What Size Solar Panel to Charge 100Ah Battery?

Solar with battery storage is the most popular energy solution for small business, off-grid activities. However, how to make sure that the solar panel will charge the battery effectively is quiet important. Before you select the solar panel kits, let’s read the blog post and find out what size solar panel to charge a battery?

There are 6 factors you’ll need to consider when charging a battery:

Battery Voltage(V): What is your battery’s voltage?

Battery Amp Hours (Ah): What is your battery’s capacity in amp hours?

Battery Type: lead acid or lithium (LiFePO4) battery?

Battery Depth of Discharge (DoD): What level of discharge is your battery at? 100% means fully discharged and 0% means fully charged.

Solar Charge Controller Efficiency: Will you be using a PWM or MPPT charge controller?

Desired Charge Time (in peak sun hours): How quickly do you want your solar panel to charge your battery, in peak sun hours?

Solar Charge Controller

There are two types of solar charge controllers available, is PWM based and MPPT based.

MPPT based solar charge controller is far mush advance and efficient than PWM based solar charger, due to which PWM based are not popular.

The efficiency of PWM based Solar Charge controller: 68 to 73%

The efficiency of MPPT based Solar Charge controller: 95 to 98%

High Recommended MPPT solar charger to charge battery from solar panels. Different solar charge controllers affect a lot. SIH Hybrid Inverter with MPPT solar charge contorller.

What Size Solar Panel to Charge 12V 100Ah Lithium Battery?

Let’s assuming that you have a 12V 100Ah lithium battery and an mppt charge controller, you want to charge your battery from 100% DoD in 5 peak sun hours with solar panels.

Firstly to calculate the Total Energy Capacity

Voltage(V) x Amp Hour = Watt Hour(Wh)

12V X 100Ah = 1200Wh

Amount of power generated by 1 Watt solar panels

You may think that to generate 1200VA of power in a day you will require 1200Watt of solar panels, but that’s not true. Because 1000 Watt of solar panels didn’t generate 1000 Watt of powers in one hour and you have 5 to 8 hours of sunlight to charge your batteries.

Suppose power generated by 1 Watt of solar panels

In 5 Hours: 4VA

In 8 Hours: 6VA

MPPT charge controller is 95% efficiency

The numbers of solar panels required to charge 12V, 100Ah battery for 5 hours of sunshine will be equal to 1200Ah/4/0.95 = 315 Watt of Solar panels


To charge a 12V, 100Ah lithium battery in 5 hours of sunshine you will require a minimum 1 number of 315 Watt of solar panels with MPPT based charge controller and seasonal structure.

By using PWM based solar charge controller, you require a solar panel rating will be increased by 30%.

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