Information to putting in a rooftop solar plant in your house

Guide to installing a rooftop solar plant in your apartment

Installation of a solar system on the roof in the Trifecta Starlight apartment in Mahadevapura. Photo credit: Vishnu Gattupalli

As we saw in Part 1 of this series, many apartments in Bengaluru have rushed to install solar panels on their roofs in light of the expected policy changes. These systems have helped homes significantly reduce their monthly utility bills for public areas.

Here is a guide on how to install a rooftop solar system in your apartment, based on information from the Bangalore Apartments’ Federation (BAF), a collective of nearly 500 housing associations in the city.

See Also: A Guide To Installing Solar Energy In Your Home

What is a solar system on the roof?

In this system, solar panels are installed on the roof of your home. These panels generate electricity that can be used immediately to power the public areas of the apartment or for export to the BESCOM network.

The solar energy generated can be used to power the communal area or exported to the BESCOM network. Photo credit: BAF

Why install this system at all?

The installation of a solar system on the roof offers several advantages – not only economical, but also ecological. Here are a few:

  • The solar system on the roof enables enormous cost savings. General experience with apartments in which these have been installed suggests monthly savings of almost Rs 1000 per installed kWp. (kWp is kilowatt peak power – power that is generated during peak power).
  • A 100 kWp solar system is equivalent to adding at least two new Lal Baghs in the city, as 80 tons of carbon emissions can be avoided per year. A 5 kWp solar system equates to planting 2,500 trees or not driving 4.56,000 km.
  • The source of energy is free and infinite.
  • It’s a clean source of energy, keeps the air clean, and ensures that less coal is burned to generate electricity in thermal power plants.
  • Solar panels are durable and have a lifespan of almost 25 years. They are easy to maintain and do not pose any safety concerns.

What is the benefit of setting up the system now?

Karnataka is one of the few countries that has a grid measurement policy. The directive should be amended after March 31, 2020.

In addition, the Karnataka Electricity Regulatory Commission (KERC) introduced a new directive on December 9, 2019, according to which third-party investments in solar roofs in non-residential buildings can only be taken into account as part of the gross measurement system. Experts and citizen groups now believe that KERC will soon only allow gross measurements for residential buildings.

In terms of return on investment (RoI), a solar system will pay for itself within 10 to 12 years, provided that electricity tariffs from the grid remain at their current tariffs (which is highly unlikely). If rates increase in the following years, the savings can be substantial enough to shorten that period to eight or even six years.

If you generate more than you consume and therefore have an active network export system, the costs after the return on investment (ROI) are negative. That means you would be paid for the electricity you produce.

Net metering vs gross metering

With the net metering, the apartment complex uses the generated solar power for the needs of the common room, exports excess power to the grid and uses BESCOM power for any deficits. In practice, apartments have excess electricity during the day and use BESCOM electricity at night.

BESCOM installs a bidirectional electricity meter in the complex that measures both the drawn and the exported electricity. And the apartment complex only pays the net amount consumed, that is, the units consumed minus the units exported. This helps avoid installing batteries, which are expensive and have a short lifespan, thereby reducing costs.

In the gross measurement, the total energy generated by the solar roof system should be uploaded into the network without being used directly by the consumer. BESCOM pays the system owner according to the PPA tariff (Power Purchase Agreement). The apartment uses BESCOM electricity for its needs and pays BESCOM the standard electricity tariffs.

Common technologies for solar roofs

Various technologies are used in solar modules, e.g. B. monocrystalline, polycrystalline and thin-film solar modules. Monocrystalline solar modules have higher energy efficiency rates and are also space-saving.

Workers installing a solar panel in Century Saras’ apartment, Yelahanka. Photo credit: Satish Mallya

There are also different types of inverters: string inverters, optimizers, micros and hybrid models. In the string inverter system, panels can be connected in a row to form a string which is then connected to the inverter. In the micro-inverter system, each panel can be connected to a single micro-inverter / power optimizer. Microinverters are more expensive but come with a longer warranty, free system-level monitoring, and easier maintenance.

How much money can a solar system on the roof save?

The cost of solar systems on the roof varies from apartment to apartment. The most important step in installing these systems is for the provider to conduct a technical feasibility study. The technical feasibility study will help you to know how many panels are required and of what type, what type of inverter, what shade conditions and other technical specifications.

However, there is a simple rule of thumb: 10 square meters of terrace area can be used to create 1 kWp of solar capacity.

If an apartment complex has a free roof area of ​​7500 square meters with minimal shade, a system with an output of 75 kWp can be installed.

  • Total cost of such a system: about Rs 50 lakh (depending on the technology)
  • Generation of 1.05 lakh units in the first year (which decreases by 1% every year due to the deterioration of the panel)
  • Net savings of approximately 8.75 lakh per year on utility bills
  • Payback period (time it takes to recover the investment) of approximately six years
  • Project return: 16-20% internal return (excluding subsidy)


  • These are comprehensive estimates based on current prices. Actual values ​​will depend on many other factors, such as: B. Shading, length of cables required, etc.
  • The above-mentioned IRR of 16-20% corresponds to the current BESCOM tariff. If one takes into account an increase in electricity tariffs, which is usually between 4 and 11%, the payback period is even shorter and the IRR can be higher than 20%.

BESCOM buys solar power at low rates and therefore the net export of electricity reduces the IRR. In general, it is therefore better to build a system smaller than the approved load, which only generates as much electricity as is needed for the own needs of the home.

How can investments in setting up the system be secured?

The best way is to invest part of the apartment corpus in setting up the system. If this is not possible, residents should be encouraged to create a new corpus and contribute to it.

Solar panels installed in Trifecta Starlight Apartment, Mahadevapura. Photo credit: Vishnu Gattupalli

The other option is to seek the help of specialized providers known as RESCOs (Renewable Energy Service Companies). RESCOs will invest in setting up the system and sell the electricity under a Power Purchase Agreement (PPA). According to the PPA, the entire investment is made by RESCO, but in return, lower electricity costs are guaranteed than paid by your association to BESCOM.

The Bengaluru Apartments Federation (BAF) does not recommend this model. A 100% system is far more beneficial for the home.

How do you make sure your investment doesn’t fail?

  • In order to determine the right provider and the right configuration for your apartment, a lot of research is required, as each apartment has different availability of space, requirements, shadows, etc.
  • Always have long-term maintenance contracts with the provider that go beyond the free maintenance period and can vary between one and five years. Also, look for generation guarantees (guarantee of a certain amount of electricity being generated from the panels) where possible.
  • In general, solar panels only require good maintenance and no repairs. However, if one of the panels breaks it must be replaced immediately as a panel is shipped as a single unit. Other parts of the system – cables, AC / DC distribution boxes, etc. – are readily available in the market

Some well-known providers are:

  • Hyde Source & Green Energy Technologies
  • Ecosoch
  • Solar Square
  • Renxsol Ecotech
  • Insolare Energy Private Limited
  • PlaySolar Systems Pvt Ltd.
  • Lakeforest Green Energy

Documents required for installation

  • Purchase and maintenance contracts with the seller
  • 25 years of PPA at BESCOM and some certifications

The provider takes care of most of the BESCOM-related documents.

A CSTEP project – CREST provides high resolution aerial imagery to help you choose the ideal location with the least shade and maximum radiation for your rooftop solar system. More information is available at

Note: Meera K contributed to this article.


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