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Old 02-20-2020, 08:57 PM   #61
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Originally Posted by TurnerFam View Post

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Now, realistically, even with 'full sun', solar is not always a power source that will be there - for instance, at a off-grid campground on a lake in the Yukon, the only camp parking sites were all under tree cover. Great for the shade, but hardly for the solar, especially if it's permanently attached to your roof. Another time we parked on a roadside pulloff while coming out of Jasper, on the way to Banff, on the Icefields Parkway, on the Athabasca river(beautiful!), the sun was full out, but just over the trees - another 'generator' overnight.

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Your trip was exactly the kind of RV use that makes me want a small motorhome with Volta-like design and capabilities. It doesn’t need to cost $20,000 though.

We want to be able to park just about anywhere overnight and be comfortable without a generator. That means enough battery to power A/C overnight (not too difficult to pull off in a well-insulated van). Once you commit to that much battery as a requirement, then it’s much easier to make do without a generator.

Additionally, to charge in a “reasonable” amount of time, you need so much power that solar won’t help much, so contribution would be minimal.

Bottom line is that the proliferation of all-electric or mostly-electric (those still using propane or diesel for heat) motorhomes are based primarily on desire to power air conditioning with batteries at night. Once you give in to that dream, eliminating the generator and solar becomes a lot easier.

I’m hoping that mini-Volta-like small motorhomes can be built using the Ford dual-alternator option. If they get 2 hours of A/C for each hour of driving, I’d be happy enough with that. Cost could be under $5,000.
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Old 02-20-2020, 09:37 PM   #62
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What's a typical kWhr/day for AC in a small camper? Just trying to get a handle on how big a battery bank it would take. Given that 1 kWhr is about 100 amp hours at 12V with losses, you would need probably 500 -1000 amp hours? I need at least 100 amp hours just to run my fridge!

FYI the battery in a Chevy Volt gen 1 was about 10 kWhr usable and weighed 500 pounds.
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Old 02-21-2020, 03:24 AM   #63
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What's a typical kWhr/day for AC in a small camper? Just trying to get a handle on how big a battery bank it would take. Given that 1 kWhr is about 100 amp hours at 12V with losses, you would need probably 500 -1000 amp hours? I need at least 100 amp hours just to run my fridge!

FYI the battery in a Chevy Volt gen 1 was about 10 kWhr usable and weighed 500 pounds.

Lithium battery weight (chemistry used in most RVs) is approximately 30 pounds for 100 Ah, so roughly 25 lb/kWh.

At night, when it’s cooler, an efficient typical RV A/C runs on about 1,000 Watts of power. Based on my experience, I’d estimate it would need to average less than 5,000 BTU/hr in a well-insulated Class B, so no more than 50% cycle time.

Many of the B vans set up to do this have +/- 600 Ah of useable lithium capacity, or just over 7.6 kWh. In theory it should be enough for 8~10 hours through night. Reports suggest it’s in right ballpark.

The Travato lithium has a little more battery capacity (8.7 kWh going from memory), and they estimate 6~8 hours while running other items like electric refrigerator. I think that’s based on daytime conditions, and also using an inverter to power the 11,000 BTU/hr Power Saver.

Newer vans that I saw at Tampa Super Show are now also going with a DC air conditioner that not only runs without an inverter, but is more efficient according to manufacturer’s published data. Additionally, at night when cooling loads are lower, the A/C can run slower, making it even more efficient.

RoadTrek, now back in business, offers their EcoTrek batteries in “200” size modules, which I assume to be 200 Ah. The most expensive Mercedes Sprinter vans are listed with up to 800 (Ah?), which is about 10 kWh. I’m not certain if that’s useable capacity, or if it has to be derated by about 20%.

To run an A/C in a van all day, or 24 hours, would take about 30 kWh, which isn’t practical at this time. That’s when you’d start engine and recharge batteries as quickly as practical.
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Old 02-21-2020, 09:24 PM   #64
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James of The Fit RV confirms in “real-world” testing that solar doesn’t “move the needle” when a Travato Class B with higher-capacity 11,600 Watt-hour battery bank is compared with and without 230-Watt solar.

The short video is well worth watching for anyone thinking of buying a motorhome with very high capacity batteries. Review and test is not technical and very easy to follow.

Also nice views of Big Bend National Park.


https://www.thefitrv.com/rv-tips/doe...ium-batteries/
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Old 02-21-2020, 09:47 PM   #65
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So if I'm doing the math correctly, his 11,600 Watt-hour battery bank (assuming a 12 volt system) has 966 amps to draw from. Also assuming he will not take that below 50%, he has 483 amps to use.

Nobody would try to charge a bank that size with a 115 watt panel, so of course it doesn't "even move the needle". The system I am currently installing (5 - 245 watt panels) would put 100 amps into the bank per hour (perfect conditions of course) and make it possible to recharge the battery bank in 5 hours.

Of have I missed something?
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Old 02-22-2020, 02:09 PM   #66
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That’s great that you can install 1,225 Watts of solar on your roof.

I’d expect that a typical solar system that size should make about 4 kWh of energy on average days. That’s over 300 Amp-hours daily so I expect you must have a very large battery bank.

The Volta system in newest Winnebago Travato that James of The Fit RV tested is based on 48-Volts nominal, and also the useable battery bank capacity is based on 90% depth of discharge. Hence useable capacity is about 10 kWh.

It would take about 2.5 days for a solar system your size to recharge that battery from 10% SOC. However, unless running Air Conditioner, the 16% of battery capacity James consumed daily would be easy to replace. The problem is that a van has so little room on roof that you’d never come close to installing that much solar. The Winnebago comes with 230 Watts and there’s not much free space on roof for a lot more.

The key to these high-capacity systems is air conditioning. If you’re not going to run A/C from batteries, none of this design makes a lot of sense in the first place.

I agree with James 100% on this:

Quote:
Originally Posted by James
Let’s talk about the elephant in the room.* This is what it’s all about!* When everyone talks about using large lithium batteries and large inverters in their RV, all they really care about is powering the air conditioner.* Anything else you typically run in an RV can get by with much less battery or inverter capacity.* The success of any RV power system is going to be measured by how long it can run an air conditioner.
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Old 02-22-2020, 03:09 PM   #67
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That’s great that you can install 1,225 Watts of solar on your roof.
I'll admit, there isn't going to be a lot of extra room up there after the install.

And no, the limiting factors of his van renders solar a no-go. In this case, he really wouldn't have any other way to keep that size of batter bank charged unless he used a non-renewable energy source.

The video has good info in it but I think the headline "Does Solar Power Matter on RVs with Large Lithium Batteries?" is a bit ambiguous. Agreed, it doesn't matter in his van, but only because he lacks the room to mount enough panels to supply the battery bank. In my case, I do have enough room.

The application will direct the methods...

We have a creek that runs through our property and I've been working on setting up a Pelton Wheel to create power for a cabin that we hope to build. Even if the area were exposed to 100% sunlight for 8 hours a day, it could never produce like hydro. So even though the battery bank at the cabin will be approximately the same size as the motor home, using solar to keep it charged would be foolhardy.

I like alternate forms of energy and I tend to use them even when they are not the most inexpensive methods. Perhaps not the smartest approach, but hey, I find it interesting and somehow fulfilling. It may have something to do with my inner goals of acquiring self sufficiency.
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