Solar Battery Charge Time Calculator

Use this solar calculator to figure out the estimated charge time of any voltage (12v, 24v, 48v), Capacity, and type of battery (lead-acid, AGM, Lithium, or LiFePO4)

Make sure to read the instructions given below to understand this process better.

And also I’m gonna share some more tips on “how you can increase the efficiency of your solar system”

so if you’re a newbie i would highly recommend you to read that part which will help you select the right size and type of solar system for you

Solar Battery Charge Time Calculator​

Solar Panel Size
Watts
Battery Capacity (Ah)
Ah
Battery Volts (V)
Volts
Battery Type
Battery Depth of Discharge (DoD)
%
Charge Controller Type

Disclaimer:

1- The estimated charge time is not the total number of sunlight hours but the number of peak sun hours (Read below for better understanding)

2- The estimated battery charge time is based on if there’s no load connected with the battery while charging (Don’t worry I’m going to cover this in detail If you’re running any load while charging)

Calculator Assumptions

  1. Lead-acid, AGM, & Gel Battery charge efficiency: 85% 
  2. Lithium (LiFePO4) charge efficiency: 98%
  3. MPPT Charge Controller: 98% efficient
  4. PWM Charge Controller: 80% efficient
  5. Solar Panel Power Output: 80% of its full capacity (which is the most common figure)

Use this calculator to figure out how many watts of solar panel you would need to recharge your battery in desired peak sun hours.

How Many Peak Sun Hours In A Day?

Solar peak sun hours are the number of hours when the intensity of sunlight is 1kw per meter square (1kW/meter2)

Because solar panels are designed to produce 100% of their rated wattage power in standard test conditions (STC)This includes 1kW/meter2 sunlight intensity, 20o C temperature, No wind, & perfect tilt angle

So that is why you’ll see most of the experts refer to peak sun hours when talking about solar charging time or solar panel output

  • 1 peak sun hour = 1000 watt/meter2
  • 0.5 peak sun hour = 500 watt/meter2

in the morning sun hours, you may receive about 200 watts/meter2 of sunlight intensity and in the noon time it can go up to 1000 watts/meter2

How to calculate peak sun hours

So here in Florida city we receive about 5 peak solar sun hours or 5000 watts/meter2 of sunlight intensity in a day on average Click here to check the number of peak sun hours in your location

For Example, it would take 6.7 peak sun hours to charge my jackery 1000 portable power station with my Renogy 200W solar panel.

So in real life, it means it would take one day and 3-4 hours of the next day to fully recharge it.

That is why i have purchased two 200W solar panels so i can recharge my portable power station in one day during my RV trip

How To Calculate Battery Charging Time?

Here are some simple steps which you can do to calculate the charging time of any size battery in the future without any need for an online calculator

Step 1 – Convert Battery Capacity Into Wh

Battery capacity is measured in amp-hours but the solar panels are rated in watts so converting battery amp-hours into watt-hours will make the calculation easy

Battery Capacity Wh = Battery capacity (Ah)*Battery volts

Use this formula to convert the battery capacity in watt-hours

For example: 12v 200Ah battery

200*12 = 2400Wh

if you have a lead-acid or AGM battery which usually has a depth of discharge limit of 50%

2400*0.5 = 1200Wh

So you’d require 1200Wh total capacity output from your solar panels to recharge lead-acid 12v 200Ah battery

Step 2 – Divide The Battery (Wh) By Solar Panel Wattage

Battery charge time formula

Battery charge time = (Battery capacity Wh/Solar panel Watt) + 30%

30% is added to cover the losses which will occur due to various reasons which i’ll cover in a bit

For Example: if you’re using a 400 watt solar panel with an MPPT charge controller

1200/400 = 3
3 + 30% = 3.9 peak sun hours

400 watt solar panel would take about 4 peak sun hours to charge a 12v 200Ah lead-acid battery from 50% depth of discharge using an MPPT charge controller

Must Read: Maximum Charging Current & Voltage For 12v Battery

Note: if you’re using a PWM charge controller then multiply this value by 1.2 for battery charge time hours. Also, i assumed that you’re using the right size cable for the charge controller and from the charge controller to the battery bank

Don’t know how to select the right size cable? Keep reading I’m gonna cover this in a bit.

