A spike in an electricity “capacity auction” means the supply price for Ameren Illinois will increase significantly on June 1. Ameren has estimated that could increase the average monthly bills of a typical residential customer by 18 percent to 22 percent, or roughly $38 to $46 per month, over the summer. (Ameren’s price is expected to decrease in October.) Read CUB’s Q&A and visit CUBHelpCenter.com for more information.
What happened?
In April, the power grid operator known as the Midcontinent Independent System Operator (MISO) announced the results of its latest capacity auction (technically called the “Planning Resource Auction”), covering the 12-month period from June 2025 through May 2026. The auction is how the grid operator secures reserve power in its region, which includes all or parts of 15 states from the upper Midwest through Ameren Illinois’ territory in central and southern Illinois and down to Louisiana. (MISO territory also includes the Canadian province of Manitoba.)
In the latest auction, the summer capacity price skyrocketed from $30 per Megawatt-day in 2024 to $666.50 per MW-day this year–a 22-fold increase. MISO’s capacity prices are seasonal, and while they are still elevated compared with the year before for the fall, winter and spring seasons, they do drop significantly after the summer. Below are the seasonal prices from the latest auction (Ameren Illinois is located in MISO’s Zone 4):
Click the image to see MISO’s full report on the capacity auction.
What exactly are capacity costs?
Not only do you pay for the power you use now, but you also pay for power you could use in the future. Capacity refers to extra payments consumers give power plant operators for the commitment to have enough reserve electricity available if demand suddenly spikes. (Think of a hot summer afternoon, when everyone blasts the air conditioning.)
Where does a capacity price increase appear on my bill?
An increase in capacity prices will affect the supply section of your Ameren bill. For most customers, the capacity cost is one component of Ameren’s per-kilowatt-hour (kWh) supply price. On average, capacity takes up roughly 20 percent of the supply price.
(While most customers don’t see capacity costs as a separate line item, participants in Ameren’s Power Smart Pricing program–which charges you a supply price that can change hourly–do see a capacity line item on their bills.)
How much will an increase in capacity costs increase Ameren bills?
Ameren has reported that its electricity supply rate, also known as the “price to compare,” is set to increase by about 50 percent, to 12.18 cents per kilowatt-hour (kWh) on June 1. This higher rate, which includes the supply price, a transmission charge and a “supply cost adjustment,” will increase summer power bills (June through September) by an average of 18 percent to 22 percent, or $37.62 to $45.98 per month for the typical customer (10,000 kWh a year), Ameren has estimated.
In October, as capacity prices come down from their summer high, Ameren’s supply price is expected to decrease–to roughly 8 cents to 9 cents per kWh, Ameren said.
How will Illinois consumers be affected?
This price spike has a significant impact on Ameren customers. Unlike with PJM’s capacity market, MISO does not require participation from power plants. That’s because most utilities in MISO are “vertically integrated,” which means they generate their own electricity and deliver it to their customers at supply and delivery rates set by their state. Such utilities also supply or secure much of their capacity separate from the auction, and only rely on MISO if they have a shortfall.
But Ameren Illinois does not generate its own power and relies more than other utilities on MISO’s auction to secure its capacity needs.
So who’s making money off the price spike?
Power generators–large corporations that own power plants and sell power to utilities like Ameren–are making big profits. Ameren Illinois, the utility, is not making money off this price spike. The utility passes supply costs–including capacity payments–onto consumers with no markup.
(Note: Ameren does make money off another part of the bill–the delivery charges–and CUB challenges the utility’s proposed delivery rate hikes before state regulators. However, this supply price spike has nothing to do with Ameren’s delivery rate hikes.)
Why did this happen?
No doubt, increased demand fueled by data centers is part of the challenge. But the main driver of the price spike is policy shortcomings by MISO. A summary of the root causes of the price spike:
Anti-consumer market rules. Perhaps the biggest factor in the price spike was MISO’s new pricing methodology, called the Reliability-Based Demand Curve (RBDC). The grid operator used the RBDC for the first time in this auction, with the intention of giving better price signals that would incentivize developers to build more power plants. But consumer advocates raised deep concerns that the new method unacceptably compromised affordability. Douglas Jester, a clean energy policy expert, said the RBDC allowed MISO to overbuy capacity above minimum reliability levels, increasing costs. (MISO actually touted the RBDC for buying extra capacity and reducing the per MW-day summer price–but the price was lowered to $666.50, which is hardly a deal when the capacity cost was $30 last summer.) Also, the lucrative prices may incentivize generators to delay retiring dirty, outdated power plants.
