CAISO Investor-Owned Utility Service Areas
PG&E
Pacific Gas & Electric
Northern and Central California. Largest IOU in CAISO by geography. Major load centers: San Francisco Bay Area, Sacramento Valley, San Jose, and Central Valley agricultural loads. New solar and storage predominantly sited in San Joaquin Valley corridor.
Key constraint: Bay Area import limit binding at ~5,600 MW during peak summer demand. Metcalf and Vaca-Dixon 500kV substations serve as primary POIs for large-scale resources.
Key 500kV POIs
Metcalf 500kV
Vaca-Dixon 500kV
Tesla 500kV
Gates 500kV
Midway 500kV
SCE
Southern California Edison
Central and Southern California, excluding LA city proper (LADWP) and San Diego County (SDG&E). Inland Empire, Riverside, San Bernardino, and LA suburbs are primary load centers. Desert Southwest is the dominant development area for utility-scale solar and battery storage.
Key constraint: Tehachapi wind-to-load export path (Path 66) operating near 4,500 MW thermal limit. Large Devers substation complex serves as gateway for Desert Southwest imports.
Key 500kV POIs
Vincent 500kV
Colorado River 500kV
Mira Loma 500kV
Devers 500kV
Eldorado 500kV
SDG&E
San Diego Gas & Electric
San Diego County and southern Orange County. Smallest CAISO IOU by geography and customer count, but highest EV penetration in the US (~20% of vehicles). Significant Baja California cross-border energy flows through Otay Mesa DC Tie.
Key constraint: San Diego import limit of ~3,500 MW with single-corridor vulnerability (Southwest Powerlink). Any transmission outage causes binding import constraint.
Key 500kV / 345kV POIs
Miguel 500kV
Otay Mesa 345kV
Penasquitos 230kV
Adjacent Non-CAISO Entities
Municipal Utility
LADWP — Los Angeles Dept. of Water & Power
Serves LA city proper (4M customers). Largest municipal utility in the US. Not a CAISO participating transmission owner — operates its own balancing authority. Has scheduling coordination agreements with CAISO. Projects inside LA city limits interconnect through LADWP, not CAISO process.
Irrigation District
IID — Imperial Irrigation District
Imperial Valley — one of the highest-solar-irradiance regions in North America. Not in CAISO. Projects here interconnect through IID's own process. IID has DC Tie to CAISO (Pacific DC Intertie connection) enabling energy trading but not full CAISO queue participation.
Federal Power Marketing Agency
WAPA — Western Area Power Administration
Federal agency operating hydropower and transmission across 15 western states. WAPA operates key 500kV transmission in the Southwest that interfaces with CAISO scheduling. Not a CAISO member but coordinates on path ratings and flows.
Nevada Utility
NV Energy
Nevada investor-owned utility. Joined CAISO's EIM (Energy Imbalance Market) in 2015. Major importer from CAISO for Nevada peak loads. Nevada solar projects can export to CA via Path 46 (Desert Southwest). Part of ongoing Western Energy Imbalance Market expansion discussions.
CAISO Major Transmission Paths & Transfer Limits
| Path / Interface |
Voltage |
Transfer Limit |
Primary Resource Type |
Constraint Status |
| Pacific AC Intertie (PACI) | 500kV | 4,800 MW | Wind + Hydro (PNW imports) | Constrained — peak summer |
| Path 26 (NW–SW California) | 500kV | 3,000–5,000 MW | Renewables interchange | Seasonal limit — varies |
| Tehachapi (Path 66) | 500kV | 4,500 MW | Wind + Storage (Kern County) | Near capacity — frequent binding |
| Bay Area Import (Path 45) | 500kV | 5,600 MW | Mixed — solar + imports | Binding during heat events |
| SW Powerlink (San Diego) | 500kV | 3,500 MW | Solar + Cross-border | Binding — single corridor |
| Desert Southwest (Path 46) | 500kV | 10,700 MW | Utility solar + BESS | Adequate headroom |
| Pacific DC Intertie (PDCI) | ±500kV DC | 3,100 MW | Pacific Northwest hydro | Reliable — PDCI upgrade planned |
| Humboldt OSW (Future) | HVDC proposed | TBD | Floating offshore wind | Under study — no path yet |