How Plant Simulation Accelerates Net-Zero Manufacturing in Automotive Paint Shops

Picture a curing oven on a quiet night shift. Somewhere upstream, a colour change, a short stoppage, or a dry buffer has created gaps between the vehicle bodies coming through. The oven is half empty. Its fans and burners don't know that. They keep pushing out the same hot air and heat they would at full load, even as production slows or stops altogether.

That quiet waste is where net-zero manufacturing is won or lost. Plant simulation builds a virtual, time-based model of a production system, and once you feed it live data, it becomes a digital twin. In the paint shop, simulation lets engineers spot waste before it happens and try out fixes without putting a single body at risk. We think it's the most practical route to net-zero in the part of the plant that matters most.

Why the paint shop decides a plant's net-zero journey

Ask where the biggest loads sit in a vehicle plant, and you'll hear the same answer every time: the paint shop. Exactly how big its share is depends on the plant, the process and what you count. One widely cited figure puts it at 50–70% of an assembly plant's energy (Cronrath, Lennartson and Lemessi, IEEE CASE 2016). Lawrence Berkeley National Laboratory's ENERGY STAR guide says paint systems account for 27–50% of plant electricity, with HVAC taking another 11–20%. A 2022 review in Physics of Fluids comes in at about 36%. The numbers vary. The ranking doesn't. Every source we looked at puts the paint shop at the top.

Carbon follows the same pattern. Stellantis says its paint shops produce around 65% of a plant's CO₂, use about 60% of its natural gas, 50% of its electricity, and 55% of its water. Its plan to reach net-zero carbon by 2038 runs straight through them.

And the pressure keeps building. The IEA lists fourteen major automakers, including BMW, Mercedes-Benz, Toyota and Volkswagen, with carbon-neutrality targets between 2038 and 2050. In India, SEBI's BRSR Core makes Scope 1 and 2 emission intensity a mandatory disclosure, and assessment or assurance reaches the top 1,000 listed companies in FY2026-27. Carbon intensity per painted body is now a number boards care about.

Where does the energy actually go?

Mostly to three places. The thin film of paint is the smallest part of the story.

The oven. Industry estimates suggest drying alone takes about a third of a paint shop's energy, and that roughly half the heat still escapes to the environment, even with exhaust-heat recovery. Researchers report that more than 25% of an oven's energy goes into hours when it isn't curing anything. And of the energy it does use, very little heats the paint. Most of it goes into warming the body and the 200–350 kg carrier it rides on.

The air. Booths need tightly conditioned air, and the LBNL guide says airflow control is where a paint booth's biggest savings tend to lie. Toyota Kentucky shows how big those savings can get. By cutting outside-air intake on one line by more than 55%, it brought annual paint booth energy costs down by over 80% and picked up a 2026 US Department of Energy award for it.

The sequence. This is where the supply chain meets the shop floor. The paint shop feeds painted body storage, which in turn feeds the final assembly. Every colour change between consecutive bodies means cleaning the paint system, losing paint and changing guns. When upstream supply stutters or downstream assembly stops, buffers starve, and the oven runs part empty.

Why equipment upgrades alone won't get us there

Hardware matters, and the gains are real. Stellantis reports that its paint shops have cut energy use by 27% against 2021, and that applying four coatings with two curing ovens instead of four saves up to 30%. Its Gliwice plant runs at 245 kWh per vehicle, comfortably under a 2025 fleet target of 321. Experts reckon switching to green electricity can cut a conventional paint shop's CO₂ by about 40%.

But equipment only sets the ceiling. Operations decide how close you get to it. One research team studying a real paint shop showed that energy use can drop significantly through production system design alone: no new chemicals, no new painting processes, no new oven or booth controls. Part-load running, ramp-ups and mix changes all drag performance away from the design point, and Dürr notes that energy losses are substantial even during commissioning and ramp-up.

