The forecast spans five scenarios covering a range of market outlooks: a base case, faster zero-carbon cost declines, gas prices in either direction, and demand growth in line with SPP's own Future 2 planning case.
Each scenario is a separate capacity expansion and production cost run. The arms differ only in a named set of input levers, so a gap between two runs traces back to a specific assumption rather than to model noise.
Overview matrix
Each scenario adjusts a set of levers relative to the Base Scenario. Bold values differ from the Base Scenario.
| Lever | Base | High Renewables | High Gas Prices | Low Gas Prices | High Demand |
|---|---|---|---|---|---|
| NREL ATB capital cost trajectory | Moderate | Advanced, gas held at Moderate | Moderate | Moderate | Moderate |
| Storage capital cost to 2035 | 1.0× | 0.75× | 1.0× | 1.0× | 1.0× |
| Coal retirement | Announced date, else 62 years | Announced date, else 55 years; existing fleet retired by end-2045 | Announced date, else 62 years | Announced date, else 62 years | Announced date, else 62 years |
| Delivered gas price | 1.0× | 1.0× | 1.15× | 0.90× | 1.0× |
| Gas capital cost, combined cycle and combustion turbine | 1.0× | 1.0× | 1.06× and 1.03× | 0.94× and 0.97× | 1.0× |
| Annual gas build limit | Base | Base | Lower | Higher | Rises with demand |
| Annual solar, wind and storage build limits | Base | Base | Base | Base | Rise with demand |
| Large loads | SPP 2026 ITP Future 1 | SPP 2026 ITP Future 1 | SPP 2026 ITP Future 1 | SPP 2026 ITP Future 1 | SPP 2026 ITP Future 2: all submitted loads |
| Large-load demand response | None | None | None | None | Extra load interruptible |
| Transmission expansion | NREL moderate demand, approved 765 kV lines | NREL moderate demand, approved 765 kV lines | NREL moderate demand, approved 765 kV lines | NREL moderate demand, approved 765 kV lines | NREL high demand, every planned 765 kV line, plus Holcomb – Potter County |
| Tax credits | Current law | Current law | Current law | Current law | Current law |
Total new build to 2050 separates the arms most clearly on storage and gas. Wind and solar lead every scenario, because both are the cheapest way to add energy across the SPP footprint regardless of which lever moves.
Base
The Base Scenario is Modo Energy’s view of the most likely path for SPP. Every lever sits at its committed setting, and the other four scenarios are described as deviations from it.
Delivered fuel prices follow the unified Henry Hub curve plus each hub’s delivered premium, with no multiplier applied. New-build costs track the NREL Annual Technology Baseline (ATB) Moderate trajectory. Demand carries the high-confidence tranche of large loads from SPP’s Integrated Transmission Plan, retirements follow announced dates, with coal otherwise retiring at 62 years in line with the coal retirements in SPP’s Integrated Transmission Plan, and tax credits are modeled at current law. The transmission backbone is the 765 kV projects SPP has approved. See the other pages in this section for each assumption in full.
High Renewables
High Renewables assumes zero-carbon technology costs decline faster than the reference case, and coal retires in line with recent US retirements. Wind, solar and storage capital costs move to the NREL ATB Advanced trajectory, while combined cycle and combustion turbine costs are held at Moderate. Storage carries a further reduction, with capital cost 25% below the Base Scenario by 2035, tracking the ATB Advanced battery cost decline. Coal retires at the earlier of its announced date and 55 years of age, close to the age at which US coal units have retired over the past decade, rather than at the Base Scenario’s 62 years. None of the existing fleet runs after 2045.
High Gas Prices
High Gas Prices describes a world where turbine lead times and financing costs push new gas capacity out of the money. Three levers move together. Delivered gas prices sit 15% above the Base Scenario, raising the marginal cost of the thermal fleet. Gas capital costs rise, by 6% for combined cycle and 3% for combustion turbine. Supply chain constraints also limit how many new gas plants can come online each year.
Low Gas Prices
Low Gas Prices is the mirror image. Delivered gas prices run 10% below the Base Scenario, gas capital costs fall by 6% for combined cycle and 3% for combustion turbine, and supply chains scale up, allowing more new gas plants to come online each year.
High Demand
High Demand is built on SPP’s own planning scenarios. SPP’s 2026 Integrated Transmission Plan studies two futures: Future 1, whose large loads the Base Scenario carries, and Future 2 (Accelerated Decarbonization). Large loads are most of what Future 2 adds, and High Demand takes its large-load forecast in full: every submitted load energizes, not only the high-confidence tranche. That is 18.8 GW of large load by 2030, 29.6 GW by 2035 and 33.4 GW by 2045, against 10.2 GW, 17.8 GW and 20.4 GW in the Base Scenario. Future 2’s smaller allowance for electrification of existing demand is not yet included.
Several further levers move with the extra load, so that the system can serve it:
- Large loads connect on timelines SPP’s tariff allows. CSWS loads run behind the meter for their first five years, as SPS loads already do in the Base Scenario, and WAUE loads connect a year later than in the Base Scenario.
- The extra load is interruptible. The large load this scenario carries above the Base Scenario connects on interruptible terms, as SPP’s Conditional High Impact Large Load Service allows. Each load type offers a share of its demand as price-tiered demand response. Oil and gas load is curtailed only in emergencies.
- Build limits rise with demand. The annual limits on how much gas, solar, wind and storage can be built rise with this scenario’s extra peak demand.
- Transmission grows with the load. Transmission follows NREL’s high-demand build. Every planned Integrated Transmission Plan 765 kV line is built, including those SPP has deferred or not yet approved. A Holcomb – Potter County 765 kV line into SPS is added from 2034, a candidate SPP has flagged for future plans if load keeps growing.
What separates the scenarios for storage
Storage is where the arms diverge most, both in size and in timing. The chart below shows cumulative new build by scenario, one technology at a time.
Two patterns hold across the arms.
- Most storage arrives after 2030. The queue-anchored fleet covers the near term, so the model’s own battery build is small to 2030 in every scenario, at 2.3 GW or less. It then grows through the 2030s and 2040s. The Base Scenario builds 2.0 GW by 2035 and 6.6 GW by 2050.
- What storage competes against matters as much as what it costs. Cutting storage capital costs and retiring coal sooner in High Renewables adds 16.0 GW against the Base Scenario. Constraining and repricing gas in High Gas Prices adds 12.1 GW. Cheaper gas in Low Gas Prices removes 3.8 GW.
Revenue opportunities per scenario
Each scenario builds a different fleet, and that fleet sets different prices. The two-hour top-bottom (TB2) spread measures the annual revenue available to a two-hour battery from the daily gap between the highest and lowest prices, summed across the year, taken here at the SPP system price.
High Demand is the strongest revenue environment, and the only arm with wider spreads than the Base Scenario. The other three sit below it, for different reasons.
- High Demand adds load rather than supply. Demand grows faster than in any other arm.
- High Gas Prices builds nearly three times the Base Scenario’s batteries and lands below Base. Dearer gas widens the opportunity, and the storage that answers it competes most of it away.
- Low Gas Prices lands further below Base, with the fewest batteries. Cheaper fuel lowers the cost of the plant that sets price at the evening peak, which narrows the daily spread even with little storage competing for it.
- High Renewables is the weakest. It builds the most batteries of any arm, 22.6 GW, and that competition outweighs the deeper midday trough that its extra solar creates.