Forecasting Ameren-IL’s Price-to-Compare Rate: The best-laid plans of MISO and men often go awry
Publish Date: June 12, 2025
Written by: Tom Michelman and Sahil Bakht
Estimated Reading Time: 7 Minutes
Apologies to Robert Burns.
Recap. If you’re an Illinois Community Solar developer, you know that the Price-to-Compare (PTC, the value of credit provided to subscribers) for Ameren-IL this summer (Jun-Sep) increased 51% from last summer to 12.1 ¢/kWh for residential (rate DS-1) subscribers and increased 60% from last summer to 14.5 ¢/kWh for small commercial (rate DS-2) subscribers. See chart below for a graphical history of Ameren’s recent PTC rates.
It doesn’t take brilliant insight to infer that a large part of the latest PTC increase was caused by the even larger relative increase in the MISO summer (Jun-Aug) wholesale Planning Resource Auction (PRA) capacity prices from $30/MW-Day (2024) to $666/MW-day (2025, a 2000+% increase) announced on April 28 2025. We further infer that few, if any, in the industry planned on including increases of these magnitudes into their financial projections prior to late April.
Another reason that Ameren’s PTC rate increased so dramatically this summer was caused by other plans going awry.
In this case the Illinois Power Agency (IPA) procures energy and capacity for Ameren’s PTC customers. As you can read in their Final 2025 Electricity Procurement Plan (Plan), the IPA planned to purchase hedges of all of the forecasted energy requirements and 75% of the forecasted capacity requirements of Ameren’s PTC customers. Unfortunately, for those customers things didn’t work out as planned. The key point from the Illinois Commerce Commission’s Final Order on the Plan goes as follows.
The IPA explains this was an improvement in quantities over the results of the IPA’s previous capacity procurements since the seasonal capacity construct was approved in 2023, but fell short of the established procurement targets, leaving Ameren eligible retail customers hedged at 14%, 9%, 0% and 2% for the summer, fall, winter, and spring seasons of the 2025-2026 delivery year, respectively.
Thus, Ameren’s PTC customers took the brunt of the $666/MW-day spike by being only modestly hedged, and those capacity costs flowed through to summer 2025 PTC rates.
Ameren’s PTC rate setting and therefore forecasts have additional quirks beyond the fact that the layered hedging for capacity and energy prescribed in the IPA’s approved Plans do not always manifest themselves in practice, and these include:
- As implicit in the figure above, while rate DS-2 is a single block rate year-round, rate DS-1 is a single block during the summer and a double block rate during the “winter” (Oct-May).
- Further note in the figure above that the 2nd block for rate DS-1 (>800 kWh per billing month) is always lower than the 1st block (<= 800 kWh per billing month). This is a feature, not a bug; per the Ameren workpapers, all capacity costs assigned to Rate DS-1 are assigned to the 1st block.
- While not shown here, transmission rates are embedded into the PTC, and these have had a very robust compounded annual growth rate of over 10% for the last eight years for Rate DS-2, with substantially more transmission investment planned.
As with ComEd’s PTC discussed in our Accounting for ComEd Community Solar Rate Forecasting Idiosyncrasies blog, the primary driver of Ameren’s PTC rate variability is the Purchased Electricity Charge (PEC) component. Unlike ComEd
- The capacity requirements for Ameren’s PTC are generally (putting aside the 2025/2026 delivery year exception noted above) robustly hedged.
- Ameren is part of MISO, while ComEd is part of PJM, thus each is served by different wholesale markets.
In the end we were able to arrive at a similar analysis step for Ameren’s PTC as we did for ComEd; we derived a very high (97%) correlation between the PEC (net capacity costs) and weighted average electric futures as foundational to our Ameren PTC forecasts (see figure below).
Purchase the Ameren PTC Forecast and Explanatory Slide Deck
If you want to purchase an Ameren-IL PTC price curve for both Rates DS-1 and DS-2 with an explanatory slide deck for your business planning providing the detail and understanding that we don’t think you can find anywhere else, you can do so by visiting our webstore here.
At the SEA webstore, you will find other DG solar market revenue analyses and forecasts for the MA, ME, NY, PA markets, and the other major Illinois market, ComEd updated in May.
We will be rolling out an updated version of the NY VDER Customized Calculator (with storage and without storage) in the next couple of weeks, and in parallel we will be updating and adding PA markets PTC analyses forecasts.
After that we move on to providing MD CSEGS and NJ-SUSI DG solar forecasts.
If you need analysis of a different DG solar market, we also have and continue to perform an array of bespoke DG solar (with and without BESS) analyses, forecasts and market primers (IL, MA and NY within the last year). So, if you don’t see what you want, or have more questions, contact us.
Best regards,
Tom Michelman & Sahil Bakht
p.s. There was one more plan that went awry caused by the complexity of Ameren-IL’s PTC rate setting. Ours!!!!
We planned to roll-out the Ameren’s PTC analysis and forecast in May. Unfortunately given the depth and lengths that were necessary to provide a forecast embedded with a superior understanding and fundamentals of the PTC, combined with bandwidth constraints (pesky clients asking us for bespoke analysis in the meantime), meant that this analysis was delayed. We hope it was worth the wait.
p.p.s. We (Tom and Sahil) will be attending CCSA’s 2025 Community Solar Innovation Summit June 26 – June 27, 2025 in Westminster, Colorado. For attendees, we look forward to meeting up with you (or a colleague of yours) there. If you want to schedule an in-person meeting you can use Tom’s scheduling link for the conference.