Onsite solar is the one route to lower power cost in Mexico that does not depend on a CRE generation permit, a Usuario Calificado registration or a change of supplier. For a plant with roof or yard space and a daytime load, it is the shortest path from decision to a lower bill. It is also the route where the rules are most often described wrongly, and where a schedule slips because of it.
The regime is generación distribuida, and it is capped at generating capacity below 0.5 MW. That is a small system next to a large plant's load, which is exactly why the design question matters more than most vendors admit. It also means one plant can host a compliant array while a neighboring plant with a different roof cannot.
What follows is what a plant director, energy manager or CFO needs to establish before signing: what the threshold limits, what approval is genuinely removed and what is not, how surplus energy is treated under each contract modality, and what a savings number is measured against.
The 0.5 MW threshold, and the two things people get wrong about it
Generación distribuida in Mexico is capped at generating capacity below 0.5 MW. The threshold comes from SENER's Manual de Interconexión de Centrales de Generación con Capacidad menor a 0.5 MW, published in the DOF on 15 December 2016, and from CRE Resolución RES/142/2017, published in the DOF on 7 March 2017. It has not changed since.
Two details get misstated often enough to break project schedules. The limit applies to the generating capacity of the plant, not to the facility's load, so a 5 MW plant can sit behind a sub-0.5 MW array with the rest of its demand still served by CFE. And the limit is written in MW of capacity, not in kWp of DC panel rating, which is a different measurement and normally the larger number on a modern system. A proposal quoted in kWp needs to be reconciled to the capacity basis the regulation uses before anyone signs it.
Staying under the threshold removes a permit, not the paperwork
Below 0.5 MW no CRE generation permit is required. That is the real benefit and it is worth having. It does not mean the project has no approvals.
The project still requires an interconnection contract with CFE Distribución under the small and medium-scale interconnection regime. CFE Distribución runs the technical review, installs or authorizes the bidirectional meter, and sets the energization date. That sequence sits on the critical path and it is not controlled by the EPC contractor. A schedule built on the phrase "no permits required" is a schedule built on the wrong risk, and it is the single most common reason an onsite solar project misses its first billing cycle.
Surplus energy: what medición neta actually does
CRE RES/142/2017 sets three contract modalities, and the choice is commercial rather than technical. It is the decision that determines what a surplus kilowatt-hour is worth to you.
- Medición neta (net metering). Exported energy is netted against the site's own consumption. Surplus accrues as energy credits usable for up to 12 months, and only credits still unused after that period are paid out, at the Precio Marginal Local. This is the default.
- Facturación neta (net billing). Generation and consumption are metered and valued separately. Exports are compensated at hourly market prices rather than netted against the retail tariff.
- Venta total (total sale). All output is sold at Precio Marginal Local values. It applies where there is no associated consumption contract at the interconnection point.
Migration between modalities is permitted only after one year of operation, so the initial choice holds for at least twelve months. Medición neta is not selling power back to the grid, and describing it that way overstates the value of exports. Under medición neta a surplus kilowatt-hour offsets a retail kilowatt-hour you would otherwise have bought, and only if you consume it within twelve months. Only venta total is an outright sale.
The practical consequence for system sizing: on a site with a strong daytime load and low weekend consumption, oversizing into large weekend surpluses under medición neta produces credits that may expire unused. That is a design decision with a cash consequence, and it should be modeled from interval data rather than from an annual consumption total.
The resource, in numbers rather than adjectives
SENER and the Instituto de Investigaciones Eléctricas reported that roughly 90% of Mexican territory receives daily global solar irradiation between 5 and 6 kWh per square meter per day, with the highest values in the northwest across Baja California, Sonora, Sinaloa, Chihuahua, Coahuila and Durango, and the lowest along the Gulf and in the southeast. That work was presented at COP16 in Cancún in December 2010 and remains the most widely cited official characterization of the national resource.
The cost side moved further than the resource ever will. IRENA put the global weighted-average total installed cost of utility-scale solar photovoltaic at USD 883 per kW in 2020, down 81% from USD 4,731 per kW in 2010, in Renewable Power Generation Costs in 2020, published June 2021. Those are global utility-scale figures. A small rooftop system will not price at them, but they establish the direction and the magnitude of the change.
What the savings number is measured against
Onsite solar in Mexico is commonly presented as delivering savings of up to 25% on a facility's electricity cost. Savings in this range are measured against current CFE supply and vary with tariff class, region, load factor and consumption profile. The figures are illustrative. No range can be confirmed for a specific site without interval data and 12 months of billing.
The reason the range is wide is structural. A CFE GDMTH account is billed on time-of-use energy across base, intermedio and punta periods plus a demand charge. Solar generation lands mostly in the base and intermedio hours. It reduces energy charges in those hours and it does very little for a punta-period demand peak that occurs after sunset. Two plants on the same tariff with the same annual consumption can therefore see materially different results, and the difference is visible in interval data long before it is visible in a proposal.
Financing structures and what they are conditional on
Structures that require no upfront capital are available subject to credit review and contract term. In these, engineering, equipment, installation and construction are recovered through the energy tariff in a power purchase agreement rather than through a capital outlay. The trade-off is that the counterparty is pricing your credit and the length of the commitment, so a weaker balance sheet or a shorter term produces a higher tariff.
Onsite PPAs for this class of project typically run 10 to 20 years. A longer term supports a lower tariff. A shorter term costs more per MWh and preserves the option to reprice as equipment costs fall or as the site's load changes. The question is how confident the operations team is in that site's load and occupancy a decade out.
Reliability, and what it is and is not worth
Onsite generation reduces a facility's exposure to distribution and transmission interruptions caused by weather, equipment failure and demand-driven curtailment. It does not, on its own, keep a plant running through an outage. A grid-tied photovoltaic array without storage disconnects when the grid goes down, because anti-islanding protection requires it. Continuity through an outage requires storage or generation sized and configured for island operation, which is a separate capital decision and a separate conversation about battery storage.
One client's account, stated as what it is
Industrial clients in Mexico tell us their own customers now raise onsite renewable generation during commercial reviews. In one case, a client told us that rooftop solar had come up as a condition in a contract renewal discussion. That is one client's account of one negotiation. We report it because it is the kind of requirement that arrives without warning and lands on a plant with a two-year lead time, not because a single account establishes a market trend.
What an assessment requires
To evaluate onsite solar options for a facility we need the site location and 12 months of CFE billing. The site review covers available roof and ground area, roof material and structural condition, remaining roof life, shading, and the electrical room and point of common coupling. A preliminary savings analysis and proposal follow roughly three weeks after the initial call. For a small onsite project, the period from PPA signature to start of supply typically runs six to eight months, with the CFE Distribución interconnection steps the least controllable part of it.
Where a site is in a region with its own grid constraints, the local picture matters as much as the national one. Our note on the energy outlook for Baja California covers one such case, and the broader regime is set out in our piece on distributed generation in Mexico. Interval data is the input that decides most of these questions, which is why we treat energy monitoring as the first step rather than the last.
Establish whether your site qualifies and what it would save
Mexico Energy Partners can size a compliant sub-0.5 MW system against your actual load shape, model it under each of the three CRE modalities, and set out the CFE Distribución interconnection sequence with its realistic timing. The review needs 12 months of CFE billing, interval data where the meter records it, the site address and a single-line diagram if one exists.