Gallery: SunCat: Solar Batteries Powered by Sunshine


Designer and inventor extraordinaire Knut Karlsen recently unveiled an inspired approach to portable power that can’t be beat for its elegant simplicity: a prototype battery capable of charging itself when exposed to sunshine. His slick set of SunCat C-cells are wrapped in flexible photovoltaic panels and will slowly recharge when left to bask in the sun – just like a cat.

Rechargeable batteries are a boon to eco-enthusiasts who use portable electronics, however all too often they require additional peripherals in order to keep them charged. These devices generally take the form of a black box loaded with non-biodegradable plastics and heavy metals – not very earth-friendly.

Karlsen’s SunCat batteries circumvent chargers completely by integrating solar cells within the batteries themselves. To make these prototypes he attached 1.8V flexible photovoltaic cells onto 1.5V NiMH rechargeable batteries and connected them with a conductive silver pen and a few flat wires. The effect is similar to a trickle charger, which slowly charges a battery and can be left attached indefinitely without overcharging.

Karlsen plans to continue to tweak the batteries, adding capacitors to charge the batteries more efficiently and electronics to check when the batteries are full. We’re excited to see the results of his testing – finally, a justification for all those see-through gadgets with clear cases!

+ SunCat Batteries

Photos by Knut Karlsen

Via Notcot


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  1. Thoiseqa August 28, 2011 at 5:37 am

    For example, a breakthrough in better batteries could supplant hydrogen. Better solar cells could replace or win out in this race to the fuel of the future. Those, I see, as the three big competitors: hydrogen, solar cells and then better batteries. ying yang Team

  2. fjk July 22, 2009 at 1:51 am

    Solar panels ought ot be placed where optimum charge is archieved. The shape and location of the panels on the batteries themselves does not seem optimal. Also ‘gmoke’ sun in not only in north. The predominant location of the sun depends on the hemisphere/latitude at which you are located. Ie sun is generally in the north for those countries in southern hemisphere.

  3. madwaxer May 7, 2009 at 2:26 pm

    now use some ultra capacitors and woha!
    me want 3Million of these on the roof of my house, under a bullet proof glass sheet in mineral oil. (to stay cool)
    hmm might need a bigger house!

  4. Taz Abas March 8, 2009 at 10:32 am

    We are manufacturers of various products that utalizes AA Batteries. We are interested to purchase CunCat Solar Rechargable battaeries.

    Please contact me.
    Taz Abas

  5. Zaphraud March 2, 2009 at 6:14 pm

    Assume a 10% solar efficiency, which from what I understand is a little generous, but still… now, look at the maximum cross-sectional area that the side of the battery can present to the sun* and the solar power per square meter, and feed all that into Google calculator:

    1000 watts/meter^2 * 1.9 inch * 1 inch * .10 = 0.1225804 watts

    Probably enough that a good design could prevent loss thru self-discharge.

    Of course, as an actual Arizona resident, the first thing that comes to mind is the fact that its a profoundly bad idea to leave any type of battery in direct sunlight for extended periods of time. It really wears them out!

  6. mdf February 22, 2009 at 10:35 am

    Off by a full 3 orders of magnitude! How embarrassing. Ah well.

  7. mdf February 22, 2009 at 9:05 am

    The idea seems cool … until some arithmetic is done.

    The area of a C cell (excluding the end-caps of the cylinder) is about 0.004 square metres. So if the panel had perfect efficiency, and you illuminated it all with a full Arizona sun (~1000W/m^2), this battery would collect about 4mW of power. A typical NiMH today is about 2.9Ah, or about 3700mWh of energy (this is probably a high estimate, but not by much). So we can expect a total charge time of about 3700/4 = 925 hours = 38 days. The sun doesn’t shine for 24 hours — even in Arizona — so this 38 days is going to be more like 80 or 90 days in reality. Add in the fact only half of the cylinder is under illumination, and the circular geometry says reduces this by half again (cosine), and that the panel is going to be about 15% efficient, it looks like it’s going to take a several years to recharge the battery.

    In essence, the average rate is about 0.1mW of power.

    However, NiMH have a fairly high self-discharge rate of about 1% per day, after about a 5-10% drop on the first day (from a fully charged battery). Ignore the first day, we have: 3700*.01 = 37mWh loss/24hours = 1.5mW average. A discharge rate in excess of the trickle charge rate from these solar panels, suggesting the panel can’t even maintain the charge on a fully charged battery.

  8. Lucky Archer February 20, 2009 at 10:53 am

    YES! This is a brilliant idea. Bravo. Two thumbs up. (Y) (Y)

  9. angie717 February 19, 2009 at 8:14 pm

    I like the idea of this solar-powered battery. Maybe one day someone would go a big step further (this may be a dumb idea, I’m not a science genius) and put a solar panel on a car battery. No more beeing marooned on the side of the road with no one to jump your battery!

  10. dareka1 February 19, 2009 at 9:31 am

    Why stick them on each battery? Why not have it as a sleeve that you pop the battery into? That way you don’t have to throw away the solar panel when the batter is finished, and it won’t damage the solar panel when you put it into the appliance.

  11. gmoke February 18, 2009 at 10:56 pm

    There is no reason to wrap the solar cells completely around the battery. Sunlight comes from the South not the North. I would also suggest that Karlsen start with AA cells rather than C cells as AAs are the most common batteries in use.

  12. mahalie » Mithun February 18, 2009 at 8:54 pm

    Brilliant…and dare I say, obvious in retrospect. All batteries should be equipped like this!

  13. Helman700 February 18, 2009 at 11:42 am

    Didn’t I learn when I was a kid not to sit batteries out near a heat source because they explode? I may be making that up.

  14. hannan February 18, 2009 at 7:30 am

    A great idea! innovative :)

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