• Multiple developers report high interconnection rejection rates and unclear WSCR policy.
• ICC complaints demand review of Ameren’s practices and updated project evaluations.

Carson Power filed a complaint with the Illinois Commerce Commission (ICC) alleging Ameren Illinois of violating sections of the Illinois Public Utilities Act through its enforcement of a Weighted Short Circuit Ratio (WSCR) screen as part of its review process, which uses arbitrary means and results in discriminatory interconnection practices, according to a January 8 filing.

Developers including Cultivate Power, Dimension Energy, ForeFront Power, GreenKey Development, Trajectory Energy, and Sol Source Power have filed similar complaints with the ICC over the last couple months.

“Upon information and belief, the WSCR screen has resulted in rejections of approximately 90 to 95% of interconnection applications for renewable energy projects that sought interconnection to an Ameren distribution substation,” Carson wrote in the complaint.

Ameren Illinois’s WSCR screen requires each project to have a WSCR value higher than 10 to qualify for interconnection, according to the complaint. Carson Power described the enforcement of the screen to be “technically inappropriate and fundamentally flawed,” and “not an adequate or efficient measure of stability.”

“Even if the WSCR were a relevant screen (which it is not), Ameren’s threshold of 10 is arbitrary, excessive, unsupported by technical literature or scientific study and serves as an unjust and unreasonable barrier to renewable energy development in violation of the Illinois Public Utilities Act and Illinois public policy,” the complaint states.

Carson Power also argued that the utilization of the WSCR screen procedures is inconsistent with the information posted online and in the utility’s Interconnection Guide, for which Ameren has failed to maintain up-to-date information.

Sol Source’s complaint was filed in November in connection to eight of its community solar project subsidiaries, NPM reported. In the complaint, Sol Source said they were also unable to find a copy of the WSCR policy online and said Ameren representatives said they would send them a copy but failed to do so.

NPM has also been unable to locate the policy online and in December, asked Ameren Illinois for a copy, but a spokesperson declined to provide the information.

According to Carson’s complaint, ERCOT designed the WSCR metric to assess voltage stability in high-voltage transmission systems in the Texas panhandle due to a high penetration of wind farms existing in close proximity to each other. WSCR was not designed as a metric to assess small community solar projects interconnecting to the distribution system in Illinois.

Carson also argued that the WSCR does not take into account the real electrical network connections among renewable energy resources; and therefore, may not reflect the actual grid strength at a particular point of interconnection.

Carson Power’s projects in dispute include, Alta Solar A and Alta Solar B, two community solar projects 5 MW or less proposing interconnection to a line greater than or equal to 30 kV and less than or equal to 69 kV, qualifying for a Level 2 review.

Both interconnection applications were submitted in February of 2025 at feeders in Peoria County, Illinois. Supplement reviews were returned in December 2025 with the project denials.

Carson Power and Ameren held a virtual conference on December 18 and were unable to resolve the dispute, the complaint states. “Although Ameren stated that it is continuing to review the issue and acknowledged that it is impacting a large number of projects, Ameren provided no possible solutions or alternatives. Ameren advised that it is still gathering information on individual inverter short circuit ratios and that the threshold WSCR screen could go up or down in the future.”

Carson said Ameren also did not provide an explanation as to how it adopted a value of 10 as the threshold to pass its WSCR screen and refused to consider any adjustments to the WSCR screen for the projects at the time.

Carson ultimately asked the ICC to compel Ameren to re-conduct the Level 2 review of each of the projects without the WSCR screen and award any additional relief deemed appropriate and just.

Other developers working on DERs with Ameren Illinois have reported similar frustrations with the utility, many citing prolonged interconnection timelines and internal errors within interconnection queues that would shift project positions without rhyme or reason, NPM reported.