what size solar panel to charge 100ah battery

What size solar panel to charge 100ah battery is determined by the wattage of the solar panel you need to buy

If you have a 12 volt 100ah battery and you buy a 300w solar panel, it will take you 4 hours to fully charge the battery, you can calculate this using the following formula

W (watts)/V (volts) = A (amps)

We can calculate from the formula 300/12=25A which means that the output current of this panel is 25A

Then we can calculate how long a 12 volt 100ah battery can be fully charged

According to the formula 100AH/25A=4H which means that to fully charge a 12 volt 100ah. It would take 4 hours to fully charge

If you have a 24V 100ah battery, it will take 8 hours of work for your 300w solar panel to fully charge this battery.

In fact, the actual charging time is still longer than this, this only means that the solar panel is always working at 300W, you also need to consider the household light environment, suppose your home receives 6h or less of light per day, then your charging time will require two or more solar panels or higher efficiency to charge your battery, of course it is best to have a controller to to adapt the power supply for charging.

Nowadays, solar panels can also work at night, but their efficiency is very low compared to the sunlight during the day, so if possible, you can place different solar panels at different locations in your home to ensure that the whole home or the whole power system works.

In summary

If you have a 12 volt 100ah battery and you buy a 300w solar panel, it will only take you 4 hours to fully charge it.