navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address - following recent spam/hack attempts on the forum, all security is set to "high", and "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: newbie needs a bit of schooling regards things electrical  (Read 1848 times)
soojooko
Newbie
*
Offline Offline

Posts: 3


« on: April 27, 2010, 11:55:12 AM »

Hello all

Im trying to figure out a solar system for my home. I plan to go for the basic: solar panels > controller > battery bank > inverter > me.

I understand the basic maths for calulating amps, volts and wattage. What I dont understand is the relationship between amp hours on a 12v/24v battery and the electricity used through a 240v inverter. For example, if I have a 1 amp device running at 240v through the inverter ( 240w ), does this equate to 240w/12v = 20amps = 5 hours use out of a 12v 100ah battery. Have I got my numbers right or do I need to go back to school?

Thanks in advance
Logged
stephendv
Hero Member
*****
Offline Offline

Posts: 928



WWW
« Reply #1 on: April 27, 2010, 12:07:52 PM »

Yep the numbers look right, except for the assumption that you'll get 5 hours at 20A from a 100Ah battery.  For specially designed deep cycle batteries you can draw them down to 80% without damage, but you will shorten the life.  For off-grid use, most people recommend a maximum use of 50% Depth of Discharge (DoD).  The less you discharge the longer the batteries will last.

You might also have noticed that it's the Amps that are the limiting factor on a lot of the devices involved (e.g. solar chargers, battery chargers, etc).  So choosing a higher voltage battery bank, means you can often save in equipment and in cabling. 

Some useful background info here: http://www.windsun.com/Batteries/Battery_FAQ.htm
Logged

http://www.casanogaldelasbrujas.com
2.8kW PV, SMA Sunny Island 5048, 5 PzS 700 battery bank, stinky diesel.
soojooko
Newbie
*
Offline Offline

Posts: 3


« Reply #2 on: April 27, 2010, 01:36:01 PM »

Thanks stephen

I figured there are other factors. I just wanted to get the raw maths straight in my head before I consider the actual battery size. In other words, if I can get 5 hours out of 100ah battery, but never want to discharge beyond 50% then 200ah batteries is what I need, right?
Logged
stephendv
Hero Member
*****
Offline Offline

Posts: 928



WWW
« Reply #3 on: April 27, 2010, 01:49:59 PM »

Yep exactly.  I find it easier to work in Wh everywhere, e.g. 1A load at 240V for 1 hour = 240Wh.  200Ah battery at 12V = 2400Wh.  100Ah battery at 24V also = 2400Wh. 
Once you start factoring in the energy from the solar panels, this will also be in Wh, so it's easy to compare.

Logged

http://www.casanogaldelasbrujas.com
2.8kW PV, SMA Sunny Island 5048, 5 PzS 700 battery bank, stinky diesel.
soojooko
Newbie
*
Offline Offline

Posts: 3


« Reply #4 on: April 27, 2010, 02:02:24 PM »

ok!

Thanks very much. Smiley
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!