Clearway Restores Visibility and Reliability with SCADA Retrofit Across Three Legacy Solar Sites

Company
Clearway Energy Group LLC is a leading developer and operator of renewable energy assets across the United States. With a diverse portfolio that includes utility-scale solar, wind, and energy storage, Clearway is committed to modernizing its infrastructure to ensure long-term performance, reliability, and grid compliance.

Situation
At three early-generation utility-scale solar sites in California, Avenal Park (6 MW), Sand Drag (19 MW), and
Sun City (20 MW), Clearway faced a growing operational risk. The plants were originally built using inverters and control systems that are now obsolete. As the hardware aged, support became increasingly difficult. Spare parts were no longer available, and Clearway staff could not modify the proprietary control software. Most critically, Clearway had lost real-time telemetry from one of the sites for over two years, significantly limiting visibility and analytics.

The inability to monitor performance metrics in real time meant plant operators could not determine whether underperformance was caused by soiling, equipment faults, or other issues. Any required updates or changes
(even simple ones like adjusting ramp rates) had to go through a different supplier—at significant cost and delay.

To establish a path forward, Clearway assessed the Avenal Park site to determine if there was a business justification for an upgrade. Clearway reviewed the 5-year outlook of the plant and analyzed potential risks associated with a plant failure, including examining the risk of future failure of the control hardware. This meant reviewing the age of the assets, including the servers and the Real-Time Automation Controller (RTAC). If legacy assets are no longer functioning properly, frequency response, reactive power, and ramp rates are impacted, and can put the plant at a higher risk of not being able to meet grid compliance requirements. 

Clearway prioritized identifying any obsolete hardware or conditions that could result in unsatisfactory lead times. Their objective was to avoid the costly delays of run-to-failure scenarios, ensure compliance with Power Purchase Agreements, and maintain long-term reliability and performance.

Solution
Clearway turned to Merit, a trusted partner they had worked with on successful greenfield projects in the past. Merit began with comprehensive site walkthroughs to define a clear scope, identify which components could be retained, and map out the retrofit strategy. Merit’s solution included a full SCADA and control system upgrade across all three sites, replacing the outdated Emerson hardware with a modern,
open-platform system using SEL RTAC controllers and Ignition for HMI functionality.

The retrofit was carefully phased. Merit first upgraded the Avenal Park site, monitored its performance for a month, and then returned to complete the upgrades at the other two sites. During implementation, Merit encountered a major challenge: five of the site’s six inverters used a different Modbus map than the first inverters, causing communication errors. Rather than delaying the project, Merit methodically diagnosed the issue, manually remapped the data points, and brought the system back online quickly.

Results
What stood out most to Clearway was Merit’s reliability, responsiveness and flexibility. Merit communicated clearly, worked collaboratively with Clearway’s engineers, and consistently delivered on time and within budget. The retrofit project was completed as planned, delivering desired results quickly.