[MLB-WIRELESS] Solar Power - How much battery?

[Andrew Leech]

Another consideration is that to estimate power output from a day of sun 
you actually have to assume there's only about 4 hours of rated power on 
a nice sunny day. This is to take into account the angle of the sun with 
reference to the panel, when the panel isn't facing dead on at the sun 
there's only a percentage of power generated depending on the angle. 
cos/sin and all that. That's why sun tracking solar panels are nice :-)

So for a good sunny day you can only expect to get 4hours x 80W = 
320W-hours.

You'll want to measure the amount of power the ap's draw as well, the 
rating on the back of them is just a max rating the power adaptor should 
be able to supply, they shouldn't draw anything near that.

So going by the example of 2A @ 12V = 24W,
hence power required over a day is then 24W x 24hours = 576W-hours. 
That's not sounding too good. umm... I suggest getting ap's that don't 
need 2A to run.

Andrew


Steven Haigh wrote:
> On Thu, Dec 06, 2007 at 02:53:30PM +1030, Kim Hawtin wrote:
>   
>> gregsonm at aanet.com.au wrote:
>>     
>>> Question... how do you calculate the amount of battery a solar panel can
>>> charge?
>>>
>>> I know some of you will say it depends on how much sun there is... which
>>> would be right. But I am looking for a basic calculation to make sure I
>>> have the maximum battery capacity possible.
>>>
>>> For example, if I use an 80 watt solar panel, what would be the amount of
>>> battery amp hours I could charge?
>>>
>>> All advice greatly appreciated... Mark
>>>       
>> see if you can dig out the video that the guys in north island new zealand
>> at linux.conf.au in dunedin in 2006, on their Wireless Network.
>>
>> anyhow, i asked them a lot of questions afterwards about this topic and
>> they designed their system to go three days without significant daylight.
>> so, that solar panel and battery array need to be three times the size
>> of what you need to deliver in a given day.
>> so power consumption in a day, needs to be delivered in 5-9 hours of daylight.
>> and then you need to be able to fully charge you batteries in say, 7 hours.
>> that 7 hours charge needs to be enough to run the AP for 3 x 24 hours.
>> that make sense? i don't know the area you are putting this in, but the
>> NZ guys AP was literally on the top of a mountain, that was a days hike up
>> and a days hike down. hopefully your AP is not quite that remote ;)
>>     
>
> More food for thought using back-of-napkin type calculations...
>
> You'd need 2 x 80W panels + ~550Ah of batteries to run a load (2 x APs etc) drawing 2A @ 12v on a 24/7 basis based on fixed solar panels etc.
>
>