Demand

How demand is modeled across SPP

Demand is modeled at the zonal level with hourly resolution. Each settlement zone has a forecast peak that grows over the horizon and an hourly shape drawn from a historical weather year, with large loads layered on top.

Zonal demand forecast

Demand is built per SPP planning area and mapped to the model’s settlement zones; where several planning areas fall within one zone, their load is summed. For each area, a forecast peak level is combined with a historical hourly shape.

The peak level is anchored at two points and interpolated between them:

• Historical anchor: the area’s recent observed peak, derived from metered EIA-930 sub-region data.
• Forward anchor: the area’s ten-year-out peak from SPP’s 2025 Integrated Transmission Plan (ITP), the planning study SPP uses to assess its own system.

Years between the two anchors are interpolated linearly. Beyond the forward anchor, peaks grow at a low single-digit annual rate consistent with SPP’s own long-term peak trajectory. This produces a peak forecast for every zone and forecast year. The hourly shape it is scaled to comes from a historical weather year (see Weather years).

Forecast

Large loads

Large new loads (primarily data centers, alongside oil and gas electrification, industrial, and manufacturing demand) are added on top of the baseload demand forecast. SPP’s planning work points to roughly 19 GW of new large load by the mid-2030s across the footprint, which would be the largest single driver of demand growth.

The additions build up over time rather than appearing at once, and are concentrated in a handful of zones identified in SPP’s planning work rather than spread evenly. The zone-specific magnitude and split come from SPP’s 2026 Integrated Transmission Plan spot-load forecast. Data center load follows a month-by-hour profile from the PowerGEM Long-Term Reliability Assessment (LTRA), reflecting its near-flat, high-utilization operating pattern; other sectors are held flat within the day.

Weather years

Hourly shapes are tied to a single historical weather year, 2023 in the current forecast, selected from recent years of metered data. For each area, an hourly unit shape is built from EIA-930 sub-region data and scaled to the area’s forecast peak. The same weather year is used across all forecast years, so each year shares one intra-annual pattern scaled to its own peak.

The demand weather year is aligned with the renewable capacity factor weather year, so load and wind and solar output stay weather-consistent. Alternative weather-year shapes can be layered on to support higher and lower demand scenarios.

Load profiles

Assumptions and caveats

• WAUE settlement share: the WAUE zone is largely Basin Electric, whose load splits across SPP, MISO, and WECC, so only the portion settled in SPP is included. 90% of WAUE load is treated as SPP-settled, matching Basin Electric’s SPP share.
• Single weather year: every forecast year reuses one historical weather year’s shape, so it does not capture year-to-year weather variability within a single run.

Data sources