Duh! Why not run AC instead of DC?

[danda]

I posted a few weeks ago about a long run (approx 140 ft) from my arrays ( 5500 kw and growing ) to the battery bank and inverter.  I got several good suggestions, one of which was to use aluminum wire.   I did that.... bought 1000 ft of 4/0, plus some adapters to "pigtail" the ends with copper for terminal connections.  So I've got plenty of wire now.  But would need at least 4 strands for 6Kw, and 2 more if I make it to 9kw, etc.

A friend of mine asked a simple question.... why not put the battery and inverters out in the field with the array, and run AC instead?   I got to thinking about it, and I figure that with my two SW4048 in series, I could generate split phase 120/240 near the panels and run standard AC 3 wire ( 2 hots, 1 neutral, plus 1 smaller ground ).  I found an online voltage calculator that says my voltage drop for 220v AC is way less, like 0.4% versus 2.5% for the DC runs.   Plus, I can continue to expand the solar arrays and I don't have to add more wiring for the long run.

So my new plan is to build a little shed out by the panels that will contain the combiner boxes, battery bank, charge controllers,  inverter panel, etc.  And the wiring going to the house looks just like regular AC service entrance, except for the extra equipment ground wire.

I guess the biggest drawback I see is that I won't be able to look at the displays from the inverters, charge controllers and tri-metric inside the house, so usage monitoring could be tough and might lead to unexpected outages.  I'm contemplating running an ethernet cable as well, so perhaps I can do something tricky to send that info along for display on my laptop.  or maybe even via WIFI.

Does anyone see any other drawbacks or problems to this?

Anyone have experience with remotely displaying panel output from a trace SW inverter?

Perhaps this strategy can be helpful to others faced with planning for large arrays situated a distance away from the point of use.

[bob g]

how cold does it get in the winter? and
how hot in the summer months

both of which can dramatically affect battery performance

in some very cold climates it is conceivable that you could run the batteries down, and have them
freeze some very cold night, unless you provide for some heat.

also if the shed is out in bright sun in 110 degree heat, it might well go way over 120 degree's F and that
shortens the life of your cells as well.

just more to consider

bob g

[DanG]

Its my understanding of stacking that it's one or the other, 120 or 240, but not both simultaneously - think load balancing, surges and the general voodoo keeping them synced. I am hoping to have a layout using a 240 grid tie inverter that monitors two matched 120 inverters locked together which kicks in to balance 240 loads - I've seen it drawn out, will try and link the schematic when I find it.

One cheat I've often pondered is going with a european 50hz 220-240VAC inverter or a South Korean non-export 60hz 220-240 inverter for a well pump and/or machinery motors...

[Volvo farmer]

I remotely monitor my Outback inverter, though it is only about 100 feet away. I also have a trimetric  running at that same distance from the batteries. If you are only at 140 ft from the batteries, I think that is definitely within the range of remote monitoring through ethernet, or phone cables.  It is unclear in your post exactly how far away you want to remote monitor this system. It might be a challenge at 1000 ft.

 In my case, I happened to scrounge a whole spool of shielded telephone wire with 12 twisted pairs in it.  I bought a ethernet crimping tool and a handful of ends and wired it up for the inverter and mate. I had enough pairs left over to wire the trimetric as well.  If you are pulling these wires through conduit or burying them, I recommend installing twice as many twisted pairs as you think you need, as you could surely find a need for them later and the wire is cheap.   

Having lived with batteries in an unheated shed for 3 years, I disagree with Bob g that it is a big deal.  However, we are only discharging our batteries  about 15% of their capacity overnight.  I have seen -10F here in the winter and 100F in the summer and have not had any noticeable degradation of the batteries.  Several hundred pounds of lead takes a long time to heat up or cool down so the thermal mass tends to stabilize somewhere in the middle of the diurnal swing.  I'm sure we have some diminished capacity in the winter time as the batteries get down to about 40F in their insulated box, but because of the way we sized our batteries to our loads, we do not notice the decrease in capacity.  Also, the batteries self-heat to some degree when charging.

Lastly, build a little path to your shed as you will certainly be going out there a lot. Even with remote monitoring, I find myself going out there a couple times a week to check things over.

