What Size Solar Panel to Charge 100ah Battery?

What Size Solar Panel to Charge 100ah Battery?

If you are looking to use solar power in your home– or for other applications, like an RV– you will need to look into things like battery charging and battery capacity. It is important that you are able to install the right setup for your needs. For instance, if you are working with a 100Ah battery, you will need to know the wattage required to charge it, and the size of the solar power that will be able to complete the task successfully. 

Considerations When Calculating Solar Panel Size

Before you calculate the size of the solar panel that you will need, you should know a few things. First off, you will need to know how many amp-hours are being used. If you know the amount of energy that has been discharged, you will know how much needs to be put back in, and can size the solar panel accordingly! 

You will also want to know what type of battery you are working with– lithium or lead-acid batteries. Lead-acid batteries are more commonly in use, so it is very likely that your battery has a lead-acid cell design. 

When Connecting a Battery to a Solar Panel

Now, when you are connecting a solar panel and a battery, it is important that you do not connect the two directly. This might be okay, however, if the panel power is so tiny that there is barely any power output. Otherwise, you may damage the battery. If you do decide to connect them directly, they must be monitored to avoid any issues.

Instead, fuse your system by placing one fuse between the charge controller and the positive battery terminal, and then another between the positive battery terminal wire and the charge controller. This is a safer way to set up the solar power system. When hooking up your system, you should also be sure that you are taking proper safety precautions by wearing gloves and goggles while you work. After all, it is always better to be safe and take all recommended precautions in case something goes wrong! 

How to Measure Remaining Battery Capacity

When you purchase a battery, it is clear what the total battery capacity is. However, it is not quite as easy to figure out the battery capacity that is left once you start using it. After all, more often than not, your battery is not going to have a battery charge gauge like on your phone! So, how can you measure the remaining capacity of your battery? 

The easiest way to do this is to check the terminal volts with a simple tester, like a multimeter. However, it is important that the battery is left dormant for at least 6 hours before you take the reading to avoid any chemical reactions from interfering with it. 

Battery SOC

You may see the term “battery SOC” when researching battery capacity and solar panels. What is it, you ask? Battery SOC refers to the battery state of charge. The state of charge is the amp-hours that are left in the battery. Battery SOC is measured in percentage points and is an alternative form of battery DOD.

Battery DOD

Another term you may encounter is “battery DOD”. So, what does that mean? It is basically the same as battery SOC, so the terms may be used interchangeably in some places. This stands for battery depth of discharge, which indicates how much power has been taken out from the battery. Battery DOD is the energy that will then need to be replaced with solar, so the term is more suitable for these sorts of conversations. 

What Size Solar Panel Will Charge a 100Ah Battery

If you need to find out how many watts you will need to charge your battery– and therefore, the size of the solar panel you need– you can easily find a calculator online where all you have to do is plug in the values to get your answer! When it comes to a 100Ah battery, you would generally need 180 watts of power to fully recharge from 50% discharge if you have about 4-4.2 peak sun hours a day. If our battery needs to fully recharge, it would take 8 hours to do so with a fully clear sky. It is best to get a solar panel that is more powerful in order to charge the battery faster or to charge it if more than 50% of the energy has been discharged.

Frequently Asked Questions

How many solar panels does it take to charge a 100Ah battery?

If you are trying to charge a fully discharged 12v 100Ah battery, you will need 3 100-watt solar panels. This is calculated with the assumption that the average peak sun hours in your area is 4 hours. If the battery is discharged to 50% of its capacity, you will need 2 100-watt solar panels. 

How fast will a 100W solar panel charge a 100Ah battery?

A 100-watt solar panel that is using an MPPT solar charge controller will be able to charge a 100Ah battery in about 12.5 hours. It is recommended that you use 200 watts of solar panels in order to charge a battery in one day if you are using it for home energy storage. 

How many solar panels do I need to charge a 100Ah battery in 5 hours?

If you want to be able to charge your 100Ah battery in 5 hours, you will need about 240 watts of solar power. This can either be a 240-watt panel, or 2 120 watt panels that are wired in series. 

Can a 100W solar panel charge a 100Ah battery?

You would need a series of 100-watt panels to charge a 100Ah battery. Typically, just one 100-watt panel will not be able to charge your battery successfully. You would need three 100-watt panels because it usually takes 200 to 240 watts to charge.