It's not so much the WATTS you want. as the Watts you NEED
to run your bus. Start counting. Max. then actual needs to run.
THEN figure requirements.

And with that old girl. I'd be going GOOD quality wet cells over AGM etc.
Plenty of open air storage apace.
Exide extreme's etc. there are several.
Check for current best reputation on net.

Permanently on the panels. for 30 odd yrs. Yachts and vans.
My Extremes. and others, gave me an average of around 6 1\2 to 7plus yrs
per battery. Just check water levels regularly.
Keep up to a bottom of filler tube I found.
Hot climes, allow a little for expansion.
Will save a LOT of initial outlay and easier to top up if necessary.

I've had 2 AGM's (good ones $300plus each, then.). Calk after a coupla three yrs.
WHEN coupled to solar.

Hi,

You have posted this request in two places on here?? Why ?

Please read my reply on the other one !!

Jaahn

Hi MissGuided,

(I see you've also posted this question under "Techies Corner" so I've repeated my reply below)

It all starts with how much power you're intending to use - as others have said.

Once we have the daily consumption, then we stand a chance of getting a system that works well.

If you're having trouble getting power consumption figures then maybe this will help:  http://12voltblog.com.au/how-much-power-does-12volt-stuff-use/

Cheers

       AJC

Hi
Misguided
What system lithium or Agm or flooded/wet ?
Assuming Agm
You need to have some idea of your consumption
batt sizing to solar
At a guide you will have 1/2ah to 1 ahr per watt
either 800ah or up to 1600 ahr
Remember batteries need filling to 100% almost every day for longevity so u will need performance which will then restrict u to around the 800ahr

Even thou its all theory ultimately u can only use what u can recharge .........

200 watts harvests produces 11 amps
Average sun at 100% is 5.5 hrs per day 4.5winter 6.5summer
5.5hr x 11 = 60.5ah less electrical loss 20%
60.5 - 20% =48.4 ahr harvest in 24 hr period
48.4x 8= 387.2ah

Mppt controller adds around 13% This was measured on panels at noon .
Panels laying flat potentially donot harvest as much

-- Edited by swamp on Wednesday 19th of April 2017 08:07:00 AM

1600w @ 12v nom? Allowing for the general rule of thumb that you get 70% of the actual advertised capacity, 1600 x 0.7 = 1120w /12v = 93 amps charge rate. This is where battery chemistry is important, flooded cell will require a continuous charge rate of no more than 10% of the advertised capacity and will accept that rate till around 70% SOC, so that would require roughly 1,000Ah capacity, AGM have a better charge rate at 20% of the advertised capacity to the same 70% SOC, so they would require a min of 500Ah, Li (LiFeP04 or LiYFeP04) recommend around 50% of the advertised capacity, so 200Ah would handle the charge rate all the way to around 95% SOC, 400Ah to around 98% SOC. That means you could use all 400Ah out of the 400Ah Li battery and still fully recharge with the solar you have in 5 peak sun hrs, you can not do that with any form of lead acid battery whether it be flooded cell, AGM, Gel or Lead Crystal.

As far as cycle life, you plan to go full off grid but you don't mention if you also plan to use the batteries 24/7? You also have to consider how deeply you will discharge the battery pack, if down to 50% SOC each cycle you won't see 7 yrs out of the lead acid battery pack, maybe only discharged to 70% SOC you might be lucky to see 7 yrs, but then you haven't discharged the battery pack enough to accept the full charge rate your solar can put out, so now you would require an even bigger lead acid battery pack.

The formula might work for those that draw very little as far as discharge rate from small battery packs with small solar set ups, but it doesn't scale up, the increase in battery capacity needs to expand at a much higher rate. This is not the case with Li batteries, the formula remains constant, if you want 100 amps for 1 hr a 100Ah Li battery will deliver that yet still be at 12v under load at the end and recharge at least 1,000 times, to do the same thing from a lead acid battery will require 10 times that capacity and will only deliver all 100Ah for maybe 700 cycles at best. So you need to understand that it is not only how many watt hrs per 24hr but also the max discharge rate at any one time if you want to size a lead acid battery correctly, lithium only requires the number of watt hrs you want and that you have enough charging capacity to replace it.

T1 Terry

Bagmaker wrote:

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Macka the OP didn't state the amount he wanted to spend but its a good point.
LiFePo4 (NOT Li-Po) lithium is much cheaper per watt if used as a full time power supply.
Read that carefully (c h e a p e r) !!!
The initial outlay is slightly higher, sure, but the bang for buck is much stronger and goes for much longer.
Other motorhomers have settled on around 400-600 Ah of Li batt, double if using lead, simple fact is that if you want to spend time with a happy mrs -"All power too her".
But leave a bit extra for the beer fridge. As frugal as some may be -and good for you- a couple of hundred watts is just past backpacking.
A 12m bus has real estate above for 1.6kw of solar, may as well use it!

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 ditto