Solar for Injection Moulding Units: Sizing, Roof, Approvals and Payback (50 kW+)

A 50 kW+ solar plant suits a plastics and injection moulding unit that runs machines through the day. Size it from the daytime share of your bills, not from sanctioned load alone, and cap it where your state's rule caps it. The sector-specific risks are hot machine halls, compact roofs, and shifts that leave night load a solar plant cannot serve.

Why moulding is a good fit, and where it is not

Moulding units run machines, mould chillers, dryers and compressed air for long hours, so the load is steady and mostly active in daylight. That is the ideal profile for rooftop solar, because every unit generated at noon replaces a unit you would otherwise buy at the energy-charge rate. Cooling for moulds and hydraulic oil follows the machines, which means the cooling load is also highest when the sun is.

The limits are just as specific. A unit that runs two or three shifts consumes a large part of its energy after sunset, which solar alone cannot cover. Roofs on moulding sheds are often small and crowded with exhaust fans, skylights and ducts. And the shed holds combustible polymer granules and finished goods, so a roof array changes the fire picture. Treat each as a design input, not an afterthought.

Size the plant from the bill, in five steps

1. Collect 12 months of bills. Note monthly kWh, maximum demand and, where the meter shows it, the energy recorded in daytime time-of-day slots.
2. Find the daytime base load. The lowest daytime consumption you can count on, with machines running, sets the ceiling for self-use. A 24-hour data logger on the main incomer for two weeks is better than a guess.
3. Apply the regulatory cap. Rules differ by state. In Haryana's 2021 rooftop regulations, for example, the plant may not exceed the sanctioned load (or the contract demand for an HT connection), net metering is allowed for loads up to 500 kW or the sanctioned load, whichever is lower, and net-metered generation is capped at 90% of annual consumption.
4. Check roof area. This site's planning figure is about 100 sq ft of shadow-free roof per kW, so 50 kW needs roughly 5,000 sq ft, before access paths and obstructions. The solar roof load calculator checks the structural side.
5. Leave headroom. A new machine next year raises the base load. Decide whether to build the plant to today's load or to a staged plan with space and electrical capacity reserved.

The solar sanctioned load calculator tests a size against your sanctioned load, and the solar calculator estimates generation and savings for the size you pick.

Which approval route applies?

Two further Haryana provisions affect timing. The DISCOM may allow only a share of a distribution transformer's capacity for rooftop solar, 50% of the distribution transformer rating or 30% of the power transformer rating in that state, on a first-come basis, so ask early whether your feeding transformer has room. And net metering is not available to a consumer drawing power under open access. Our notes on net-metering delays and open access versus rooftop captive cover the choices above 500 kW.

Roof, heat and fire in a moulding shed

Machine halls run hot, and hot air rising from exhaust fans and roof vents sits under the modules. Modules lose output as they heat, so leave a ventilated gap under the array and keep exhaust discharge away from it. Many moulding sheds are pre-engineered buildings with light sheeting, so purlin spacing, clamp type and leaks beneath the fixings need design attention; see PEB roof loads, clamps and leaks. If the roof is too small, look at a car-park canopy or an adjacent ground area.

On fire, polymer granules and finished goods are combustible, and a DC array is a possible ignition source. Plan DC cable routes away from stored goods, label isolators, keep inverters out of stores, and show the array on the drawings given to the fire officer. The fire NOC file should include the solar layout, so that the two designs do not contradict each other.

Payback logic using the published band

Simple payback is the installed cost divided by the first-year saving. For C&I rooftop solar, our published range is ₹24,000–32,000 per kW excluding GST (see solar EPC); the final price depends on roof, structure type, capacity, inverters and site access. First-year saving is the generation multiplied by the energy rate you avoid. At the site's planning default of 120 kWh per kW per month, a kW generates about 1,440 kWh a year, so each kW costs ₹16.7–22.2 per kWh of annual generation at the two ends of the band. Dividing that by your avoided rate gives a simple payback in years.

Two cautions keep this honest. The avoided rate is the energy charge on your bill, not the average rate per unit: Haryana's regulations say a consumer with credits still pays fixed or demand charges, and if you are on a time-of-day tariff, injection is first set against consumption in the same time block, so a plant that injects in a cheap block saves less than one that offsets a peak block. And the formula leaves out O&M, degradation, inverter replacement, tax treatment and financing, all of which change the real figure. Use the solar calculator for the full treatment, and ask any bidder to state its generation assumption.

How Secured Engineers helps

We design the plant in-house, using the shed's actual load, roof and structure, and we file DISCOM net-metering applications, along with Fire NOC and CEIG filings where needed, in-house. Solar and the shed's electrical, HVAC and fire work can be delivered under one contract from our Noida (Delhi NCR) and Ludhiana offices. The company has delivered 535+ projects across 18+ states, with 89.77% repeat clients.

For a size and route that fit your unit, start from the solar for factories page, then send 12 months of bills and a roof photograph on WhatsApp, call +91 70099 85817, or ask for a free proposal.