Northern California Power Agency (NCPA), USA: DCS automation solution enhances their geothermal operations

The Northern California Power Agency (NCPA) operates two geothermal power plants located in Sonoma and Lake Counties, California. Since the mid‑1980s, these facilities have generated more than 27 million megawatt-hours of electricity for NCPA’s 11 member utilities.

Together, the sites include 77 geothermal wells, two 110‑MW plants (each with two 55‑MW units), and the associated steam pipeline systems necessary for delivering clean, baseload renewable power to the region.

To ensure continued reliability and prepare the facility for future system expansion, NCPA set out to modernize one of its geothermal plants by introducing a comprehensive, easy‑to‑maintain Distributed Control System. The objective was to deploy a complete control package using pre‑designed integration drawings, with minimal installation challenges. A key part of this modernization included updating the BoP, generator and turbine control systems to a state-of-the art DCS system, that could easily be expanded into a plantwide DCS system in the future. Another goal of the modernization was to improve the control of the steam valves with a high pressure oil system and closed loop servo control steam valves.

Siemens Energy provided a comprehensive modernization solution based on the Omnivise T3000 platform, an object‑oriented control system designed to improve efficiency, transparency, and long-term operability. By using pre-built functions blocks and templates Omnivise T3000 maximizes programming and configuration efficiencies. The built-in I&C diagnostics require no additional equipment, allowing for optimized maintenance strategies. Omnivise T3000’s intuitive, role-based operator interface enables structured monitoring and control of the entire generation system, giving operators, engineers, maintenance teams, and managers exactly the information suited to their responsibilities. Also performed during the modernization was the conversion from a low-pressure lube oil system to a high-pressure DEH system to enable the plant to achieve better performance to meet the demands of today’s market. The updated high-pressure hydraulic system for steam valve control utilizes a servo-based closed loop design, one of Siemens Energy’s many custom solutions.

The modernization project delivered significant benefits across NCPA’s geothermal operations. With BoP and all related systems now unified within a single DCS platform, the facility operates with greater consistency and reliability under one system and one supplier. Operators benefit from improved situational awareness through real‑time data and meaningful alarm structures, which streamline everyday operation and enhance responsiveness. Maintenance teams gain from integrated diagnostics that simplify troubleshooting and support more proactive maintenance strategies. The switch to the high‑pressure servo‑based valve control system further optimizes plant performance by improving turbine responsiveness and enabling the facility to adapt to changing operational and market conditions.