600ft distance from open field to meter/panel

[worldwander]

Looking for feedback on a solar install where the place we need the power is 600ft from an open field in the woods surrounded by tall trees.

Have a remote property that we purchased, and the bunkhouse is in the woods and to get to the open field is a 600ft run. The utility ran underground power 400+ ft from the transformer to the meter with a 200 amp panel breaker/service(20+ years ago). In July(Florida location) the peak hour was 13KWh, so assume a 50 amp average indicating AC on in the house and the workshop.

Planning an expansion of larger building out to the "open field area", so long term that will become the primary driver of power. Would like to centralize solar and SOL-ARK 15K, batteries, generators out in the field given that SOL-ARK can expand capacity by adding additional units.

When I did the voltage drop calculator from Southwire can't do a wire big enough for a 600ft run at 240V and 200 amps. Even at 240V and 100 amps would require a 600KCMIL cable which is direct burial and very expensive at $18 a foot for 750-750-500. Going with a 240-480 to 480-240 voltage 50KVA transformer from Maddox is $2200 each for $4400 then allows for 4/0 cable($6 a foot). This solves the getting power to the existing panel at a cost of $8000. To add in the ability to net meter and run off the grid would need to add an additional appropriately rated cable to bring power from the meter 600ft to the SOL-ARK unit trying to centralize in the field. Assuming SOL-ARK 15K, when running off of the grid doesn't do a AC-DC transform and then back to AC for the load, so if the meter is the primary source of voltage, it is already 400ft to the meter from the utility company transformer plus 600ft to the solar hut and then 600ft back to the main panel. Not good.

Option B is to put SOL-ARK and batteries at the existing panel/meter location and run high voltage DC from 10KW of panels over three strings to the SOL-ARK DC input. for 10 panels per string 43V per panel at 10 amps = 430V. Running three strings 600 ft of 4-4-4 wire is $2000 in wire costs. Saving $6000 and in theory, a more optimal interface to the grid.

As we add buildings out in the field(farming related) would not be able to leverage existing solar/AC/grid infrastructure. With net metering, any excess solar beyond topping off the batteries can go back as a credit and in theory could use that as a virtual meter credit if we end up adding another meter out in the field. Not really worried about net metering, but don't want to do anything that prevents it if the future is going to bring KWh rates 2X and 3X what we have today.

Has anyone found a reasonable price 50KVA 240-480V transformer for less than $2000? Ideally would like to do 240-600 if the wire for direct burial is rated for 600V but haven't found that option. The best options I could find was at maddoxtransformer.com

Any good options for wire? The prices are coming down but still a major cost. The best price bulk cable I can find and includes free delivery is at https://nassaunationalcable.com/collections/clearance-sale

Has anyone gone the high voltage DC route for 10KW of solar over 500+ ft and had issues/problems?

 

[timselectric]

High voltage DC is the best option.
Keeps everything else together, and requires a lot less wiring. Which translates to less cost.

 

[DThames]

What is "Running three strings 600 ft of 4-4-4" ? 4-4-4?

 

[Bluedog225]

The 5 or so hours mid day are the solar production hours that count most. Is your closer location in shadows mid day? If not, it may be useable.

 

[MisterSandals]

for 10 panels per string 43V per panel at 10 amps = 430V. Running three strings 600 ft of 4-4-4 wire is $2000 in wire costs. Saving $6000 and in theory, a more optimal interface to the grid.

10000W / 30 panels = 333W panels
333W / 43V = 7.75A
Each 430V string should be 7.75A

Voltage drop is only 2.57% (acceptable) with 10AWG.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[worldwander]

What is "Running three strings 600 ft of 4-4-4" ? 4-4-4?

Yes planning to use two bundles of 4-4-4 to have 6 wires for the three strings.

 

[worldwander]

10000W / 30 panels = 333W panels
333W / 43V = 7.75A
Each 430V string should be 7.75A

Voltage drop is only 2.57% (acceptable) with 10AWG.

View attachment 123416

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

27 panels JKM430M-72HLM-TV which has max voltage of 43.23 and current 9.83 so in theory 430 watt panel. Rounded up to 10 per string to simplify the math. The reality is won't see the 430 watts but design for the specs.

 

[worldwander]

The 5 or so hours mid day are the solar production hours that count most. Is your closer location in shadows mid day? If not, it may be useable.

Buried in the woods with tall trees blocking the eastern sky and not a really good spot to put the panels close by that would even come close to getting maximum light. Using bifacial panels and will be installed at 12+ ft as a roof to test farming under the panels. So panels have value out in the larger field.

