PrePlanning and need help with calculations

[Tyler702]

I've settled on a 24V system. (based off of Will's 24V setup) Off grid in my garage. Here's my proposed setup along with my question regarding calculations.
2X12V100Ah battleborns
40A Epever MPPT
2000W Pure SW inverter
1 x 250W 24v Mono panel
Using kill-a-watt, I've compiled and logged an average 7day usage for my home fridge, (and a typical 50 minute cycle for my gas laundry dryer and other misc appliances)
Results for the Fridge: Consumes an average of 1.98kwh per 24 hr period.
Question. Assuming a 100% full charge on the battery bank to start the test, and no PV charging at all during, if I run my fridge for 24 hrs, what % capacity will be used? Or where will my battery bank capacity be left at, after the 24hr period? (fridge pulls 6.5A peak during startup per the tag btw)
I'm sure there's a formula to calculate all this, I just cant seem to get it to sink in. Is it best to convert everything to watt hrs and calculate from there? Its just not clicking with me so far.
Thanks in advance.
Tyler

 

[gnubie]

Notionally your batteries contain 2.4kWh, 12V x 100AH x 2. The actual capacity will be higher but not usefully, probably around 2.5kWh. If your fridge really does use that sort of power, and TBH that's a fair whack, that's about 80% discharge of the battery. 1980 / 2500 about 79% used, ie 21% remaining.

What's the make / model of your fridge? You should have average daily power use from the manufacturer to work on but since you have used the kill-a-watt your figures probably are pretty accurate.

Bringing everything to watt hours is definitely the way to do these types of calculations.

 

[Tyler702]

It's a whirlpool 18.2 cu ft. Older unit made in 2000 I just discovered! But it still works great, although probably not as efficient as the newer ones. So, simply put, I have 2400w of usable power. Fridge uses 1980. My gas dryer for a typical 1 hr load uses .23kwh =230w. So I can run my fridge for 24hrs and dry one load of laundry. 1980+230=2210 /2400 means I've used 92% leaving me 8%. Am I figuring that correctly? I'll factor in the inverter efficiency later, but I'm just trying to get a baseline understanding for now.

 

[Craig]

You are correct but You probably do not want to run batteries that low on a daily basis. Obviously if you have any solar power you will not be running that low. If it were me and your draw was that High I would double battery size or buy a new fridge which could actually be cheaper than 2 battle born cells. Or make your own battery for much less