On 14 January 2026, FERC issued 194 FERC ¶ 61,031 in Docket ER26-247-000, accepting Southwest Power Pool's tariff revisions "to add a High Impact Large Load (HILL) study process and High Impact Large Load Generation Assessment (HILLGA) process," effective 15 January 2026, subject to condition and a compliance filing within 30 days.
If you are siting a data centre, a hydrogen plant or any other concentrated industrial load anywhere in SPP's fourteen-state footprint, that order is the rulebook you are now inside. It is worth reading the order rather than the summaries, because the thresholds, deposits and geographic limits are specific, and several of them will decide whether a site works.
Why SPP filed it
The order records SPP's own account of the pressure. "In every year since 2021, transmission customers, specifically large loads of over 100 MW, have submitted requests to interconnect, in the form of Attachment AQ requests, in SPP totaling multiple gigawatts (GW)." That "growing trend in large load interconnection request submissions peaked in 2022 at nearly 11 GW, but since that peak, there has been a relative drop to approximately 6 GW in 2024, which, according to SPP, could be due in part to SPP's inability to study and interconnect large loads quickly enough to meet their commercial needs."
That last clause is the tell. SPP is not describing a demand slump; it is describing developers going elsewhere because the study process could not keep up. The order goes on: large load developments "frequently request transmission service within months rather than years of their intended commercial operation," which strains "the legacy regulatory frameworks, planning processes, and market mechanisms that were originally designed for incremental and predictable load growth."
What counts as a HILL
The proposed definition, quoted in the order, is:
A new commercial or industrial load, or increase in commercial or industrial load, at a single site connected through one or more shared Points of Interconnection (POIs) or delivery points, where such load is either (1) 10 MW or more if connected to the Transmission System at a voltage level less than or equal to 69 [kilovolts (kV)]; or (2) 50 MW or more if connected to the Transmission System at a voltage level greater than 69 kV. An Electric Storage Resource is not considered a HILL.
Four details matter more than the headline numbers.
The threshold is voltage-dependent, and the low one is low. SPP told FERC it consulted the NERC Large Load Task Force, whose survey participants "qualified large load as load greater than 50 MW," and then added the 10 MW tier because "although the NERC definition of the Bulk Electric System includes only transmission elements of 100 kV or higher, the proposed additional 10 MW threshold is necessary due to the prevalence of 69 kV lines in the Eastern Interconnection portion of SPP's footprint." A 12 MW facility on a 69 kV tap in Arkansas or Missouri is a HILL. A 12 MW facility on a 138 kV line is not.
"At a single site connected through one or more shared POIs" defeats the obvious workaround. Splitting a campus across two delivery points does not split the load for threshold purposes.
An increase counts. Phased build-outs cross the threshold on the increment, not only on day one.
Storage is carved out. An Electric Storage Resource is not a HILL, which keeps co-located batteries from being swept into a load process designed for something else.
The definition is forward-looking: "A load may be categorized as a HILL after the initial effective date of Attachment BA of the Tariff," and existing loads that would meet the definition are not retroactively captured.
The studies, and what they cost
HILLs run through new Attachment BA. The order describes a High-impact Definitive Planning Study (HDPS) and a host transmission owner's local study, with hard money attached.
For the HDPS, "the Transmission Customer must return the HDPS Agreement, a $10,000 non-refundable application fee, and a $100,000 deposit to SPP within 30 calendar days." If SPP "determines that an EMT study is necessary, it will require an additional $200,000 deposit from the Transmission Customer." The host transmission owner's study requires "an advance deposit of $25,000." Deposits are true-ups, not caps: SPP "must refund any excess deposit funds to the Transmission Customer, and the Transmission Customer must reimburse SPP for any unpaid study costs in excess of the deposit."
The EMT trigger deserves attention. Electromagnetic transient study is the modelling regime normally reserved for inverter-based resources and weak-grid problems; SPP proposes it here for loads, because a concentrated, power-electronics-heavy load behaves like one. SPP's justification, per the order, is that these studies "are more complex and detailed" and reflect "higher study costs compared to traditional load interconnection studies."
Budget, then, for a plausible $335,000 of study money before anyone has drawn a line on a map — and understand that it is a floor, not a ceiling.
HILLGA: one generator, for one load, within two substations
HILLGA is the more interesting half, because it is a genuinely new species of interconnection service: "a new generator interconnection process" for generation "serving a HILL," which SPP argues "meets" the requirements of Orders 2003, 2023 and 2023-A "by providing a path to ensure that HILLGA interconnection customers are able to interconnect to the transmission system, albeit on a [limited] basis."
