INEGI reported on 9 July 2024 that Mexican plants built 1,996,136 light vehicles between January and June 2024 and exported 1,721,852 of them. Behind that output sits an electricity bill whose largest controllable line is usually not the kilowatt hours. On CFE's Gran Demanda en Media Tensión Horaria tariff, the demand charges are set by a small number of quarter hours, and the plant decides when those quarter hours happen.
That is the decision in front of plant managers and finance directors at automotive sites in Mexico. Before approving solar, storage or a chiller replacement, the site needs a measured baseline showing which systems set peak demand and what a kilowatt of avoided peak is worth across twelve months of invoices. Without it, every capital case rests on a vendor's assumption.
What the plant is buying under GDMTH
CFE publishes the GDMTH schedule monthly for each distribution division. It charges energy in three time bands, base, intermedio and punta, and it charges demand twice. The cargo por capacidad is billed on demand coincident with the punta window. The cargo por distribución is billed on the site's maximum demand in the month, whichever hour that falls in.
The two respond to different actions. Moving a load out of punta cuts the capacity charge and the punta energy charge. It does nothing to the distribution charge unless the new maximum is lower than the old one. At an automotive plant that monthly maximum is often manufactured rather than inherited. Compressors restarting together after a shutdown, a paint line returning to temperature and chillers ramping on a hot afternoon can coincide for fifteen minutes and set a charge that then sits on the whole invoice.
Resequencing those restarts costs no capital. Finding out that they coincide requires interval data at the main incomer and at the four or five largest feeders, which many plants do not record. That is the first gap a baseline finds and the cheapest one to close.
Where the electricity goes inside the plant
A vehicle assembly plant with a paint shop and a Tier 1 component plant running presses or injection molding do not share a load profile. Both run compressed air, and compressed air is almost always the worst converter of electricity on site. The US Department of Energy put the wire to work efficiency of an industrial compressed air system at around 10% in Improving Compressed Air System Performance, report DOE/GO-102003-1822, published in November 2003. The same sourcebook states that leaks waste 20 to 30% of a compressor's output.
Those two figures set the order of work. Before any capital measure, establish the leak load, the artificial demand created by running the header above what the application needs, and how many blow off points could run on a blower instead of process air. A leak survey and a pressure study take days and need no capital approval. That sequence is the same one that decides where industrial efficiency savings come from in Mexico, and a plant that has skipped it has no basis on which to judge a solar quotation.
The carbon side runs on the same measurement. SEMARNAT set the Factor de Emisión del Sistema Eléctrico Nacional for 2023 at 0.438 tCO2e per MWh for Registro Nacional de Emisiones reporting. Each GWh drawn from the grid therefore carries 438 tCO2e of Scope 2. In that reporting a gigawatt hour removed by efficiency counts the same as a gigawatt hour replaced by clean supply.
The Código de Red obligation runs on voltage, not on state
Automotive production clusters in Puebla, San Luis Potosí and Nuevo León, and those sites do not sit on the same part of the grid. SENER's PRODESEN describes the Sistema Interconectado Nacional as seven regions, with CENACE regional control centers in cities including Puebla and Monterrey. What does not vary by state is the compliance obligation, which follows connection voltage.
CRE issued the Código de Red as RES/151/2016, published in the DOF on 8 April 2016, and reissued it as RES/550/2021, published in the DOF on 31 December 2021 and in force since 1 January 2022. It applies to Centros de Carga connected at media tensión, above 1 kV and up to 35 kV, and at alta tensión, 35 kV and above, regardless of contracted demand or supply scheme. Media tensión sites owe studies on voltage variation, transient voltage, frequency variation, short circuit, protections, control systems, information exchange and current imbalance. Alta tensión sites owe those plus power factor, current harmonic distortion and voltage flicker.
Measurements must be taken with Class A instruments under NMX-J-610/4-3-ANCE or IEC 61000-4-30. Load centers already connected on 8 April 2016 had until 9 April 2019 to comply, and where a site was not compliant a work plan signed by its legal representative was required before that date. CRE holds compliance and sanction authority. CENACE operates the system and the market and does not sanction load centers.
Two practical points follow. CRE does not authorize or certify inspectors for these studies, so a plant may run them itself or contract a specialized firm. And a site connected at 35 kV or above carries three obligations that a medium voltage neighbor in the same industrial park does not. The differences that shape energy work at automotive plants in Mexico are connection voltage and load profile, not the state on the address, so read the single line diagram before accepting any vendor's scope.
