Demand in WECC

Zonal Demand

Description

Demand is modeled at the balancing authority level with hourly resolution to capture both intraday shape and seasonal effects. The primary input is the CPUC SERVM 2026 load forecast. The model uses its net load series: the demand left for grid-connected supply to serve once every load modifier in the CPUC’s forecast is applied.

Net load starts from gross (economic) load. It then applies the CPUC’s load modifiers:

• Added load: Electric vehicles (EVs), building electrification and other fuel substitution, and data centers.
• Reduced load: Additional achievable energy efficiency (AAEE) savings.
• Behind-the-meter (BTM) generation: Rooftop solar and BTM batteries are netted off demand, so they are not modeled as supply.

California’s forecast is anchored on the CEC’s 2025 Integrated Energy Policy Report (IEPR). The CPUC publishes selected forecast years, and the model interpolates between them. After 2045, demand grows at 1.5% a year.

Large loads

Large loads, such as data centers, hydrogen production and industrial projects, are taken as already inside the CPUC load forecasts. This applies in and out of CAISO. The model adds no separate inventory of large-load projects on top.

Forecast

EV charging moves CAISO’s daily peak into the late evening

Each load component has its own daily profile. EV charging is the largest source of growth, adding about 10 GW to CAISO’s average load by 2045. The CPUC forecast places most of it overnight. Rooftop solar only reduces load in daylight hours, so its effect is concentrated around midday.

As EV charging grows, the evening trough fills in. CAISO’s average daily peak holds at 18:00 through the 2030s and moves to 23:00 from 2040.

Winter peaks close in on summer

Electrification and EV charging add load in the winter evenings, when there is no solar output to offset it. The annual peak stays in summer, but by 2045 the January and December peaks sit within about 6 GW of August.

Assumptions and Caveats

• Demand is modeled at the zonal (balancing authority) level throughout the forecast horizon.
• Demand follows the CPUC’s own assumptions for EV adoption, electrification, energy efficiency and BTM solar. The model does not adjust these components.
• Large-load growth is limited to what the CPUC forecasts include.

Data Sources