PV panels' cable question

[harleyman_1000]

 Hey John when your done can I bring my bus by for you to start on?

[Ralph7]

         Rather than golf cart batteries look at L16 batts , same foot print as golf cart just taller, but higher usable amps.
        Check them out.

[Iceni John]

I don't know how your banks are configured but I would configure them so I had each 12 volt series separately cabled down to the controller and parallel them at that
point on a large bus bar.  Smaller wiring and easier to drop a leg if you a cell.  Just a thought but keep us updated I can see this in my future. About how big is a 1,000 watt panel? 

That's an idea worth some shower-time.   (I do my best thinking in the shower.)
The 240W panels I'm interested in are about 3ft x 5ft-something.   They'll be hinged to either side of a walkway running along the center of my roof from one roof hatch to the other  -  there's 26ft of clear space between them, enough for four panels hinged on their long sides.   This way half my panels can be tilted up to face the sun, and the other half will lay down about 15 degrees below level against the curved roof.   Obviously this isn't quite as good as having all the panels tilt up, but it's a reasonable compromise.   Either side can tilt up depending where the sun is.   The walkway will be 12"-wide diamond-plate aluminum anchored substantially to the roof ribs that are only 19" apart (school buses are stout, and Crowns especially!)   To make washing down the panels easier, I'll put two quick-connect water outlets on the roof, then I can just plug in a washdown brush and easily clean bird poop etc off the panels without needing to lug heavy buckets of water or hoses up to the roof.   Whatever space I have left over on the roof will have some simple homemade water heating panels, probably something along the lines of coiled black pipe in a glass-topped shallow box, and the recirculation pump for this will run off the PV  -  free hot water in the summer!

My plan is for a bus that will comfortably support one person for at least a month, or two people for at least a fortnight, entirely off-the-grid and not using a generator  -  that's taking showers every night and living comfortably.   Water will be the limiting factor, but I've got 220 gallons of fresh and a BIG poo tank.

John 

[Iceni John]

        Rather than golf cart batteries look at L16 batts , same foot print as golf cart just taller, but higher usable amps.
       Check them out.

The only reason I'm thinking of plain-Jane golfcart batteries is that they're available everywhere and are reasonably cheap.   With constant recharging ability, plus not discharging them more than 25 to 30%, I should get a long life from them.   If one goes bad, a replacement pair is available almost anywhere.

My pull-out battery trays are 13.5" wide and 30" deep, each big enough for four golfcart, L16 or Group 31 batteries.   I'm hoping my modest intended power consumption will allow me to use golfcart batteries, but if I need more power I can use L16s.   We'll see.

I'm going to make a place for several bottles of distilled water next to the batteries, then rewatering them will be simple and quick.   I'll have a gravity-fed tube to bring water to each battery as needed  -  easy!

John    

[technomadia]

John -

2000W of solar on a bus will be awesome - I look forward to hearing about your project as it comes together.

The one quick bit of advice - wire your panels in series, and increase the voltage dramatically running down the wire.  No need to target 12V - this is going to hurt your efficiency a lot.

My top pick charge controller is MorningStar Tristar MPPT - it can handle 150V input with a 12V battery bank output.  Here is more detail:
http://www.morningstarcorp.com/en/tristar%20mppt

With higher solar array voltage, you can get away with 4 gauge or 8 gauge wiring to the roof - a lot cheaper and easier to work with.

Cheers!

   - Chris

[Ralph7]

           Yes the Morningstar MPPT will handle 150Volts , But I was informed by Northern wind n Sun , you loose efficiency in the controller if above 70Volts through heat loss due to the controller dropping the Volts to battery volts.
          Also on another forum one person had series panels and their friend had parallel , on the parallel units, a power line shadow over just one panel caused a large loss in volt/amp output.     

[harleyman_1000]

 First I need to say I know nothing at all about solar, but isn't there technical information on which is the proper way to install it?  I am wanting to install it on what I hope to be my first bus next month.

[bobofthenorth]

Take Chris's advice.  If the panels are identical wire them in series to an MPPT controller.

[technomadia]

           Yes the Morningstar MPPT will handle 150Volts , But I was informed by Northern wind n Sun , you loose efficiency in the controller if above 70Volts through heat loss due to the controller dropping the Volts to battery volts.

Good point - I have heard the same.  70V is probably the practical max when dropping down to a 12V battery bank.  It still gives you a ton of headroom versus trying to set up a 12V solar array.

          Also on another forum one person had series panels and their friend had parallel , on the parallel units, a power line shadow over just one panel caused a large loss in volt/amp output.     

This is a great and VERY important point.  Most solar panels drop off to producing very little power if even a small part of the panel is even slightly shaded. Power lines, AC shrouds, antennas - these all can cut your power output down dramatically even on a sunny day.

When wired in parallel - one partially shaded panel can pull down all the others.  When wired in series, this is not an issue.

Cheers,

  - Chris

[Iceni John]

I hadn't considered wiring each bank of four panels in series, but that would solve the issues of shading and of needing heavy feed cables.   With 2 ga cables close to $5 a foot I'm all for running lighter cables, providing the panels' combined voltage isn't too much for the controllers.   I'll have to research this further.   Sounds good to me.

Thanks for everyone's good advice,
John

[Ralph7]

   Boy did I get it WRONG, SERIES is where there is a big drop in volts is!!!!! 
Chris ,, I did not reread my post, my wrong,  the series performed a little less.   
   Yes on parallel panels you drop amps on that shaded unit.

[belfert]

$5 a foot is steep for 2 AWG.  Try GenuineDealz.com or WaytekWire.com  GenuineDealz is $3.25 a foot with free shipping and a bit less if you want 100 feet.  Waytek Wire will probably be less, but they will have a minimum perhaps as high as 100 feet.

[technomadia]

   Boy did I get it WRONG, SERIES is where there is a big drop in volts is!!!!! 

Indeed with series wiring there is a big drop in voltage when a panel is shaded, but as long as the panel array is still putting out a higher voltage than the battery bank, the MPPT controller handles it.

If your 70V array drops to 60V in partial shade, no big deal with MPPT.

   - Chris

[Iceni John]

Ok, so series is not such a good idea?!   If one of four panels is shaded, the net voltage is reduced by 25%, but the net amperage is still the same?   For four parallel panels, if one panel is shaded the net voltage is still the same but the net amperage is down by 25%?   Am I right here?   If so, which is better  -  having a MPPT controller get 25% less voltage or 25% less amps?   Either way, isn't the total wattage reduced by 25% whether from reduced volts or from reduced amps?   Less power is less power, regardless of what causes it. and that's less power getting into the batteries.   Am I on track with this?

Who here has panels wired in series, and who has panels in parallel?   Let's hear some real-world experience from you folk.   I'm all ears.

Thanks, John

[Tony LEE]

A single power line isn't likely to cause problems with shading because the umbra part of the shadow won't reach down that far unless the line is very close to the panel. Also modern panels have bypass diodes across each cell or group of cells and so are greatly less susceptible to shadowing than older ones. I recently bought a 200W panel and was testing available short circuit current and found that my whole arm shadow made almost no difference to the output. Obviously I wasn't checking available power, but the effect was markedly less than it was on similar panels bought a few years ago.