An energy audit at a manufacturing plant put three measures in front of the client: control retrofits on the chillers, capacitor banks to correct power factor, and a 500 kW rooftop solar array. Mexico Energy Partners modeled 18% lower annual electricity consumption and 25% lower CO2 emissions across the three, with a blended payback near three years. Those are model outputs. No post-implementation invoice has been measured against them.

Two of the numbers do not survive a check against the rules that govern a Mexican industrial bill. A capacitor bank cannot cut a whole electricity bill by 12% unless the plant is running near a power factor of 0.75, because CFE bounds that adjustment by formula. And a 500 kW array is not generación distribuida under the Ley de la Industria Eléctrica, which changes both the permit and the interconnection route.

What follows is what the audit measured, what it modeled, and the four items a plant director should demand before releasing capex against any of the three measures.

What the audit measured and what it modeled

The measured part is the baseline. MEP reviewed the plant's billing history to set consumption benchmarks, then metered the chillers, the compressed air system and the HVAC plant through a monitoring period to establish where the load actually sat. That work produces real numbers for the site.

The savings are not measured. They come from scenario modeling built on top of that baseline, run against equipment upgrades, power factor correction and a rooftop array. The 18% consumption figure, the 25% emissions figure and the three-year payback are Mexico Energy Partners' own modeled outputs. They have not been checked against a post-implementation invoice, and this note does not present them as billed results.

No cash figure appears here. MEP has not published the plant's baseline spend, its currency or its CFE tariff class, and a percentage without those three cannot be converted into money by a reader. Ask for all three before you use the number in a business case.

Why the power factor saving is bounded

CFE applies a power factor surcharge and bonus set out in the Acuerdo que modifica las disposiciones complementarias a las tarifas para suministro y venta de energía eléctrica, published in the Diario Oficial de la Federación on 31 October 2000. Where the average power factor in a billing period falls below 90%, the surcharge is three fifths of ((90 divided by FP) minus 1), taken as a percentage. Where it reaches 90% or more, the bonus is one quarter of (1 minus (90 divided by FP)). The surcharge is capped at 120% and the bonus at 2.5%.

Run the arithmetic on a real plant. One averaging 0.85 pays a 3.53% surcharge. Correcting to 0.95 turns that into a 1.32% bonus. The whole swing is 4.85% of the billed supply amount, not 12%. A 12% surcharge needs a power factor of 0.75, and the audit never says the plant was there.

The mechanism matters more than the percentage. Capacitor banks cut reactive demand and remove the penalty. They do not cut a single kilowatt hour of real energy. An audit that puts a 12% bill reduction against a capacitor bank is either carrying savings from another measure or has the basis wrong. MEP has set out how the power factor adjustment is applied on a Mexican invoice.

A 500 kW array sits above the generación distribuida line

Article 17 of the Ley de la Industria Eléctrica, published in the DOF on 11 August 2014, requires a permit from CRE for any Central Eléctrica with capacity of 0.5 MW or more. CRE's RES/142/2017, published in the DOF on 7 March 2017, sets the contracts, technical specifications and contraprestación methods for distributed generation, which reaches only to plants below 0.5 MW.

A 500 kW array is 0.5 MW. It is on the wrong side of both lines. It needs a generation permit, and it cannot use the distributed generation interconnection contracts or their compensation models. Size the same roof at 0.499 MW and the project stays inside the exempt generator route.

This is an engineering decision with legal consequences, not a paperwork detail. It moves the schedule, the transaction cost and the way exported energy is settled. Any board asked to approve the array should see both versions priced separately. MEP has written on rooftop solar economics in Mexico in more detail.

The three percentages do not reconcile as published

The audit modeled the array at 30% of the facility's energy needs. If that means 30% of annual kilowatt hours, solar on its own displaces more purchased energy than the 18% headline. Both figures cannot describe site electricity consumption.

The chiller number has the same problem. On our read, the 20% modeled for the control retrofit has to be 20% of the chillers' own consumption. Taken as a site figure it would push total displacement past 40% once the array is added, which the 18% rules out.

Tariff structure explains why aggregates mislead. Under the GDMTH schedules approved by CRE in Acuerdo A/058/2017 on 23 November 2017, capacity and distribution are billed on kilowatts, while energy is billed on kilowatt hours split into punta, intermedio and base periods. A measure that cuts consumption outside the punta window leaves both kilowatt lines untouched. Ask for the saving per measure and the invoice line it comes off, not a blended percentage.

The emissions figure depends on the factor you use

A 25% cut in CO2 is arithmetic: displaced grid kilowatt hours multiplied by an emission factor. SEMARNAT published the Factor de Emisión del Sistema Eléctrico Nacional for 2023 at 0.438 tCO2e per MWh, the figure used for Registro Nacional de Emisiones reporting. Change the year of the factor and the tonnage changes with it.

All three measures act on purchased electricity, so the reduction lands in scope 2. None of them touches process fuel. A plant reporting under RENE should publish the factor and its year beside the tonnage, or the claim cannot be checked by anyone outside the company.

What to ask for before you approve the capex

The audit is worth commissioning. The published percentages are not enough to release money against. Four items close the gap.

• Installed cost for each measure separately, with the date of the quotation.
• The measured average power factor from twelve consecutive CFE invoices, and the peso value of the adjustment line on each.
• Confirmation that the array is sized below 0.5 MW, or a schedule and cost for the CRE permit route.
• Modeled annual generation with its irradiance source and the assumed specific yield.

The last item has a public benchmark. The World Bank and ESMAP report Global Photovoltaic Power Potential by Country, published in June 2020, places Mexico among the 70 countries whose long-term daily PV output averages more than 4.5 kWh per kWp, which is above 1,640 kWh per kWp a year. That is a national average across good and poor sites. A model for one flat industrial roof has to show the irradiance source and the loss assumptions that get it to its own number. For scope, see what an industrial energy audit covers.

Have the same three checks run on your plant

MEP reviews twelve months of CFE invoices for the site, the billed or measured power factor, the chiller schedule with nameplate capacity and age, and the usable roof area. It returns a measure by measure list with installed cost, modeled annual saving, payback, and the invoice line each saving comes off. You supply the twelve invoices, a single line diagram or switchgear schedule, and the chiller list. Send the form below and MEP will confirm the scope and the cost before any work begins.

Sources

• Diario Oficial de la Federación. Acuerdo que modifica las disposiciones complementarias a las tarifas para suministro y venta de energía eléctrica. 31 October 2000. Power factor surcharge and bonus formulas and their caps.
• Diario Oficial de la Federación. Ley de la Industria Eléctrica. 11 August 2014. Article 17 permit threshold of 0.5 MW.
• Comisión Reguladora de Energía. RES/142/2017, distributed generation provisions. DOF, 7 March 2017.
• Comisión Reguladora de Energía. Acuerdo A/058/2017, tariff schedules for basic supply including GDMTH. 23 November 2017.
• SEMARNAT. Factor de Emisión del Sistema Eléctrico Nacional 2023, 0.438 tCO2e per MWh. Published 2024.
• World Bank and ESMAP. Global Photovoltaic Power Potential by Country. June 2020.