22 June 2009

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

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).


  1. I wanted to say they I really enjoyed this post as well as a lot of the other information you've shared here.

    This is an awesome blog!

  2. Thank you Frank.
    You are one of the few that bothered commenting on my blog.
    At more than 6500 hits to date I assume that most people are:
    a) too busy to leave a reply (but have enough time to read it)
    b) too smart to leave a reply (but seem to refer to it often)
    c) too unappreciative to leave a reply (...)

  3. Gnarly - lots of thought and effort put in to your blog articles. As a newby to kayaking, hope to one day put into practice some of your tips, tricks and gizmo guides.

  4. on: http://www.westcoastpaddler.com/community/viewtopic.php?t=3157
    Mark Schilling says:
    >>Posted: Thu Jul 09, 2009 12:12 pm Post subject:


    Looks like a good setup. I'm not totally up on how input voltage affects different battery types, but the regulator in your setup may not be required - my guess is that the input voltage to the battery is probably within the acceptable range (better to be too high than too low!). What is the output voltage from the regulator like?

    I've used a similar setup with good results, but the SLA's seem not to last very long (they're pretty cheap though, so no biggie. I just don't like going through them quickly as they're quite toxic to the environment to keep buying new ones!). SLA's seem to prefer a lower current to charge, so the only things I'd want to keep an eye on are related to overcharging the battery or charging at too high a rate and / or charging the SLA for too long during the day. A bit of basic math shows that your setup (4.5watt 12V panel outputs a maximum current of about 375mA, so to charge a 1.3AH battery should take about 3.5 hours at 100% efficiency, or about 4.5 hours actual) might charge the battery a little faster than it really would prefer for maximum battery life (I think 1/5C or about a 5 hour charge is recommended as a maximum). Typically you probably lose about 25% efficiency so you're probably ok - I wouldn't try to charge any faster. For best performance you'll want to ensure you're not leaving the panel connected too long, as the battery will overcharge and you can greatly reduce the capacity of the battery by doing so.

    Oh wait - it looks to me like your regulator has an automatic cut-off when the battery reaches a voltage of about 13.8 volts, so that's probably a good investment. There are better ways of charging but they require more bulky 'smart chargers' (they go into a trickle charge mode and taper off the charge rate) so yours is probably the best mix of size, cost, and minimal complexity.

    Charging your devices from the 12V system is straightforward and pretty much ideal - if the device (phone etc.) comes with a 12V car charger, let it do the work of regulating input voltage and cut off the current supply when it's charged. It's a bit more bulk to carry around a 12V charger for each device, but still the best option to protect costly equipment with chargers that were designed specifically for each unit.

    I seem not to be doing a lot of longer trips these days, so I'm going to stick with my simple 12V 12W panel and a 4-cell AA 'smart' charger. It'll charge AA's and AAA's for my cameras, and I'll just have to conserve batteries with other devices (cell phone, PDA, VHF etc.). Perhaps if I start doing more multi-week trips I'll put together another setup like yours with a 12V battery and regulator. I'd be hard pressed to come up with a design that's better for the average user than yours though - that is, while keeping it simple, effective and as little bulk as possible. Nice work.

  5. Hi Gnarly. My wife and I cruised on a 32-foot sailboat in the 1980s using both solar panels and wind generators to keep the electronics (ham radio, etc.) working. I did not use any "regulator" except that I did put a germanium (not silicon) diode in the circuit to eliminate reverse current. SLA batteries (deep cycle) and probably bigger than yours but in the tropics. No problems with 18vdc "voltage" from the panels (disconnected). These were 30-watt (two) panels. Worked very well but their UV protection failed. Would have been ok if I had just kept them out of the sun.

    I kayak now from a "mothership" (www.nwkayaking.net) and so far have not needed solar chargers but I'm always looking at the technology if I take longer trips. Nice blog.

    Craig Jungers
    Moses Lake, WA

  6. Craig, thank you for your input.
    Hmmm, a few people have mentioned to not bother with the regulator.
    I might have to do a bit of testing myself and maybe revise the system.
    However I don't think that the regulator is taking away much power.
    Skipping the regulator would make the set up cheaper too...

  7. Very Helpful Article!
    Solar Batteries

  8. sounds pretty cool it would be great to know the weight & dimension of solar charger.

    kabel adapter

  9. I recently came accross your blog and have been reading along. I thought I would leave my first comment. I dont know what to say except that I have enjoyed reading. Nice blog. I will keep visiting this blog very often.



  10. dimensions for solar panel are: 165mm X 232mm.
    I don't have weights available (sorry, no accurate scale handy to measure that...)

  11. another gnarly convert here.

    I'm heading off next week for 8 or 9 nights in Macquarie Habour / Gordon river and am last minute trying to work how how to fly under my finance ministers budget radar and set up a solar system.

    I think i'll do my best to copy your system. My major sticking point to date has been getting the power to a battery in a sealed bulkhead. Putting it all in a bag is genius.

    Also de-shelling the cells from the hard case, again brilliant.

    Like you "dog" i have a similar battery on the bilge and see the benefit of being able to interchange them.

    Most Appreciative.

  12. lots of thought and effort put in to your blog articles. As a newby to kayaking, hope to one day put into practice some of your tips, tricks and gizmo guides.

    how to build a solar panel

  13. Thanks for the recharging idea. I am going to try and modify this technique for an up coming trek in Nepal. I am going to elimanate the 12 volt battery ( to heavy to pack (poor sherpa)), and buy a second lithium battery and charge it while running on the first battery.

    thanks Mark

  14. my best to copy your system. My major sticking point to date has been getting the power to a battery in a sealed bulkhead. Putting it all in a bag is genius.
    miami limo

  15. Well, I used to have various outdoor gadgets and I find it pretty expensive to purchase batteries every now and then.. Today, I have my car solar powered, and the batteries too!



  16. Thanks mr gnarlydude for a most informative blog all round, esp this post. Not knowing the difference between a volt and milliamp hour, I've shamelessley borrowed a few of your and Matt's ideas, spent a few bucks at Jaycar and come up with my own version to power phone, vhf, cameras, gps etc. Excellent (as long as the sun's shining!) I guess you don't worry about that too much in qld :-). my only 'improvement' is to house the battery, regulator etc in a $2 tupperware container from the reject shop - rather than a pelican case like Mattie - just in case the map case leaks.

  17. Guy, there is no "shame" in borrowing my ideas or why would I bother posting them on the blog :-).
    I believe in sharing my ideas for NON commercial purposes.

    Putting the components into a sealed box is good however the regulator is already sealed and so it's the battery.
    An accidental dunking should not kill those components however continued exposure to salt water probably will.

  18. Hi there,

    Stumbled across your blog as i am looking for a solar unit to charge my camera battery and possibly a small laptop so that i can transfer memory to external hard drive. I will be in Patagonia, climbing for two months and therefore a unit such as the one you use could what i am looking for. Where did you purchase it and how much. Also, do you think it would be sufficient for what i have in mind, taking into consideration weight and the amount of power i would need. Thanks and good luck with future trips.
    my email is r.safeasmilk@gmail.com

  19. Rhys, the solar panel and charging system in this post is regarded as a low cost solution for sea kayaking were weight is not really a big issue.
    The SLA battery is rather heavy and I think there are better solutions out there but more expensive. Chances are you will keep you solar panel stationary at base camp and it will be able to charge the battery while you will be out for the day. Laptop could be directly charged that way. I don't know your circumstances and your power requirements. It would be worth looking at site/blogs in the climbing/backpacking community.
    I think flexible solar panels are more suited to your requirements.


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