If your provider offers you a medium-voltage UPS with zero transfer time that also promises to monetize your demand peaks, you should review Mexico’s regulatory framework before signing. It is a design promise that is already being built in Texas and Europe, and that is starting to show up in AI data center quote sheets. In Mexico, since April 16, 2026, there is a rule on energy storage that sets hard limits on that promise: the same framework that exempts a data center from permits also prohibits selling or injecting the energy you store in your batteries.
This article is the text, its design consequences and the questions that have to be put in writing before signing.
One clarification before going further: this is not legal advice nor a compliance opinion. The National Energy Commission Agreement on the integration of electrical energy storage systems into the National Electric System was published in the DOF on April 16, 2026, took effect the next business day and repealed the previous agreement of March 2025. Several of its pieces —the variability analysis methodology and the permit formats— had a later publication date, so part of the framework is still under construction.
What the medium-voltage UPS promises — and who backs it
ON.energy markets its AI UPS promising zero transfer time, 3.5\text{ MW} per line, N+1 to 2N+1 redundancy and IP55 weatherproofing. The two key metrics in its catalog are the capacity to absorb load swings of up to \pm 70\% in milliseconds and the monetization of grid services (50\text{–}200\text{ USD/kW-year}).
Although these are manufacturer figures, the technology already has third-party validations: Crusoe committed 5\text{ GW} of these systems across its hyperscale campuses to meet the interconnection requirements of the Texas operator ERCOT. The technical reason, as validated by the National Laboratory of the Rockies, is to damp the transient spikes of AI clusters, which can jump from 5\% to 100\% load in milliseconds and impact grid stability.
Mexico set the rule: what the April 16 Agreement says
The National Energy Commission regulatory framework classifies storage into modalities where two apply directly to your data center: SAEE associated to a load center and SAEE of self-consumption. Under these schemes you do not need a storage permit, but the regulation sets very strict operating limits:
Prohibition of sale and injection: The energy stored in your batteries must be consumed exclusively on site; selling it or injecting it into the transmission or distribution networks (RNT / RGD) is prohibited.
Power limit: The capacity of the system cannot exceed your demand or your contracted load with CFE.
Administrative track: If your site is new, you must declare it from the original connection application before CENACE; if it is an existing site, you process a technical modification.
Mandatory fault current: Interconnection studies must contemplate a resistance to fault currents of at least 2\times the nominal current during 700\text{ ms} at the SAEE terminals, in addition to certifying under IEC 62619, IEC 62933, UL 9540 and NOM-001-SEDE-2012.
The table your provider will not show you
| Question | What the medium-voltage UPS offers | What the Mexican rule allows |
|---|
| Storage permit? | The manufacturer does not require one | As SAEE-CC it does not require a permit; as SAEE not associated with 0.7 MW or more, it does |
| Selling the stored energy? | Grid services from 50 to 200 USD/kW-year | No: the stored energy cannot be injected or be the object of a sale |
| Injecting into the grid? | Continuity during voltage dips and ERCOT compliance | Not in SAEE-CC: injection at the point of connection is prohibited |
| How large can it be? | 3.5 MW per equipment line | The SAEE power must be equal to or lower than the demand and must not exceed the contracted load |
| What procedure? | The integrator defines it | New site: declare it in the connection application. Existing site: technical modification and notification to CENACE |
| What safety standards? | IEC 62040-3 Class 1, IEEE 1547, ASHRAE TC 9.9, TIA-942 | IEC 62619:2022, IEC 62933-5-1:2024, IEC 62933-5-2:2025, UL 1973, UL 9540 and NOM-001-SEDE-2012 |
| Fault current test? | It is not a product requirement | At least 2 times the nominal current sustained for 700 ms at the SAEE terminals |
The five questions that have to be put in writing
Which modality does your storage system fall under? Is it part of your load center installations or is it proposed as an unassociated system? The answer decides whether a storage permit is needed and whether the project can sell services. An integrator that does not say so in the first proposal is avoiding the difficult conversation.
What is your contracted demand and what storage power is proposed? The system power must be equal to or lower than the load center demand and cannot exceed the contracted load. If the storage proposal does not fit within that number, the project is not designed: it is quoted.
What happens to the energy when the UPS discharges? The framework prohibits selling it and injecting it. The design of your system must assume that the stored energy is consumed on site, and that completely changes the grid services equation that catalogs promise.
Who processes it and within what timelines? If the site is new, the declaration goes inside the connection application; if it already exists, it is a technical modification with notification to CENACE. And the agreement obliges CENACE to publish the variability analysis methodology within ninety calendar days and the permit formats within thirty, so the framework they are going to quote you today is still being completed.
What standards does your equipment declare and who evidences the fault current? The safety standards of the agreement are not optional, and the fault current of two times the nominal current during 700 milliseconds is a study requirement, not a footnote on the spec sheet.
A medium-voltage UPS is not only an electrical architecture decision: in Mexico it is a regulatory decision. In a brownfield site, integrating storage that exceeds your contracted load or intends to sell energy to the grid is not a minor omission: it is a guaranteed rejection in the next technical modification before CENACE.
That is why we audit the complete power chain and your medium-voltage intake before you acquire the largest piece of equipment in the catalog.
Actions for the next 30 days:
Demand the modality in writing: Ask your integrator to define whether they propose an SAEE-CC or an unassociated SAEE, and who will assume responsibility for the declaration before the authority.
Contrast realistic capacities: Compare the storage power against your contracted demand, not against the nominal capacity of the equipment.
Validate regulatory compliance: Review with your electrical team whether the design complies with the National Energy Commission provisions and NOM-001-SEDE-2012.
Audit before signing: Request an assessment of your data center or cross-check the criteria against our energy audit to lock down the technical specification.
Sources
Diario Oficial de la Federación. “ACUERDO de la Comisión Nacional de Energía por el que se emiten las Disposiciones Administrativas de Carácter General para la integración de Sistemas de Almacenamiento de Energía Eléctrica al Sistema Eléctrico Nacional” (Acuerdo CT/4.SE/3-2026, published April 16, 2026; numerals 1.5, 2.11.4, 2.12, 2.13.10, 4.1 to 4.6.5 and transitorios) — https://dof.gob.mx/nota_detalle.php?codigo=5785045&fecha=16/04/2026
Centro Nacional de Control de Energía. “DACG integración Almacenamiento Energía al SEN” (official reproduction of the agreement published in the DOF on April 16, 2026) — https://www.cenace.gob.mx/Docs/16_MARCOREGULATORIO/Almacenamiento//(DOF%202026-04-16%20SENER)%20DACG%20integracion%20Almacenamiento%20Energia%20al%20SE.pdf
ON.energy. “AI UPS™ Grid-Safe Technology” (product specification: transfer time, power per line, backup duration, redundancy, IP55, upstream-of-switchgear placement, grid services and applicable standards) — https://on.energy/solutions/grid-safe-ai-ups-technology
Data Center Dynamics. “Crusoe to deploy 5GW of ON.energy’s AI UPS systems across data center portfolio” (Zachary Skidmore, July 22, 2026) — https://www.datacenterdynamics.com/en/news/crusoe-to-deploy-5gw-of-onenergys-ai-ups-systems-across-data-center-portfolio/
Canary Media. “A new class of batteries helps data centers play nicely with the grid” (Jeff St. John, October 15, 2026) — https://canarymedia.com/articles/data-centers/on-energy-ups-battery-grid-interruption