Interconnection delays. The problem isn’t as severe as with the northern Illinois grid operator, PJM, but energy generators still have an average wait time of 3.5 years in MISO’s “interconnection queue.” That’s the waitlist for new power plants seeking review and approval by the grid operator so they connect to the grid and begin to provide electricity. Most of these stalled power plants are clean energy generators and they total more than 300 gigawatts (GW)–which could help bring down prices and maintain reliability. (One GW is enough energy to power 750,000 homes.)
Over-reliance on gas. In the past, CUB has urged MISO to fix its interconnection problem by fast-tracking clean energy projects that could bring down prices. But in 2025 MISO sought federal approval of a plan that would have instead fast-tracked new gas power plants, while leaving hundreds of gigawatts of competitively bid solar, wind, and battery projects stuck in the queue. The Federal Energy Regulatory Commission (FERC) “rightly rejected” the proposal to favor gas projects over “clean energy projects that have been waiting years to connect to the grid,” a representative from Earthjustice said in a statement.
Over-reliance on gas is a familiar theme for power grid operators. While MISO has made renewable energy gains, the grid operator reported in this latest auction that coal and gas generation still ranged from about 64 percent to 69 percent of the capacity power secured, depending on the season. Wind, solar and battery power took up about 7 percent to 13 percent.
So what can we do to combat these high prices?
The following actions and reforms would be a good step in the right direction.
- Give customers short-term relief: CUB calls on Ameren to work with customers to keep them connected in what could be an expensive summer for far too many customers.
- Fix MISO’s RBDC pricing methodology. When announcing the capacity auction results, MISO said its “market reforms” helped provide “pricing signals that improve market efficiency and enhance reliability.” But consumer advocates are concerned that this new pricing model has skewed the reliability-affordability balance and easily leads to over-buying capacity.
- Speed up the process for connecting new power plants to the grid. There is plenty of potential power generation to keep the grid reliable and affordable, but those projects are stuck in line at MISO.
- Strengthen state policy. Illinois must continue to take steps to strengthen the power grid, including passing comprehensive energy legislation to implement a number of commonsense, pro-consumer clean energy policies that emphasize affordability and sustainability. That includes expanding cost-effective energy efficiency, battery storage and other programs that help cut electricity demand, reduce prices and strengthen reliability.
How can Ameren customers try to lessen the impact of the supply price increase?
Some steps you can consider to lessen the impact.
- Contact your utility. If you are having trouble affording your energy bills, it is vital that you contact your utility. Find out if you can set up a payment plan to give you a longer time to pay off your bills; and inquire about no or low-cost energy efficiency programs the company offers.
- Ask Ameren Illinois about special programs. In addition to efficiency programs, consider signing up for Ameren’s Peak Time Rewards program, which gives residential customers the opportunity to earn small bill credits by reducing electricity usage during times of high electricity demand, typically summer afternoons.
- See if you qualify for energy assistance. Please know that assistance is no longer available in several counties because available funding has been used up. To learn more about the Low Income Home Energy Assistance Program (LIHEAP), visit www.helpillinoisfamilies.com or call the Help Illinois Families Assistance Line at 1-833-711-0374.
- Practice energy efficiency at home. For tips and information about helpful efficiency programs, visit CUB’s Clean Energy page and Ameren’s energy efficiency page. Also, read our blog: Tips on fighting high summer electric bills.
- Consider a community solar deal to help ease costs. Community solar offers currently guarantee savings compared to the utility’s supply price. But be a careful shopper: Get more information at our special website, SolarInTheCommunity.com.
- If you’re interested in installing solar panels, consider the next steps. Read our rooftop solar fact sheet. Also, there is an excellent program for income-qualified customers interested in solar called Illinois Solar for All.
- Beware of energy rip-offs. Alternative supplier sales representatives pitching you via door-to-door, phone or direct mail marketing may try to use this impending price increase to lure you into a bad deal. Remember: Alternative supplier prices will also go up because of this development. A lot of people have lost money with alternative suppliers over the last decade. One possible exception: If your community has a municipal aggregation deal, see what price it’s offering and if it can protect you from the Ameren supply price spike. Depending on the term of the community power deal, it might be able to secure savings–but don’t assume that. Ask what price the community deal offers and for how long. See CUB’s fact sheet on community power deals, and check out this list of community deals from the Illinois Commerce Commission (ICC) to see if your community is on the list.
Are Commonwealth Edison customers impacted by capacity prices?
Yes. ComEd’s capacity market is run by a different power grid operator, called PJM Interconnection. The prices in PJM’s auction also have skyrocketed.
