This is a very simple calculation to find out roughly how many panels you need for your solar PV system. This does not include losses. Okay, let’s get to it.

Step 1: Get your monthly Electricity consumption

You’ll easily find your monthly electricity consumption (in kWh or units). Let us say this is around 1000 kWh.

Step 2: How much of the imported electricity do you want to offset?

This is the percentage of the electricity you want to offset from your electricity bills. If you want to offset it by 60%. Then multiply your electricity consumption by 60%. For our example, this would be 600 kWh.

Step 3: Find the Peak Sun Hours in your location

You can do this using a free tool developed by NREL called PVWatts.

1. Enter your desired location using co-ordinates (Lat, Long)

2. i) Ground-Mount Systems: Enter your desired location using co-ordinates (Lat, Long)

ii) Roof-Mount Systems: Enter the tilt angle as the roof tilt angle. If you do not know what this is, keep it as 15^{o}

3. Find the Annual Average Solar Radiation ( kWh/m^{2}/day). This will be highlighted in orange. This is the Peak Sun Hours. Let’s say this is 4.

Step 4: Find the total rated power of your system

Divide your monthly electricity consumption you decided to offset by your peak sun hours for a month i.e. for 28 days. You want to keep this number low so you do not over design This will give you the rated system power. Continuing the example above, this would yield 5.36 kW.

Step 5: Choose the rated power output for the solar panel you want to use

Well this is your personal choice. You can check this blog for further clarity. Lets assume, this is 330 W.

Step 6: Finding the number of Solar Panels

This is the final step and it’s pretty simple. You just divide the Total rated power of your system (Step 4) by the Rated power for one solar panel (Step 5). You get 16 panels.