1. What size solar panel do you need to charge your 12V battery?

This answer is not fixed, because the size of the solar panel has a direct relationship with its power output, so in principle, as long as the power of the solar panel is not too low (too low power can not make the battery fully charged) or too high (too high a power will lead to a short circuit), in a range can be for your 12V battery charging, only that different sizes of solar panels to fully charge the 12V battery in different times. It’s just that different sized solar panels take different amounts of time to fully charge a 12V battery.

Here is the formula for calculating the size of solar panel needed to charge your 12V battery:

1. First, you need to know the specific parameters of your 12V battery, such as the capacity of the battery and the current required to fully charge the battery. Let’s assume that the voltage of the battery is 12V and the capacity of the battery is 100 ampere-hours.

Immediately after that you need to calculate the energy required to fully charge the battery.

Battery energy required = battery voltage x battery capacity x charging current.

The battery demand factor refers to the ratio of the maximum current needed to charge the battery to its rated capacity. In simple terms, the battery needs to receive a certain amount of current from the solar panel in order to fully charge the battery for a fixed period of time, and this factor is usually 0.1 to 0.3.

Assuming a demand factor of 0.2, the charging current would be 1.2A, and substituting the above known data, the energy required by the battery would be 14,440Wh.

2. Next you need to determine how many hours of effective light you need to fully charge your battery. Assuming that you need to fully charge your battery in 5 hours of effective light,

the output of the solar panel = energy required to fully charge the battery ÷ hours of effective light

and substituting this into the data gives you an actual output of 288 watts for your solar panel.

3. Subsequently, you need to consider the solar panel work process will occur during the loss of energy, according to the data show that the actual output power of the solar panel is about 80% of the nominal output power of the solar panel.

So the actual output power = nominal output power x conversion efficiency,

substitute the data to get the nominal output power of the solar panel is 360 watts.

4. Finally, you need to know the peak power density of the solar panel (peak power density refers to the maximum output power per square meter of the solar panel), in general, the peak power density of common solar panels on the market is 160 watts per square meter to 200 watts per square meter.

Assuming that the peak power density of the solar panel you choose is 180 watts per square meter, then according to the formula,

the nominal output power of the solar panel = the area of the solar panel x the peak power density of the solar panel

and substituting the data to get the area of the solar panel is 2 square meters.

In summary, if you want to fully charge your 12V 100Ah battery under 5 hours of effective light, 2 square meters of solar panels with an output of 360 watts. Of course, if you choose a more powerful solar panel, then it will not take 5 hours of effective light to fully charge your 12V battery.

2. Summary

By knowing the formula for calculating what size solar panel you need for a 12V battery, you will be able to do the math before you buy a solar panel so that you can get the right one for you. Of course, you can also consult the solar panel manufacturer directly and they will be happy to answer your questions.