Is my battery size correct?

If you use 15 kWh per day, then at 48 volts you would need 312.5 Ah if you ran the batteries completely dead. I'd think you don't actually want to do that. So I suggest you either get bigger batteries or more of them.

8 Batteries x 200Ah = 1600Ah x 12volts=19,200 watt hours.

Will  four 12v  battery connected in  series  give 48 volt  ?    Eight  12v  battery  in 2 parallel  strings of 48 v   will  get you 19200 watt hours I think .  I  have 12 strings of  64 volts battery  connected in parallel   with 12 fuse and breaker  and 4/0 welding cables .    

5 hours ago, Bear said:

Have I got the right idea regarding battery sizing?

Our daily power use is 14.5kwh so round that up to 15kwh?

7 Batteries x 200Ah = 1400Ah x 12volts=16,800 watt hours. But I can't use that as I have a 48volt system, so I have to go for another battery, right?

8 Batteries x 200Ah = 1600Ah x 12volts=19,200 watt hours.

No matter how I figure it out, larger or smaller volt or amp batteries, 15kwh is an odd number and I end up having to add a battery.

Am I right or have I goofed up somewhere?

 

Are you planning to be 100% off-grid?  If so, what kind of power source do you have?

Wind?

Solar?

Hydro?

Over-unity free energy generator?  (Let me know if you ever get one to work, haha!)

I personally exclusively have solar.  On sunny days, it's great--I can easily attain ~100% of the nameplate capacity.  However, on cloudy days for 80% of the year, I'll usually get somewhere around 8-12% nameplate capacity.  But in the middle of winter (i.e. right now) when it decides to be an extremely dark, gloomy "Indian summer" at 46F outside...I will get as little as 2% of the nameplate capacity during the day.

That's right...55W off of a 2,940W-rated array.  0.2kwh for the entire day. 

On a good clear sunny day, that very same exact array will happily produce 14-15kwh.

If your load demands are approx. 15kwh for the entire day, you will need WAY more than 15kwh of energy storage IF you have an intermittent and unpredictable energy source (i.e. wind/solar) and need to power loads for a couple of "low power" days.  45kwh will get you ~3 days of usage assuming little to no power coming in.  But then your generation capacity has to be able to recharge that in a reasonable timeframe...when the power does come in.

Generation capacity is also important for intermittent power sources (solar/wind).  It takes a LOT of solar to generate 15kwh for a cloudy day.

I personally have ~12kwh of battery storage--but the ONLY significant loads (that we can't do without) are a refrigerator and a chest freezer.  (Average daily usage of those 2 items is ~3kwh.)  With just under 11kw of solar rated capacity, we usually have enough power to run both of those appliances without issues on "average cloudy" days--though we adapt our power usage to the amount of power we have coming in (i.e. don't plan to run every appliance in the house all day long if it's cloudy outside).

If your load demands are approx. 15kwh for the entire day, you will need WAY more than 15kwh of energy storage IF you have an intermittent and unpredictable energy source (i.e. wind/solar) and need to power loads for a couple of "low power" days

You explain  how  unreliable  solar panel and how little power it produce most of the time .  I  now know that is true and all my battery  will not run a 12kw inverter for more than  8 hours .   Sean say on youtube  many times also .   ATS grid  backup feature for the 12kw GS inverter is necessary to recharge the battery .   I  use 15kw during the winter almost every day  and still  need 8 hours to recharge the  battery  and 12 hours  if cloudy .   The GS  6kw split sync 120vac  will not work for ATS grid backup because no  240 vac input  according to Sean .   My friend who live completely off grid  use only propane generator  and wood burning stove for heat .  No solar or inverter as his job is installing  generator for business  and  most people living off grid  know nothing about solar  and is scare of using inverter .   

On 1/3/2022 at 7:24 PM, dickson said:

8 Batteries x 200Ah = 1600Ah x 12volts=19,200 watt hours.

Will  four 12v  battery connected in  series  give 48 volt  ?    Eight  12v  battery  in 2 parallel  strings of 48 v   will  get you 19200 watt hours I think .  I  have 12 strings of  64 volts battery  connected in parallel   with 12 fuse and breaker  and 4/0 welding cables .    

I think you have the wrong end of the stick old chap  🙂    I was being a tight arse, trying to get all that power in to an even amount of batteries, as 7 batteries had what I thought was the correct power. I didn't want to buy 8 if I could get the required power by getting a different amp / watt/ volt batteries. Tight ass lol.

