Updated February 2015

Highlights

  • Rooftop solar power can meet up to 30% of your bank’s electricity requirements in India
  • If your bank 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 bank will be seen as a trendsetter and early adopter of solar power

Overview

Banks are similar to many other offices with regards to energy consumption. Typically, peak load is during daytime and only minimal critical load like security systems function 24/7. The critical loads are the ideal candidates for solar plant, but there are several constraints in using solar power; both advantages and constraints will be discussed below.

Advantages

  • 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 cost 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

Constraints

  • Rooftop space –The capacity of the solar plant that can be installed in a bank 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 loads should 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
  • 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 bank include

  • Lighting
  • Fans
  • Security systems
    • Emergency alert
    • Monitoring
    • Vault protection
  • Workstations (desktops/laptops)
  • Servers
  • Air Conditioning

Air conditioning and security system is the major load, accounting for more than 70% of 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, security systems, workstations, and lighting are critical to the continuity of business.

The security system is the most critical load in the banking sector. There are different kinds of security systems in banks; the security systems must operate 24/7 irrespective of grid supply.

Our Recommendation

utility power, diesel generator, and/or batteries.

Based on the unique needs and constraints faced by banks, Solar Mango recommends

  • Net metering – If available for banks in your state, net metering can ensure that excess solar generation (such as during holidays, when loads are low), can be monetised
  • 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 inverterallows the solar plant to integrate with a diesel generator in addition to the utility grid. Here the rooftop 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 rooftop solar plant
      • In addition to the other functionality described above, hybrid inverters also incorporate charge controllers to regulate battery charging
  • 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, security systems, 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 rooftop solar plant can be used to reliably support critical loads such as the security system, servers, and workstation. Implementing such a solution would require that the critical loads be fed through a dedicated circuit
    • Some critical loads like the security system should work 24/7 irrespective of the availability of grid power. Higher capacity of battery back-up may be required for powering the security system during the non-sunshine hours
    • Additional care must be taken while sizing solar plant for security systems like vault protection and emergency alerts which must be combined with an alarm to warn in case of power failure from solar to the security systems

With this configuration, banks 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.

Prominent Installation

  • India
    • IndusInd Bank – Chennai (45 kW)
    • Deogiri Bank – Aurangabad (4 kW)
    • Assam Gramin Vikash Bank – Guwahati (3 kW)
  • International
    • Asian Development Bank – Mandaluyong, Philippines (571 kW)
Takeaways
  • Solar power costs Rs. 4.5-5/kWh or less, compared to Rs. 18/kWh or more for diesel power
  • Solar power combined with a battery backup can be used to ensure that critical loads 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
    • Additional batteries capacity may be required for critical loads such as security system to ensure they perform 24/7
  • 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
    • Integrating a solar plant with a diesel generator requires careful design and sizing of your solar plant with respect to your diesel generator