batt. aH defined

[BenD]

first of all, Thank you Will, and i have read many posts on here so thanks to all, great knowledge base here. Will, your video's on youtube have broadened my mind in terms of solar, just a couple of things not so far well defined.
1; I have heard you say before something to the point of don't worry too much about amp hour ratings of manufactures (batteries) but the overall watt rating, volts x amps. But doesn't a 100aH batt. drain quicker, or have half the storage than a 200aH batt. at the same load drain even if the total watts are the same. I know, it is simple, I am a expert at overthinking things. The course of thinking here is price mostly, 950 BB at only 100aH, or diy LiFePO4 200aH, 24 volt, so 4 BB at 3,800 compared to 1,500 give or take depending where they come from.
2; I am having trouble reverse engineering the common concept of finding the total watts of what you want to run to decide the converter size. I would rather size the converter to the batt. bank so i know that I could power these items with bank, and the recharge would take this long for replenishment (this part I have lined out already)
3; why are some LiFePO4 batt. okay for series connection and others are not, is there a way to tell when it is not specified ( as it comes to diy batt. cells). IDK is it obvious or??
I know these basic Q's make it sound like I'm a simpleton, I do have a background with electricity Totally new to solar, intrigued, and sometimes it's the basics that get skimmed over.

 

[SCClockDr]

AH vs WH:
The reason for my considering watt hours when sizing is it eliminates some of the math. A 12VDC WH is the same as a 120VAC WH.
A watt represents power.
So when sizing up your consumption in watts*hours (WH) you can judge your storage needs in WH as a direct comparison for a 12VDC, 24VDC, or a 48VDC battery. If you were to use AH you would need to factor in the battery voltage as well to accomplish the same comparison.
Watts/Volts=Amps
Watts/Amps=Volts
Amps*Volts=Watts
Sizing a solar array is a bit more complicated due to exposure & efficiency factors needing to be considered. Once you have chosen those factors combine them & just reduce the panel wattage by that factor to arrive at a workable WH # for sizing purposes.
So we are clear, I'm talking DIY conceptualization vs engineering precision, the principles are the same.

 

[BenD]

Thanks for the advice. I figured 70% efficiency of the panels. Running 6 total 200 watt panels, 3 in series 2 parallel, for 21.052 x 3 =63.156v and 9.5 x 2 = 19a a total of 1200 watts. 1200 x .7 efficiency = 840 watts.
The charge controller was based off max so 1200w / 24v= 50a controller. For a little head room I figured the victron 150v/60a tr.
I'm thinking a smaller BMS at 80 amp because it's only 40 bucks and I only have it in there for management and cutoff. With the inverter running off a victron 220 amp battery protect.
If this is all sounding familiar, yes it is almost cut n paste off of one of will's videos. The major stumbling block is ofcourse the battery. Leaning toward 8 3.2v 200ah cells for 24v 200ah battery. Just don't know about aliexpress. I know for the most part all battery is coming from China, even if assembled in the USA, it looks like customs and duty taxes are included in price.

 

[BenD]

Oh yeah 24v x 200ah= 4800w / 840 w expected w from panels is 6 hour recharge and not planning on complete DOD maybe 70/80%

 

[BenD]

At 80% of batt. 4800 x .8 = 3840/ 840 is around 4 1/2 hour recharge

 

[SCClockDr]

@BebD I'd lower your efficiency factor to between 0.5 & 0.6 for the # of hours you are considering. With no clouds solar production follows a bell curve with its peak near noon for about an hour or two.
You could insert a wattmeter into the solar to battery wire and actually measure a weeks worth of solar production and then you would know a reasonable factor to use. Do that for each month & you would have reasonable seasonal numbers to use. I've got one on its way to do just that & will get another to audit my loads using a daily sampling process.