[MLB-WIRELESS] Solar power for nodes

[Clae]

>Hi Does anyone have any good references for sites about how you go about
>sizing the solar pannel and batteries so that you can reliably power an
>access point using 1-2 watts? Have not had much luck finding good sources
>for this material.

Check out the website of the Alternative Technology Association 
http://www.ata.org.au and the Solar working group 
http://melbourne.wireless.org.au/wiki/?WGSolar

The Australian standard for sizing a battery bank is to run for five 
days with no charging input, and to discharge lead-acid batteries 
only 30% of capacity over that time.  Lead-acid batteries will suffer 
reduced lifespan if they are fully discharged.  NB this only applies 
to deep-cycle batteries, normal car batteries are designed to be 
constantly topped up.

NiMH batteries will handle a full discharge without complaint, so 
even though they are more expensive per watt-hour, it's worth looking 
into them.  Jaycar seem to have the cheapest ones (cheaper again for 
10+ quantities), but try Battery World as well.

I would personally aim for at least two or three days without a 
top-up - this will account for a string of cloudy days.

Multiply the power draw (1 -2 watts) x 24 hrs x no of days to get a 
size in watt-hours for the battery bank.  If you are using NiMHs just 
use that number.  If you are using lead acids, multiply by 3 to allow 
for the shallow discharge.  Round up to a nice round number to allow 
a safety margin.

( and 1 Wh = 1000 mWh )

You'll want at least twice and probably three times the device's 
current draw on your solar panels, so that there is enough power to 
run the appliance and charge the batteries at the same time.  And add 
one of the low-cost solar battery regulators, in kit or module form, 
from
jaycar.com.au, oatleyelectronics.com, or a solar supplier.  This will 
extend the life of your batteries by regulating the charging, and 
stop them from discharging into the panels at night.

Keeping your batteries cool and away from direct sun will help too.

Clae.

-- 
Arthur C. Clarke wrote "Any sufficiently advanced technology is 
indistinguishable from magic" and for those who don't study science, 
the "sufficiently advanced" bar is low enough that scientific 
credibility can attach to unscientific belief. 
http://www.chipcenter.com/columns/rci/tesla/tesla4.html

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