Updated July 2014



  • Rooftop solar power can meet up to 30% of a software company or BPO’s electricity requirements
  • If your IT/ITES enterprise consumes a lot of diesel for power generation, rooftop solar can abate up to 20% of your diesel bills, subject to timing of load shedding
  • 100 SF of shade-free rooftop space can provide 4 kWh of solar power per day, on average


When it comes to energy consumption, software companies and BPOs differ from other sectors, such as many factories, by depending on electricity for most of their operations and have little need for heat energy. Many of them are also 24/7 operations with continuous electric loads and spiralling diesel bills. This makes them ideal candidates for rooftop solar power but there are also several constraints in using solar power; both will be discussed in detail below.


  • Energy security – Rooftop solar plants can deliver power during load-shedding, ensuring that critical loads are always running
    • 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
  • Reliable – A 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
  • Flexible configurations – Solar panels can be installed on different kinds of roofs, including covered parking areas, as long as the structure 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


  • Rooftop space – One of the prominent constraints faced when installing a rooftop solar plant, particularly in India, is lack of sufficient shade-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
  • 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. Therefore solar power for critical loads has to be used in conjunction with another source of power, such as grid power
  • 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 your enterprise experiences 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

Typical Loads

As the rooftop space may not be sufficient to support the entire electrical load of your facility with solar, it becomes necessary to estimate the different kinds of loads to identify loads that can be/need to be supported by solar.

Electrical loads are estimated by calculating the wattage or amperage of electrical equipment in use (as shown here), which can be further classified as light loads and heavier loads.

Companies in the IT/ITES sector typically feature the following electric loads that are used continuously

  • Lighting
  • Workstations (desktops/laptops)
  • Servers
  • Air Conditioning

Air conditioning is usually the heaviest load, accounting for more than half the energy consumed; however most air-conditioning isn’t critical to business operations (air conditioning for server rooms being the usual exception) while the servers, workstations, and lighting are critical to continuity of business.

Our Recommendation

The need for 24/7 power and limited roof space necessitates rooftop solar power being used in conjunction with other sources of power such as utility power, diesel generator, and/or batteries.

Based on the unique needs and constraints faced by the IT/ITES sector, Solar Mango recommends

  • Hybrid inverter – A rooftop solar PV system that utilises a hybrid inverter will allow the solar plant to integrate with a diesel generator. Here the solar plant serves to reduce diesel bills by supporting part of the 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
  • Battery backup – A battery bank can be used which will be charged by solar power, and will support critical loads for short durations during the daytime when solar output may be reduced, and at night time during power failure. Workstations, servers, and even lighting (if required) can form part of the critical load to be supported by solar+batteries
    • Battery sizing decides the duration of battery backup available. Batteries add significantly to the cost of the project, need to be replaced every few years, require maintenance, and impose weight and space requirements. Therefore we recommend limiting the battery bank to about an hour of backup
  • Powering critical loads – When combined with a battery bank, a solar plant can be used to reliably support critical loads such as the servers or workstations. Implementing such a solution would require that the critical loads be fed through a dedicated circuit.

With this configuration, an IT/ITES company can run only their air conditioners on the diesel generator, or even turn off the DGs during load shedding if the solar plant is large enough to support all other loads.

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

  • Solar power costs Rs. 4.5-5/kWh or less, compared to Rs. 18/kWh or more for diesel power
    • Cost of solar power is fixed for the next 25 years, whereas diesel cost keeps increasing
  • Solar power combined with a battery backup can be used to ensure that business critical loads, like workstations and servers, are kept running even during load shedding
    • As batteries are quite expensive, we recommend limiting the backup duration to an hour, subject to specific needs at your site
  • As your rooftop space may not permit a solar plant large enough to power your entire load, your solar plant may need to integrate with your diesel generator. Proper integration requires careful design and sizing of your solar plant with respect to your diesel generator