In short, you need about 100-200 watts of solar panels to fully charge a 12v 80ah lead-acid battery from 50% depth of discharge and 250-350 watts of solar panels to fully charge a 12v 80ah lithium (LiFePO4) battery from 100% depth of discharge in a day.
” What size solar panel do you need to charge 80ah lead-acid or lithium battery? ” use the calculator given below to find out.
Solar Panel Size Calculator For Battery
Note! If you already have a solar panel and want to know how long it will take to charge your battery, use this solar battery charge time calculator.
- Lead-acid Battery Charge efficiency rate: 85%
- AGM Battery Charge efficiency rate: 85%
- Lithium (LiFePO4) Charge efficiency rate: 99%
- PWM charge controller: 80% efficient
- MPPT charge controller: 98% efficient
- Solar Panels Efficiency during peak sun hours: 80% (meaning a 100 watt solar panel will produce 80 watts during peak sun hours, i’ll explain why…)
- Charge controller is the only load connected with the battery
How To Use The Calculator?
Enter the following info into the calculator ( located at the top of this page )
- Battery Capacity: Enter your battery capacity in amp-hours (Ah). in this case it’ll be 80
- Battery Volts: is this a 12v, 24v, or 48v battery?
- Battery Type: Select the battery type, is this a lead-acid, AGM, or lithium-ion (LiFePO4) battery?
- Battery Depth of discharge DoD: is the percentage of the battery that has been discharged relative to the total battery capacity. for half discharged battery you’d enter 50, (if the battery is fully discharged which you can achieve on lithium battery, ENTER 100)
- Charge Controller Type: Are you using a PWM or MPPT charge controller to charge the battery?
- 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? (keep reading i’ll explain how you can calculate the number of peak sun hours)
After entering the information, click “Calculate” button to find the required size for a 200ah battery.
Attention! Scroll down to the bottom of this page ( or click here ) to find out how you can calculate the size solar panel in future without any need of a online calculator.
Suppose you have a 12v 80ah lead-acid battery with 50% depth of discharge and an MPPT charge controller. You want to recharge your battery in one day (during summer days) and your location receives 6 hours of peak sunlight
You’d need about 110 watts of solar panels to fully charge a 12v 80ah lead-acid battery from 50% depth of discharge in 6 peak sun hours using an MPPT charge controller.
Read the below post to find out how fast you can charge your battery.
What Are Solar Peak Sun Hours?
Before explaining peak sun hours and why to use them, first, let’s see how solar panels are rated.
“ Solar panels are designed to produce their rated wattage output under standard test conditions – STC ”
- 1000 watts per meter square (1kw/m2) of sunlight intensity hitting the solar panels directly
- 25oC temperature
So to calculate the sunlight intensity we use peak sun hour as a reference.
- 1 peak sun hour = Average of 1kw/meter2 of sunlight intensity for one hour.
This number will depend on the location to location. To calculate how many peak sun hours your city receives use this PVwatt solar calculator.
Step 1: Enter your full address of just a city name & Click GO
Step 2: Click on results
Now you’d be able to see the total amount of solar radiation your location receives per day (from month to month)
Note! it would have to place my solar panels all day long under sunlight to get those total solar radiations per day.
Solar Panels Efficiency
As we know that solar panels are rated their power under a controlled laboratory environment. But in the real world, there will be some power losses
These power losses will occur due to various reasons, here are some examples
- Manufacturer’s output tolerance (+-3%)
- Dirt and grime on panels (+-5%)
- DC cable loss (+-3%)
- Temperature derating (+-10 – 20%)
On average. A solar panel will produce about 80% of its rated wattage output in real-world conditions.
This percentage is based on my personal experience with 400 watt solar panels. I collected the 30 days of total output from the solar panels and divide it by that month’s peak sun hours.
Yes, there’ll be sometimes when you’ll get 100% output from the solar panel but it’s rarely gonna happen and will last for a few minutes
I have a detailed post about this topic and shared some tips to get the maximum output from your solar panels.
What Size Solar Panel To Charge 12v 80Ah Lead-acid Battery?
Here’s a chart about what size solar panel you need to charge a 12v 80ah lead-acid battery in different peak sun hours.
|Charge Time||Charge Controller Type||Required Solar Panel|
|4 peak sun hours||PWM||200 watts|
|5 peak sun hours||PWM||160 watts|
|6 peak sun hours||PWM||130 watts|
|10 peak sun hours||PWM||80 watts|
|4 peak sun hours||MPPT||165 watts|
|5 peak sun hours||MPPT||130 watts|
|6 peak sun hours||MPPT||110 watts|
|10 peak sun hours||MPPT||70 watts|
- You need around 160 watts of solar panels to charge a 12v 80ah lead-acid battery from 50% depth of discharge in 5 peak sun hours with a PWM charge controller
- You need around 130 watts of solar panels to charge a 12v 80ah lead-acid battery from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller
What Size Solar Panel To Charge 12v 80Ah Lithium (LiFePO4) Battery?
