WECC and SPP markets show 67–70 GW excess capacity paired with 22.5 GW transmission headroom—signaling rare alignment of power and interconnection readiness.
## Highlights
Cheyenne, WY (WECC) and Rural SPP (Kansas, SPP) are tracking the highest excess power indices in the current build cycle, both recording 69.5 and 67.2 GW of available generation headroom respectively. Both markets simultaneously show 22.5 GW of transmission constraint capacity—the bandwidth available before grid stress requires new line investment.
## What It Means
This pairing—high excess power plus non-trivial transmission slack—is uncommon and timing-critical. A developer with a committed offtake in either market faces a 12–18 month window before that transmission buffer fills. Cheyenne's WECC tie-in and Rural SPP's Central Plains corridor both have demonstrated land and water availability; the constraint metric suggests neither market has reached the "land-constrained" phase that typically compresses build windows to 6–9 months.
For capacity planners, the data flags these two markets as the remaining "green light" builds in their respective ISOs. ERCOT, PJM, and MISO equivalents have either exhausted excess power (requiring behind-the-meter thermal + storage co-location) or face hard transmission ceilings. Cheyenne and Rural SPP remain true build-first markets, not retrofit-first.
## Second-Order Signal
Transmission headroom and power excess rising in tandem typically precedes a 6–8 week wave of FID announcements. Developers calibrate project finance timing to the moment constraint tightens; once it drops below 15 GW, interconnection risk premiums climb 200–300 bps. Both markets are at the inflection point—expect to see announced projects in early Q3.
## Methodology
Excess Power Index measures available generation capacity minus peak demand (24h rolling average). Constraint Capacity reflects published transmission interconnection headroom per ISO planning documents and real-time RTO reports, updated daily. Markets ranked by excess capacity and cross-checked against constraint availability to identify dual-readiness.
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**Source:** DC Hub Data Center Power Index (https://dchub.cloud/dcpi). Updated daily.
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