Updated: May 17, 2022
At the end of tutorial, you will be able to;
To calculate the number of solar panel (with rating)
To calculate the rating of Solar panel
To calculate the rating of batteries for Solar panel system
To calculate the backup time of batteries
To calculate the required and charging current for batteries
To calculate the charging time for batteries
To calculate the rating of charge controller
How much watt solar panel we need?
Connect Solar Panel in Series or Parallel?
How to select the proper solar panel for home
Inverter Rating for load requirement and much more…
Installing solar power by yourself can be a cost-effective and rewarding experience; you can save a significant amount of money by cutting contractors out of the equation and take pride in your own handiwork.
However, for the aspiring solar DIY-er, knowing how to install solar panels can seem daunting. Fear not! Whether you’re considering a grid-tie system or an off-grid solution, we’ve created a comprehensive, step-by-step solar power installation guide to help you through each stage of the solar installation process.
Anyone who follows the simple steps (this tutorial) below can install and connect solar panels in home for residential applications.
Suppose, we are going to install a solar power system in our home for a total load of 800W where the required backup time of battery is 3 hours (You may use it your own as it is just for sample calculation)
Load = 800 Watts
Required Backup time for batteries = 3 Hours
What we need to know?
Inverter Rating =?
No. of batteries for backup power =?
Backup Hours of batteries =?
Series or Parallel Connection of Batteries =?
Charging Current for Batteries =?
Charging Time for batteries =?
Required No of Solar Panel =?
Series or Parallel Connection of Solar Panels =?
Rating of Charge Controller =?
1. Inverter Rating:
Inverter rating should be greater than 25% of the total load (for the future load as well as taking losses in consideration)
800 x (25/100) = 200W
Our Load + 25% Extra Power = 800+200 = 1000 Watts
This is the rating of the Inverter i.e. We need 1000W Inverter for solar power installation according to our need (based on calculations)
2. Required No. of Batteries
Now the required Back up Time of batteries in Hours = 3 Hours
Suppose we are going to install 100Ah, 12 V batteries,
12V x 100Ah = 1200Wh
Now for one Battery (i.e., the Backup time of one battery)
1200Wh / 800 W = 1.5 Hours
But our required Backup time is 3 Hours.
Therefore, 3/1.5 = 2 → i.e., we will have to connect two (2) batteries each of 100Ah, 12V.
3. Backup Hours of Batteries
If the number of batteries are given, and you want to know the Backup Time for these given batteries, then use this formula to calculate the backup hours of batteries.
1200 Wh x 2 Batteries = 2400 Wh
2400 Wh / 800 W = 3 hours.
In the first scenario, we will use 12V inverter system, therefore, we will have to connect two (2) batteries (each of 12V, 100 Ah) in Parallel. But a question raised below:
4. Series or Parallel Connection for Batteries
Why Batteries in Parallel, not in Series?
Because this is a 12V inverter System, so if we connect these batteries in series instead of parallel, then the rating of batteries become V1 + V2 = 12V + 12V = 24V while the current rating would be same i.e.,100Ah.
Good to Know: In Series Circuits, Current is same in each wire or section while voltage is different i.e., Voltages are additive e.g., V1+V2+V3….Vn.
That’s why we will connect the batteries in parallel, because the Voltage of batteries (12 V) remains same, while its Ah (Ampere Hour) rating will be increased. i.e., the system would become = 12V and 100Ah +100Ah = 200Ah.
Good to Know: In parallel Connection, Voltage will be same in each wire or section, while current will be different i.e., current is additive e.g. I1+I2+I3…+In
We will now connect 2 batteries in parallel (each of 100Ah, 12V)
i.e., 2 12V, 100Ah batteries will be connected in Parallel
= 12V, 100Ah + 100Ah = 12V, 200 Ah (Parallel)
Good to Know: Power in watts is additive in any configuration of resistive circuit: P Total= P1 + P2 + P3. . . Pn (Neglecting the 40% installation loss)
5. Charging Current for Batteries
Now the Required Charging Current for these two batteries.
(Charging current should be 1/10 of batteries Ah)
200Ah x (1/10) = 20A
6. Charging Time required for Battery
Here is the formula of Charging Time of a Lead acid battery.
Charging Time of battery = Battery Ah / Charging Current
T = Ah / A
For example, for a single 12V, 100Ah battery, the charging time would be:
T = Ah / A = 100Ah / 10A = 10 Hrs. (Ideal Case)
Due to some losses, (it has been noted that 40% of losses occurred during the battery charging), this way, we take 10-12 A charging current instead of 10 A, this way, the charging time required for a 12V, 100Ah battery would be:
100Ah x (40/100) = 40 (100Ah x 40% of losses)
the battery rating would be 100Ah + 40 Ah = 140 Ah (100Ah + losses)
Now the required charging current for the battery would be:
140Ah / 12A = 11.7 Hours.
7. Required No of Solar Panels (Series or Parallel)?
Now the required No of Solar Panels we need for the above system as below.
Scenario 1: DC Load is Not Connected = Only Battery Charging
We know the famous power formula (DC)
P = VI ………… (Power = Voltage x Current)
Putting the values of batteries and charging current.
P = 12V x 20 A
P = 240 Watts
these are the required wattage of solar panel (only for battery charging, and then battery will supply power to the load i.e., direct load is not connected to the solar panels)
240W/60W = 4 Nos of Solar panels
Therefore, we will connect 4 Solar Panels (each of 60W,12V,5A) in parallel.
The above calculations and system were only for battery charging (and then battery will supply power to the desired Load) to AC electrical appliances, which will get power through inverter and DC loads via Charge controller (via charged batteries).
Scenario 2: DC Load is Connected as well as Battery Charging
Now suppose there is a 10A directly connected load to the panels through inverter (or may be DC load via Charge Controller). During the sunshine, the solar panel provide 10A to the directly connected load + 20A to the battery charging i.e., solar panels charge the battery as well as provide 10A to the load as well.
In this case, the total required current (20 A for Batteries Charging and 10 A for directly connected load)
In this case above, total required current in Amperes,
20A + 10 A = 30A
I = 30 A, then required Power
P = V x I = 12V x 30A = 360 Watts
I.e., we need 360 W system for the above explained system (This is for both Direct Load and Batteries Charging)
Now, the number of solar panels we need
360/60W = 6 Nos of Solar Panels
Therefore, we will Connect 6 Nos of Solar panels in parallel (each of 60W, 12V,5A)
9. Rating of Charge Controller
As we have calculated above that the charging current for 200Ah battery is 20-22 Amperes (22A For Battery Charging+10A for direct DC Load), therefore we can use a charge controller about 30-32 Amp.
For more details on how to select solar charge controller click here
The above calculation is based on ideal case, so it is recommended to always choose a solar panel some bigger than we need, because, there are some losses occurs during battery charging via solar panel as well as the sunshine is not always in ideal mood.
How Much Watts Solar Panel We need?
We have shown a very simple method in the previous post “How Many Solar Panels Do You Need?” depends on the sunshine time and the load in watts we need to power up an electrical appliance.
Get Started on Your Solar Panel Installation
We hope this solar power installation guide has helped familiarize you with every stage of the solar system installation process. While we have gone over general steps and guidelines, every single solar installation project is different and comes with its own unique challenges.
If you have any specific questions related to your solar system installation, please feel free to contact us. We’re dedicated to helping you get the right system for your needs, and providing support throughout the entirety of your installation process!