What Size Solar Panel To Charge 120ah Battery? (Calculator)

What size solar panel to charge 120ah battery? Use our solar panel size calculator to find out or follow the steps given below to calculate the required solar panel size manually.

Calculate solar panel size to charge 120ah battery

Note: Not sure what peak sun hours are and how to calculate them? Follow our guide about peak sun hours.

Calculator Assumptions

• Battery charge efficiency: Lead acid - 85%; AGM - 85%; Lithium - 99%
• Charge controller efficiency: PWM - 80%; MPPT - 98%
• Solar panels efficiency during peak sun hours: 80%
• There is no load connected to the battery.

How to determine what size solar you need for 120ah battery?

Use our above solar panel size calculator and follow these steps:

1. Enter battery capacity in amp-hours (Ah): I have already put 120ah for you.

2. Enter battery volts: Is this a 12v, 24v, or 48v battery?

3. Select battery type: Is this a lead-acid, AGM, or lithium-ion (LiFePO4) battery?

4. Enter battery depth of discharge DoD: DoD is the percentage of the battery that has been discharged relative to the total battery capacity. For half discharged battery Enter 50, if the battery is fully discharged which you can achieve on a lithium battery, ENTER 100.

5. Select charge controller type: Do you have a PWM or MPPT charge controller?

6. Enter desired charge time (in peak sun hours): How fast would you like to charge your battery or how many peak sun hours your location receives?

Now click "CALCULATE" button to find out the solar panel size.

Example

Let's suppose...

• Battery capacity: 120ah
• Battery volts: 12v
• Battery type: lead acid
• Battery DoD: 50% (half discharged)
• Charge controller type: MPPT
• Desire charge time: 7 peak sun hours

Turns out you need about 140 watt solar panel to fully charge a 12v 120ah lead acid battery from 50% depth of discharge in 7 peak sun hours using an MPPT charge controller.

Note: Use our battery charge and discharge rate calculator to find out the recommended charge and discharge rate of your battery.

What Size Solar Panel To Charge 120Ah Battery?

Here are charts on what size solar panel you need to charge 120ah lead acid or lithium battery.

12v 120ah lead acid battery

Charge Time	Battery Type	Required Solar Panel Size
5 peak sun hours	Lead-acid	200 watts
10 peak sun hours	Lead-acid	100 watts
15 peak sun hours	Lead-acid	65 watts
20 peak sun hours	Lead-acid	50 watts
25 peak sun hours	Lead-acid	40 watts

Summary

• You need about 200 watt solar panel to charge a 120ah lead acid battery from 50% depth of discharge in 5 peak sun hours.

12v 120ah lithium battery

Charge Time	Battery Type	Required Solar Panel Size
5 peak sun hours	Lithium (LiFePO4)	350 watts
10 peak sun hours	Lithium (LiFePO4)	170 watts
15 peak sun hours	Lithium (LiFePO4)	120 watts
20 peak sun hours	Lithium (LiFePO4)	90 watts
25 peak sun hours	Lithium (LiFePO4)	70 watts

Summary

• You need about 350 watt solar panel to charge a 12v 120ah lithium battery from 100% depth of discharge in 5 peak sun hours using an MPPT charge controller.

6 steps to calculate solar panel size for 120ah battery (manually)

Here are some steps to manually calculate the solar panel size for your battery.

Steps

1. Convert the battery capacity in watt-hours by multiplying the amp-hours with battery voltage. 

Let’s suppose you have a 12v 120ah battery.

120ah Battery capacity in watt-hours = 120 × 12 = 1440 watt-hours

2. Calculate the battery discharged capacity in watt-hours by multiplying the battery capacity in watt-hours by the battery depth of discharge limit.

Lead-acid, AGM, and gel batteries come with a 50% depth of discharge limit, and lithium batteries with 100% DoD. For a more accurate number ask your manufacturer to look at the battery specs sheet.

Let’s suppose you have a 120ah lead-acid battery.

Discharged Battery capacity in Wh = 1440 × 0.5 = 720 watt-hours

3. Take into account of the battery charge efficiency rate by multiplying the battery capacity after DoD by 1.15 for lead acid and 1.01 for a lithium battery.

Battery charge efficiency rate: Lithium: 99%; Lead-acid: 85%;

Power required to charge 120ah battery = 720 × 1.15 = 828 watt-hours

4. Calculate solar power required to charge the battery in one peak sun hour (1kW/m² of solar radiation) by dividing the battery capacity value (after adding charge efficiency factor) by the desired number of charge peak sun hours. 

Let’s say you want to recharge your battery in 4 peak sun hours.

Solar power required in peak sun hour = 828 ÷ 7 = 118 watts

5. Take into account the charge controller efficiency rate by multiplying the solar power required in peak sun hour by 1.2 if you're using a PWM charge controller and 1.02 for an MPPT charge controller. Charge controller efficiency: PWM: 80%; MPPT 98%.

Let’s suppose you’re using an MPPT charge controller.

Solar panel power required after charge controller = 118 × 1.02 = 120 watts

6. Now add 20% to cover up the solar panel inefficiency for real world conditions.

Solar panel size required = 120 + 20% = 144 watts

120ah Battery Capacity In Watts

• 12v 120Ah battery is equal to 1440 watts or 1.4kWh
• 24v 120Ah battery is equal to 2880 watts or 2.8kWh
• 48V 120Ah battery is equal to 5760 watts or 5.7kWh

Related Posts

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• How Long To Charge 120ah Battery?

I hope this guide was helpful to you. still, have any confusion? LEAVE A COMMENT or contact us. Thank You!