DS-4 with Hourly Supply Service combines wholesale energy, capacity supply, transmission, distribution, and delivery riders. This forecast is designed for a constant, firm load supplied entirely from the grid.
Service overview
| Item | Coverage |
|---|---|
| Service | Illinois · MISO · DS-4, supply voltage above 100 kV, with Hourly Supply Service. |
| Rate basis | DS-4 and PBR-R delivery schedules; HSS supply and TS transmission riders. |
| Billing basis | Monthly peak imports and interval energy. Summer, fall, winter, and spring capacity prices follow the MISO planning year. |
| Dollar basis | 2026 uses filed rates at their nominal value; 2027 onward uses real 2025 dollars. The 2026 energy price is the actual Ameren Illinois load-zone day-ahead average for January–September 2026. |
Charge breakdown
| Line item / what it pays for | Tariff Charge Type | How the Charge Is Assessed | Calculation basis |
|---|---|---|---|
| Electricity supply and associated supply adders | Supply | Energy | Imported MWh multiplied by adjusted energy-supply rate. |
| Capacity supply | Supply | Capacity (demand-based) | Monthly peak imported MW multiplied by loss and reserve factors multiplied by seasonal capacity price multiplied by service days multiplied by supply-cost factor. |
| Transmission service | Transmission | Capacity (demand-based) | Monthly peak imported MW multiplied by loss factor multiplied by daily transmission rate multiplied by service days multiplied by multiplier for unpaid bills. |
| Distribution demand | Distribution | Capacity (demand-based) | Monthly peak imported MW multiplied by monthly delivery rate multiplied by share of the month served. |
| Customer service | Distribution | Fixed | Monthly customer amount allocated to covered calendar days. |
| Metering | Distribution | Fixed | Monthly metering amount allocated to covered calendar days. |
| Delivery programs and recovery adjustments | Rider | Energy | Imported MWh multiplied by the combined applicable rider rate. |
| State electricity excise tax | Rider | Energy | Imported MWh multiplied by an average tax rate calculated for a reference consumption profile. |
How charges are calculated
Energy supply and riders
The supply rate combines day-ahead energy prices, grid-balancing services, and procurement charges. A multiplier covers working capital and unpaid bills. A separate rider adds a further allowance for unpaid bills. Delivery riders and the state excise tax are separate charges per imported MWh.
The supply rate starts with the day-ahead price and supply adders. Their combined value is multiplied by the supply-cost factor, then the separate rider is added. The resulting rate is multiplied by imported MWh.
Capacity supply
Capacity supply pays for generation available to meet peak demand. This forecast uses the customer’s highest monthly grid import to estimate the capacity needed. It increases that quantity for grid losses and reserve requirements:
Capacity needed in MW is calculated from monthly peak imported MW, increased by the loss factor and reserve-margin factor.
Capacity cost is calculated by multiplying the capacity needed in MW by the seasonal price in $/MW-day, the covered days, and the supply-cost factor.
The supply-cost factor covers working capital and unpaid bills.
Transmission and distribution
The uncollectibles factor below is an allowance for unpaid bills.
Transmission cost is calculated by multiplying billing MW by the loss factor, the transmission rate in $/MW-day, the covered days, and the uncollectibles factor for unpaid bills.
Transmission uses the monthly peak as an estimate of the customer’s demand at the utility peak, increased for transmission losses. The distribution loss multiplier is 1.00 at transmission voltage. Rider TS applies the Hourly Supply Service allowance for unpaid bills to this charge. Distribution uses the same monthly peak with its $/MW-month rate. Monthly distribution, customer, and metering charges are prorated by the share of the month served.
Forecast methodology
| Charge | How its rate changes |
|---|---|
| Energy supply | Passes through day-ahead prices. Supply adders retain their individual treatment in nominal dollars or real 2025 dollars. |
| Capacity supply | Uses published auction prices for MISO Local Resource Zone 4 (LRZ4) for planning year 2026/27, then the LRZ4 capacity forecast. Seasonal reserve margins stay at their 2026/27 values. A 2% transmission-loss assumption, based on Zone 5 auction results, applies to both capacity and transmission charges. |
| Transmission | Forecast Ameren Illinois transmission costs divided by the zone’s coincident peak demand, calibrated to the filed retail transmission rate and converted to a daily rate. |
| Distribution | Filed 2026 and 2027 rates, followed by assumed annual real growth. Apparent-power rates are converted using the assumed power factor. |
| Customer and metering | Filed rates, then amounts held constant in real 2025 dollars from 2028. |
| Delivery riders | Separate program budgets, continuation dates, and recovery periods. Energy-efficiency charges assume an eligible-customer opt-out from 2030. |
| Excise tax | A blended rate based on a reference consumption profile; tax tiers are not recalculated for each site. |
Assumptions and limitations
| Assumption | Effect on results |
|---|---|
| Constant imports | With constant imports, customer demand is the same at the site’s peak and the system peak. If imports vary, these quantities must be measured separately. |
| Distribution demand | The full on-peak/off-peak demand rule is approximated by monthly maximum imports. |
| Partial periods | Transmission and capacity charges use the number of service days. Monthly delivery charges use the share of the calendar month served. A partial month can miss the customer’s highest demand. |
| Exclusions | Municipal taxes and site-specific exemptions are excluded. The forecast assumes the campus owns its substation, so the transformation charge is zero. A utility-owned transformer adds $0.23/kW-month. Customer-specific excess facilities charges under Rider EFC are excluded, as are the Hourly Supply Service market settlement proxy and supply balancing true-up, which are expected to net toward zero over time. |
Public tariffs and regulatory filings
| Source | Coverage |
|---|---|
| DS-4 tariff | Service and demand terms. |
| Ameren rates and riders | PBR-R sheet 8.014; HSS sheets 23; TS sheets 50; delivery riders. |
| Rider HSS — Hourly Supply Service | Sheets 23 onward: energy supply, capacity obligations, and supply adjustments. |
| Rider TS — Transmission Service | Sheets 50 onward: transmission billing quantities and recovery. Supplier Terms and Conditions sheets 5.010–5.012 set loss adjustments. |
Methodology version: October 2026. 2026 uses nominal rates; 2027 onward uses real 2025 dollars.