By Vvon Engineering Team | Published | Updated
Evaluate injection-moulding demand intervals, heater and auxiliary loads, power quality and the evidence needed to estimate PV savings.
Solar EPC & street lighting RFQ checklist (TXT)
A plastics factory's restart sequence can create a substantial demand as heaters, chillers and compressors start together. Determine whether that pattern affects the billed demand from the tariff and interval records rather than assuming that one start-up peak sets the charge.
That single fact does more to shape the economics of a rooftop plant on a plastics or packaging site than anything on the module datasheet, because it is the part of the bill a solar plant is least able to touch.
An injection moulding machine draws in bursts. Clamp close, injection, hold, cooling, screw recovery, clamp open, eject, and around again. On a machine with a fixed-displacement pump the motor runs through the whole cycle and the peak is smoothed out. On an accumulator machine the injection peak is sharp. On an all-electric machine the peaks are sharper still, with regeneration on servo deceleration putting energy back.
With thirty machines cycling out of phase the aggregate at the incomer smooths into something close to a steady load. With four large machines it does not, and when their injection strokes happen to coincide the plant sets a new maximum demand for no productive reason at all. That is worth knowing before anyone blames the tariff.
Around the moulding machines sits a second layer of load that behaves quite differently, and it is the layer that determines whether solar is worth building.
| Load | When it runs | How well solar matches it |
|---|---|---|
| Moulding machine drives | Whenever the line runs, in short peaks each cycle | Partly. The energy matches; the peaks do not. |
| Barrel and hot runner heaters | Heavy at start-up, then cycling to hold temperature | Badly at start-up, well once running |
| Process chillers and cooling towers | All day, and hardest on hot bright afternoons | Very well. The best match on the site. |
| Air compressors | Continuously while the plant runs | Very well |
| Material dryers and dehumidifiers | Near constant while hoppers are loaded | Very well |
| Granulators | Intermittent and operator driven | Neutral |
| Lighting, packing and offices | Shift hours | Well during the day shift only |
PV can supply any load connected behind the same approved metering arrangement. Use the table to build a measured aggregate profile; it is not evidence that solar serves only the auxiliaries or that those loads never spike.
Read the tariff and recent bills to identify the demand basis, integration interval, any contractual minimum and power-factor treatment. A demand reduction matters financially only if it changes the billed quantity.
PV generation consumed on site can reduce purchased energy; exported or curtailed energy has different value. Where demand billing is based on measured net demand, compare PV output with the same integration intervals and seasonal production patterns. Solar alone does not guarantee a lower demand charge.
What does reduce demand charges on a moulding site, in the order most factories should try them:
That list is not an argument against solar. It is an argument for selling solar on the thing it actually does, which is displacing a large, steady, daytime energy consumption at the retail rate.
A moulding hall is hot, and the roof above it is hotter. Module output falls as cell temperature rises, so a coplanar array lying flat against an uninsulated sheet roof over a hot hall gives up yield every sunny hour of its life. Mount on rails that leave a real air gap under the modules so that the underside can shed heat, and resist the temptation to reduce that gap to save on rail.
The inverter room deserves the same attention. String inverters derate above their rated ambient temperature. An inverter room on the sunny wall of a moulding hall will reach its derating threshold at around midday, which is exactly when the array is producing most. Put the room on a shaded elevation, ventilate it properly or air condition it, and check the manufacturer's derating curve against a realistic room temperature rather than against an ambient figure taken from a weather table.
Roof structure on packaging and plastics sheds is usually modern light steel with wide-span portal frames, which is good news: large contiguous roof planes, few obstructions and clean access. Check purlin section and spacing anyway, and check what is already hanging from the structure, because moulding halls accumulate ducting, cable trays and evaporative coolers over the years.
Servo-driven machines, variable frequency drives on chillers and compressors, and inverter-driven auxiliaries all put harmonic current onto the busbar. Most plastics factories also have a capacitor bank for power factor correction, and a good number of those banks are untuned.
Connecting a fleet of solar inverters to a board that already carries significant harmonic distortion and an untuned capacitor bank can excite a resonance between the bank and the supply impedance. The symptoms are failed capacitors, tripping contactors and overheating in the bank, and they are almost never attributed to the solar plant because they appear weeks later.
Vvon's published project portfolio includes 260 kWp at Innovation Plastic Cans. Capacity and installation alone do not demonstrate a particular self-consumption percentage, demand saving or payback. Request measured operating evidence before using the project as a financial comparator.
The question to ask of any proposal at this scale is simple and it is rarely asked: on a bright day in April at one in the afternoon, is the factory's own consumption higher than the array's output? If the answer is yes with margin, the plant is sized sensibly. If the answer is only yes when every machine happens to be running, the plant will export more than the model assumed, and the return will land lower than the spreadsheet said.
Getting that answer takes a logger on the incomer for a week, and any EPC contractor worth signing with will ask for one before quoting a capacity.
Consult the relevant edition and the documents for the exact equipment and site: SREDA: Net Metering Guidelines and current application documents; Schneider Electric: power-factor correction equipment and selection.
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