# How Many Solar Panels Do You Need For a 300ah Battery?

300 ah battery is an ideal companion for solar panels. No matter how much energy your system generates, it needs batteries to store energy for future use. 300 ah battery is a good choice because it provides capacity and efficiency. But the question is, how long does it take to recharge? How many solar panels do we need? In this article, we will talk something about this.

It takes at least 8 x 100W solar panels to fully charge a 12V 300ah battery in 5 hours. If the battery is only 50% discharged, it will be ready in about 2.5 hours. Lithium deep cycle batteries have a discharge rate of 85-100% and are more efficient.

Battery capacity is measured in amp hours (ah) while solar panels use watts (w). To find out how long the battery will take to charge, you have to convert amp hours to watts and find out how many peak sun hours are available in your area.

If you want to charge an empty 12V 300ah battery in 5 hours, you need 8 x 100W solar panels. The formula is: battery amp hours x volts / available sun hours = watts needed per hour. Using our example again:

300ah x 12V = 3600W; 3600W / 5 sun hours = 720 watts per hour

Your solar power system must produce at least 720 watts an hour: 720 x 5 = 3600 watts.

With 8 x 100W solar panels, your system can generate up to 800 watts an hour. Because solar power is not 100% efficient (more on that later), you should have additional power available. If you need at least 720 watts as in this example, it is better to have an output of up to 800 watts an hour. You can even bump that up to 900 or 1000 watts to be sure.

Why are My Solar Panels not Charging at Full Power?

One of the things you quickly learn about solar panels is you should have more power available than what you currently need. The reason is solar panels cannot produce their rated output continuously.

If you install 300W solar panels on your RV, you might get an average of 285W an hour. This is not a defect but has to do with how solar energy works.