[defed]

my solar panels will be at least 100' from the house.  right now, i only have 700w (175wx4) and need to run them in series pairs (2 sets of 2) to meet the mppt's input requirements.  i can't get 3 in the series due to my potential voltage output in 0F weather.

originally, i was going to combine the 2 sets at the array and run it to the house.  then thought that if i ran the 2 pair individually to the house, then combine them, it would be easier (less amps).  but, my array is nowhere near as big as yours!

i was going to set up a temporary outpost w/ the controller, batteries, etc in an insulated box.  my concern here was the mppt wants to be "indoors"...so just putting a box over it didn't seem good enough.  i was going to fully insulate, shingle and side the box just as a house would be.  this might be over doing it, but i don't want my $500 controller getting trashed.  i would have 2 compartments to keep the batteries away from the electronics.

another thing i was going to do was put a 25w incandescent bulb in there with some sort of thermostat to add some heat, for the batteries and the electronics....i don't think LCD type readouts like the cold.

[alcul8r]

I posted a few weeks ago about a long run (approx 140 ft) from my arrays ( 5500 kw and growing ) to the battery bank and inverter.  I got several good suggestions, one of which was to use aluminum wire.   I did that.... bought 1000 ft of 4/0, plus some adapters to "pigtail" the ends with copper for terminal connections.  So I've got plenty of wire now.  But would need at least 4 strands for 6Kw, and 2 more if I make it to 9kw, etc.

A friend of mine asked a simple question.... why not put the battery and inverters out in the field with the array, and run AC instead?   I got to thinking about it, and I figure that with my two SW4048 in series, I could generate split phase 120/240 near the panels and run standard AC 3 wire ( 2 hots, 1 neutral, plus 1 smaller ground ).  I found an online voltage calculator that says my voltage drop for 220v AC is way less, like 0.4% versus 2.5% for the DC runs.   Plus, I can continue to expand the solar arrays and I don't have to add more wiring for the long run.

You said 5500 KW, but the rest of the note makes it look like 5.5 KW. Are you sure you need that big a wire for this little electricity?

[DanG]

That is not little electricity. Even using the 4/0 (107mm2) at 48VDC there will be the equivalent of six-plus 50-watt solar panel outputs heating that 4/0 cable he bought while the rest of the wattage gets passed through. Wire is cheaper than solar panels and it lasts longer too. To get losses less that 5% would take 350kcmil cable (177mm2) and that would be nosebleed expensive.

[defed]

Are you sure you need that big a wire for this little electricity?

i thought the same thing...in my situation, i have 120', 60Vdc (worst case high air temp), 6 amps....requires #4 copper to stay under 1% loss!!!

http://www.nooutage.com/vdrop.htm

[SparWeb]

A picture of my own setup may be helpful:



That cluster of sheds is 200 feet away from the house.  Rather far to run a DC battery cable!
The wind and solar both feed into the small "cabinet" box that you see under the anemometer.  The batteries are inside it with the charge controller and inverter - a bit too compact but I can live with it.  I have not experienced any visible corrosion on any electronics - the batteries are sealed Lead-acid and I doubt they gas very much at all.  The battery cabinet is insulated though not very well sealed.  The thermal mass of the batteries definitely keeps them at an "average" daily temperature all right.  It has required 3 or more sustained days of -40C outdoors to bring the battery box interior below -30C too.

For heat in the box in winter I put the resistance dump load inside the box.  I know that's crazy, but it works and I keep them in their own steel box + fans and do several other things to prevent problems.  They make a big difference and on windy days the temp difference inside the cabinet can be 20C more than outside.

[Isaiah]

The guy with the used battery's should put a de sulfater on his bank and maybe charge the battery's with a vibrator type charger.( gives a ripple effect in the current)
 we run the De sulfater on all our battery banks.
IF those are automotive battery's have you checked the water level?
A lot of the new maintenance free battery's still can be filled with water.
They have a sticker on the top and you can get a hold of it and peal it off, then you'll see the 6 little plugs.pop them out and check the water level and add if necessary.. The plugs come out hard unless you make a tool similar to my description below.
 I took a 3/8's piece of round stock about 6'' long and drilled a hole  about 3'' from each end then I took a long dry wall screw and welded it in the hole, making it a T handle, a couple of turns and the screw is in the cap enough  to pull it out. works good !
I have one of those cheap battery's that there is no plugs to pull out and we thought it had a cell down and i was about to give up on it when I got the idea we have a 55 gal barrel of rain water.
I put a broom handle through the battery lifting handle and submerged it in the barrel you could see the bubbles coming out of the vents.
If you run your battery down recharge it some how leaving it below its working rate for even 1 day can damage it and shorten its life.
hope this helps someone.