February 26, 2009 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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