Company details how qualifying facilities’ capacity replaces proxy resources and why avoided megawatts differ

Rocky Mountain Power told the commission that, under the partial displacement differential revenue requirement (PDDRR) used in the Schedule 37 methodology, the company compares a QF's capacity contribution to the contribution of a like‑for‑like proxy resource in the preferred portfolio and displaces the proxy by the equivalent capacity contribution.

As Dan McPhail described it: "We displace a capacity contribution equivalent amount of a proxy resource... we look at the capacity contribution of the QF, and we look at the capacity contribution of the next like for like resource. So for solar, find the next solar resource. For wind, find the next wind resource." He said the company measures capacity contribution against the hours identified in its loss‑of‑load study, not against annual average capacity factors.

Rocky Mountain Power gave numerical examples demonstrating the effect. For a 10‑MW tracking solar QF in Utah North, the company used a proxy solar resource in Central Oregon with a comparable contribution that resulted in a 9.7‑MW proxy displacement. By contrast, a 10‑MW wind QF in Utah had an 18.9% contribution while a Wyoming wind proxy had a 30.6% contribution, leading to only about 6 MW of proxy wind displaced for a 10‑MW Utah wind QF. The company explained that differences arise from local capacity factors and, more importantly, how the resource performs during hours the system identified as at risk in the loss‑of‑load analysis.

Intervenors asked whether the schedule 37 proxy resource shapes would be changed from prior filings; the company said it generally uses the same IRP shapes when available, noted an enhancement to use nearly 20 years of historical hourly shapes for the 2025 IRP, and confirmed fixed‑tilt versus tracking technology differences materially alter capacity contributions.