Rooftop Solar for Hospitals

Updated February 2015


  • Rooftop solar power can meet up to 20% of a hospital’s electricity requirements
  • If your hospital 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
  • Your hospital will be seen as a trendsetter and early adopter of solar power


Hospitals both in urban and rural areas consume a lot of energy throughout the day as the electrical equipment used directly or indirectly to treat patients require uninterrupted power.

Many hospitals have considerable unused rooftop space. Combined with power shortages and rising cost of diesel, rooftop solar power makes a compelling case for implementation in hospitals; there are several advantages but also several constraints that need to be considered when deciding on and designing a rooftop solar power system for a hospital, such as using a variable source of power like solar to power equipment used in life saving situations. These are discussed in greater 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 – The capacity of the solar plant that can be installed in a hospital 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
  • 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 equipment should be used in conjunction with another source of power. This is a critical part of the design for hospitals, where solar may be used to power life-saving equipment
  • 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 hospital 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 Load

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, with solar being used to support the light loads.

Typical electrical loads in a hospital include

  • Lighting
  • Fans
  • Refrigeration units
  • Other electrical equipment
  • Air conditioning

Air conditioning is usually the heaviest load, accounting for more than half the energy consumed. Air conditioning is not a critical load in many companies; hospitals, however, may have some air conditioning load, such as in operation theatres or ICUs, where air conditioning has to run even during load shedding.

Our Recommendation

The need for uninterrupted, constant power and possibly 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 hospitals, Solar Mango recommends

Alternative 1 – With clear separation of loads

Where it is possible for some loads (typically the lighter loads) in the hospital to be isolated and fed using a dedicated feeder, the following architecture can be used

  • Powering some critical loads – When combined with a battery bank, a solar plant can be used to reliably support some critical loads; which critical loads can be decided in consultation with the hospital’s infrastructure team. In the event of a power failure these loads will be supported by solar power and the battery bank will compensate for any deficiency in solar power at that time
  • Battery backup – The battery bank will be charged by solar power, and will support critical loads for short durations during the daytime when solar output may be reduced. Night time support is also possible, depending on the size of the battery bank
    • 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
  • 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

Alternative 2 – Without clear separation of loads

If it is not possible to isolate critical loads through a dedicated feeder, the solar power will have to be fed along with the diesel generator/EB power to the entire facility. Such a plant will contribute to savings in diesel, but support to specific loads in the event of a power failure will not be provided.

This configuration also require a hybrid inverter, but batteries will not be required. It should be noted that in the event of a power failure, if the DG is shut down the solar plant will also shut down.

For either alternative, we recommend net metering to ensure that excess solar generation, if any, is monetised.

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.

Prominent Installations

  • India
    • Medanta Medicity Hospital – Gurgaon (500 kW)
    • Holy Family Hospital – New Delhi (300 kW)
    • Kamalnayan Bajaj – Aurangabad (100 kW)
  • International
    • Medanta Medicity Hospital – Gurgaon (500 kW)
    • Holy Family Hospital – New Delhi (300 kW)
    • Kamalnayan Bajaj – Aurangabad (100 kW)
  • When powering life-saving equipment, solar should always be used in conjunction with another source of power such as EB, diesel, or battery, as the output varies based on cloud cover and other meteorological conditions
    • As batteries are quite expensive, we recommend limiting the backup duration to an hour, subject to specific needs at your site
  • 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
  • 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