Case Study: Cost Of installing a 1 kW solar rooftop system in Chennai

Table of Contents

This case study is an actual detailed financial analysis for a 1kW solar rooftop system in Chennai. Through this case study, we will also be discussing other financial parameters such as Payback period, Internal rate of return(IRR) and total savings (upto 25 years).


Total upfront cost is one of the most important parameter which influences the decision of a residential home owner that whether he will go solar or not.

This cost factor basically includes these key aspects:

  • The total upfront cost (with and without subsidy)
  • Total savings (over a period of 25 years) and
  • Payback period and
  • Internal rate of return (IRR)

Through this case study we demonstrate the above factors for a residential home owner in Chennai. Chennai has an active residential market with amazing policy support offered by nodal agencies. Moreover for this entire study, we have used TSL design studio for

  • Creating the 3D model of the site
  • Shading analysis
  • Generation simulation and 
  • Financial analysis

Methodology Followed

Collecting the site information

After the preliminary site data collection, TSL was used to perform the designing part.

Making 2D and 3D layout

First the 2-D layout was created with precise mapping of the obstructions present on the roof. 3-D models were created with panel placement.

Fig 1: 3D view of the site

A total number of 3 modules were placed with row spacing of 0.807 m. The panels were placed in portrait orientation with 20° tilt and 180° azimuth.

Shadow Analysis

Shadow analysis was done to make sure that all the panels are shade free. From the shadow analysis report for June 21st and December 22nd from 9 AM to 5 PM, we can observe that the panels are shade free for 99.87% of solar time throughout the year. The shadow patterns for 21st June and 22nd December from 6AM to 6 PM is shown below.

Fig 2: Shadow pattern on 21st June from 6 AM to 6 PM.
Fig 3: Shadow pattern on 22nd December from 6 AM to 6 PM.

Selection of system make

After finalizing on the design part, systems make were selected. These included:

  1. Modules – Waaree Energies WS-330 (18 No.)
  2. Inverter – Growatt New Energy: GROWATT 1500-US (240V) 240V [CEC 2011] (1 No.)
  3. Mounting structure – Premium

Energy generation estimates

energy est.JPG

Detailed Financial Analysis

The financial report generated from TSL clearly highlights these parameters:

  1. Cost per kW
  2. Total Savings
  3. Payback Period
  4. Internal Rate of return

Financial Analysis


Table of various financial estimates for a 1 kW installed capacity

Factors which mainly affect the above numbers are

  • The cost of BOS: This includes the cost of systems used in the plant such as panels, inverters, wires, ACDB and DCDB, lightning resistors, mount type etc. These cost vary with the system make and size.  
  • The size of installation: Larger will be the size of installation, lesser will be the per kW cost.
  • Site location: This is an important parameter since the BOS varies from place to place. The per kW cost in Chennai will not be same as per kW cost in West Bengal.
  • The total upfront incentives available at the time of installation:  Subsidies can significantly influence the total upfront cost and Payback period numbers.


Other residential customers like Mr. Rajesh, who decide to choose solar are concerned about the huge upfront investment. This case study tries to highlight the actual cost of choosing solar rooftop system in Chennai. As discussed above, these costs can vary depending upon various parameters.

Know more in details about the calculation behind the financial terms used in this case study such as payback period and internal rate of return.

Mr. Rajesh took a wise and informed decision of choosing solar. Both Mr. Rajesh and his wife are working parents and they hardly spend time at their house during the day. So there day time electricity consumption was very less. They didn’t want any unused or extra units (Kwh) generated by the panels to be sent back to the grid, so they opted for Zero export devices instead of Net Meters. Know more about Zero export devices.

This entire financial report has been generated using our TSL software. TSL is a SAAS provider, providing one stop solution to solar design engineers for all their designing needs. At The Solar Labs, our objective is to help you, as an installer, deliver to your clients as much power as promised, giving them the desirable return on their investment. Most importantly, our product strives to help you save time and money. Installers can optimize their workflow and reduce their number of sales cycle while closing a deal. Know more about what our software offers.

We would like to thank Aaqib Quraishi (CEO, OffCarbon), for providing us with all the relevant client information for carrying out this case study. OffCarbon is an end to end home solar energy consultancy that enables customers to switch to solar. Apart from just acquiring projects and finishing them, their aim is to educate everybody – even potential customer – about the benefits of Solar Energy and its positive impacts on the Environment.

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