Size and type of battery bank

[crstainbrook]

After some great responses from my other questions I have decided to purchase a Xantrex sw2512 or sw4024 inverter for my cabin up North.  What I am trying to determine now is the proper battery bank size and type of battery I should be looking at.  What I plan to run would be a few low watt lights, be able to recharge two laptop computers, stereo, and a few other things that may come along.  Although I am not planning on living in my cabin in Alaska for more than just this coming summer and winter, I hope to gain enough working knowledge during this time to be able to live totally off of the grid when my wife and I buy a house in the next year or two.  So, can anyone give me an idea of how large a battery bank and explain amp hours from a battery and what is good vs. bad about the whole battery bank aspect of a system?  As I stated in my other postings, I am completely new to off the grid living so I am searching for anyone to guide me!!!

Thank you in advance,

Chris

[fungus]

Hi,

Firstly you have to find out your average power consumption. For example, the low watt lights could take around 30 watts, your laptops about 150 watts, your stereo around 10.

This is around 200 watts. If you are using a 12v battery bank then this will take around 16 or 17 amp/hours out of your battery every hour(200/12). Lets say you use all of these for 5 hours a day, that would be about 80 or 90 amp/hours out of your battery. This would be half the amp/hours if you had a 24v battery bank. An amp/hour is the energy used by an appliance that takes one amp if used for an hour(around 12w at 12v).  

 Secondly, you would have to know what you are going to charge the battery with(ie solar or wind) and how many watts you will be charging with. Lets say you have solar panels that total 500 watts, and you have around five hours of sunlight each day. This would total around 2.5kw, which would be approximately 200 amp/hours into your battery.  You may lose about 10% of the energy you put in as batteries are not totally efficent. You would have about 180 a/h into your battery. Using your inverter you will have an approximate 15% loss again so you will be taking out around 230 watts per hour with all of your stated appliances. Your battery should be around 20 times more than your input. This means that you should have a battery bank of around 3500 a/hours. Someone please correct me if I'm wrong, but that should be approximately the right size assuming 500 watts of pv. You would have around 610 amps that could be used as batteries shouldn't be discharged below 80%. Watts are amps*volts and watthours are 1 watt used for an hour.

[fungus]

Oops! Made a mistake! That would be a 800 ah battery bank and you'd have 160 a/h to play with. Sorry