Sol Source Power and eight of its community solar project subsidiaries have filed a complaint with the Illinois Commerce Commission (ICC) alleging Ameren Illinois of violating sections of the Illinois Public Utilities Act by using unjust and arbitrary means for distribution level interconnection applications, according to a November 26 filing.

More specifically, Ameren’s new enforcement of a Weighted Short Circuit Ratio (WSCR) screen as part of its review process, which requires projects registering a WSCR of higher than 10 to qualify for interconnection is resulting in discriminatory interconnection practices, complaint states.

Under Illinois Administrative Code, electric distribution companies (EDCs) such as Ameren, must conduct a series of prescribed studies prior to offering a distributed energy resource (DER) an interconnection agreement. EDCs may implement certain screens to evaluate interconnection requests. However, for Level 2 reviews, EDC’s are not allowed to impose additional requirements unless the applicant agrees.

Level 2 reviews apply to certified inverter-based systems meeting specific nameplate capacities based on the voltage of the line and the proposed point of interconnection, among other requirements.

Sol Source said in the complaint that it submitted interconnection requests for the eight projects between December 2023 and December 2024. Ameren determined infeasibility based on WSCR for the projects beginning September 2025. Sol Systems said it had not agreed to any additional requirements for Level 2 reviews.

For the McCarthy solar project, which was submitted in December 2023 requesting interconnection at Ameren’s Havana S U73-583 feeder in Mason County, Sol Source received the supplemental review on October 6 stating that the project would need to be downsized to proceed at the current point-of-interconnection (POI) or be withdrawn. The company was also told that if it did not respond by October 27, the application would be withdrawn.

On October 10, following correspondence between the two companies, Ameren deemed the McCarthy solar project infeasible due to WSCR. Ameren also advised Sol Source at that time that the Level 2 WSCR screen was a newly implemented measure, according to the complaint.

For the McRray project, which was submitted in July 2024 requesting interconnection at Ameren’s Greenville Rural N15-850 feeder in Bond County, Sol Source said it received the supplemental review for it on September 12 with a similar message as the McCarthy project. For this project, Sol Source made the decision to downsize the project which cost USD 1,500 for a re-review on October 1. About a month later, Sol Source was advised that the review had been completed but downsizing and mitigation options studied would not improve the WSCR to an acceptable value; “Due to this, the project is not feasible.”

Similar scenarios occurred with the other six projects, with Ameren determining that none of the projects passed the WSCR screen with a value of 10 or more.

Sol Source initially challenged the findings, requesting an informal meeting with Ameren representatives. A teleconference was held on November 7 where according to Sol Source, Ameren said that the implementation of the WSCR screen had resulted in rejections of approximately 90%-to-95% of interconnection to Ameren distribution substations.

Additionally, Sol Source said they asked the representatives during that meeting for the WSCR policy. Representatives advised them that there was a copy available online but would provide them a copy. At the time of the complaint, Sol Source said it had yet to receive a copy and was unable to find it online. NPM was also unable to locate the policy.

NPM reached out to Ameren Illinois requesting a copy but an Ameren spokesperson declined to share the data.

“Ameren’s enforcement of the WSCR screen to distribution-level projects is both technically inappropriate and fundamentally flawed. It is not an adequate or efficient measure of stability. It is not just or reasonable,” the complaint states.

“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. “The threshold of 10 is also prohibitive to the State’s policy initiative to achieve 100% clean energy by 2050.”

Ameren is also refusing to consider other potential options for mitigation and grid stability strategies, according to the complaint.

Ultimately, Sol Source asked the ICC to compel Ameren to re-conduct the Level 2 review without the WSCR screen, apply a WSCR screen of three instead of 10 to projects proposing interconnection consistent with certain scientific studies, and award additional relief as the Commission deems necessary.

The ICC has scheduled a prehearing conference on the complaint for December 17.

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.

*This story was originally published exclusively for NPM subscribers.