Bus conversion PV

Iceni John

I've been reading these forums for a while and have learned a lot - this is my first post here.

I'm converting a 40-foot Crown bus to a self-contained motor home that I (and my GF, I hope) can potentially full-time in, and it's being set up for extended off-grid boondocking. I recently bought eight Sharp 255W panels, and my intention is to be 100% self-sufficient from solar electric power - I do also have a small 3500W generator that I've converted to run off propane, but it will be for emergencies only.

Along the center of the roof between the two roof hatches will be a 26'-long walkway of 12"-wide diamond-plate aluminum that will be 3" above the roof. Onto each side of this walkway will be the hinged support frames for four panels, allowing one side or the other of panels to be raised up to 50 degrees from horizontal. When stowed, all the panels will lay down against the curved roof at about 20 degrees below horizontal. This way, I can have half my panels raised up to face the sun directly (assuming I've parked pointing east or west), and the other half will be tilted 20 degrees - it's not quite as good as having all my panels fully raise up, but it's way better than most RV setups where they're usually flat on the roof and even partially shaded by roof warts or poo pipes. None of my panels will ever be shaded by anything on the roof. There will also be two water outlets on the roof to make washing down the panels easy - no lugging buckets of water or dragging hoses up to the roof for me! One incidental benefit to shading almost the entire roof will be much cooler interior temperatures.

Each bank of four panels will feed through its own 11'-long 4AWG welding cable to a marine breaker that feeds a Morningstar MPPT 60A charge controller, then each CC will feed four golfcart batteries in series and parallel. This way there will be essentially two separate systems, so if one CC or bank of panels or batteries goes down I will still have half my power. The house power system for the bus is 12V, so I've decided to use each bank of four panels in parallel. By my calculations I think I'm on the right track, but please feel free to tell me if I'm way off course! Each bank of panels is 1020W, so derating at 0.77 gives each charge controller about 785W, within its stated 800W maximum input. 785W charging at 14.7V is about 53A, within each CC's 60A rating. Four golfcart batteries in series/parallel are about 450Ah, so 53A should charge them well. Each panel is rated at 38.6V Voc, 9.0A Isc, 30.2V Vpmax and 8.45A Ipmax. I will use as many 12V lights and appliances as possible, and I'll use a chest fridger with its own inverter.

I've just finished stripping all the old paint of the roof, using a 1.5" putty knife and a hot air gun (no fun!) - with my bus parked in an RV yard I couldn't strip it any other way, but at least I got a good tan doing it. Next month I'll completely repaint the entire roof, using Hy-Tech ceramic additive mixed into the top coats for some additional heat insulation. When the roof's painted I can then start making the walkway and the panels' support frames. The cables and PEX water lines will run inside the roof ribs, and they'll all terminate at waterproof outlet boxes on top of the roof under the walkway. The charge controllers and inverters etc will be mounted on swing-out supports for easy access in the under-floor luggage bay, and next to it but separated by a steel bulkhead will be the batteries in their own vented compartment; the batteries will be literally just inches from the CCs and inverters, so no voltage losses there!

After a few years of hard work putting in the water tanks, waste tanks, plumbing and pumps, propane, and relocating the start batteries (which will also get their own small MPPT charger) and doing a multitude of other grunt jobs, it's good to be finally doing something with a foreseeable payoff. I've wanted to convert a bus for many years, so finally my dream is coming to fruition.

Per ardua ad astra,
John

zoneblue

Re: Bus conversion PV

Sounds like a lot of fun. Put us up some pics?

BB.

Re: Bus conversion PV

You need to make sure that the welding cables are in conduit/wrapped to protect them from the Ultra Violet of the sun--Otherwise, the insulation could be compromised in a few months ot a year of sunlight.

Also, if the size of the cabling is an issue, you can always think about placing two panels in series, then the two strings in parallel... That will dramatically reduce your cable diameter (AWG) requirements.

-Bill

tons001

Re: Bus conversion PV

I agree with zoneblue ... pics of the whole project would be cool to see.

Iceni John

Re: Bus conversion PV

Because four panels' combined maximum current is only 36A, an 11' run of 4AWG welding cable should not cause any significant voltage loss to each charge controller. From the batteries to the inverters and DC distribution panel I will use some heavy 4/0 welding cable I had left over from when I relocated my starting batteries. The 4AWG welding cables down from the roof to the CCs, and their corresponding THHN cables for the negative feeds, will be entirely protected inside the hollow roof ribs and behind some windows I've blanked over, so no possibilty of UV touching them. Each panel's extension cable to the roof-mounted outlet boxes will be UV-resistant 12AWG cable inside conduit. All these cables and the boxes will be under the walkway, well protected from sun.

I only want to do this job once, so I'll do it as best as I can now. Mounting anything on a moving vehicle always means that you have to pay attention to every last detail. The walkway and panels' support frames will be 6061-T6, and all hinges and fasteners will be stainless. When it's all done and running, I want it to look like it could have come from the factory that way - nothing will be less than the original build quality, and Crown made the best buses in their day.

When I have something to show for my efforts I'll try to post some pictures, but I'm "photographically challenged", i.e. my pictures usually aren't worth a thousand words . . . I'll try anyway!

Thanks, John

BB.

Re: Bus conversion PV

If you are working with stainless bolts and nuts, many stainless alloys "gall" very easily... Just a bit more than finger pressure (light wrenching) and the stainless to stainless threads can gall and lock up.

Get some anti-seize compound from an auto-parts store and put it on the threads before running the hardware together (or use brass/bronze nuts, etc.).

-Bill

Iceni John

Re: Bus conversion PV

BB. wrote: »

If you are working with stainless bolts and nuts, many stainless alloys "gall" very easily... Just a bit more than finger pressure (light wrenching) and the stainless to stainless threads can gall and lock up.

Get some anti-seize compound from an auto-parts store and put it on the threads before running the hardware together (or use brass/bronze nuts, etc.).

-Bill

Yup, after working on bicycles all my life I know that! I'm one of the dying breed of mechanics who always lubricate threads as a matter of course, with oil, grease, PTFE tape, anti-seize or Copaslip - there's very few threads I deliberately keep dry. A combination of stainless Nylok nuts with lubed threads is absolutely secure, yet makes disassembly easy even after many years down the road.

John

boonhauler

Re: Bus conversion PV

Any update on this project, I'd love to see what this thing looks like!

unyalli

Re: Bus conversion PV

boonhauler wrote: »

Any update on this project, I'd love to see what this thing looks like!

X2 me too love to see projects like this.