It turns out Sid has pointed out that of course, I need my daily power requirement times three, for bad weather days. In England that is more often than not.  

So I have to find some real big battery bargain to stop my wife cutting my lunch off in my sleep. 🙂  Anyone

14 minutes ago, Bear said:

I think you have the wrong end of the stick old chap  🙂    I was being a tight arse, trying to get all that power in to an even amount of batteries, as 7 batteries had what I thought was the correct power. I didn't want to buy 8 if I could get the required power by getting a different amp / watt/ volt batteries. Tight ass lol.

It turns out Sid has pointed out that of course, I need my daily power requirement times three, for bad weather days. In England that is more often than not.  

So I have to find some real big battery bargain to stop my wife cutting my lunch off in my sleep. 🙂  Anyone

An alternate setup would be more like Sean is doing with the current prototype 12kw inverter...though I don't particularly like off-grid equipment being connected to the mains (due to potential inverter damage resulting from lightning strikes/surges).  Basically, if his battery voltage reaches a setpoint on the inverter, it'll auto switch FROM the grid to batteries, and run loads until a "low battery" setpoint is reached--at which point it'll switch back to grid.

For sunny days, you can run mostly off-grid.  But on those cloudy days (or winter days you don't feel like cleaning the snow off the panels), you can just use grid power.

Basically a grid-tie system that wants to be an off-grid system 😉.

Or...you could put the "non-critical" loads (i.e. that heated pool, heated driveway, all the neighbors' Christmas lights, and *gasp* maybe even the hot water heater and A/C) on the AC mains--and run smaller (but more critical) loads such as water (assuming you don't have city water), refrigerator(s)/freezer(s), computers, Internet, etc. off a solar system.

In time maybe 100% off grid, for now make do with what I can get away with spending, and cutting corners and looking out for bargains.

I'm going to have to buy less batteries than the 45kwh for now, and I'm going to try and make a wind turbine or two. Ya never know they may actually work.

Hydro, ooh nice. I'd like that. Live in an old mill next to a river and export to the grid. I've seen a New Zealand guy on youtube live off grid, running water through an old washing machine. Very cool.  

28 minutes ago, Sid Genetry Solar said:

An alternate setup would be more like Sean is doing with the current prototype 12kw inverter...though I don't particularly like off-grid equipment being connected to the mains (due to potential inverter damage resulting from lightning strikes/surges).  Basically, if his battery voltage reaches a setpoint on the inverter, it'll auto switch FROM the grid to batteries, and run loads until a "low battery" setpoint is reached--at which point it'll switch back to grid.

For sunny days, you can run mostly off-grid.  But on those cloudy days (or winter days you don't feel like cleaning the snow off the panels), you can just use grid power.

Basically a grid-tie system that wants to be an off-grid system 😉.

Yup that's what I'm going to have to do until I get enough batteries, and solar panels. If I can get enough to do the job, as I am very restricted for space : 6 panels on a garage roof and five on the back of my house 90 degrees for the morning summer sun (not even 4kw on the best day).  Why did I buy this place, really what on earth was I thinking 🙂

Well, I've got 36 panels that are mounted directly south-facing (2/3rds at 15 degrees tilt, and 1/3 at closer to 60 degrees tilt), without tree shading...AND those gloomy cloudy days still give me heartache. 

Afraid 11 panels is going to be a good start...to be frank!

2 cents worth of comment, not sure if you are considering lead acid or lithium, Bear, but if typical lead acid make sure you can bring that battery bank to a proper full absorption charge at least once a week otherwise it will go the way of the dodo all too quickly.

Rolls Battery posted a really good set of talks on youtube regarding proper lead acid battery charging and maintenance.

Lifepo4, but I have 4 lead acid, brand new 2 years ago, unused in my garage and kept uncharged until a month ago, now on 5amp panel 10amp mppt. Woooops. 🙂

I bought them before I knew what I was doing. The voltage was above 12volts so all was well right, lol. Of course they have sulfated by now.

I don't know what I'll use them for, they can't be good for much. 

Might try a lead-acid battery desulfator.  I personally ditched all my lead-acid several years ago (with no regrets) for LiFePo4...but one of the people I gave the batteries to says that a small, cheap "advanced MCU technology" desulfator worked wonders for restoring battery capacity.  They also observed that upon cracking open this supposedly "advanced MCU" desulfator, they found nothing more than analog circuitry (i.e. stuff like NE556, LM358)...not an MCU in sight.  Good for a laugh anyway...but it reportedly DID work quite well.