The Sprinter originally had a nominal 12 volt 135 watt panel that was the largest panel that could be shipped with UPS. The major load in the Sprinter was the refrigerator which used 40 watts when it was running. The house battery was a 255 amp-hr AGM. What I found out was in clear weather the 135 watt panel produced about same amount of power that the refrigerator used. It could not catch up with grey days. A year before I sold the Sprinter I replaced the 135 watt panel with a 205 watt higher voltage panel. That change eliminated the need for any charging other than the solar panel. I still had a backup capability from by second vehicle powered inverter that could produce "shore power" for charging while driving. The last year of Sprinter ownership I never charged with shore power. I did cheat at times by turning on the vehicle powered inverter while driving. That caused the refrigerator to automatically switch to 120 volt AC power instead of 12 volt DC house battery power. Then all the solar power generated could be used for house battery charging instead of part to run the refrigerator and part for charging. Did not want multiple panels with a combiner box and lots of wiring on the roof and the required support structure. Installed just one panel with four feet bolted to the roof. The Transit will have a couple of improvements. I purchased the same physical size panel as the Sprinter 205 watt panel but it is rated at 300 watts. I also changed the vehicle powered inverter from a 600 watt to a 1000 watt inverter. The vehicle powered inverter will provide enough power for the backup charging to charge at the full maximum 50 amps that the Magnum house inverter is rated at. Had to limit the charging amps to 30 amps with the 600 watt Sprinter inverter. I also wanted the larger vehicle inverter so I could reduce my shower water heating time and be able to add a built in 750 watt baseboard electric air heater.
Will use the same Morningstar SunSaver MPPT 15 amp solar controller that I had in the Sprinter. It may be possible that I might not be able to harvest all the panel power with this controller. A good assumption is the panel will never produce more than 75% of its rated output due to incorrect orientation to the sun and high temperature. So maximum is probably about 225 watts or about 7 amps from the 32 volt panel. The purpose of a MPPT charger is to convert the 32 volt panel's amperage to more amperage at the battery charging voltage. For discussion purposes we will assume a charging voltage of 13 volts. The MPPT does not create power but it does change the panel high voltage and low amperage to low voltage and high amperage for charging. Watts in must match watts out. The 7 amps @ 32 volts is changed to 17 amps @ 13 volts. The maximum output of the Morningstar is 15 amps so I could lose a small amount of power around noon in ideal conditions. Doubt that will actually happen. I do know that I do not need more than 15 amps to cover my elecrical usage.
The 300 watt solar panel is a LG Momo X Neon and is 64.57 inches long x 39.37 inches wide. Selected for the high wattage for that size panel and because the aluminum extrusion frame is a tube. Did not fabricate any additional support frame. Added four 6" long 1 1/2" x 3/16" angles to the existing panel mounting holes. The angles gave me a vertical leg with two holes. Then bolted 6" long 14 ga. formed stainless angles to the aluminum angles. The stainless angles had a slightly more than 90 degree bend so the bottom leg of the angle matched the Transit roof angle. One 11/32" mounting hole in each SS angle for a through the roof bolt. Did not want to use the existing Transit tapped holes because that would require additional supports and the additional supports would be closer to the edge of the roof. Want to be as stealth as possible. The Transit roof is not rigid. I added four 1 1/4" x 2" stiffeners glued to the underside of the roof at each mounting bolt. The stiffeners span the gap between the Transit roof ribs. The bottom of the panel extrusion is about 1" above the roof on the van centerline.
The LG panel has two MC4 connectors on the positive and negative leads. Wanted to retain these connectors for easy disconnect so punched two 7/8" diameter holes in the roof above my electrical panel location and under the panel. Did not want the connections visible so could not use the existing plugged Transit roof holes. Used two 90 degree aluminum cord bulkhead fitting for the roof penetration. McMaster-Carr part # 8317-K2 Aluminum. Bought a 15' MC4 extention cord and cut it in two to feed t hrough the bulkhead fittings.
Solar panel wiring is simple. The solar positive 10 ga. wire terminates at a 15 amp Blue Sea circuit breaker. From the breaker a 10 ga. wire is connected to the solar panel positive terminal on the Morningstar controller. The 10 ga. negative c able is connected to the solar panel negative terminal on the controller. From the solar controller the positive output 8 ga. wire is connected to a 20 amp Blue Sea circuit breaker. From the 20 amp circuit breaker the 8 ga. wire terminates at the 12 volt house system positive bus. The solar controller negative terminal is connected with 8 gage wire to the 12 volt house system negative bus. The circuit breakers are used to allow the power from the solar panel and or the controller to be disconnected. The panel is wired so the output passes through the Magnum shunt.
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The installation was not difficult. The following procedure was followed:
1. Built a scaffold on a pickup bed to get a platform to work from.
2. Bolted the eight angles to the panel and added a 1/8" x 1" aluminum flat under the panel using two of the angle mounting bolts. Tie wrapped the two panel cables to the aluminum flat to get them to the side of the panel and then put the wires into water pipe insulation which is tucked into the panel aluminum extrusion.
3. Glued four 1 1/4" x 2" wood stiffeners under roof between the roof ribs where the panel mounting holes would come through the roof. Two were 19 1/2" long and two were 32 3/4" long. The Transit roof would sag with the panel weight without the stiffeners.
4. Put a blanket on the roof and set two of the panel legs on the blanket. Slid blanket and panel on the roof into correct location. Removed blanket and added four rags under the feet to keep from scratching the paint. Moved panel to final location and drilled through one mounting hole through the roof and the wood stiffener glued under the roof. Temporarily bolted that leg. Checked alignment and then drilled the second roof hole on that side and installed a bolt. Went to other side of van and drilled the other two holes through the panel foot holes.
5. Loosened the 4 bolts that bolt the two angles together on one side so I could lift the other side of panel.
6. Removed the four angle to angle bolts the other side and blocked up the panel on that side. Put mastic under the SS angles on that side and sealed the edges and the bolt head with Dicor 501LSW sealant. Used same method of sealing the angles as I had used installing the roof vent.
7. Lowered panel after adding sealant and reinstalled the four angle to angle bolts loose.
8. Repeated the procedure on the other side.
9. When panel was blocked up on the cable roof penetration side, the two MC4 wires where fed through the roof bulkhead fittings. Both the wire openings and the fitting bases were sealed with the Dicor sealant.
9. Lowered the panel and tightened all eight angle to angle bolts.
10. When connecting the wiring insde the van a blanket was put over the panel to eliminate power production.