do charge controllers with boost capability exist, and who might sell them?

[louisphily]

I am interested in capturing some of the low voltage electricity coming from a solar panel (that are used to recharge batteries) on a cloudy day. These solar panels come with a charge controller to regulate the electricity that goes into charging the battery, but it rejects all the electricity that is below a certain voltage (for example anything below 8 Volt). So I was wondering if they are any charge controllers out there that also has the capability to boost the low voltage electricity to a higher voltage, so that this low voltage electricity is saved. i tried asking digikey and sunkeeper but none of the say they sell such a device.

 

[James]

Check out the page below.

You get maximum power from a solar cell when you maximize the product of junction voltage and current. You get maximum voltage when no current flows, and maximum current when there is no potential across the junction, but in either case the cell is doing no work. The best value is somewhere between the two conditions.

You can't get more power out of a cell than this theoretical maximum, but it is definitely possible to step up (and the controller you mention very likely does this). Unfortunately, this incurs a loss in efficiency, and at some voltage the amount of power gained from the cell just breaks even with the converter loss. You could add a boost converter but you might find that it doesn't provide enough power to run the charge controller.

You might get away with charging batteries in 2V banks during low cell output, and then switching them over to a higher voltage configuration to discharge or charge under better light.