Help with my understanding of solar

[Dan Sea]

Anyone who has experience with small solar setups I need some guidance and a check of my understanding so far.

Equipment:
Renogy 50W 12V Polycrystalline Solar Panel and 10A PWM Charge Controller

My understanding:
If my equipment used in conjunction with a 12v 100aH deep cycle battery (20 hr rating) I could store/1200 watt hours of electricity. That is to say, the battery would provide 1200 watts per hour (DC current) for 20 hours. If I were to hook up another battery in parallel I would maintain the same voltage but increase the amount of time ie. 2 batteries would provide 1200 watts per hour for 40 hours rather than 20 hours.
To convert DC current to AC I will use an inverter ... this is where the math escapes me. With my 1200 watt hour battery wired to a 400w inverter, I can now power anything up to 400 watts (AC) for ... 60 hours? 1200 watt hours ÷ 400 watts = 3 × 20 hour battery rating = 60 hours?
I realize all this will change depending on load and I know that I shouldn't drain the battery less than 50%. That being said ... how would I know how much juice is left in my battery bank? Volt meter?
Thanks in advance for any corrections and insight.

[Greg9111]

Dan, do some searches on the site. We have had a few posts in the past that may have addressed this.

[Kevin WQRE722]

greg is correct there is a post on this somewhere. but its buried im sure. because its been a while since this came up.


when you convert 12v dc to 120v ac you cannot compare it the normal way that you would.
it becomes so inefficient on the 12v side its not even funny


I know that this is not the 100% correct formula but this is to just give you an idea of what I am talking about.

if a device requires 100 watts at 120 volts to work. take the common law of electricity as the volts go down the watts go up.

so in theory that same device at 60 volts would require 200 watts to produce the same output.

again this is just a bullshit example to help understand how it works there are more factors that need to be factored in but we will talk abou tthat another time

so now lets do it again that same device at 30 volts would then require 400 watts to produce the same output.

I think you get it at this point.

but when you talk a.c vs dc
the dc draw is usually higher
and more in demand.

so a 400 watt 120 volt power inverter is probably drawing somewhere around

keep it simple stick to wattage

1000 watts

1000 watts  divided by 120 volts  = 8.3 amps draw on the ac side
1000 watts divided by 12 volts    = 83.3 amps draw on the dc side