Making solar-powered batteries

Energy & Sustainability Technology
Making solar-powered batteries

Norwegian maker Knut Karlsen got some flexible solar material and decide to try his hand at prototyping solar-powered batteries. He wrapped the cells around some NiMH rechargeables he had on hand and wired them up. He writes:

This setup is in fact a (quite weak) trickle charger. It is not ideal, but really convenient. A second version would have some electronics (to check when full) and capacitors to charge the batteries more efficiently, but the battery would then be smaller if it all needs to fit within a C-cell battery.

The SunCat Batteries – DIY prototypes

16 thoughts on “Making solar-powered batteries

  1. Jon says:

    Wouldn’t nicads (aside from their undesirable properties) be a better choice than NiMH? I was under the impression that the former likes trickle charging while the latter prefers a pulse in the charging profile.

  2. Jeff says:

    I have adapters that fit around a AA battery so that it fits inside the space of a C cell. There’s lots of empty space inside one of those adapters; I’m sure some crude charging electronics could be integrated in there for more efficient charging.

  3. jammit says:

    Actually, both NiCd and Nimh batteries can charge with a trickle charge or pulse. NiCd are better suited to trickle charging because at low charging currents they can take an overcharge. They simply convert the extra to heat, which it can easily dissipate at low current levels. The Nimh can be overcharged like a NiCd, but they don’t like it too much. A fancy charger looks at both the temperature and the dip (NiCd) or rise (Nimh) in voltage that occurs when you’re near the end of charging. It would be pretty neat to do this to a Li+ cell, but use one of these to protect the battery:

  4. Justin says:

    Those flexible solar cells look great! I’ve got flexible cells, but they’re the brown ones that have been around for a few years, their primary feature is their flexibility rather than efficiency. These ones have that blue silicon look, which suggests they’re higher efficiency (and they look very pretty too – good for decorating ipods and the like).

    But there is no indication that this tech is available to us in the public sphere yet.

    Does anyone have any leads on where/how to obtain some?

  5. garethb2 says:

    You can get flexible solar cells on eBay.

  6. JanSchotsmans says:

    I’ve been told all my life never ever to leave battery’s in direct sunlight because they’ll start to leak and some types might even go ballistic.

    Isn’t that the case NICA and NIMH’s?

  7. Justin says:

    No, the ones on ebay are of the type I already have. They’re not the same thing.

  8. jimmyjo says:

    Single junction silicon cells generate about 0.53V not even close to the 1.2 or 1.3 needed to charge a NiMH or NiCD.
    Right now the solarcells are actually draining power from your rechargeable batteries as you dont have a diode in series.

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Gareth Branwyn is a freelance writer and the former Editorial Director of Maker Media. He is the author or editor of over a dozen books on technology, DIY, and geek culture. He is currently a contributor to Boing Boing, Wink Books, and Wink Fun. His free weekly-ish maker tips newsletter can be found at

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