 

[Vigo]

May sounds funny but consider that adding panels to offset voltage drop is probably cheaper than burying larger pieces of copper!

Voltage drop is different in ac and dc in that the ac devices work in a narrower window and may actually be damaged by low voltage conditions. On the dc side your 450v+ mppt fully expects to see a range of several hundred volts not just guaranteed daily as the sun goes down, but from moment to moment from passing clouds. Losing a chunk of volts to the wire means next to nothing as long as the wire can dissipate that heat load.

Let’s say you make 10kw of solar and size the wire to drop 5% (gads!). Well, you’re now heating your wiring with 500w of heat. Is that a problem? Well, what’s the surface area of your six conductors at 600ft long each (3600 linear feet, ~2/3 of a mile)? Less than 1 watt of heat per foot of buried wire, unless you mean per conductor then it’s 0.13w of heat per conductor, per foot. Even if they are bundled and touching each other in some kind of jacket, it just wouldn’t matter. The temp rise wouldn’t even be detectable anywhere but the exposed ends, and there’s a big difference between ‘detectable’ and ‘problem’ anyway. So with that amount of direct burial wire using several acres of your property as a heat sink, you can basically drop all the volts you want and just offset the loss with a couple extra panels on the front end. Your wiring has surface area comparable to an actual ground loop HVAC system. It can dissipate some watts..and your panels and mppt don’t care either.

Just sayin’..

 

[worldwander]

May sounds funny but consider that adding panels to offset voltage drop is probably cheaper than burying larger pieces of copper!

Voltage drop is different in ac and dc in that the ac devices work in a narrower window and may actually be damaged by low voltage conditions. On the dc side your 450v+ mppt fully expects to see a range of several hundred volts not just guaranteed daily as the sun goes down, but from moment to moment from passing clouds. Losing a chunk of volts to the wire means next to nothing as long as the wire can dissipate that heat load.

Let’s say you make 10kw of solar and size the wire to drop 5% (gads!). Well, you’re now heating your wiring with 500w of heat. Is that a problem? Well, what’s the surface area of your six conductors at 600ft long each (3600 linear feet, ~2/3 of a mile)? Less than 1 watt of heat per foot of buried wire, unless you mean per conductor then it’s 0.13w of heat per conductor, per foot. Even if they are bundled and touching each other in some kind of jacket, it just wouldn’t matter. The temp rise wouldn’t even be detectable anywhere but the exposed ends, and there’s a big difference between ‘detectable’ and ‘problem’ anyway. So with that amount of direct burial wire using several acres of your property as a heat sink, you can basically drop all the volts you want and just offset the loss with a couple extra panels on the front end. Your wiring has surface area comparable to an actual ground loop HVAC system. It can dissipate some watts..and your panels and mppt don’t care either.

Just sayin’..

Completely agree. The voltage drop for DC is less of an issue but mainly trying to stay in some measure of "spec" to avoid getting into a deep dive with a future inspector if they are looking for reasons to have a concern. This is a farm installation so no requirements to pull permits or pass inspections but in the future if the property not under agriculture exemption could be an issue. Considering the panels will not be optimal, clouds etc the voltage and current will be dynamic. The bigger question is how well will the MPPT circuit perform with 600ft of cable in the mix. Will call into SolArk and see if they have any guidance on MPPT over 600ft of cable.

 

[timselectric]

May sounds funny but consider that adding panels to offset voltage drop is probably cheaper than burying larger pieces of copper!

Voltage drop is different in ac and dc in that the ac devices work in a narrower window and may actually be damaged by low voltage conditions. On the dc side your 450v+ mppt fully expects to see a range of several hundred volts not just guaranteed daily as the sun goes down, but from moment to moment from passing clouds. Losing a chunk of volts to the wire means next to nothing as long as the wire can dissipate that heat load.

Let’s say you make 10kw of solar and size the wire to drop 5% (gads!). Well, you’re now heating your wiring with 500w of heat. Is that a problem? Well, what’s the surface area of your six conductors at 600ft long each (3600 linear feet, ~2/3 of a mile)? Less than 1 watt of heat per foot of buried wire, unless you mean per conductor then it’s 0.13w of heat per conductor, per foot. Even if they are bundled and touching each other in some kind of jacket, it just wouldn’t matter. The temp rise wouldn’t even be detectable anywhere but the exposed ends, and there’s a big difference between ‘detectable’ and ‘problem’ anyway. So with that amount of direct burial wire using several acres of your property as a heat sink, you can basically drop all the volts you want and just offset the loss with a couple extra panels on the front end. Your wiring has surface area comparable to an actual ground loop HVAC system. It can dissipate some watts..and your panels and mppt don’t care either.

