A data center owner on SPP’s new non-firm service should base the tenant’s uptime promise on generation or storage behind the CHILLS meter that can serve the load without the grid, because transmission service remains subject to curtailment. FERC accepted Southwest Power Pool’s Conditional High Impact Large Load Service, or CHILLS, on June 5, subject to condition, effective July 1. It lets a large load take “as-available” transmission service for one to seven years before it has the resources or upgrades that firm service requires.
Under the accepted tariff, a load backed by designated resources has four curtailment triggers: transmission limits, system curtailments of CHILLS, emergencies, and local reliability issues. A load backed instead by non-designated accredited generation has five, including the available capacity of its supporting resources falling below the load. For that second group, system curtailment also requires an unfavorable net impact on the transmission system. SPP also sets the reserved capacity after its studies, offering a portion when transfer capability falls short.
The supporting generation may also be unavailable in the emergency that triggers a curtailment. If it came through SPP’s dedicated-generation interconnection process, SPP can direct it to run above the load’s forecast during emergencies. Enchanted Rock protested that SPP could then curtail the load and send its generator to the wider market at the same time. FERC rejected the protest, noting that the rule was already in SPP’s tariff and that participation in CHILLS is “entirely voluntary.” SPP answered that a load needing continuous power, emergencies included, must have generation or storage that does not use the transmission system. Metering also limits what counts: output from a generator on the network-load side of the network service meter, and not behind a CHILLS meter, cannot be used to meet a curtailment.
For a hypothetical 200 MW campus with one tenant, the first number I would ask the sponsor for is the megawatts behind the CHILLS meter that can carry the building without the grid, and for how long. The owner decides whether that plant exists and how large it is, though its permits and fuel supply depend on others. The sponsor’s estimate of curtailed hours depends on grid conditions and SPP’s response under a service in effect only since July 1. I would ask how that estimate reflects the constraints identified in SPP’s studies. Any uptime the lease promises during a curtailment beyond what the on-site plant carries depends on how much grid service remains available. The lease should either leave those hours with the tenant or price them as credits the owner expects to pay.