A CFE medium voltage invoice carries four lines that can be wrong or badly set. The power factor adjustment. The tariff assignment between GDMTO and GDMTH. The contracted demand that drives the guarantee deposit. And the metered demand used to bill capacity and distribution. All four can be checked from the invoice itself. A plant holding a measured power factor of 0.85 pays a surcharge of about 3.5% on its energy, capacity and distribution charges, which is roughly 424,000 pesos a year where those charges run a million pesos a month.

Mexico Energy Partners is launching BillGuard & Tarifa, a monthly subscription that reviews each CFE invoice for one or more sites and returns a one page report with a peso value against every finding. What follows sets out the four calculations the review runs. A plant manager or a finance director can use them to work out, before asking for a quote, whether a monthly review is worth paying for at their own site. The same method is applied in a BillGuard and Tarifa review at an automotive parts plant in Puebla.

How the power factor charge is calculated

CFE applies a power factor adjustment to medium voltage supply. Below a measured power factor of 0.90 the invoice carries a surcharge. Above 0.90 it carries a credit. The surcharge percentage is three fifths of the quantity 0.90 divided by the measured power factor, minus one, expressed as a percentage. The credit is one quarter of the quantity one minus 0.90 divided by the measured power factor. Both are applied to the sum of the energy, capacity and distribution charges. CFE caps the surcharge at 120%, which is reached at a power factor of 0.30, and caps the credit at 2.5%, which is reached at unity.

The arithmetic is short. At a power factor of 0.85, 0.90 divided by 0.85 is 1.0588. Subtract one, multiply by three fifths, and the surcharge is 3.53%. Applied to energy, capacity and distribution charges of one million pesos in a month, that is 35,300 pesos. Held for twelve months it is 423,600 pesos. Two things about that figure. It is arithmetic from the published formula rather than a measured result at any one plant, and it assumes the power factor and the charge base both hold steady across the year. A site whose power factor moves with the production schedule will land somewhere inside a range, and only the meter can say where. The mechanics are set out in more detail in how CFE calculates the power factor penalty.

Power factor is also a compliance matter and not only a cost line. The Comisión Reguladora de Energía issued the Código de Red as resolution RES/151/2016, published in the Diario Oficial de la Federación on 8 April 2016, and it sets technical requirements for load centers connected at medium and high voltage. Failure to meet them is sanctionable under the Ley de la Industria Eléctrica. A capacitor bank sized only to clear the CFE surcharge does not by itself close a Código de Red gap.

GDMTO or GDMTH, and how the choice is made

The two large demand medium voltage tariffs differ in metering rather than in voltage. GDMTO bills on ordinary metering. GDMTH bills energy in three daily periods, base, intermediate and peak, and charges capacity and distribution separately. In its February 2018 briefing on final basic supply tariffs in medium voltage, the Comisión Reguladora de Energía put the dividing line at 100 kW. Demand of 100 kW or more falls under GDMTH. Below that, GDMTO applies. A service that has stayed under 100 kW for twelve consecutive months can request reclassification to GDMTO.

That request is worth testing after any load reduction, because tariff assignment does not follow a plant that has shed a production line, relamped a building or moved a shift. The move is not automatically cheaper. Hourly metering rewards load that sits in the base period, so a plant running nights and weekends can pay less under GDMTH than under GDMTO at the same consumption. The comparison has to be run on twelve months of interval data rather than on a single invoice. The demand side of that comparison is worked through in beating GDMTH demand charges.

Contracted demand and the guarantee deposit

The CFE mercantile contract for basic supply in medium voltage sets contracted demand at no less than 60% of total connected load and no less than 10 kW. When measured maximum demand exceeds the contracted figure for three consecutive billing periods, CFE raises the contracted demand and charges the difference to the guarantee deposit in the following cycle. That adjustment arrives without any decision by the customer.

The reverse does not happen on its own. A plant that has cut load keeps the old contracted demand, and the deposit that sits behind it, until someone asks for a change. Comparing the metered peak against the contracted figure every month is what catches it. On a site that has reduced peak demand by 300 kW and never told CFE, the deposit is working capital tied up against capacity the plant no longer uses.

Disputing a charge with CFE

A billing error is only worth finding if it can still be recovered. Under the CFE medium voltage supply contract, the customer files an aclaración within one billing period of the event that gave rise to it, through a customer service office, the 071 line, the web portal or the CFE app. CFE answers within ten business days. If the answer does not settle the matter, the route runs on to Profeco or to the regulator. Claims for damage tied to a supply failure run on a separate and shorter clock of fifteen business days from the failure.

Those windows are the reason a bill review has to be monthly rather than annual. An invoice first examined in March cannot be disputed in September. Mexico Energy Partners prepares the evidence in the form CFE accepts and hands it to the client. Whether CFE agrees with it is CFE's decision, and the ten business day answer window is the only timing anyone outside CFE can point to.

What the monthly review covers

• Energy in kWh by period, billed demand, capacity and distribution charges and the power factor adjustment, each set against the prior twelve months.
• Whether the assigned tariff still fits the load profile, tested on interval data rather than on the tariff already printed on the invoice.
• Contracted demand against metered peak, with the guarantee deposit consequence stated in pesos.
• Month on month variance, with any movement above an agreed threshold traced to a cause before the report is issued.
• A one page report carrying one to three recommendations, and a quarterly video call with the plant and finance teams.

The report is written for a reader who does not work in energy. It states what changed, what it cost, and what action is open, in that order.

Who it fits, and the number that decides it

The test is arithmetic. Ask for the monthly fee alongside the first review and set it against one percent of the monthly CFE invoice for the site. If the fee is larger than that, the review is unlikely to pay for itself on billing corrections alone and the money is better spent on metering or on a power factor fix. If the fee is smaller, a single mis-set tariff or one uncorrected power factor month covers the year.

Groups running several plants get something a single site cannot. Cost per kWh, load factor and power factor placed side by side across sites on the same tariff show which site is the outlier and by how much. That ranking is the fastest way to decide where the next capital goes, and it needs no new hardware to produce.

Send one site's invoices for a first review

The first review needs twelve months of CFE invoices for a single site, the RPU, the contracted demand in kW and the tariff currently applied. Interval data helps and is not required. Mexico Energy Partners returns the power factor adjustment total for the period, the metered peak against contracted demand, and a tariff fit test, each with a peso value and the calculation shown. Nothing in that first review commits either side to a subscription, and no saving is promised before the invoices have been read. Use the form below to request a bill review.

Sources

• Comisión Reguladora de Energía, Sesión informativa con CFE: Tarifas Finales de Suministro Básico, Media Tensión, February 2018. Basis for the 100 kW dividing line between GDMTO and GDMTH and for the twelve month reclassification rule.
• Comisión Reguladora de Energía, resolution 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, Diario Oficial de la Federación, 8 April 2016.
• CFE Suministrador de Servicios Básicos, Contrato mercantil para el servicio de suministro básico de energía eléctrica en media tensión. Basis for the contracted demand minimum, the three period automatic adjustment, the guarantee deposit and the aclaración process and its deadlines.
• CFE, published tariff schedule for Gran Demanda en Media Tensión Horaria, app.cfe.mx. Basis for the power factor adjustment applied to medium voltage supply.
• Comisión Nacional para el Uso Eficiente de la Energía, Herramienta para el ajuste del factor de potencia, gob.mx. Supporting the 0.90 threshold and the surcharge and credit caps.
• Comisión Reguladora de Energía, Memoria Documental: Tarifas Finales del Suministro Básico, 31 October 2018. Background on the structure of the medium voltage tariffs.