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  • Writer's pictureHyde Source

How to correctly size a Grid-Tied Rooftop Solar PV System?

To calculate the Solar PV Capacity required, we need to first gather some data from your electricity bill to proceed further.

1. Get the Sanction Load Details from your electricity bill, as shown in the image below:


2. Get your energy consumption details from your electricity bill:

Gather the consumption data for your past six months and calculate the average consumption in units/month.

With the data available, we can now calculate our On-Grid Solar PV System Requirement.

Now to calculate your Solar PV requirement, divide your average consumption by our previously calculated value i.e.

Solar PV Capacity Required =Average Consumption/ (Units Generated in a month/kW)

= 179/120= 1.491 kW of Rooftop Solar.



It is always recommended to undersize your installation capacity rather than oversize it to improve your return on investment. Let's see why, with an example.

It shows a drop in savings by installing an oversized system that generates 100 units every month, i.e., a surplus of 100 units every month.

The returns of your rooftop solar system are reduced by half, for the surplus power generated every month. So it's essential to size your Solar PV system as per your consumption and not to exceed it.


3. Once you have decided on the exact requirement based on your consumption, it's time to assess the rooftop space required to install a Solar Power Plant.

One can consider 80 square Ft. of shadow-free rooftop area for every kW of Solar Installation.

For ex. For a 3kW system- We would require around-

3 x 80 = 240 sq. ft. of rooftop area


Points to Remember:

1. Sanction Load- Your Sanction Load tells you the maximum solar capacity that can be installed on your roof. One can install up to 100% of the sanctioned load as per the current policy in Karnataka.

2. Consumption- Divide the units consumed every month by 120 to calculate the solar PV Capacity required to offset your energy charges.

3. Undersize- Always install a capacity lower than or equal to your requirement. Never Oversize your Solar PV Installation unless you are planning to add any extra loads (equipment's) in the foreseeable future.

4. Rooftop Space- 80 sq. Ft. of rooftop area is required per kW of Solar PV Capacity. The type of panels chosen can significantly impact the overall space occupied. If you have space constraints on your roof, select higher-capacity panels, or you could select an elevated structure. Mounting a solar PV System on your terrace floor ends up utilizing all the space and makes it completely unusable.

An elevated structure can help you make full use of your roof space and generate your power simultaneously.

If you're still confused, don't worry, we are here to guide you every step of the way. Contact us for a free consultation, and we will help you assess your Solar PV requirement and type of structure required.


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