What is Rooftop Solar

India is endowed with vast solar energy potential. About 5,000 trillion kWh per year energy is incident over India’s land area with most parts receiving 4-7 kWh per sq. m per day. Hence both technology routes for conversion of solar radiation into heat and electricity, namely, solar thermal and solar photovoltaics, can effectively be harnessed providing huge scalability for solar in India. Solar also provides the ability to generate power on a distributed basis and enables rapid capacity addition with short lead times. Off-grid decentralized and low-temperature applications will be advantageous from a rural electrification perspective and meeting other energy needs for power and heating and cooling in both rural and urban areas. From an energy security perspective, solar is the most secure of all sources, since it is abundantly available. Theoretically, a small fraction of the total incident solar energy (if captured effectively) can meet the entire country’s power requirements. It is also clear that given the large proportion of poor and energy un-served population in the country, every effort needs to be made to exploit the relatively abundant sources of energy available to the country. While, today, domestic coal based power generation is the cheapest electricity source, future scenarios suggest that this could well change.

The promotion of RTS in the State is aligned to India’s global pledge of reducing GHG emissions and meeting at least 40% of its total electricity requirement from renewable energy and other low-carbon sources by the year 2030. Achievement of the 2,100MW target will contribute a 26.39 million tonnes reduction in the CO2 gas emissions. Further, this initiative is expected to result in the creation of some 69,300 full time equivalent employment opportunities in the State, many of which will be in the ‘green’ employment sector.

The development of RTS will have a positive bearing on the transmission and distribution losses of supply companies, as power generated from RTS can be consumed locally. An additional benefit envisaged for distribution utilities would be a reduction in the amount energy that they would need to procure; reduced by the equivalent of the power generated through RTS.

Key observations with respect to the installation of RTS in Kolkata:

  • Solar rooftop installation can provide a significant amount of energy to cover in-house loads and can reduce peak energy demand during the day.
  • Depending on the rooftop area available, it would be possible to optimise the available solar energy resource of the State;
  • The retail tariff for some categories of consumers, such as, domestic, private utilities, etc. will be higher than the Levelised Cost of Energy (LCoE) of RTS; these consumers may not adopt RTS until provided with some form of financial support/ incentive.
  • Distribution utility companies must agree to take/ purchase the power generated by RTS;
  • A forecasting mechanism must be put in place, so that the utility companies do not face difficulties in maintaining grid stability.

For a successful RTS policy, it is imperative to strike a balance between the interests of the distribution utilities and that of the consumers/ developers implementing the projects.

It is also important to assess the impact of RTS on the Government of West Bengal (GoWB), in the event that financial support needs to be provided by the State Government to either the distribution utilities or to the consumers.

  • Maintaining power grid stability for inclusion of RTS system
  • Forecasting of solar power generation for power management of grid
  • Proper upgradation of existing grid infrastructure by distribution utilities, considering that grid connected Solar PV is a distributed generation system
  • Extensive grid planning
  • Ensuring an able grid integration and management system to meet high solar demand

A Success Story –Deshapriya Park: Carbon Neutral Solar PV Street Lights

Carbon-neutral non-battery solar street lighting of Deshapriya Park has a number of advantages:

High power lighting up to 180 watt LED could be used, giving light approximately as good as a 400 watt sodium vapour lamp.
High illumination level matching with the park’s need.
Highly reliable – streetlights works with grid power during the night.
No batteries – reducing recurring expenses to almost nil.
Totally climate responsive.
No additional infrastructure costs other than solar panels and micro inverter.
Continuous monitoring of its carbon neutrality possible.

Rooftop Solar

  1. Shadow-free area
    • 120 square feet for 1 KW
    • 600 square feet for 5 KW
  2. At present, less than 5KW, though allowed, is not eligible for incentives / grid connectivity
  3. At present, only institutions / organisations are eligible for incentives / grid connectivity
  4. Eligibility criteria for applying institutions / organisations
    • Electric metre in the name of the applying institutions / organisations
    • The applying institutions / organisations have to be a consumer of CESC / WBSEB
    • Desirable: In areas where there are no power-cuts during day time
  5. Cost – Around 4 to 4.5 lakhs for 5KW plant in 600 square feet area
  6. Life-span of the system – around 25 years
  7. Solar companies / channel partners approved by MNRE for installation
  8. West Bengal is divided in three zones, based on solar radiation – North, South, and West

North Bengal

A 5KW plant will generate 5000 KWH With current tariff around Rs.8 per unit – Rs.40,000 savings in electricity bill So pay-back in approximately 10 years (40,000 x 10 = 400,000/-) [Cost of the system – 400,000/] Hence next 15 years of free electricity

Western Bengal

A 5KW plant will generate 7500 KWH With current tariff around Rs.8 per unit – Rs.60,000 savings in electricity bill So pay-back in approximately 7 years (60,000 x 7 = 420,000/-) [Cost of the system – 400,000/] Hence next 18 years of free electricity

Kolkata and South Bengal

A 5KW plant will generate 7000 KWH With current tariff around Rs.8 per unit – Rs.56,000 savings in electricity bill So pay-back in approximately 7.5 years (56,000 x 7.5 = 420,000/-) [Cost of the system – 400,000/] Hence next 18.5 years of free electricity

Note: This has been calculated with the approximate current tariff of electricity per unit. Most likely this tariff is going to increase over the years and therefore the break-even point will be reached in lesser time. Moreover, the cost of generating solar power has significantly reduced in the last 5 - 6 years and it is likely to reduce further in the coming years.

1 KWH reduces 700 grams of Carbon Dioxide (CO2). Therefore, by generating 5000 KWH (5000 x .7 kg) – 3500 kg of CO2 reduced per year. Such a system in Kolkata, hence will be able to reduce around (7000 x .7kg) – 4900 kg of CO2 per year.


Coming Soon


Lighting Department, KMC