice place the Kenai is. I'll be interested to hear about the ground heat system. I've got a couple hundred acres and heat primarily with an outdoor wood boiler. Sounded like a good idea about 15 years ago...

The step up or step down transformer, there was an off grid acquaintance that though about doing that and backed out at the last minute. Turns out he was selling out and moving. He hooked up to the grid so a buyer could get financing. In his researching I do remember him mentioning something about expensive, troublesome or really inefficient. That was about 12 years ago so I'm guessing there is better residential type equipment out there today.

I don't have any comments right off on your original question, have to stop long enough to think about it. High winds and generator problems at the shop are keeping me moving way too much for a cold, winter Sunday.
 

AlaskanNoob

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Nice place the Kenai is. I'll be interested to hear about the ground heat system. I've got a couple hundred acres and heat primarily with an outdoor wood boiler. Sounded like a good idea about 15 years ago...

The step up or step down transformer, there was an off grid acquaintance that though about doing that and backed out at the last minute. Turns out he was selling out and moving. He hooked up to the grid so a buyer could get financing. In his researching I do remember him mentioning something about expensive, troublesome or really inefficient. That was about 12 years ago so I'm guessing there is better residential type equipment out there today.

I don't have any comments right off on your original question, have to stop long enough to think about it. High winds and generator problems at the shop are keeping me moving way too much for a cold, winter Sunday.
Yeah, I think there is a ten percent power hit from using the transformers which is less than ideal. If we are correct that we can use 1 AWG wire to send the power via AC then perhaps we won't need transformers anyway. That would be nice.
 

LB3

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We must have done our wire sizing incorrectly if you're showing the wire would cost us $15,000 to go 500 feet. That would definitely be a huge reason to go to the DC run with multiple inverters, batteries, and charge controllers OR to go with the transformer.

When I double the 500 feet in the calculator to 1000 feet (which I still don't understand if I need to do this or why, since it's a 500 foot run) then it comes up with 4/0 cable which is around the $30 a foot you mentioned. So I assume not doubling that 500 foot run was my error.
I didn’t do any math. I was just going worst case for 4/0 cable. I have a 12v system in my RV and used quite a bit more than I would have imagined.
 

AlaskanNoob

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I didn’t do any math. I was just going worst case for 4/0 cable. I have a 12v system in my RV and used quite a bit more than I would have imagined.
Thank God! That stuff is super expensive!
 

LB3

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Thank God! That stuff is super expensive!
Did I miss how many amps you’re running?

I just did some math. With 1ga cable for 120v ac power you reach 3% voltage drop at 1400 watts or just shy of 12A. (1000 ft total return path to inverter). You will need a good ground rod regardless, but if you’re in a wet location, a good earth ground at each end might help you get a few volts back.

Most 120v home wall outlets are on 20A beakers so you probably don’t want to be running any table saws or vacuum cleaners if you have much else running at the same time. You will see a 5% loss at ~19.5A.

The good news is you don’t have to rely on a utility company setting your grid voltage so you can safely dial your inverter voltage to 105% of nominal voltage or around ~126v

Assuming you don’t want to see your service drop below ~114v (95% of nominal) you can run up to 32A.

Be mindful that these numbers are just for the 1awg cable run and not any 12awg runs within your structure so some additional margin is warranted.

I don’t know your power needs but I would plan for some growth over time.
 

AlaskanNoob

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Did I miss how many amps you’re running?

I just did some math. With 1ga cable for 120v ac power you reach 3% voltage drop at 1400 watts or just shy of 12A. (1000 ft total return path to inverter). You will need a good ground rod regardless, but if you’re in a wet location, a good earth ground at each end might help you get a few volts back.

Most 120v home wall outlets are on 20A beakers so you probably don’t want to be running any table saws or vacuum cleaners if you have much else running at the same time. You will see a 5% loss at ~19.5A.

The good news is you don’t have to rely on a utility company setting your grid voltage so you can safely dial your inverter voltage to 105% of nominal voltage or around ~126v

Assuming you don’t want to see your service drop below ~114v (95% of nominal) you can run up to 32A.

Be mindful that these numbers are just for the 1awg cable run and not any 12awg runs within your structure so some additional margin is warranted.

I don’t know your power needs but I would plan for some growth over time.
The biggest draw we will have will be the Ground Source Heat Pump which I think needs 230 VAC. I've seen some that requires a little less. Was planning on running the AC from the Multiplus II at 230V. If I have to go to 1/0 wire I'll do that. I don't know anything about electrical power transmission and I don't know anything about GSHP so it's fun trying to plan this out.
 

