Solar for Foundries: Sizing, Roof, Approvals and Payback (50 kW+)

A foundry can run rooftop or ground-mounted solar well when the plant is sized to the melt shop's real daytime load rather than to the roof. Take the smallest of three numbers: daytime base load, the capacity your sanctioned load allows, and the usable area. Then survey harmonics from the furnaces and plan for dust before you fix the design.

How big should a foundry's solar plant be?

1. Find the daytime share. Pull a month of interval data from the meter if it records half-hourly demand, otherwise use the shift pattern. A foundry that melts in daylight uses most of its energy while the sun is up. One that melts mainly after midnight uses far less of a solar plant's output.
2. Find the daytime base load. This is the load that is on even at the quietest daylight hour: compressors, sand plant, dust collectors, fettling and holding furnaces. A plant sized above that exports at those hours.
3. Check headroom. Most DISCOMs cap rooftop capacity at or below the sanctioned load or contract demand, and some states set a lower percentage. Our sanctioned load calculator shows the ceiling before design starts.
4. Take the smallest of the three, including roof or ground area. The plant area calculator gives the area a given size needs.

One decision can move all of this. Under the Time of Day tariff rules notified in June 2023, solar-hour energy is priced 10 to 20 per cent below the normal tariff and peak-hour energy 10 to 20 per cent above it, for commercial and industrial consumers with maximum demand of 10 kW and above from 1 April 2024. A foundry that has been melting at night for cheaper power should check what its own tariff order now says, because shifting a melt into daylight changes both the bill and the solar plant it can use.

What is different about a foundry?

CPCB's classification of industrial sectors lists foundry operations with an induction or arc furnace, and those using a cupola, in its Orange category (entries dated 12 February 2025). Your consent file is therefore already part of your routine. A rooftop plant does not change your process, but tell the pollution board if you are adding melting capacity at the same time.

Will furnace harmonics upset the inverters?

They can, and this is the risk that is specific to your sector. Furnace converters distort the supply, and a power-factor capacitor bank on the same bus can resonate with those harmonics. The usual symptoms are inverter trips, capacitor failures and complaints from the DISCOM. Ask for a survey of the incoming supply across a full production cycle, with current and voltage distortion recorded.

The CEA's connectivity regulations for distributed generation say harmonic current injected by a generating resource shall not exceed the limits in IEEE 519, and that DC injection shall not exceed 0.5 per cent of full rated output at the interconnection point. For connections at 11 kV and above the applicant must install power quality meters and share the data with the licensee. Ask any bidder to state which harmonic limits the inverter meets and how the plant rides through voltage dips. Review the capacitor bank at the same time with our power factor calculator.

Roof or ground?

Foundry sheds are tall, hot and crowded with crane gantries, ridge vents, skylights and flue stacks, and many carry decades of settled dust. Check sheeting age and purlin capacity with the roof load calculator and a structural survey, and plan access away from stack outlets. Most estates leave some open land inside the boundary. A ground-mount there avoids the roof question but uses land you may want for a new bay. Keep modules out of the plume of any stack, and agree who cleans them, how often and with what water.

Which approval route applies by size?

• Up to your state's net-metering limit. The central rules, as amended in 2021, allow net metering up to 500 kW or the sanctioned load, whichever is lower; states can set their own limits. Since the February 2024 amendment the DISCOM has 15 days to finish the feasibility study for systems above 10 kW, with deemed approval if it does not, and its time to commission a rooftop system was cut to 15 days.
• Above that. Gross metering, captive use, group captive or open access. The Green Energy Open Access Rules, 2022 lowered the open access threshold for green energy from 1 MW to 100 kW and set a 15-day approval with deemed grant, and the Electricity (Amendment) Rules, 2026 clarified captive ownership and verification. Banking and wheeling terms are set state by state, so read our guide to open-access solar before you size beyond the net-metering limit.
• HT connection. Larger foundries usually take supply at 11 kV or above, so the plant interconnects on the HT side and needs protection coordination and, where your state requires it, the electrical inspector's approval before charging.

What decides the payback?

Payback is the capital cost divided by the yearly saving, and the saving is units generated multiplied by the rate you avoid. For a foundry on an HT tariff the avoided rate is the energy charge in the hours the plant produces, adjusted for the Time of Day band, not the blended bill rate. Solar should not be counted on to reduce maximum demand, because a furnace start or a cloudy half-hour can set the demand figure.

Our published C&I band is ₹24,000–32,000 per kW excluding GST, with larger plants nearer the lower end. At that band 100 kW is about ₹24–32 lakh and 500 kW about ₹1.2–1.6 crore before a survey, and what moves a price inside the band is roof type and height, structure and wind design, HT or LT interconnection, cable length and the make of modules and inverters. Put your own bill into the solar calculator for a first estimate, then ask for a site-specific proposal.

How Secured Engineers helps

We design the plant in-house and file the DISCOM net-metering application, and the CEIG file where it is required, ourselves. MEPF and solar can sit under one contract, which matters on a foundry site where the same panels, cables and fire systems serve both. We work from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients.

If you have a recent bill and the shed drawings, send them and we will tell you what the load profile, the sanctioned load and the roof allow. See our solar for factories page, message us on WhatsApp, call +91 70099 85817, or ask for a free proposal.