Solar Power Advantages for Chennai

• Energy security – Rooftop solar plants can deliver power during load-shedding, ensuring that critical loads are always running in the commercial/industrial facility
  • Not all solar plant configurations can deliver power during load-shedding. More details here
• Cost-effective – Rooftop solar power has a levelised cost of Rs. 4.5-5/kWh (or less), considerably lower than diesel power at Rs. 18/kWh (or more). Additionally, your energy cost is now fixed for the next 25 years, unlike diesel power which keeps increasing
  • Grid power tariff is about Rs. 6 for Industrial and Rs. 7.6 for Commercial consumers in Chennai. If penalties are imposed for excess consumption the effective tariff is even higher. Rooftop solar power may be cheaper than even grid power, but this varies on a case-to-case basis
• Reliable –A rooftop solar power plant has no moving parts, ensuring reliable power over 25 years
• Minimal maintenance – A solar plant requires very little maintenance from the energy consumer
  • As Chennai has a lot of dust, cleaning the solar panels once in every 2-3 months is recommended to ensure that sunlight is not blocked from reaching the solar cells. More frequent cleaning may be required if your plant is located in a very dusty environment
• Flexible configurations – Solar panels can be installed on different kinds of roofs, including parking lot roofs, as long as the structure/mounting points can bear the weight of the panels. They are also highly scalable, with rooftop plants ranging in capacity from less than 1 kW to more than 1 MW

Constraints for Solar Power in Chennai

• Rooftop space – The capacity of the solar plant that can be installed may be constrained by lack of sufficient shadow-free rooftop space. Roof requirements are discussed in detail here; a rule of thumb is that you will need about 100 SF of shade-free roof area for 1 kW of solar panels. Insufficient roof area will mean that the capacity of the solar plant on your roof may be sufficient to meet only part of your electrical load
  • When estimating the available roof area any alternate uses of the roof should be considered. Elevated mounting structures may be used if the alternate use of the roof is to continue
• Infirm power – Solar power is dependent on the sun shining, and output varies depending on meteorological conditions e.g., passing clouds can temporarily reduce the solar plant’s output; monsoon rainfall can also reduce the solar plant’s output. Therefore solar power for critical equipment should be used in conjunction with another source of power
• Cyclones – As Chennai is in a cyclone prone area, the mounting structures for the solar panels should be designed to withstand wind speeds of 120-150 kph
• Salt corrosion – As Chennai is a coastal city, the solar panels chosen should have cleared salt mist corrosion testing (IEC 61701/IS 61701 compliant)
• Daylight power – Solar power is only available when the sun shines. Therefore night time applications will require other sources of power, or power from batteries charged through solar
• Load-shedding timings – If you experience load shedding primarily at night, solar power may not help in reducing your diesel consumption as it is available only during the day
• Inverter weight – The DC power output from the solar panels needs to be converted to AC via an inverter which can be very heavy: a 100 kW inverter will weigh about 1,000 Kgs but occupy only a few square feet of space. If the construction cannot support this weight the inverter may need to be placed on the ground floor, with appropriate cables chosen to compensate for energy loss

Our Recommendation for Rooftop Solar in Chennai

Based on the above discussion, Solar Mango’s recommendation for solar plants in Chennai is

• Multiple power source integration – As the output from a rooftop solar plant varies, it must always work in conjunction with other sources of power, typically utility grid power and diesel power. This is achieved using
• Hybrid inverter – A rooftop solar PV system that utilises a hybrid inverter allows the solar plant to integrate with a diesel generator in addition to the utility grid. The solar plant serves to reduce diesel bills by supporting part of the overall load
  • Integrating a rooftop solar plant with a diesel generator involves several challenges (discussed here) that need to be overcome with careful design and sizing of the solar plant
• Corrosion resistant panels – Only panels that areIEC 61701/IS 61701 compliant (salt mist corrosion testing) should be used in coastal cities like Chennai
• Cyclone rated mounting structures – Mounting structures that can withstand 120-150 kph wind speed should be used

Cost of a Rooftop Solar Plant

The cost of a rooftop solar plant is discussed in detail here (including incentives and subsidies) and returns from substituting diesel with solar are discussed here. As a rule of thumb, a 1 kW solar plant that generates 4 kWh of solar power per day (on average) will cost Rs. 1 lakh (without considering subsidies, including installation charges but excluding batteries).

Batteries, if required, can add about 30% or more to the cost of the plant depending on the extent of battery backup required.