The requirements are deliberately steep. A HILLGA Request must include:
- an executed HILLGA Study Agreement and executed HDPS Agreement;
- "a nonrefundable application fee of $20,000";
- "a study deposit of $250,000 for HILLGA Requests up to 500 MW and $500,000 for HILLGA Requests over 500 MW";
- demonstration of site control;
- a definitive point of interconnection;
- nameplate capacity, maximum injection capability and network resource deliverability of the generating facility;
- "a security deposit equal to $8,000/MW of the requested maximum injection capability";
- "reasonable evidence that the HILLGA Customer satisfies at least one of the listed development milestones (i.e., executed contracts, attestation that the generating facility is included in a state resource plan, and application for a land use permit)";
- and, if applicable, charging parameters and control technologies.
The commercial operation date "must be within five years from the execution date of the HILLGA Study Agreement."
SPP is explicit that this is harder than its normal queue: "the application fee and security deposit for HILLGA Requests are double those in the DISIS process, and the study deposit for HILLGA Requests can reach up to $500,000, whereas the study deposits for the DISIS process are capped at $250,000 regardless of the size of the generating facility." And the milestone test moves to the front: "the development milestone requirement for HILLGA Requests is at the beginning of the HILLGA process, whereas for the DISIS it is not until the end." The stated purpose is to "encourage the entry of commercially viable, shovel-ready generating facilities and deter speculative interconnection requests."
At $8,000/MW, a 400 MW gas plant posts $3.2 million of security to enter — plus a $500,000 study deposit if it is over 500 MW, plus $20,000 that does not come back.
The two rules that will move your site
Two geographic and sizing constraints in the order will kill more HILLGA structures than the money will.
The two-substation rule. "The POI identified in the HILLGA Request must be no more than two substations away from the HILL at most." A generator may support multiple HILLs, but only "if no more than five substations are involved and no more than two existing transmission line segments are used between each substation." SPP's stated intent is "to ensure that the proposed generating facility can support the HILL(s) in a localized area."
This is the whole design philosophy in one clause. HILLGA is not a route to build merchant generation quickly by pointing at a data centre a hundred miles away. The generator has to be electrically next door.
The 125% cap. SPP caps "the HILLGA Customer's generating facility's projected capacity accreditation MW value, as determined pursuant to Attachment AA of the Tariff, at the requested MW load amount of the associated HILL, multiplied by the higher of: (1) 110% plus the highest approved Planning Reserve Margin percentage effective at the time of the HILLGA Study Agreement and outlined in the SPP Planning Criteria; or (2) 125%."
Note the unit: accredited capacity, not nameplate. For a resource with low accreditation — solar, or a short-duration battery — the nameplate you can build under this cap is considerably larger than the load. For a gas plant accrediting near nameplate, it is roughly load × 1.25 and no more. SPP's rationale is "to ensure that only the generation capacity necessary to serve the HILL is processed through the HILLGA process, while recognizing the load responsible entities' requirement to secure sufficient resources to cover the Planning Reserve Margin."
One more structural rule: "a HILLGA Customer must submit a separate HILLGA Request for each generating facility associated with a HILL." No portfolio filings.
CHILLS: the bridge, filed separately
The piece that did not make the January order is the one most large loads actually want — permission to energise before everything is finished. SPP filed Conditional High Impact Large Load Service in Docket ER26-1323-000 on 10 February 2026, and FERC acted on it in 195 FERC ¶ 61,196 on 5 June 2026.
CHILLS is a conditional, curtailable bridge to long-term firm service: it lets a HILL begin taking power using transfer capability that remains available after higher-priority load has been served, while network upgrades and designated resources are still being completed. Read against HILL and HILLGA, the three pieces form one policy: study the load properly, let it bring its own generation if that generation is genuinely local and genuinely committed, and let it energise early only on terms that put existing customers first.
What to do about it
Check your voltage before your megawatts. Ten megawatts at 69 kV and below is the trigger. Sites that assumed a 50 MW test everywhere are wrong in the eastern half of the footprint.
Put $335,000 of study money in the pre-development budget, and treat the EMT deposit as likely rather than exceptional for a power-electronics-heavy load.
If you plan to bring your own generation, site it within two substations. This is a siting constraint, not a contracting one, and it should be checked before land is optioned.
Size the generator against accredited capacity, not nameplate, and against the higher of 110% plus the planning reserve margin or 125%.
Get a development milestone in hand early. Executed contracts, inclusion in a state resource plan or a land use permit application — one of them has to exist at the start of the HILLGA process, not at the end.
Read Commissioner Rosner's concurrence if you want a sense of where the Commission's thinking may go next on large loads using the transmission grid.
Related on this site
- Live SPP grid conditions — load, fuel mix and nodal prices across the footprint
- ERCOT's large-load interconnection standard — Texas's very different answer to the same problem
- US data center directory — where the load on public record actually is