Just sayin’..

The problem with this is by adding more amps, you would increase the voltage drop even more. Or adding more volts, could push the VOC too high.
It's a catch 22. Can't win, either way.

 

[timselectric]

Completely agree. The voltage drop for DC is less of an issue but mainly trying to stay in some measure of "spec" to avoid getting into a deep dive with a future inspector if they are looking for reasons to have a concern. This is a farm installation so no requirements to pull permits or pass inspections but in the future if the property not under agriculture exemption could be an issue. Considering the panels will not be optimal, clouds etc the voltage and current will be dynamic. The bigger question is how well will the MPPT circuit perform with 600ft of cable in the mix. Will call into SolArk and see if they have any guidance on MPPT over 600ft of cable.

The MPPT doesn't know or care how long the conductors are. It just sees voltage, pulls amps, and tries to get as much power as it can.

 

[DThames]

Yes planning to use two bundles of 4-4-4 to have 6 wires for the three strings.

You didn't explain what you are calling 4-4-4. If that is some way of saying 4 gauge, as others have said, you don't need that heavy a wire for what you have described.

 

[DThames]

Completely agree. The voltage drop for DC is less of an issue but mainly trying to stay in some measure of "spec" to avoid getting into a deep dive with a future inspector if they are looking for reasons to have a concern. This is a farm installation so no requirements to pull permits or pass inspections but in the future if the property not under agriculture exemption could be an issue. Considering the panels will not be optimal, clouds etc the voltage and current will be dynamic. The bigger question is how well will the MPPT circuit perform with 600ft of cable in the mix. Will call into SolArk and see if they have any guidance on MPPT over 600ft of cable.

Yes call Sol-Ark if you are concerned but 3 pair of 10ga would likely be plenty heavy wire. They actually have a support request form that you can direct to a "design review" type group so they can review and comment on your design solution.

This guy Gain Solar, has a lot of good videos on Sol-Ark installs and he sells stuff to. You might touch base with someone that does this all the time and for some consulting fee might help you a lot.

 

[sunsurfer]

Why not go aluminum?

 

[Mike 134]

I can see some wrong answers already about wire size (10 ga won't cut it), 600' is a long way, even your utility would bring a high voltage leg (2300-7000V #6) to the end before mounting a stepdown transformer on the pole for your 120/240.

The higher you can keep the voltage over the 600' the better off you'll be.

 

[OzSolar]

You didn't explain what you are calling 4-4-4. If that is some way of saying 4 gauge, as others have said, you don't need that heavy a wire for what you have described.

It's direct burial rated URD aluminum wire called "Vassar". Each size has a nick name. 4-4-4-4 would be Tulsa. Wish I knew the background of that.

Side note: the manufacturer rates it's ampacity higher as direct burial.

 

[timselectric]

Why not go aluminum?

4-4-4 is a direct burial aluminum group.
#6 aluminum would be enough. But not as regularly available.

 

[timselectric]

It's direct burial rated URD aluminum wire called "Vassar". Each size has a nick name. 4-4-4-4 would be Tulsa. Wish I knew the background of that.

It's not a nickname. It's the actual description of the conductors. The numbers tell how many and what size they are.
4-4-4-4 is 4 x #4 gauge conductors.
2-2-2-4 is 3 x #2 gauge and 1 x #4 gauge.
The last conductor (if smaller than the others) is usually the ground conductor.
Vassar is just one of the manufacturers.

 

[worldwander]

Yes copper is hard to come by and carries a price premium even if you can go with lower gauge wire. I suspect the accountants are pricing the product to keep it a push if you have option A or B. For direct burial, copper options are limited as well and hard to find long runs. Running three strings need 6 conductors so using 4-4-4 aluminum or 6-6-6 aluminum can put down two 600 ft runs and get the 6 conductors needed. 6-6-6 is $1.24 a ft and 4-4-4 is $1.99 a ft at https://nassaunationalcable.com/collections/clearance-sale which I have used prior and includes free delivery. From southwire voltage calculator a 600 ft run of 6-6-6 aluminum 430V at 10 amps the voltage drop is 1.93%. If you select copper then you can use 10 awg for a 2.97% voltage drop. For 10/3 copper $1.83 a ft. https://nassaunationalcable.com/products/10-3-heavy-duty-flat-grnd-thw-copper-600v 6-6-6 aluminum ends up cheaper by the foot and definitely seems like a "stronger/robust" cable for direct burial. The good news is prices on wire are coming down.