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CPUC INA applies ELCC accreditation, sets ~15% perfect-capacity PRM target and retains 4 GW unspecified import cap with ramping
Summary
CPUC staff will use an ELCC-for-all accreditation approach, with ServM-derived ELCC surfaces for solar and storage, and reported a 2035 perfect-capacity planning reserve margin near 14–16%; staff will keep a 4 GW unspecified-import limit but implement a ramped hourly profile to avoid an abrupt import cliff.
CPUC staff explained revisions to reliability and transmission inputs in the draft INA: method updates for ELCC accreditation, a proposed planning-reserve margin target, transmission deliverability clusters and interconnection headroom limits, and an approach to modeling imports and out-of‑state candidate deliveries.
On reliability accreditation and PRM: Erin and colleagues presented an “ELCC for all” approach that credits every resource by its effective load-carrying capability (ELCC) in Resolve. Using ServM loss-of-load modeling with a perfect-capacity construct, staff reported that the total perfect-capacity planning reserve margin needed to meet the CPUC’s 1-in-10 standard in 2035 is “roughly a 15% annual reserve margin.” Staff said they performed PRM calculations across multiple years and obtained similar results (about 14–16%). Staff explained they will apply ELCC curves and a three-dimensional ELCC surface for solar + 4‑hour + 8‑hour storage to capture saturation and interactive effects between solar and storage.
On imports: staff reviewed historical CAISO import behavior and heat‑wave events, noting minimum imports during stressed hours have been roughly 5 GW and contracted imports in supply‑plan filings total roughly 5–6 GW. The INA retains a 4 GW unspecified‑import limit for peak net‑load hours (with specified imports counted separately), and staff proposed a ramped hourly profile that reduces imports gradually rather than a single, abrupt cliff from 11.7 GW to 4 GW. Staff said ServM simulations show the cap, when applied with the ramp, has a small net impact because imports are already limited in the relevant hours in many modeled years.
On transmission and interconnection: Maddie and colleagues described how Resolve will use transmission‑capability white‑paper data and a substation-to-constraint mapping to create clusters; each cluster becomes a build decision in Resolve with specified first-available years, capacities and upgrade costs. Staff also added generic transmission‑upgrade options (500 MW per year tranches first available in 2037) and interconnection headroom limits (per-bus capacities by voltage class) with upgrade costs and multi-year construction lead times.
Out-of-state resource modeling: staff reiterated that candidate out‑of‑state resources (Wyoming wind, New Mexico wind, Nevada geothermal, Oregon geothermal) are modeled with likely tie-in substations and deliverability costs; if selected, those resources are modeled as fully contracted to CAISO using new transmission, and thus are treated outside the 4 GW unspecified-import limit.
Why it matters: ELCC methodology and import assumptions determine how much firm or equivalent capacity Resolve finds necessary and what resources it values most. Transmission clustering and interconnection constraints limit where resources can be built or must pay for upgrades to be deliverable.
Ending: Staff solicited comments on PRM, ELCC surfaces, import limits and transmission upgrade cost/first-available-year assumptions for final INA revisions.
