A spike in an electricity “capacity auction” means that Ameren Illinois’ summer supply price for power increased significantly on June 1.
Ameren’s 11.326 cents per kilowatt-hour (kWh) summer supply rate is about 39 percent higher than the price in the summer of 2024. Thankfully, Ameren’s price is expected to go down on Oct. 1, but that price has not been finalized. 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 2026 through May 2027. 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.)
Although the price isn’t as high as last year ($666.50 per Megawatt-day for the summer of 2025*), it is still elevated, at $424.30 per MW-day. That price is about 14 times what the capacity price was in 2024 ($30 per MW-day). MISO’s capacity prices are seasonal, and they do drop significantly after the summer. The graphic below shows the seasonal prices from the 2026 auction (Ameren Illinois is located in MISO’s Zone 4).
*Note: The 2025 capacity auction summer price was elevated for a number of reasons, but one factor was a software coding error. Because of that error, Ameren customers received a credit on their bills earlier in 2026.
Click the image to view a MISO report on the auction results.
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’s electricity supply rate, also known as the “price to compare”—which includes the supply price, a transmission charge and a “supply cost adjustment”—is 11.326 cents per kWh through September.
That’s slightly down from last year’s summer price (12.18 cents per kWh), but still 39 percent higher than the price two summers ago. Compared with the summer of 2024, Ameren customers will be paying nearly $16 more for every 500 kWh of electricity they use. (Ameren has said in the past that a typical customer uses about 10,000 kWh annually.)
Unlike with the capacity market for PJM, the other major power grid operator in Illinois, 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. 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 made money off the price spike?
Power generators–large corporations that own power plants (mostly fossil fuel plants) and sell power to utilities like Ameren–made 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?
This price spike is due to a number of factors, including the proliferation of data centers as well as poor policy from the power grid operator.
Increased demand fueled by data centers. Rising electric bills due to soaring demand from new and proposed data centers has become a national issue. Capacity prices are based on a formula that forecasts future demand, so new and proposed data centers have driven up prices. Unfortunately, the current way energy costs are allocated means that everyday consumers are paying higher power bills to cover costs that Big Tech data centers should be covering themselves. Energy policy has not caught up with this problem, and that’s why CUB is pushing for a number of reforms to make data centers pay their fair share. In Illinois, we’re pushing for the General Assembly to pass the POWER Act, a series of reforms to hold data centers accountable for their energy-related costs. (Urge your legislators to pass the POWER Act.)
Anti-consumer market rules. Prices spiked the last two capacity auctions, after MISO implemented a new pricing methodology, called the Reliability-Based Demand Curve (RBDC). The grid operator launched the RBDC with the intention of giving “better price signals” (read: higher prices) that would incentivize developers to build more power plants. But CUB and other consumer advocates have raised concerns that the new method unacceptably compromises affordability. 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 about three-and-a-half years in MISO’s “interconnection queue.”That’s the waitlist for new power plants seeking review and approval by the grid operator so they can 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 about 750,000 homes.)
Over-reliance on expensive fossil fuels. In the past, CUB has urged MISOto 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. In the last planning auction more than 60 percent of the summer capacity was from coal and gas plants. Wind, solar and battery power took up about 13 percent of summer capacity.
So what can we do to combat 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.
- Fix MISO’s RBDC pricing methodology: CUB and other 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: We must bring more power generation and battery storage to the grid to keep it reliable and affordable, but those projects are stuck in line at MISO.
- Strengthen state policy: CUB helped pass the Clean and Reliable Grid Affordability (CRGA) Act in 2025, in response to last summer’s price spike. The CRGA Act expands energy efficiency and brings more battery storage to the grid to help protect consumers from this type of market volatility. The watchdog also is working to pass the Illinois POWER Act. The bill (SB 4016/HB 5513) would implement a number of reforms, including requiring data centers to bring their own new clean power if they want electric service that won’t be curtailed at times of high demand. (Send a message to your legislators in favor of the POWER Act!)
How can Ameren customers try to lessen the impact of high power bills?
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. 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. For tips and info about efficiency programs, visit CUB’s Clean Energy page and Ameren’s energy efficiency page.
- 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 lure you into a bad deal. Remember: Alternative supplier prices are also impacted by the same market factors that cause Ameren’s price to increase. Illinois consumers have lost billions of dollars to alternative suppliers over the last decade. If your community negotiated an offer with an alternative supplier, something called “municipal aggregation,” do not assume it will save you money. Savings aren’t guaranteed with any alternative supplier. Ask what price the community deal offers and for how long, and how that compares with Ameren’s supply price. 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.