Here’s a chart about what size solar panel you need to charge a 12v 80ah lithium (LiFePO4) battery with different peak sun hours.
|Charge Time||Battery Type||Required Solar Panel|
|4 peak sun hours||PWM||350 watts|
|5 peak sun hours||PWM||280 watts|
|6 peak sun hours||PWM||230 watts|
|10 peak sun hours||PWM||140 watts|
|4 peak sun hours||MPPT||290 watts|
|5 peak sun hours||MPPT||230 watts|
|6 peak sun hours||MPPT||200 watts|
|10 peak sun hours||MPPT||120 watts|
- You need around 280 watts of solar panels to charge a 12v 80ah lithium (LiFePO4) battery from 50% depth of discharge in 5 peak sun hours with a PWM charge controller
- You need around 230 watts of solar panels to charge a 12v 80ah lithium (LiFePO4) battery from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller
How To Calculate Number Of Solar Panels Required For Battery?
This is the most accurate way to calculate the required number of solar panels to charge any size battery.
1- Multiply the battery amp-hours (ah) by battery volts to convert the battery capacity into watt-hours (Wh). let’s suppose you have a 12v 80ah battery
Battery capacity in Wh = 80 * 12 = 960wh
2- Multiply the battery watt-hours to the battery depth of discharge limit.
lead-acid, AGM, and gel batteries come with a depth of discharge limit of 50%, and lithium batteries with 100% DoD. let’s suppose you have a lead-acid battery
Battery capacity in Wh= 960 * 0.5 = 480wh
3- Multiply the battery capacity after DoD by 1.15 for lead-acid and 1.01 for lithium battery ( Battery charge efficiency rate, lithium: 99%; Lead-acid: 85%; )
Power required to charge the battery = 480 * 1.15 = 552wh
4- Divide the battery capacity value (after adding charge efficiency factor) by the desired number of charge peak sun hours. let’s suppose you want to recharge your battery in 5 peak sun hours
Solar power required in peak sun hour =
/ 5 = 110 watts
5- Multiply 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 a PWM charge controller
Solar power required after charge controller = 110 * 1.2 = 132 watts
6- Add 20% to the solar power required after controller to cover up the solar panel inefficiency
Solar panel Required = 132 + 20% = 158 watts
What Size Charge Controller Do I Need To Charge The Battery?
The job of the charge controller is to regulate the voltage coming from the solar panels to safely charge the battery and prevent the battery to be overcharged.
To select the right size charge controller according to your solar panel size. Follow these 2 steps
- Divide the solar panel rated wattage by battery volts (e.g by 12 for 12v battery and so on…)
- Now add an extra 25% to the result value to keep the system safe in case of any fluctuations.
- Now the value will be the size of charge controller you’d need with your particular solar panel size to charge the battery.
let’s suppose you have a 100-watt solar panel and a 12v battery. the calculation will look like this.
100 / 12 = 8.33A
8.33 + 25% or 8.33 * 1.25 = 10.4 A
you’d need a 10A charge controller with a 100-watt solar panel to charge a 12v battery.
PWM vs MPPT
– PWM charge controller
will only decrease the voltage coming from the solar panels and will not increase the amps (current).
which as a result will cause power losses and which makes the PWM charge controllers 20-30% less efficient.
The formula to power is… ( Watts = amps * volts )
Remember: a 12v solar panel will produce about 18 volts under direct sunlight conditions… and the amps will be lower.
Note! If you’re using an PWM charge controller the voltage of solar panel and battery should be the same. ( eg. 12v solar panel for 12v battery and 24v solar panel to charge a 24v battery ). Otherwise you’ll experience a huge power loss. If you have different voltage solar panels and battery then use an MPPT charge controller.
– MPPT charge controller
An MPPT charge controller will not only decrease the voltage coming from the solar panel to charge the battery but will also increase the amps to cover up the losses.
which makes them 98-99% more efficient than a PWM charge controller.
Pro Tip: if your solar panel system is higher then 100 watts then i would suggest using an MPPT charge controller.
Related Post: How Many Watts Can A Charge Controller Handle?
80Ah Battery: FAQ’s
a 12v 80ah means 960 watts. To calculate battery capacity from ah to watts ( watts = battery Ah * Battery volts )
80ah battery will last 8 hours while running a 10a DC load. After this your battery will be fully discharged, so if you’re using a lead-acid battery which usually has a DoD limit of 50%. so it’ll last 4 hours.