Chart – How Long To Charge 12v Battery With Solar Panel

Here’s a chart on how long it will take to charge a 12v battery with any size solar panel

12v Battery (Ah)
Lead-acid (50% DoD)
Solar Panel SizeEstimated Charge Time
(Peak Sun Hours)
20Ah100 watt1.7 Peak sun hours
50Ah100 watt4.4 Peak sun hours
70Ah100 watt6.1 Peak sun hours
100Ah100 watt8.7 Peak sun hours
120Ah100 watt10.5 Peak sun hours
150Ah100 watt13.1 Peak sun hours
200Ah100 watt17.5 Peak sun hours
220Ah100 watt19.2 Peak sun hours
300Ah100 watt26.2 Peak sun hours
400Ah100 watt35 Peak sun hours

How long to charge a 12v battery with 100-watt solar panel? 100-watt solar panel would take around 4-17 peak sun hours to charge most of the 12v battery sizes from 50% depth of discharge

How Long To Charge 100ah Battery

here’s a chart explaining how long it will take to charge a 100Ah battery with different size solar panels

12v 100Ah Battery
50% Depth of discharge
Solar panel size (W)Estimated charge time
100Ah20 watt43 Peak sun hours
100Ah25 watt35 Peak sun hours
100Ah30 watt29 Peak sun hours
100Ah50 watt17.5 Peak sun hours
100Ah100 watt8.7 Peak sun hours
100Ah200 watt4.4 Peak sun hours
100Ah250 watt3.5 Peak sun hours3.5
100Ah300 watt2.9 Peak sun hours
100Ah350 watt2.5 Peak sun hours
100Ah400 watt2.2 Peak sun hours
100Ah500 watt1.7 Peak sun hours

Summary

  • 20-watt solar panel would take 43 peak sun hours to charge a 100Ah battery from 50% depth of discharge
  • 30-watt solar panel would take 29 peak sun hours to charge a 100Ah battery from 50% depth of discharge
  • 50-watt solar panel would take 17.5 peak sun hours to charge a 100Ah battery from 50% depth of discharge
  • 100-watt solar panel would take 8.7 peak sun hours to charge a 100Ah battery from 50% depth of discharge

Solar System Power Loss – Causes & Solution

if you’re a newbie in the solar world then there will be many questions about the Assumptions part that i have mentioned above

Solar Panel

Solar panels will only produce 100% of power output under standard test conditions which i have described earlier, So in the real world, it would rarely happen when you’ll receive 100% power output from your solar panels

Speaking from experience i receive about 70-80% power output from my 200W solar panels in one peak sun hour

The less efficiency of solar panel output will be a result of many reasons like if there’s wind, a partially cloudy day, Solar panel tilt angle, temperature,

and the wiring will also cause some power losses between 6-15%. To make this almost zero choose the right size cable for your solar system

Also, make sure to tilt your solar panels at the right angle according to your location. Use this calculator to find out the ideal tilt angle for you

How To Select The Right Size Wire For Solar Panel – Chart

wire gauge chart

Use this chart to select the wire size from solar panel to charge controller and from the charge controller to the battery bank

From solar panel to charge controller calculates the maximum amps by using this formula

(Amps = Solar Panel capacity (Watts)/Solar Panel operating voltage (Vmp) which will be mentioned on the back side of your solar panel

Now from the charge controller to the battery bank use this formula (Amps = Solar Panel Capacity (Watts)/Battery Volts (12,24,48V)

Use this chart to figure out the wire size from battery bank to inverter.

What size of cable should I use with my inverter and battery?

Solar panels produce DC current and also batteries store DC (Direct current) but our household appliances required AC (Alternating current) to run, to make this conversion we use an inverter

So to let you know, inverters are also not 100% efficient so there will be some power loss when converting DC to AC. Which you can calculate with the help of this calculator

Related: What will an inverter run and for how long?

Charge Controller

The charge controller regulates the output voltage from the solar panel according to the battery volts

PWM charge controller will only decrease the voltage of solar panel output but will not increase the amps (current) which makes them 20-30% less efficient

Because we calculate total power as (watts = amps*volts)

On the other hand, the MPPT charge controller will decrease the voltage but will increase the amps coming from the solar panels which makes them 98-100% efficient

i would advise you to use an MPPT charge controller if your solar array is above 400 watts

Related Post: How Many Watts Can A Charge Controller Handle?

Battery Depth Of Discharge

Lead-acid, AGM, and Gel batteries have a discharge limit of 50%. which means you can’t discharge them beyond 50% or it will decrease the battery lifespan

On the other hand, Lithium or LiFePO4 batteries are designed in such a way that you can discharge them up to 100% without causing any damage to the battery cells

So that is why the depth of discharge of lead-acid and lithium batteries is being used as 50% and 100% accordingly

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I'm an experienced Sales Consultant with a demonstrated history of working in the renewables and environment industry. Skilled in Photography, Customer Service, and Sales.

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