If you want to figure out how long to charge a 12V battery with solar panel, the formula you need isn’t complicated, but you must take into account a few important things. It’s tempting to try to calculate charging time by looking at your battery size and solar panel power; unfortunately, this isn’t enough information.
How Long Is It to Charge a 12V Battery With a Solar Panel?
How to Calculate Solar Charging Time for Your 12V Battery
Here’s the basic calculation to determine how long to charge a 12v battery with a solar panel:
Watt-hours of the battery when fully charged / battery capacity
Here’s how to get your watt hours of battery when fully charged:
Number of volts X amp-hours
Here’s an example: if you have a 12-volt battery with 26 amp-hours, you’ll have 312 total watt-hours of power when your battery is fully charged (12X26=312). If your battery capacity is 50 watts, you’ll 6.24 hours of sun to fully charge your battery (312/50=6.24.
Factors That Impact Charging Time
As we’ve already mentioned, however, calculating how long to charge a 12v battery with a solar panel isn’t that simple, and there are many reasons for this. To start with, you’re likely not starting from zero. Most solar batteries aren’t designed to be completely drained and should be recharged by 50%, meaning your total charge time will be much lower.
However, you should also consider that environmental factors heavily impact how long it takes to charge a solar panel. The angle of the sun (or the angle of the solar panel to the sun), for example, has a huge impact on how much power is “collected.”
Another factor is the temperature. Your panels will charge at their optimal efficiency at 25 degrees Celsius, but if it’s hotter, you’ll start to loose charging efficiency, which will take longer. Many people become frustrated with their batteries in the winter, thinking there’s a problem, but it’s not the hardware at fault, it’s the sun. A day or two of cloudy weather, for example, could significantly lengthen how long you’ll have to wait for a fully charged battery.