Solar wrapped batteries charge themselves

21:45 February 25, 2009 PST

The solar rechargeable battery

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From the files of “why don’t they make that?” comes a rechargeable battery with integrated solar cell charger. The “SunCast” prototype uses flexible solar cells from IFE and some C sized NiMH rechargeable batteries. Scientists at IFE have been experimenting with the production of flexible solar cells and were kind enough to send some samples to the “SunCast” battery designer Knut Karlsen.

The flexible solar cells are rated at 1.8v and are wrapped around the batteries and connected to the positive and negative terminals with some flat wires from a broken camera lens. Once connected the solar cells act like a very weak trickle charger.

There is no other circuitry so Knut plans to make a second version that includes some electronics to check when the cell is full to prevent over charging, as well as add some capacitors to charge the batteries more efficiently. With added circuitry the battery would then need to be smaller if it all needs to fit within the same dimensions as a C-cell battery.

While it seems like one of those ‘so obvious it must be good’ ideas many readers will note that putting batteries in direct sun light for extended periods may not be such a great idea. As the battery cells are cylindrical only a small percentage of the solar cell will be in direct sun light at any one time therefore considerably reducing their efficiency. The flexible solar cells have no output current quoted and as the inventor himself has not tested the prototype, it may in fact be a good idea to hang on to that plug in battery charger just a while longer.

Paul Evans

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User Comments (3)

Now this could inspire more devices being made with transparent battery covers.

Abandonvehicle

- February 27, 2009 @ 06:02 am

if solar thin film photovoltaic collector will be blocked from incoming sunlight, you could put the battery or batteries on top of a mirror surface so that the batteries will take advantage of the solar thin film better. otherwise, the batteries can be manufactured with smaller thin film area on them, such as only half of the battery that will be exposed to sunlight. you mentioned the problem of the batteries getting too hot in sunlight; a small portion of the electricity can be used to power a small fan to increase cooling rate for a large array of these batteries; the heat produced in this way could be used to heat the hot water for a household, while the batteries can be the battery to provide solar elecricity at night. so you would have a combined photovoltaic electric collector with battery array and solar hot air, which can be applied to direct air heating and/or preheating the hot water supply partially to reduce other fuel consumption.

- February 27, 2009 @ 10:02 am

Since putting batteries in direct sunlight is generally a bad idea, why not coat a battery-operated device with cheap solar cells and let the device charge it's own batteries.

Polly Anne Mobley Aylor

- February 28, 2009 @ 10:02 am