So sustainable production needs operational optimisation. And optimisation needs somewhere to test ideas that isn't a live paint shop.

How paint shop simulation finds hidden energy

A discrete-event simulation model follows each body through the conveyors, buffers, booths and oven zones. Give each machine state (running, idle, standby) an energy figure, and the model reports energy right alongside throughput. Three use cases pay off the most.

1. Sequence bodies to keep ovens full and colour changes few

An oven's energy needs depend on how many bodies are in each zone. An air-management controller tracks body count zone by zone and factors in each body's weight and surface area, so gaps and shifts in model mix change the load. Simulation shows where those gaps come from, and lets engineers test sequencing rules and buffer logic against real mix and disruption patterns.

A discrete-event model built for a General Motors paint shop conveyor showed that regrouping colour batches significantly cut paint head changes, saving both cleaner and paint. A colour-batching study across 170 problem instances reduced colour changes by considerable margins compared with existing methods.

2. Rehearse energy-saving modes before running them live

What should the oven do during a planned stop, or when a buffer starves? Drop the airflow, lower the temperature, or hold steady? Each option carries a restart penalty and a quality risk. Cut the fresh air in a straight-through oven, for example, and you can weaken the air seals and end up with condensation, which is why its engineers relied on flow simulations. A model lets you map out those trade-offs for your own oven, line speed and stoppage pattern.

How much you save varies. Cronrath and colleagues modelled an energy-sensitive on-off control strategy for a typical paint shop and found savings of 7% overall, more than 300 MWh a year. In a published discrete-event model of a paint shop's electrical load, the scenarios saved anywhere from about 1.4% to 30%, with the biggest gains coming from production scheduling during periods of low demand.

3. Separate value-added from non-value-added energy

Not every kilowatt-hour earns its keep. Value-added (VA) energy brings a body up to cure temperature and applies the coating. Non-value-added (NVA) energy just keeps equipment ready and waiting: idle ovens, over-ventilated booths, standby at full load. Factory simulation tags each machine state as VA or NVA and reports kWh per painted body at different volumes. Because much of the NVA energy behaves like fixed overhead, kWh per body usually climbs as volumes fall. That's where the savings are hiding.

Energy value stream mapping makes the pattern clear. In one case, idle energy fell from 86.27 to 31.82 kWh, a drop of about 63%, while operating energy barely moved (398.86 to 387.34 kWh). Ovens and booths follow the same logic. In our own manufacturing engineering programmes, VA/NVA analysis has improved station productivity by 5%.

From simulation to a net-zero roadmap

A single model answers a single question. A mature simulation framework answers the next fifty. It starts with a calibrated model of the line, adds energy states and tariffs, and then connects to live plant data. That's digital twin technology, the core of an Industry 4.0 smart factory. On top of it sits a library of scenarios: sequencing rules, standby policies, volume ramps, the switch from gas to electric curing, changes in renewable supply.

That library becomes your roadmap. Operational fixes that need no capital come first. Capital projects such as electric ovens or air recirculation are then sized and phased against the modelled load profile, including peak demand, rather than a figure from a brochure. Every step is measured in kWh and CO₂ per painted body before any money is committed, so green manufacturing claims hold up with auditors and boards.

Sites in the World Economic Forum's Global Lighthouse Network, a curated group of advanced manufacturers, report 30–50% reductions in Scope 1 and 2 emissions and an average 25% cut in energy and water use. At Hinduja Tech, our manufacturing engineering teams use virtual factory and material flow simulation on both greenfield and brownfield programmes. Our published results include 8–12% more production capacity from plant simulation and 15% higher line throughput from material flow simulation.

Start with the model

Nobody buys a net-zero paint shop with a single purchase order. We model it, test it, and phase it in. Planning a greenfield facility? Retrofitting a line? Or just wondering why your kWh per body won't budge? Talk to Hinduja Tech's manufacturing engineering team about building a simulation framework that turns net-zero from a target into a plan.