Solar panel setup questions.

[M_a_t_t]

I drive a 95 astro van and am looking into getting a solar setup for the roof of my van. I'm not really intending to get mpg, though that would be a plus. It would be my first solar/ battery project so I figured I would run it by some more experienced people. The roof rack is 68x44.5 inside dimensions.
Solar Panel(s) Considerations
2 100 watt plus solar controller (add an extra one)
265 watt 65x40
Battery
120 ah marine battery walmart brand.
1. Mount solar panels to roof using roof rack as base.
2. Run wiring through 3rd brake light housing to the inside of the van to the solar controller (included with kit)
3. connect charger to battery(ies)
Q1: I'm considering trying to do a dual setup on the batteries so I can discharge one then switch and use the other while charging the other one. How hard would this be? Is it as easy as switch batteries or am I missing something?
Q2:does the controller in the 2x 100watt kit charge the battery(ies) or do I need a seperate charger?
Q3: I wouldn't leave my starting battery in place and connect to one of the batteries in back, alternator in place. That would be fine correct?
Q4: I would like to make an aero cap sort of thing for the roof of the van to hopefully decrease the drag I would get from the panels. I was thinking I would attempt building it like changzuki did his body for the centurion. keeping in mind the teardrop shape should I just go for a flat top or make it an angled top? Would it be worth trying to angle the panel(s) (I understand for max power I would have to try and park facing with them facing the sun) and top or not worth the effort?
Q5: Lead acid batteries need venting for while they are charging correct? What type doesn't need venting?
Q6: The reviews for the ebay solar panel are all positive, I would rather go with ebay ones because of cost. Has anyone had any problems with ebay solar panels? (maybe not necessarily the ones I linked)

I haven't bought anything yet, so any suggestions would be appreciated. I am on a slightly tight budget, tho I can just wait for more money if its worth buying more expensive.
Thanks, Matt.

[elhigh]

A1: There are battery isolators that will allow you to place one battery on a circuit separate from your backup power while still being in the charging loop. It's usually intended to protect an RV's starting battery while allowing the RV's charging system to top up household batteries, but I think it could work in this application.

It's not hard at all to find a switch that would allow you to treat the batteries as equals, A or B. Simply put the charging circuit on the batts in parallel so they charge equally but run them individually to the A and B sides of the load switch.

NOTE: Tying the batteries together in parallel would actually run your household loads (slightly) more than twice as long as running each individually.

A2: According to the owner's manual for the charge controller, it is a charger for the batteries. Why they insist on calling it a charge controller is a bit beyond me but if I had to guess I'd say it's because it's a bit more than just a charger.

A3: Like for A1. There are isolators that will allow you to keep your starting battery in the charging circuit along with your household batts, while keeping the starting battery isolated from household loads. It would be kept aside for vehicle purposes only. Or you can have it off on its own circuit and ne'er the twain do meet. Your call.

A4: Totally your call. Adding a cap means adding area, so if you are really careful at your design and build you could wind up with a net zero. It would give you the opportunity to carefully fair in your solar panels so it has its merits. Parking with an eye toward sun orientation will yield results but again, your call. Sometimes you just have to park inside the lines.

A5: My understanding is the Lithium-Ion batts don't need venting except in the case of catastrophic failure. That catastrophic failure mode can be VERY catastrophic, flames and whatnot, so it's not a trivial concern. You could consider a battery bank built up of salvaged 18650 (laptop) cells and have a significant amount of power storage in addition to an extremely flexible form factor. Something like that could be built into tucked-away packs that lived under the van where venting into the passenger space was no longer a concern.

A6: Windy Nation has a great rating, I wouldn't hesitate to trust a company with a rating that good.

[freebeard]

I haven't bought anything yet, so any suggestions would be appreciated. I am on a slightly tight budget, tho I can just wait for more money if its worth buying more expensive.

