To calculate the numbers of solar panels require for charging of One number of 100Ah battery or 'n' numbers of 100Ah Batteries, you need to understand the following things.
By understanding all the above-mentioned points you will master the selection of solar panels for charging of any size of battery.
Amount of energy store in 100Ah battery
The amount of power stored in a 100Ah battery is equal to the multiplying of its voltage rating with its current rating.
Battery Power, VA = Battery Voltage x Battery 'Ah'
Since the most common terminal voltage for a 100Ah battery available in the market is 12V. We can calculate the power store in 100Ah battery by =12V x 100Ah = 1200VAh.
To select the rating of solar panels for the charging of your 100Ah battery you need to understand what is 1200VAh means.
‘VA’ or Volt-Ampere is the unit of power which is generally known as ‘Watt’.
So, 1200VAh will be equal to 1200 Watt Hour of power hence for the charging of a 12 V, 100Ah battery you will require solar panels that can generate 1200VA in 5 to 8 hours.
If there are some other doubts you have regarding 100Ah batteries, I highly recommend you to read our blog on "What is mean by 100Ah battery" to clear all your doubts
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.
In the above picture fig#1 shows the average sunshine hours in the USA, whereas in fig#2 average solar power production (in kWh) by 1kW of solar panels is shown.
By look into these two pictures, you will understand that a state with average sunshine hours of 5hour generates 4.2 to 4.5 kWh of power. Whereas States having sunshine hours more than 5 hours of sunshine generated 4.8 kWh units.
We can say that for 5 hours of sunshine 1kW of solar panels generates 4 kWh of power.
1kW of Solar panels = 4 kWh of Power
1000 Watt of Solar Panels Generate = 4000 Wh (or 4000 VA) of power
Hence 1 Watt of solar panels generates 4 VA of power
For some states during the summer season when sunshine time is on average 8 hours, 1 watt of solar panel can generate power as high as 6 VA per day.
All above-mentioned data is applicable for a non-movable, fixed type solar structure whereas with the seasonal solar structure you can increase the power generation up to 7% to 8% by changing the tilting angle of your solar panels.
These seasonal tilting angles are called optimal angle at which solar panels generated maximum power in a specific season.
For the winter season, the optimal angle for solar panels varies from 10 to 20 Degree and for summer seasons optimal angle for a solar panel varies from 50 to 60 Degree depends upon the geometrical conditions.
To find the optimal angle for your solar panels follow the below steps
For the winter season, minus 15 from the latitude of your place.
For the summer season add 15 to the latitude of your place.
So if your latitude is 40 Degree, then for the winter season place your solar panel at 25 degrees and for the summer season place your solar panel at 55 degrees.
And to find the latitude of your place, go to google map and right-click on your place, and your fill finds the latitude of your place followed by longitude.
The above picture shows the latitude of Newyork, the USA that is 40 Degree
Below is a picture that shows an example of a seasonal structure for solar panels. These seasonal structures are very handy in increases the output of solar panels for different seasons.
Safe charging voltage for 12V battery
For a 12V battery, it is very important, to limit the maximum battery voltage during charging otherwise the battery will be damaged. The battery voltage should not exceed 13.8 volts for long periods and 14.4 volts for short periods.
Now for Solar panels, there are two different voltages mentioned in the specification of Solar panels, Vmp and Voc, where Vmp is called maximum voltage which is generated by the solar panel on Load.
And Voc is called, the open-circuit voltage which is the maximum generated by a solar panel on no-Load.
Below is the table showing Voc and Vp for different capacity of solar panels available in the market.
As you can see from the above table, the Open circuit voltage (Voc) of the minimum size of a 50 Watt solar panel is 22.5V.
Since the internal resistance of the batteries is very low that is, 4.9 milli-Ohm for 12V, 100Ah Battery selecting solar panels on Vp (Peak voltage) will damage your battery, hence it is a standard practice to select solar panels on the Voc for both On-grid and Off-grid solar power plant.
Now you will require a solar charge controller to limit and regulate the Voltage across battery terminals and save your batteries from the high voltages of solar panels.
What is a solar charge controller?
Solar charge controller limits and regulates the voltage across the battery terminal to avoid any damage to the battery from the high peak voltages of solar panels. There are other functions of the solar charge controller too, like protecting the battery from overcharging and over-discharging.
Now, 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%
I highly recommend only use MPPT based solar charge controller to charge your batteries from solar panels. By using PWM based solar charge controller, you require a solar panel rating will be increased by 30%.
Calculation of solar panels for 100Ah battery
Considering all the above points now we can calculate the number of solar panels required to charge 12V, 100Ah Battery, which is equal to = Power store in batteries/ Power generated by 1 Watt of solar panels (in 5 or 8 Hour)/Efficiency of the solar charge controller.
Let’s sum up all the above points
Power store in 12V, 100Ah Battery: 1200VA
Power Generated by 1 Watt of solar panels
in 5 Hours: 4 VA
in 8 Hours: 6 VA
The efficiency of MPPT based solar charge controller: 95%
To take the most viable decision, while calculating the number of solar panels to charge batteries. I highly recommend you to consider 5 hours of sunshine only so that performance of your solar panels remains satisfactory.
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
How many solar panels are needed to charge 12V, 100Ah batteries in 5 Hour?
To charge a 12V, 100Ah 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.
The solar charge controller will protect the battery from high voltage and overcharging, whereas seasonal structure will help to increase the power generation from solar panels for different seasons.
Similarly, if you have multiple numbers of 12V, 100 Ah batteries you can easily calculate the numbers of panels required to charge your batteries. Let's take another example
How many solar panels are needed to charge 4 numbers of 12V, 100Ah batteries?
To charge 4 numbers of 12V, 100Ah battery in 5 hours of sunshine you will require a minimum of 4 numbers of 325 Watt of solar panels with MPPT based charge controller and seasonal structure.
How many solar panels are needed to charge 8 numbers of 12V, 100Ah batteries?
To charge 8 numbers of 12V, 100Ah battery in 5 hours of sunshine you will require a minimum of 8 numbers of 325 Watt of solar panels with MPPT based charge controller and seasonal structure.