Onsite solar stops at 0.5 MW
The renewable module in most workshop syllabi skips the constraint that decides the project. Under the Ley de la Industria Eléctrica, published in the DOF on 11 August 2014, a Generador Exento is the owner of a plant with capacity under 0.5 MW. CRE set the interconnection route and contract models for those plants in RES/142/2017, published in the DOF on 7 March 2017.
For an automotive site that is a hard ceiling on the simple option. A 0.5 MW array will not cover a load measured in several megawatts. Unless the plant's monthly maximum falls inside the midday output window, an array of that size reduces energy charges more than demand charges, which is the opposite of what most business cases assume. Anything larger moves the project out of distributed generation and into a different contracting and interconnection route. Settle that question, and the wider one of onsite against offsite renewable supply, before commissioning a roof survey.
What the tax code gives, and what it does not
Two instruments were in force in August 2024 and they cover different spending. Article 34, fracción XIII of the Ley del Impuesto Sobre la Renta allows a 100% deduction in the year for machinery and equipment used to generate energy from renewable sources or in efficient cogeneration. The condition is that the equipment stays in operation for at least five years following the year in which the deduction is taken. A solar array qualifies. A variable speed compressor, a replacement chiller, LED lighting and a submetering system do not.
The second is the decree published in the DOF on 11 October 2023, which grants immediate deduction of investment in new fixed assets at rates from 56 to 89% for taxpayers in listed export sectors. The listed activities include manufacture of engines for cars, vans and trucks, automotive electrical and electronic components and parts, and batteries for those vehicles. Qualification requires exports of at least 50% of total income, and the deduction covers assets acquired through 31 December 2024, claimed in the 2023 and 2024 tax years.
Neither instrument is a grant. If a proposal in front of you assumes grant funding for efficiency capital, ask which instrument, published where and on what date. If the answer arrives without a DOF citation, the money is not there.
What 10 hours of workshop can and cannot produce
Mexico Energy Partners runs a session for plant and sustainability managers at automotive sites in Mexico built on the material above. It produces four artifacts.
- A metering plan naming the points to instrument and the recording interval.
- A ranked measure list with capital cost bands and payback ranges.
- A baseline template tied to the site's own CFE invoices.
- A Código de Red gap check against the plant's connection voltage.
It does not produce a net zero roadmap, and no session of that length can. A credible pathway needs a measured Scope 1 and Scope 2 inventory, an agreed reporting boundary and an abatement cost curve built on the plant's own numbers. That work begins with the metering plan and runs over months. Anyone offering the roadmap first is selling the conclusion without the data.
Start with what your plant is paying
Mexico Energy Partners reviews twelve months of CFE invoices for the site, separates demand charges from energy charges, identifies the two largest consuming systems and returns a ranked list of measures with capital cost bands and payback ranges. You supply the invoices, the single line diagram and the production schedule with shift patterns. The review states which findings rest on measurement and which rest on assumption until metering is installed.
Request an automotive plant energy review
Sources
- INEGI, Registro Administrativo de la Industria Automotriz de Vehículos Ligeros, press release, 9 July 2024.
- CRE, RES/151/2016, Disposiciones administrativas de carácter general que contienen los Criterios de eficiencia, calidad, confiabilidad, continuidad, seguridad y sustentabilidad del Sistema Eléctrico Nacional, Código de Red, DOF, 8 April 2016.
- CRE, RES/550/2021, reissue of the Código de Red repealing RES/151/2016, DOF, 31 December 2021, in force since 1 January 2022.
- Congress of the Union, Ley de la Industria Eléctrica, DOF, 11 August 2014.
- CRE, RES/142/2017, Disposiciones administrativas de carácter general para generación distribuida, DOF, 7 March 2017.
- Ley del Impuesto Sobre la Renta, Article 34, fracción XIII.
- Executive branch, Decreto por el que se otorgan estímulos fiscales a sectores clave de la industria exportadora, DOF, 11 October 2023.
- US Department of Energy, Improving Compressed Air System Performance: A Sourcebook for Industry, DOE/GO-102003-1822, November 2003.
- SEMARNAT, Factor de Emisión del Sistema Eléctrico Nacional 2023, Registro Nacional de Emisiones, 2024.
- SENER, Programa de Desarrollo del Sistema Eléctrico Nacional 2022-2036, chapter 5.