Updated September 2014

Highlights

  • Rooftop solar power can meet 10-15% of a Foundry’s electricity requirements in India
  • If your foundry consumes a lot of diesel for power generation, rooftop solar can abate up to 10% 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

Overview

Foundries are one of the most energy intensive sectors, consuming large quantities of electricity for various processes; electricity accounts for 15-20% of the manufacturing cost. India is the world’s 2nd largest casting producer with more than 6,000 foundries, many of which are family owned SMEs.

With such large energy consumption, many foundries are increasingly looking to alternative energy sources to provide electricity. Solar power presents several advantages for foundries but has a few constraints as well, both of which are 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 foundry may be constrained by lack of sufficient shadow-free rooftop space. Roof requirements are discussed in detailhere; 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
  • Roof type – Solar panels can be easily installed on concrete roofs, but metal and asbestos roofed structures may present some challenges, depending on the load-bearing capacity of the roof
  • 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. Some processes such as melting require uninterrupted power supply is required in which case solar can be used in conjunction with other power sources like diesel or grid supply
  • 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 – This may be an issue in some foundries: if most of your load-shedding occurs at night, solar power may not help in reducing your diesel consumption as it is available only during the day. If possible, some of your loads may be shifted to daytime to take advantage of solar power, after considering time-of-day tariff (if any)
  • 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 available 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 foundry include

  • Melting Furnaces
  • Fans and Pumps
  • Lighting
  • Motors
  • Air Compressors
  • Polishing and Finishing equipment
  • Other Electrical Equipment

Melting or Heat Treatment process and Melt Transport are the heaviest power consuming process in foundries, accounting nearly 50% of the total consumption. Electric arc furnaces requires high voltage DC at about 300-550 kWh/ton. Air compressors and electric motors are other heavy energy consumers, while lighting and other electrical accessories consume relatively less power.

It is unlikely that solar alone can support the heavier loads of the commercial/industrial unit (due to insufficient rooftop space and heavy starting current requirements). Solar power can be used in conjunction with other sources of power such as grid power or diesel to support these loads.

Our Recommendation

Considering the unique needs and constraints of foundries, Solar Mango recommends

Alternative 1 – Larger area of available rooftop space

Where a large area of shade free rooftop space is available, Solar Mango recommends a grid-interactive configuration where solar power is supplied in conjunction with EB or diesel power. Here the rooftop solar plant serves to reduce diesel (or even EB, depending on tariff) bills by supporting part of the load

  • Hybrid inverter –A rooftop solar PV system that utilizes a hybrid inverter allows the solar plant to integrate with a diesel generator in addition to the utility grid.
    • 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

Alternative 2 – Limited area of available rooftop space

Where available rooftop space is restricted, Solar Mango recommends a battery-backed grid-interactive solar plant that only supplies specific loads such as lighting and office equipment, but can support these loads without interruption even at night. This is suitable for foundries that feature a great deal of lighting load and night time operations

  • Hybrid inverter –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. Lighting can be supported by solar with batteries this way, as can other light loads such as office equipment
    • 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 considering both current and future cost and space requirements before deciding on the size of the battery bank

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.

Takeaways
  • 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
    • Integrating a solar plant with a diesel generator requires careful design and sizing of your solar plant with respect to your diesel generator
  • A solar+battery plant can be used to provide uninterrupted support to lighter loads such as lighting