Solar sizing in the all electric class B's

[booster]

Testing the solar today, and having been reading about Davyyd's new rig, along with all the other information in that discussion, got me back to the amount of solar that one might need.

We have 200 watts, and AMsolar told me that we would get about 80AH per day in good sun. I think that is reasonable, but what I saw today would indicate that would be very near maxed out, and it would go down quickly from there. They said 40AH in lower sun conditions, but I think it could go under that in a shady site or rainy day. We use 17-45 AH for the compressor frig, and maybe 20-25AH more. So 40-65 per day, which would be OK in good sun, but we could be in a deficit in the shade. It is what we expected when we started, and are looking to extend our time, not necessarily to forever, but adding a few days.

The bigger frigs, with freezers, like they use in CS, and I assume the other higher end rigs, will use closer to 50-100AH per day, I would think, so the 245 watts of solar they use is barely going to cover the frig. Throw in a couple of microwave or induction cooktop runs, entertainment off the inverter, and you could pull the batteries down, without enough solar to bring them back full. How fast, who knows, and 400AH of batteries will get you a ways, but if you try to stay at 50%, 200AH could be only 3-4 days. You would pretty much have to run the engine generator or get shore power on a regular basis. 245 watts is also going to be pretty low amperage at maybe 15 amps max for charging 400AH of battery to full as it would be only 4% of capacity.

It would seem like if these rigs are really going to be suited to off grid prolonged camping, they should have 400-600 watts of solar. That way they would have enough to keep up even in less than stellar conditions. That much solar will also allow them to hold up the voltage high enough to get the batteries to full when conditions are good, which is much better than short cycling them.

As Davyyd has said, he doesn't like running a generator, or the van engine for longer periods, which would be required to recover batteries, and we certainly think the same way. Beyond that, you either have to drive or have shore power if you need to top off the batteries. Unless you have enough solar.

It will be interesting to see how it all shakes out over time. I know the expedition and off road type campers usually have as much solar as they can stuff on them, and many stay with the 3 way frig to save what is probably the largest use of power. It may turn out the off grid push is more of a sales thing than something that will actually be done by a lot of folks. In that case, it may be no issue of all to have smaller solar systems.

[gerrym51]

sportsmobiles solar page



http://www.sportsmobile.com/5_sys_solar.html


solar panels are only charging if you are not moving. otherwise your alternator is doing the charging.

solar panels are not charging very much if shaded. who does not park in shade if possible.

methinks solar panels work but not as well as some think-how much energy you actually get from them make the probably overated. solar panels make sense for non-movable house-5th wheels-trailers that plant themselves for a period of time. class b's? unless your going to sit and and rarely move-most with b's don't tow another vehicle-they use the b.

my 2 cents

[avanti]

Originally Posted by gerrym51

methinks solar panels work but not as well as some think-how much energy you actually get from them make the probably overated.

The best argument for a having a solar panel is that they keep the battery charged and healthy when the vehicle is in storage. Even a small panel will accomplish this, and it contributes a lot to battery lifetime. Beyond that, you are correct--making a significant contribution to duration of dry camping is often a stretch.

In our case (and, I suspect, most B-van owners), we rarely spend two nights without some driving in-between. Even when we spend multiple nights at the same campsite, we tend toward sightseeing trips and/or dinners out.

[gerrym51]

Originally Posted by avanti

The best argument for a having a solar panel is that they keep the battery charged and healthy when the vehicle is in storage. Even a small panel will accomplish this, and it contributes a lot to battery lifetime. Beyond that, you are correct--making a significant contribution to duration of dry camping is often a stretch.

In our case (and, I suspect, most B-van owners), we rarely spend two nights without some driving in-between. Even when we spend multiple nights at the same campsite, we tend toward sightseeing trips and/or dinners out.

in storage outside in view of clear sun-otherwise no.

[booster]

Those are the reasons I brought this up. Sportsmobile gets about the same answer as I did, break even on a small frig with one panel, in good conditions. Less if shaded, although the newer panels are a bit better in the shade. They claim 1/2 in the shade, but I think that is optimistic. At least Sportsmobile is giving a more realistic view of solar than some of the others. That is why I was saying, if you are selling your solar, all electric, unit as an off grid vehicle, you need a whole lot more than 250 whats of solar. Solar works off grid, but you need to be sized right, and be willing to be in the sun more than you may have otherwise.

The driving can also make up the charge, but depending on how far down you are, it may take a long time. AGMs will charge quickly, at high amps, but without a 12v to 12v charger you stand a chance of hurting them with a very high output, fixed voltage engine generator or big alternator. The old Roadtreks with separators had 50 amp breakers in the charge line, the new ones have 80 amp, but I have never seen more than about 40 amps going into our 375AH of wet cells, which charge slower. If we are down 200AH, it would take well over 5 hours of driving to get the batteries full. A twenty minute drive to a trailhead is more of typical drive for us, once we are in a nice area.

I think folks who buy one of the newer models with elect frig, induction cooktop, micro, huge inverter, etc and a bunch of batteries are probably being mislead a bit about what it will take to truly be off grid for more than a day or two. If they use all the facilities and gadgets like they are used to, the small solar system is going to nowhere near keep up, and just driving to the store for 10 minutes won't help much more. I expect that over time, the information will get better, and then either the solar will get bigger, or the expectations smaller.

We did all the calculations and knew what were going to be able to do, and not do. The only glitch we threw in was the big inverter to run the microwave, which can eat a days battery usage in a few minutes. We won't normally run the micro off just the batteries and will start the van for a couple of minutes to let the alternator help, if possible.

I have been hoping we would see a bit more information from real world users of e-treks and similar things, but there really hasn't been much yet.

[accrete]

There was mention of "expedition" style rigs and this is the type i'm most familiar with during my research (~mainly expeditionportal.com forum over the last 7+ years).

One such rig i believe has a comparable roof area to a typical class B is the XP Camper version 1. The stock version has 2x160w panels with the option to add another 155w (going into either 300ah or 600ah bank) . So with a total of 475w available you have something that, according to much of my research and what others have stated above, is a working solution.

My current DIY class B does not have a "fridge" but utilizes two 80qt Engle Deep Blue ice coolers. These coolers can remain under 40 degrees for ~6 to 7 days with a 20lb bag of ice ($2.50). WHEN/IF we do a Version2 DIY i'm not sure if it will include a compressor fridge. My reasoning is that we go into town once every 5 or so days for food/supplies/laundry. With this we can easily incorporate a night at a full service park and get bank back to 100% before nightfall. We also enjoy the freedom of parking both rigs (van conversion + 15ft tt) in the shade. I'm struggling with the pros/cons of being in the sun with one or both just for solar-charge to have a nice Engle compressor style fridge. There are also portable options in the ~80 to ~200w folding units...this might be a solution and keep the rigs in the shade.

Time will tell.

Thom