I need to use solar panels to charge lead acid batteries in an off-grid application. I understand that solar panels have a open circuit maximum voltage and an maximum amperage under no resistance, and that one can optimize the power output by regulating the load (resistance). If so, is just connecting 2 -volt solar panels to a lead-acid battery inefficient? Are there devices that will maximize 2 volt output power (by varying the resistance)? Am I on the right track here? Thanks for any help.
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The answer is actually quite complicated, but if you're planning on building just a very small system, most likely, the panel will be small and weak. In this case, connecting a panel that is 8 volts open circuit directly to a lead-acid battery is probably the most efficient way to charge. There are charge controllers that you can buy, some of which actively track the maximum power point for charging your battery. Unfortunately, those controllers might eat 5 or 0 watts, just to get you another few percent of charging efficiency. If your panel is only 50 watts in the first place, you can see that this is not a good deal. If you're getting serious panels (clue: price $500 each), then you may very well benefit from a charge controller with MPPT (max power point tracking). Lead-acid, either a flooded cell like your car battery, or AGM, are the standard for solar energy storage. Lithium ion is better in many ways, being less sensitive to temperature, state of discharge, and they are also lighter. Charging them is also more straightforward with the right circuitry. The problem is, they cost like $500 per kWh, compared with less than a tenth that price for lead-acid.
