Solar panel battery charger

There is in increasing number of gadgets available for outdoors activities.
The most common seem to be digital cameras, GPS and communication devices (radios, cell phones).
Most of these gadgets are operated by rechargeable batteries with only a few having the option of running on disposable batteries.
A few years ago, one of my criteria for buying a new digital camera was that it should be able to run on AA batteries. I wanted my camera to perform for lengthy amounts of times between locations where I would be able to recharge batteries.
Occasional trips into remote areas would see me away from power outlets.
The camera works great and I pack several sets of AA batteries with me.
But the camera is not waterproof.
My Olympus waterproof camera needs to be recharged (can not run on disposable batteries).
I needed to be able to recharge my camera's battery.
The obvious choice for a mobile power source available in the remote locations I would visit is the sun.
In Australia we have plenty of it.
A solar panel to harness the sun's energy was my next item.
While simple in concept a solar panel proved a bit more complex than first envisioned.
I needed an inexpensive solar panel that would generate enough power for my needs.
While some expeditioners equip themselves with large solar panels to be able to supply very power hungry devices (laptops) I just needed enough juice for my little camera.
I found a small solar panel that would supply enough power for my battery charger: a 12 Volt 4.5 Watt solar panel.
The panel would supply power to my charger while the sun shines (duh) but that’s when I would be using my camera.
I needed a large battery to store the power during the day and then “transfer” that power to my camera battery.
I chose a 12V Sealed Leaded Acid (SLA) 1.3 Ah unit (the same type of battery that I use for my bilge pump). Not too heavy but with enough capacity to recharge my 1200 mA camera battery.
Once I purchased the solar panel I tested the voltage output in bright sun: a whopping 20V! too much for my battery.
I solved the problem with a voltage regulator that would reduce the output from my solar panel and charge my SLA battery at the desired level.
The voltage regulator would also prevent the current from my battery flow back to the panel when the sunny conditions would not be happening (overcast, shadow over panel, left plugged in overnight).

components wired up
The solar panel was removed from it’s original plastic casing to reduce bulk and placed into a waterproof map pouch: WXtex map case.
The pouch has clips on the corners that I can secure to the perimeter lines of my kayak.

slim profile and removable
I usually place my solar panel towards the stern while paddling but I can easily remove the panel and place it in a more sunny place if the kayak happens to be resting in the shade when ashore.

WXtex waterproof map case
At night, I disconnect the SLA battery from the solar panel and connect it to the camera battery charger.
Obviously the SLA battery can be used to recharge many other devices (VHF radio, music players etc.) as long as the device charger is compatible with 12V power source (many after market chargers are).
An advantage of the removable pouch is that at times, on long trips, real estate on the deck of the kayak can be scarce and the pouch can sit on top of other items (paddles, bags etc).

PS Matt Bezzina has told me of his version of solar panel charger: here




PPS AUG09:
One reader's email prompted me to test the voltage output from the solar panel. He was under the impression that no harm would occur if the battery would be charged unregulated.
The below picture shows voltage readings at different states.


1) a reading of 18V. was achieved in full sun. The battery was connected to the regulator.
2) a reading of almost 20V. was with the regulator and no battery connected.
3) a reading of 13.6V. with the battery getting charged without the regulator.
(A reading of 22V. was given with panel alone, no regulator).
The reading of 13.6V. means that a lot of the load is getting to the battery that eventually in time will overcharge once full ruining the battery in the long run.
With the regulator the battery is charged slower and once it reaches full charge will not continue to receive current and become overcharged.
In conclusion: the addition of the regulator will extend the life of the battery substantially especially if the battery is left charging once full (unattended).