If you wait supply of these will be exhuasted:

EVTV Motor Verks Store: Flexible Solar Panel 140w, Solar, Boat and Golf, 140wsolarpanel

42x32", 140watt, $285

A 140 WATT SOLAR PANEL UNLIKE ANY YOU'VE SEEN

GET EM WHILE YOU CAN. These are the last available. The U.S. has imposed a 250% IMPORT TARIFF on these panels. These are the last we have in stock and when they are gone, we won't be buying more. YOU CAN SAVE AMERICAN JOBS simply by making things four times more expensive.


This lightweight, high efficiency solar panel is unusually well suited to electric boats, aircraft, RVs and electric vehicles.

Here's why:

LIGHT WEIGHT at just 2.68 kilograms - 5.9 pounds each.

VERY THIN - just 3 mm (0.118 inches) thick and built on a very durable flexible acrylic sheet. This means you can mount it on curved surfaces with minimal wind resistance. No frames. No glass. Laminated acrylic.

VERY HIGH EFFICIENCY This panel is made for EVTV in China using a special laminate. But the individual cells are made in the U.S. by SUNPOWER using their MAXEON back connect technology for efficiencies up to 24%.

GET EM WHILE YOU CAN. These are the last available. The U.S. has imposed a 250% IMPORT TARIFF on these panels. These are the last we have in stock and when they are gone, we won't be buying more. YOU CAN SAVE AMERICAN JOBS simply by making things four times more expensive.

What this means is that you can put solar panels in places impractical before. The lightweight, thin, flexible panels can be attached to RV roofs, boat decks, canopies, and places where the usual 45 lb stiff framed glass panels would simply be absurd.

As to the mounting, I hope you park outdoors? Flat, 3mm thick and curved to fit the roof would be best. The gains in efficiency don't justify gimbal mounting. OTOH if the panels lay on the roof under the rack, you could have hinged reflective panels on the side or end rails to catch the sunrises and sunsets.

When I got the battery isolator elhigh mentioned, it was called a latching relay.

[ChopStix]

I would choose an SLA battery type over the regular lead acid you have linked. Those tend to boil out if there's a problem with your charge controller. Where as the sealed type (SLA) better contain their guts if one fails.

[freebeard]

Yes, that too. Lead-acid is cheap and heavy. Cheap is Okay but heavy isn't.

[oil pan 4]

Solar 12v assist - EcoModder

[M_a_t_t]

I do park outside, everywhere I go.
I think I'm going to pass on the flex panels. It would have been almost $600 for those flex panels. It's a good deal but I'm not planning on needing the flex and I don't want to pay an extra $380 for a feature I may not use (even though I'll lose 80 watts )

Home depot has the 100 watt panels on sale for 109 each, and they have a 25 year warranty. They weigh more than 3x more (12 vs. 40) but considering the van is already 4,000 lbs. I'm not worried.

The 18650 cells, do you mean salvaged like literally taken from batteries, or buy new ones? Would you be that confident in using the used ones?

If I used the laptop cells I would need a different charger because of the li-ion right?

[freebeard]

It sounds like the panel[s] you choose would be a good fit within the roof rack frame. If you put quarter-round strips down the side, a bull-nose strip across the front and a partial boat-tail across the back you'd have the aerodynamic blister you want.

18650 is a cell form factor. They are used in laptop batteries a half-dozen at a time and in the Tesla using thousands in a pack that takes a forklift to move. Tesla cells have an extra thermal vent or something.

https://www.youtube.com/watch?v=gLUv0Qu0zMw

[Stubby79]

I may have missed it, but what are you going to be doing with the power you store up?

[Ryland]

Used Chevy Volt cells are cheap, cheaper then lead acid, but a pack will tend to be a higher voltage, a DC to DC converter is a good option if you need 12v, the higher voltage can save you money on wire by letting you use smaller size.

The sun is never straight above, in the winter you'll get more sun if the panels are on the side of the van.