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Old 10-27-2018, 01:09 AM   #1
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Question general solar and batteries questions: future build

Hi all

I am thinking ahead… we may possibly get a different camping setup - buying a 22’ class B Transit high roof, and turning it into a camper.

I don’t know hardly anything about solar and batteries.

so i finally got the time to do a spreadsheet of the electronics I'd sometimes need to have in the Class B van, and running on 120v - on an inverter, while in the middle of no where… boondocking.

it is just below 2,100 watts.... (max) all on an inverter.... and that is not including the 12v lights, ceiling fan, etc in the van.

I really dont want to haul a generator.

I was thinking Lifeline (or similar) AGM*Deep Cycle Marine*Batteries.

So... pardon the novice questions:

would a 2,800 watt inverter be enough? for a max draw of 2,100 watts. and that is not including the 12v lights, ceiling fan, etc in the van.

and how much battery capacity would I want to be able to run this gear (just less than 2,100 watts) for, say, 1 hour?

(maybe even…. 3 hours?)

and...

how much solar would anyone suggest…. for the roof to be able to more or less recharge in about a day.... yes I know time of year / angle of sun all is a variable.

Thanks for any and all tips… and thoughts.

John
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Old 10-27-2018, 02:32 AM   #2
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... and how much battery capacity would I want to be able to run this gear (just less than 2,100 watts) for, say, 1 hour?
You probably want the battery capacity in amp-hours. If the inverter is 90% efficient, that's 2100 / 0.90 = 2333 watts (and the inverter may be less efficient than that). The voltage depends on the current state of charge of the battery; if that voltage is assumed to be 12 V, then 2333 W / 12 V = 195 amps. An hour of 195 amps is 195 amp-hours, but keep in mind that when discharging the battery this rapidly, it has much less capacity than when discharged at a more moderate rate.

If you really run this much stuff for an hour or more a day, you need a very substantial battery (larger than the Escape optional dual 6V 230 Ah) to get through a rainy day, and multiply that for multiple days or multiple hours in one day.

To generate this much energy (2300 watt-hours or more) from solar in a few hours, that's hundreds of watts of solar panel. Van or travel trailer, you could just plan on covering all available roof space with panels.
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Old 10-27-2018, 10:04 AM   #3
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That is a lot of power use! Are you planning on an ac/dc fridge? If yes I would look into propane if it were me...it uses almost nothing for propane/day and MOST of the time works very well...that would cut back on your power use considerably and save on battery weight as well.
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Old 10-27-2018, 10:40 AM   #4
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All this is based on my experience with a much smaller system - 480 watts of solar & a 1500 watt inverter, use for far shorter lengths of time, but I suspect, if anything, I'm underestimating the size of the system.

To put this in battery terms, using Brian's amperage figures, you would need around 4 Lifeline GPL-4CT (a 220 amp hour battery at 20 hour rate) for each hour of use at the full inverter load to leave the batteries at 50%. You may even need more since you are hitting the batteries much harder than they are designed for (look up the Peukert Law).

The next problem is how to recharge them. Under ideal conditions, a 160 flat roof mounted watt panel can produce 40 amp hours per day. You will need to put back at least 200 amp hours per hour of use; with losses, probably closer to 250 or 300. While larger panels are available, once you get over 200 watts, you may find they don't fit on the roof. In any case, you are looking at a minimum of 1000 watts of panel(s) per hour of use. This does not allow for any other battery use, cloudy days, or low angle winter sun.

Again, this is off the top of my head without enough research to be dead accurate, but it is close enough to suggest that it isn't practical. I would look for ways to limit your power needs. I think I'm a power hog at 40 - 50 amp hours per day - at 4-5 times that, you need to find another way...
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Old 10-27-2018, 10:48 AM   #5
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Another way to look at this problem is you are going to need about 200 pounds of lead/acid batteries (regardless of agm vs wet). And to restore that large amount of power in one (sunny) day you will need about 200 pounds of solar panels. And even then, one cloudy day will render the inverter unusable. Your whole camping experience will revolve around making and storing power. You might - as much as I cringe to say this - consider the advantages of a generator. Put some thought and money into a sound-proof enclosure.

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Old 10-27-2018, 11:50 AM   #6
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On the battery side, Lithium would be only approach that would make sense to me for your application.
As noted above, recharging the bank becomes the issue, but the lithium bank allows more usable amp hrs which helps immensely in high draw applications.
Once you price out the cost of the Lithium bank that would be necessary to support your requirements, if you still want to move forward then you can look at the solar/generator needs to maintain it.
I’d run it by AM Solar or some similar and have them cost out what would be required.
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Old 10-27-2018, 11:52 AM   #7
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On the battery side, Lithium would be only approach that would make sense to me for your application.
As noted above, recharging the bank becomes the issue, but the lithium bank allows more usable amp hrs which helps immensely in high draw applications.
Once you price out the cost of the Lithium bank that would be necessary to support your requirements, if you still want to move forward then you can look at the solar/generator needs to maintain it.
I’d run it by AM Solar or some similar and have them cost out what would be required.
Yup you hit the nail right on the head.
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Old 10-27-2018, 12:50 PM   #8
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Thanks everyone for all the great and very helpful posts.

Looks as if my thought of using all my electronic gear for an hour, here and there, would require an extremely large and costly battery and solar setup.

So likely I would just have a capable 120v shore power, and realize that I would simply need to find a campsite that had hookups to do my work.

The good news is that I would hopefully only need to do work on the very occasional day.... not every day... so I could get away with this “find a campsite with hookups” approach.

So then I guess the question becomes .... how do I make sure I specify to the builders... that my 120v shore power system can handle the 2100 watts (max) draw for the electronics ... plus overhead for fans, lights, etc.

Thanks. :-)

John
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Old 10-27-2018, 01:42 PM   #9
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Quote:
Originally Posted by Losangeles View Post
Thanks everyone for all the great and very helpful posts.

Looks as if my thought of using all my electronic gear for an hour, here and there, would require an extremely large and costly battery and solar setup.

So likely I would just have a capable 120v shore power, and realize that I would simply need to find a campsite that had hookups to do my work.

The good news is that I would hopefully only need to do work on the very occasional day.... not every day... so I could get away with this “find a campsite with hookups” approach.

So then I guess the question becomes .... how do I make sure I specify to the builders... that my 120v shore power system can handle the 2100 watts (max) draw for the electronics ... plus overhead for fans, lights, etc.

Thanks. :-)

John
2100 watts using 120v is less than 18 amps. Two 15 amp circuits fed from separate 15 amp breakers should be sufficient.
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Old 10-27-2018, 01:55 PM   #10
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I actually prefer to convert everything to watt*hours vs amp*hours... simply multiple volts * amps * hours to get watt*hours. 2 GC2 golf cart batteries at 6V 220AH each, taken to 50% 'safe' discharge give 12V * 110AH = 1320 watt*hours total usable power. allow 10-20% power loss any time you run through a conversion like an inverter, or solar power to battery charging, or whatever.

why so much power? my wife's rather powerful 'workstation' laptop (core i7, 1TB SSD, 16GB ram, 15" high res screen) uses about 50 watts when its charging and running at the same time doing her engineering related work. all our lighting is LED, we don't need a microwave or electric coffee maker when we're camping, heating is propane, fridge is propane. a 20 lb propane bottle contains the /equivalent/ of 125000 watt*hours (!!), you'd need 200 golf cart batteries for that much power! (yes, I know, propane is for heat, not electricity, although you /could/ run a generator on it, but that would have less than 50% efficiency).
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