Proposed Solar Install thoughts

[AlbertaNewbie]

Planning my solar install and here is what I'm currently thinking. Need opinions on the pros amd cons of my install.

morningstar tristar 45amp mppt charge controller with remote temp sensor and remote meter
250watt 24V panel (to start, will be going up to 1000w next year)
8ga wire from panel to roof mounted combiner box approx 5 feet
6ga wire from combiner to charge controller 6 feet
6ga from controller to batts with 45 amp breaker 6 feet

thoughts? anything you would change?

[Redsky]

The wiring you proposed is fine for the panel to C-box and C-box to charge controller. At 24v output 8ga is all that is needed.

Too often people spec for 99% efficiency with wire sizing and it is overkill that accomplishes nothing. At 12 VDC and a 20' run the voltage drop with 2ga is 0.53% and going to 6ga it is 1.36% - not much difference between a 14.5 VDC charge dropping to 14.49 volts with the thicker cable versus a drop to 14.3 volts.

For the large gauge wire and connectors I found delcity.com to be a great source for my setup.

[mena661]

pianotuna wrote:
Hi 6 x 6 = 36 volts.

If you stick to 12 volts with 6 six volt there is only one way to wire them to be balanced. See method #3 here: correctly interconnecting multiple twelve volt batteries

Thanks PT. Totally missed the battery bank type in his post. IMO, if you haven't purchased the batteries yet, I might go with 12V for less voltage drop under heavy loads (ie the A/C) although 6 6V's will work well too. That said, don't skimp on the wires. I would not go less than 2/0 for the interconnects and 4/0 for the inverter wires. If your inverter manufacturer says go bigger then go bigger. Keep the inverter to battery run short (under 6ft). If you need to go a long way from inverter to batteries, double up some 2/0 to a bus bar near the batts then go 4/0 from there.

[pianotuna]

Hi 6 x 6 = 36 volts.

If you stick to 12 volts with 6 six volt there is only one way to wire them to be balanced. See method #3 here: correctly interconnecting multiple twelve volt batteries

[mena661]

Smk, he's got room for 8 250W panels so 2000W max. You can shrink the wire size quite a bit by going 48V on the battery bank. That way it gives you a few more options to where you can mount the inverter. How long do you plan to run the A/C?

[time2roll]

Run the air conditioner? 1000w solar might be a little light.

Consider going to a 48v battery and Morningstar MS-600-MPPT and a few more panels all in series.
DC/DC converter to supply 12v and go with a 48v inverter for that kind of power.

[TechWriter]

KD4UPL wrote:
So, for a rough idea, ignoring losses, divide 1000w by 12v to get 83 amps possible controller output.
I would recommend an Outback FM80 charge controller. It will handle 80 amps which likely won't be exceeded after you factor in losses and weather realities.

Better yet, go with a MidNite Solar Classic which is rated at 96 amps.

[KD4UPL]

AlbertaNewbie wrote:
I have room for 8 250 w panels, measured, templates laid out and cad drawing completed. maybe my calcs are wrong, but 1000w/37v=27amps x 2 for a 12v system= 54 amps, derate for efficiency losses and flat mounted panels by apprx 15-20% =43-45amps (agreed too much, will drop to 3 panels or run a second controller.)

battery bank will be 6x6v trojans wired in series/parallel for a 12v system with 00 wire between. 3000w inverter is planned to be added to be able to power mobile office and 13.5 ac as needed during the day

Good job on the panel layout.
Your electrical math is wrong. I don't know where you got 37 volts from, Voc I guess. That's irrelevant. The amp rating of a controller is it's output amp rating which will be at battery voltage. So, for a rough idea, ignoring losses, divide 1000w by 12v to get 83 amps possible controller output.
I would recommend an Outback FM80 charge controller. It will handle 80 amps which likely won't be exceeded after you factor in losses and weather realities.
For an inverter around 3,000 watts I would look at an Outback VFX2812 to match that charge controller. You can control and monitor both of them with a Mate2 mounted in the wall. Outback also makes a battery gauge they call the FlexNetDC.

[BFL13]

Your expected amps would be too low if you are anywhere down South.

I got 7.2amps noon flat with 130w at 49.3N in May and it is all proportional so you just do 1000/130 x 7.2 = 55a flat. I would tilt them up facing South to get proper amps at noon. In fact I build contraptions so I get full amps more of the day than just at noon. Anyway, you need to do some more figuring.

You can do proportional to 130 for the flat, tilted, 'tracking' I got here. MPPT is about the same as PWM maybe a tad more hardly notice despite the hype, so you can rely on this for ball park.

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/26065604.cfm

[AlbertaNewbie]

I have room for 8 250 w panels, measured, templates laid out and cad drawing completed. maybe my calcs are wrong, but 1000w/37v=27amps x 2 for a 12v system= 54 amps, derate for efficiency losses and flat mounted panels by apprx 15-20% =43-45amps (agreed too much, will drop to 3 panels or run a second controller.)

battery bank will be 6x6v trojans wired in series/parallel for a 12v system with 00 wire between. 3000w inverter is planned to be added to be able to power mobile office and 13.5 ac as needed during the day

[marcindy]

I agree with smkettner on the cardboard templates. I planned for months on my solar, and when I went to mount my 2 panels on the roof, the mounting holes where on the wrong side of the panel from where I had planned. Luckily for me it worked out, but was very close to not fitting on my roof

Marc

[EsoxLucius]

Before I comment further could you please tell us what your battery bank will be and if you will be employing an inverter? Battery make and model, how many, and how wired?

[pianotuna]

Hi,

The Tristar MPPT 60 amp is more fully featured and more efficient.

Are you sure about MPPT?

1000/12v = 83 amps--so you really need to consider a different controller. Midnight solar makes a larger one.

Or

Convert to a 24 volt battery bank.

[Shadow_Catcher]

You need to add a battery(s) monitor to the shopping list you may find you need less power than you think. As pointed out you may be limited as to how many panels you have room for.
http://www.bogartengineering.com or http://www.victronenergy.com/battery-monitors

Part of this equation is energy conservation and measures i.e. LED lights may reduce need. When boondocking we use propane to make coffee, cook...
I have two Morningstar Sunsaver MPPT controllers fed by high voltage panels one a flexible roll it out in the sun on a cord and a 185 66 cell on the roof. What I found was that the single panel works well enough that I do not need the other.
One other resource http://handybobsolar.wordpress.com

[time2roll]

Have you measured space needed for 250w panels?

Cut out a cardboard (or 4) and place them on the roof and see what fits. You need to be 12" to 18"+ from tall items like air-conditioner and open vents. Need 4" to 10" from low items such as closed vents and retracted antenna. Or will this be portable?

45w controller is good for about 700w and even that is above MS recommendations. Unless you will have a large 24v battery....

1 panel just get #10 MC4 wire and pull direct to controller.
2 or 3 panels connect in series and do the same. Amps do not increase in series. Bypass diodes minimize effects of shading.
4 panels is too high of voltage in series so you are stuck with parallel and a combiner box etc. You could go series/parallel if you think shade issues will be minimal. Then you would be back to plug and play with MC4 connectors. Can get #8 with MC4 to carry the 16 amps.

With 1000w are you planning 500+ amp hours of battery? Usually 1 to 2 watts of solar per battery amp hour is way plenty.

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