Back Again With Questions

hotdawg23 · August 2011

Yesterday i posted a question about building solar panels and went back to edit it and lost it all. But got a very good answer anyway so i will retire that question.
My next question is about distance.
Basically, how far from the panels can the batteries be? I know DC has a problem with distance.
My house is about 200 feet from the area (the barn) where the panels will be, can i put all the equipment and batteries in the barn and run the high voltage line to the house?
Thanks to you all for the help.

Cariboocoot · August 2011

Re: Back Again With Questions

The answer to this one is: it depends on the Voltage.
You're right that electricity (not just DC) suffers losses from distance. Using larger wire size will reduce the loss, but it gets to be a bit impractical after awhile: trying to run 17 Volts from a PV array through 0000 wire to the controller could get extremely expensive very fast.

That's why there are Voltage drop calculators like this one:
www.solar-guppy.com/forum/download/voltage_drop_calculator.zip
You can also find them on line, including Powerstream's site with wire gauge current limit chart: http://www.powerstream.com/Wire_Size.htm

If very long distances are necessary, the solution is to wire the array for higher Voltage and use an MPPT type charge controller which can turn that higher Voltage into charge current. Most of these will take 150 max input, but the Midnight Classic has models to 250 VDC and the new Xantrex unit (very expensive) will take up to 600. Note these are the V max limits, used with the array Voc - not operating Voltages.

Seven · August 2011

Re: Back Again With Questions

1.The closer the batteries are to the CC and the panels, the better.

2.If you equipment includes an inverter, yes. It is easier and more cost effective to run 200' of ac line at 120v than it is to run that distance with 17v.

3. Could you build another barn closer?

hotdawg23 · August 2011

Re: Back Again With Questions

Thanks for the answers.
I am beginning to get the idea that it is probably better to put all the equipment in the barn and run the high voltage, from the inverter, to the house.
Building a barn closer to the house was funny idea. Got a good chuckle from that one.

Cariboocoot · August 2011

Re: Back Again With Questions

hotdawg23 wrote: »

Thanks for the answers.
I am beginning to get the idea that it is probably better to put all the equipment in the barn and run the high voltage, from the inverter, to the house.
Building a barn closer to the house was funny idea. Got a good chuckle from that one.

Or you could build another house closer to the barn. Or move the barn. Or move the house.

Making the long run on the highest Voltage section of the system would probably be cheaper, though.

Seven · August 2011

Re: Back Again With Questions

Cariboocoot wrote: »

Or you could build another house closer to the barn.

This^^^^^^^^^^

You could go super efficient that way.

Seriously though, a pole barn would work and they arent that hard or expensive to build. You could build it with the correct roof pitch for your area and flat mount the panels to it.(with the right spacing of course) Slap a gutter on it and you have a good water collection system to boot.

techntrek · August 2011

Re: Back Again With Questions

Or build a small "power hut". I have a minimum 200 foot run, too, and have considered this. Get the PV voltage up and use the Midnight that Cariboo mentioned above, making a run 50-100 feet to a hut, then run the 240 AC the rest of the way. Basically cutting each run before voltage drop becomes an expensive problem to solve. Plus this keeps the equipment out of the house so a fire doesn't wipe it out (and a fire in the house doesn't leave you w/o a power supply to help rebuild it).

If you use the 600 volt unit from Xantrex you could use fairly thin wire and run it all the way home, no hut, but that is a really dangerous voltage.

ggunn · August 2011

Re: Back Again With Questions

techntrek wrote: »

Or build a small "power hut". I have a minimum 200 foot run, too, and have considered this. Get the PV voltage up and use the Midnight that Cariboo mentioned above, making a run 50-100 feet to a hut, then run the 240 AC the rest of the way. Basically cutting each run before voltage drop becomes an expensive problem to solve. Plus this keeps the equipment out of the house so a fire doesn't wipe it out (and a fire in the house doesn't leave you w/o a power supply to help rebuild it).

If you use the 600 volt unit from Xantrex you could use fairly thin wire and run it all the way home, no hut, but that is a really dangerous voltage.

One thing to consider is voltage drop, which actually is voltage rise on the AC side at the inverter, since the voltage at the interconnect will be what it is. Inverters have a voltage range in which they operate, and if the voltage rises to that limit they will shut down. It may be better to take the voltage drop hit on the DC side.

techntrek · August 2011

Re: Back Again With Questions

ggunn wrote: »

One thing to consider is voltage drop, which actually is voltage rise on the AC side at the inverter, since the voltage at the interconnect will be what it is. Inverters have a voltage range in which they operate, and if the voltage rises to that limit they will shut down. It may be better to take the voltage drop hit on the DC side.

That is another reason for shortening the AC run by putting a hut in the middle somewhere, yes.

200 volts DC over 200 feet requires 8 gauge to get the voltage drop below 5% @ 25 amps (roughly 5 kw array).

Spliting this over 50 feet and 150 feet...

200 volts DC over 50 feet theoretically is well below 5% using 14 gauge @ 25 amps, although I think code would require 12 gauge minimum.

240 volts AC over 150 feet requires 10 gauge @ 20.8 amps to get below 5%.

The cost difference between 50 feet of 12 gauge plus 150 feet of 10 gauge vs. 200 feet of 8 gauge probably won't offset the cost of building a hut but it might be close with today's copper prices...

hotdawg23 · August 2011

Re: Back Again With Questions

AAAAH, brings up another question. Speaking of 240 (or 220 as we call it here) volt AC... how does one get that, because all the inverters i looked at so far have been 110V ac( 129Vac). So i assume that one would use 2 inverters to produce 2 legs at 110V ac each (or 120V ac).

Cariboocoot · August 2011

Re: Back Again With Questions

hotdawg23 wrote: »

AAAAH, brings up another question. Speaking of 240 (or 220 as we call it here) volt AC... how does one get that, because all the inverters i looked at so far have been 110V ac( 129Vac). So i assume that one would use 2 inverters to produce 2 legs at 110V ac each (or 120V ac).

Well, no. There are some inverters like Outback that can be stacked that way to make 240 VAC. Never try to stack ones that aren't designed for it. Or you can use an autotransformer like this: http://www.solar-electric.com/x-240.html

But both Xantrex and Magnum make 240 VAC output inverters. A couple (but not the only) examples:
http://www.solar-electric.com/xaxwhyin.html
http://www.solar-electric.com/maenms4040wa1.html

hotdawg23 · August 2011

Re: Back Again With Questions

Ok Cariboo, but i am confused on this cause i understand the grid has the 240V but comes in 2 legs of 120V each.
Sooooo, do these converters, stacked or otherwise produce the 240 as one leg? or two 120V each.?
For example, my a/c s run on 220V but it has 2 legs of 110V each to run. If one were to stick a 220V leg to one of the legs it would most surely fry it?

Cariboocoot · August 2011

Re: Back Again With Questions

It's the 240 VAC with a neutral for split phase 120.

What your A/C probably has is a 220/240 plug with a ground or with a neutral & ground (may use 120 for controls and 240 for the compressor).

Basic NA electrical feed: L1 - N - L2
L1 to L2 is 240, L1 to N is 120, L2 to N is 120
N is also tied to Earth ground

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