1.0Citizens Utility Boardhttps://www.citizensutilityboard.orgrich600338<blockquote class="wp-embedded-content" data-secret="5e4eQZPvfw"><a href="https://www.citizensutilityboard.org/blog/2025/05/23/cub-qa-why-is-amerens-electricity-price-spiking/">CUB Q&A: Why did Ameren’s electricity price spike this past summer? </a></blockquote><iframe sandbox="allow-scripts" security="restricted" src="https://www.citizensutilityboard.org/blog/2025/05/23/cub-qa-why-is-amerens-electricity-price-spiking/embed/#?secret=5e4eQZPvfw" width="600" height="338" title="“CUB Q&A: Why did Ameren’s electricity price spike this past summer? ” — Citizens Utility Board" data-secret="5e4eQZPvfw" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" class="wp-embedded-content"></iframe><script type="text/javascript"> /* <![CDATA[ */ /*! This file is auto-generated */ !function(d,l){"use strict";l.querySelector&&d.addEventListener&&"undefined"!=typeof URL&&(d.wp=d.wp||{},d.wp.receiveEmbedMessage||(d.wp.receiveEmbedMessage=function(e){var t=e.data;if((t||t.secret||t.message||t.value)&&!/[^a-zA-Z0-9]/.test(t.secret)){for(var s,r,n,a=l.querySelectorAll('iframe[data-secret="'+t.secret+'"]'),o=l.querySelectorAll('blockquote[data-secret="'+t.secret+'"]'),c=new RegExp("^https?:$","i"),i=0;i<o.length;i++)o[i].style.display="none";for(i=0;i<a.length;i++)s=a[i],e.source===s.contentWindow&&(s.removeAttribute("style"),"height"===t.message?(1e3<(r=parseInt(t.value,10))?r=1e3:~~r<200&&(r=200),s.height=r):"link"===t.message&&(r=new URL(s.getAttribute("src")),n=new URL(t.value),c.test(n.protocol))&&n.host===r.host&&l.activeElement===s&&(d.top.location.href=t.value))}},d.addEventListener("message",d.wp.receiveEmbedMessage,!1),l.addEventListener("DOMContentLoaded",function(){for(var e,t,s=l.querySelectorAll("iframe.wp-embedded-content"),r=0;r<s.length;r++)(t=(e=s[r]).getAttribute("data-secret"))||(t=Math.random().toString(36).substring(2,12),e.src+="#?secret="+t,e.setAttribute("data-secret",t)),e.contentWindow.postMessage({message:"ready",secret:t},"*")},!1)))}(window,document); /* ]]> */ </script> A spike in an electricity “capacity auction” meant that the supply price for Ameren Illinois increased significantly on June 1. Ameren estimated that this increased 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. Thankfully, Ameren’s price did go down significantly, as of Oct. 1. 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): 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,” increased by about 50 percent, to 12.18 cents per kilowatt-hour (kWh), from June through September 2025. Ameren estimated that this higher rate, which includes the supply price, a transmission charge and a “supply cost adjustment,” increased summer power bills 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).   In October, capacity prices came down from their summer high, and Ameren’s new supply price, for October 2025 through May 2026, was significantly lower: 8.402¢ per kilowatt-hour (kWh) for up to 800 kWh of usage. 7.483¢ per kWh for all electricity usage beyond 800 kWh. The summer price spike had a significant impact on Ameren customers. Unlike with PJM’s capacity […]https://www.citizensutilityboard.org/wp-content/uploads/2025/05/MISO-2025.png1052527