A manufacturing plant in San Luis Potosí cut its annual energy cost by more than MXN 8.4 million through four measures: gas fired generation during CFE peak hours, new and retilted rooftop solar, a centralized outdoor chiller plant, and power factor correction. The figure is in Mexican pesos. At the peso to dollar rates prevailing in May 2025 it is on the order of USD 400,000 to 450,000, not USD 8.4 million.

The measures are not equivalent. Power factor correction paid back in 0.52 years and carries almost no exposure to input prices. Gas fired peak shaving produced the largest single number, MXN 3,621,703 a year, and it is the one measure whose value is a spread between two prices that both move. That ranking, not the total, is what an energy manager or plant controller should take from this.

This is Mexico Energy Partners' own engagement data. What follows sets out each measure, what was metered and what was modeled, and where the arithmetic in the original figures needs a variable the client has not published.

What the plant looked like before

The San Luis Potosí site ran a measured power factor averaging 83.20%, below CFE's 90% threshold, so it was paying a low power factor surcharge every month. Indoor chillers were decentralized, which put their heat rejection inside the building and their footprint on the production floor. An existing rooftop array was generating below its potential because of module orientation, and unshaded roof and parking area sat unused. Liquefied petroleum gas carried a cost the plant had not tested against alternatives. Peak demand was unmanaged and there was no interval metering, so nobody could see which loads were setting the monthly peak.

Each of those is a separate line on the invoice with a separate remedy. That is why the engagement produced four measures rather than one.

What was measured and what was modeled

This matters more than the total, so it is stated plainly rather than in a footnote.

Power factor correction and gas fired peak shaving are implemented measures. Their savings are calculated from the plant's own invoices before and after, against the CFE tariff in force.

The solar and chiller figures are engineering projections. The original case note says the new array "will save" MXN 1,432,220 and that the chiller works are "projected to save" MXN 1,279,296. Those two lines, MXN 2,711,516 in total, are design estimates rather than metered results. They should be read as such in any comparison with your own plant.

Three variables are not disclosed and change how the numbers should be read. First, capital cost. Only the power factor measure has a payback attached, 0.52 years, which implies capital of roughly MXN 477,000 for the capacitor banks. No capital figure is published for the other three. Second, whether the MXN 3,621,703 peak shaving figure is net of the gas the gensets now burn and of their maintenance reserve, or gross of both. That question moves the total materially. The client has not published the answer. Third, the four measures listed here sum to MXN 7,588,541. The balance to the MXN 8.4 million total, about MXN 811,000, comes from measures outside these four and is not itemized in the original case note.

None of that makes the result wrong. It makes it a set of figures with a stated basis rather than a headline. Ask for the same three variables from any vendor quoting you a savings number.

The four measures

Gas gensets during CFE peak hours: MXN 3,621,703

The plant installed 500 kW and 350 kW CUMMINS natural gas generating sets and runs them through the CFE peak window, taking load off the grid in the hours when energy and demand are priced highest.

The mechanics are worth understanding before copying them. The saving is the difference between what the displaced kWh and kW would have cost on the CFE tariff and what the gas to produce them costs delivered, less maintenance. Both sides move. A rise in the delivered gas price or a change in the peak tariff structure compresses the spread. The peak block also differs by tariff region and between summer and winter, so the window that works in San Luis Potosí is not automatically the window at another site. Check the schedule for your own region before sizing gensets.

270 kWp of new PV and a 22 degree retilt: MXN 1,769,729

Two actions, one of them cheap. A new 270 kWp array went on the parking area. The existing modules were reoriented to a 22 degree tilt. The new array is modeled to save MXN 1,432,220 a year and avoid 255,371 kg of CO2. The retilt of equipment already owned adds MXN 337,509 and 49,774 kg, taking the combined solar impact to MXN 1,769,729 a year and over 305,000 kg of CO2, which is the highest return per peso spent in the whole program.

Solar output is daytime output. It reduces the energy charge in the hours it generates and it does very little to a demand charge set in the evening, which is precisely why the gensets and not the panels carry the peak shaving job here.

Centralizing the chiller plant outdoors: MXN 1,279,296

Decentralized indoor chillers were replaced with a centralized outdoor chilled water system using high efficiency Carrier machines, a revised hydraulic layout and a thermal inertia tank. The projection is a 42.7% cut in cooling energy, 438,964 kWh a year, and 192,266 kg of CO2.

Read that as a consumption figure. A 42.7% cut in cooling kWh reduces billed demand only to the extent the improvement lands inside the meter's peak interval, and that is a separate calculation. The secondary gains are real but unpriced here: heat rejection moves outside the building, and floor space comes back for production.

Power factor correction: MXN 917,813

Capacitor banks at the main incomers lifted the power factor from 83.20% to 98%. Under the CFE surcharge formula for a power factor below 90%, three fifths of the shortfall ratio is applied as a percentage surcharge on the bill. At 83.20% that is a surcharge close to 4.9%.

That gives the reader something the original case note does not. If the whole of the MXN 917,813 is the avoided surcharge, the plant's annual electricity spend is in the region of MXN 18 to 19 million. Against that baseline, the full MXN 8.4 million program is roughly 45% of the bill. Our explainer on how CFE calculates the low power factor surcharge sets out the formula in full.

The four measures ranked

Ranked by payback and by exposure to prices you do not control, the order is not the order of the savings.

The largest number carries the most exposure, and the smallest carries almost none. A plant with limited capital should take them in the order of the table, not in the order of the savings. Power factor correction and any retilt of equipment already owned should be done before a capital committee is asked for anything.

What the program adds up to

Total annual cost saving exceeding MXN 8.4 million, of which the four measures above account for MXN 7,588,541 and the balance is not itemized in the original case note.

On emissions, the solar and chiller measures avoid 497,411 kg of CO2 between them. The reported net figure is about 354,559 kg. The difference, roughly 142,852 kg, is the direct combustion emission the gas gensets add. Netting those is the correct treatment. A peak shaving strategy built on gas buys cost reduction with a carbon cost, which matters if the plant reports Scope 1 separately.

The program also left the site with interval metering, which is what makes the next round of decisions possible. Our note on what an industrial energy audit covers describes the measurement step, and a second worked example appears in our manufacturing energy efficiency case study.

What this engagement did not touch is worth stating too. Compressed air and process heat were outside the scope. On most plants of this size they are the next two places to look.

Run the same four checks on your own plant

Mexico Energy Partners will review your CFE billing and tell you what the same four checks are worth at your site. Send twelve months of CFE invoices and the recorded power factor from those invoices. We return the low power factor surcharge you are paying today, and the capacitor bank size and installed cost to clear it. We also return the kW of billed demand that could be moved out of the peak window at your tariff and region, and whether your roof and yard support an array worth modeling. We do not quote a saving before we have seen the invoices, and we state which parts of any estimate are metered and which are modeled.

Call +52 55 8652 8023 to speak with an engineer, or use the form below.

Sources

• Mexico Energy Partners engagement data for a site in San Luis Potosí, 2025. All peso savings, equipment specifications and the 0.52 year payback come from this engagement and are not public data.
• Comisión Federal de Electricidad, low power factor surcharge applied where the measured power factor is below 90%, published with the basic supply tariff conditions. The surcharge percentage is three fifths of the shortfall ratio, which gives about 4.9% at a power factor of 83.20%.
• Comisión Federal de Electricidad, published tariff schedules for medium voltage large demand service, for the peak, intermediate and base periods that vary by tariff region and season.
• Banco de México, daily peso to dollar FIX exchange rate series, for converting the MXN figures in this case study to dollars at the date a reader needs.