LB3

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The biggest draw we will have will be the Ground Source Heat Pump which I think needs 230 VAC. I've seen some that requires a little less. Was planning on running the AC from the Multiplus II at 230V. If I have to go to 1/0 wire I'll do that. I don't know anything about electrical power transmission and I don't know anything about GSHP so it's fun trying to plan this out.
The nice thing about split phase 240 is that it cancels itself out so you don’t need a neutral. So if that’s your largest load, you can size your neutral for the 120v loads.
 

AlaskanNoob

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The nice thing about split phase 240 is that it cancels itself out so you don’t need a neutral. So if that’s your largest load, you can size your neutral for the 120v loads.
Thanks, I'll keep that in mind. I saw some transformers that some folks use to balance the load although I don't understand any of it.
 

joeblack5

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Ok, I am catching up together with your heat pump in your other thread,. Why not get multiple micro gridtie inverters and run 240vac for the long runs to your house...redundancy . then have a battery bank with quality inverter generate a local grid that complies with the requirements of the micro inverters.. something like an outback 3648 or newer..
Change your Honda to a
For instance a used Onan mcck water cooled unit.. if you need to burn fuel you at least can get the coolant heat out of it as well..

Johan
 

AlaskanNoob

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Ok, I am catching up together with your heat pump in your other thread,. Why not get multiple micro gridtie inverters and run 240vac for the long runs to your house...redundancy . then have a battery bank with quality inverter generate a local grid that complies with the requirements of the micro inverters.. something like an outback 3648 or newer..
Change your Honda to a
For instance a used Onan mcck water cooled unit.. if you need to burn fuel you at least can get the coolant heat out of it as well..

Johan
I appreciate the suggestion on how to do things better, many thanks for that.

We're not on the grid, do gridtie inverters need to be on the grid? We looked into multiple micro inverters (and DC optimizers) to the SCC but decided that since our area won't be shaded (other than clouds) that it probably wasn't worth the cost and the extra wiring. But we didn't consider redundancy. Would those microinverters be wired into the SCC and also wired directly to the cabin? Our thought now is to have them go to the SCC which will go to the Multiplus II which will send power to the cabin and to the batteries. Are you suggesting they can be wired to the SCC and also to the cabin simultaneously for redundancy?

Will definitely look into that generator.
 

joeblack5

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Micro grid tie does work fine when you create your own stable grid with an inverter. There are some complications but research here at diy solar and or outback solar forum and you will find the answer..
Essential the complication arises when the micro grid solar inverters put more power out then what you are using.. normally in a grid that would be absorbed but if you are not then that power has to be absorbed elswere. With for instance and outback inverter it will feed the excess energy back into the batteries. So all is fine upto when the batteries is full. So there has to be a disconnect at that moment or you have to start a dummy load like your water heater, house electric heater to dissipate the surplus..
I am not familiar with the multiples but it sounds complicated.

Going with micro grid inverters in your application would have advantages , at least to me . Each panel has its own inverter, so very redundant,.
The power lines to the house are ordinary 240 vac ground cable, easy to get.

Your batteries are warm in the house and we'll protected, you can run 48vdc in the house or normal 120/240 as you please.

Good luck,
Johan
 

AlaskanNoob

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Micro grid tie does work fine when you create your own stable grid with an inverter. There are some complications but research here at diy solar and or outback solar forum and you will find the answer..
Essential the complication arises when the micro grid solar inverters put more power out then what you are using.. normally in a grid that would be absorbed but if you are not then that power has to be absorbed elswere. With for instance and outback inverter it will feed the excess energy back into the batteries. So all is fine upto when the batteries is full. So there has to be a disconnect at that moment or you have to start a dummy load like your water heater, house electric heater to dissipate the surplus..
I am not familiar with the multiples but it sounds complicated.

Going with micro grid inverters in your application would have advantages , at least to me . Each panel has its own inverter, so very redundant,.
The power lines to the house are ordinary 240 vac ground cable, easy to get.

Your batteries are warm in the house and we'll protected, you can run 48vdc in the house or normal 120/240 as you please.

Good luck,
Johan
I see where you're coming from.

Our plan is to have the PV run to an insulated and warm underground structure (basically a root cellar with a shed over top) next to the PV where the SCC, inverter, and batteries will be stored. Then the inverter will supply 230VAC power over a 500 foot buried line to our cabin.
 

joeblack5

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Yes I understand but I do not see the advantage, you need a structure, it needs heat for your battery, if a breaker goes off you have to walk all the way out there.
But that is all for you to consider.
 

AlaskanNoob

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Yes I understand but I do not see the advantage, you need a structure, it needs heat for your battery, if a breaker goes off you have to walk all the way out there.
But that is all for you to consider.
The advantage is the heat will be free in the underground root cellar like structure, since it just needs to be kept above freezing, and then I can run the power from there to multiple places on the property without having to buy a charge controller, inverter, and batteries for each location and I also won't have to parcel up my PV to specific locations.
 
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