[MLB-WIRELESS] Solar components

[Lyndon David]

The spreadsheet model says that we need a solar pannel of 0.1 sq m. The
model however assumed a 20% efficiency which is wrong. I should have assumed
10% for polycrystalline cells.

This is a BP solar 20W pannel, $295
http://www.au.store.yahoo.com/solaronlineaust/sx20u.html

Now for the batteries, why use lead acid? They are heavy and bulky and dont
like being discharged more than 30%. How about
NiMh or NiCd ?

The model says that we need 5 days of power reserve which is 180 Wh assuming
1.5W for the access point.

A D size NiCd cell has a capacity of 5000mAh at 1.2v = 6Wh
180 Wh is therefore 30 cells

These cost £4.89 each from http://www.eurobatteries.com/sitepages/nimh.asp

4.89 * 30 = £146.7 which is about $380 AU

NiMh have a higher energy density. 9000mAh for a D cell. They also cost
twice as much.

For the lead acid deep cycle option.
If we can only discharge 30% then we need a battery with a capacity of 600Wh
which is 50Ah at 12V
This would be 2 Yuasa NPC24-12 and costs about the same as the NiCd option.
Two of these are 17.6 Kg !

Grand total $675

We also need a bunch of electronics that contain a high efficiency switch
mode power supply, maximum power point tracker for the PV and battery charge
controller.

Some people have said that 1.5W is too low. Your average consumer access
point will probably have a cheap linear regulator on board because it was
designed to be powered from a mains supply where it is OK to regulate by
throwing a few W away as heat. This will have to go and be replaced by a
much more efficient switch mode regulator. 1.5W should be pleanty.


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