hey battery engineer. can you help me out with this stupid solar home battery confusion i have been having?
1 battery system is 12volt X 180AH =2160WH. (lets say lead acid)
2 battery system is 48Volt x 45AH=2160WH(Lets say this is lithium)
if i am using an inverter to convert DC to AC viz 220volt where my AC appliances run, does it matter on the battery side?
if i have a load, say a pc running 1 KWH, will these two battery systems run for 2 hours both (assuming discharge rate is same, i know i know, just calculating)
i am doing this because solar batteries are being sold at 48Volt x small AH to come up with KWH but at the same time lead acid are only sold at 12Volt but high AH.
what if i buy 7AH 12Volt x 25 batteries to get same KWH?
does battery voltage or amperage matter when converting to AC? how does that work?
oh, BTW, i have a 5.2KWH solar array that is grid tied
Not the parent poster, but do have some familiarity here.
Higher battery voltage == less copper, smaller wires for the same wattage. Sometimes also a bit more efficiency too (less resistance, smaller absolute voltage drop moving current around).
Your units are a bit messed up load wise - is your computer running at 1 kWh per hour? For how long? (Yeah, that is confusing - but that would be the energy used to power a 220 volt, 4.5 amp load for an hour, every hour).
One of the confusing things with some of these units is kWh is a measure of energy, even though it has a time component in the name (kWh can be directly converted to joules). It isn’t ACTUALLY a measure of power (aka energy over time), even thought it implies it is because it has ‘hour’ in the name.
Power is energy over time.
So you have an absolute number for storage (your battery in this example can store 2.1kWh of energy - 2.1kWH is equivalent in energy to 2100 watts drawn out over an hour).
Your inverters, panels, chargers, etc. will be rated for a level of output POWER (energy over time) then will draw/convert that (say 4 or 8 kw) to/from the batteries. You can easily have an inverter that can draw down those batteries super fast (say will pull down 8kw continuous, so you’d get less than 15 minutes on that battery - if it doesn’t get damaged or explode), or one that draws power out slowly (say 200 watts max) to make it last 10 hours say.
Same with your chargers, etc.
You’re solar panels are almost certainly not rated in kWh, but kw- aka maximum instantaneous power they would be producing at any moment under ideal conditions, not aggregate energy they would be producing or storing over time. This is important because they don’t store power and actual energy production will depend on a lot of factors, like amount of time in the sun, etc.
Thanks. How we see load is, the product advertises 1000 watts so for me that means 1kwh or one unit of electricity. Same for something that is 200 watts or 2000 watts.
I am aware of the solar thing. I have a grid tied system and I sell the energy to grid. I produce around 30 kWh a day which is good.
My problem is storage. If I want to store energy, should I go with 48volt 24 ah battery or 12volt 96ah ? As I said, there will be an inverter giving 220volt output so does battery voltage matter?
Again, I think you are making the same mistake in your first sentence. 1000W does not mean 1kwh or one unit of electricity. It is a measure of instantaneous (or maximum instantaneous, there’s no way your pc regularly runs at 1KW unless you’re mining) power consumption, the “now” voltage times the “now” amperage (times the power factor… maybe).
For storage, none of that matters. What you need to look at is the cheapest total capacity in kWh after accounting for conversion losses at your median discharge rate. Let’s say your median consumption is 450W, then you see the efficiency of your inverter with 12V vs 48V input to produce a sustained 220V at 450W. Maybe it’s the same efficiency for both 12 and 48v or maybe one is 85% and the other is 80% so you need to multiply the capacity by that amount to get capacity after inverter conversion losses to account for the only difference between the two setups.
