Parker actuators optimise productivity of world’s third largest solar power plant

The 64MW Nevada Solar One plant, located about 25 miles south of Las Vegas, spans 400 acres and generates approximately 129 million kWh of solar electricity annually, enough to provide power to more than 14,000 homes, while emitting near zero CO2.

As Gilbert Cohen, senior vice president of developer Acciona Solar Power (ASP), a unit of Spain’s Acciona Group, commented, “The plant is creating a lot of interest in the energy industry because it provides a renewable energy alternative.” This is because parabolic trough systems are used, which employ a different technology to the photovoltaic solar panels common on rooftops. They use concentrated sunlight, in place of fossil fuels, to provide the necessary thermal energy to drive a conventional power plant. Curved mirrored surfaces concentrate the sun’s heat on a receiver tube containing a heat transfer fluid capable of achieving temperatures between 120°C and 260°C. This fluid is used to produce steam that drives a generator system to produce electricity.

Essential to the success of the project is the ability to capture maximum sun exposure with the 760 solar collector assemblies. To enable them to track the sun, Acciona needed a dependable precision actuator system. The electromechanical systems used in other solar fields were unable to deliver the combination of control and robust construction that they were looking for. In contrast, Parker offered a hydraulic system that would be powerful enough to track the sun accurately during the day and provide safe, secure stowing of the panels at night.

The self-contained hydraulic system that Parker designed uses the same fluid to power the system and to lubricate it. This design will deliver virtually maintenance-free operation for over 20 years, with no filters to change thanks to an intrinsically clean, sealed design. Each of the 760 solar collectors comprises a customised Parker HTR300 Series rack and pinion hydraulic actuator, control valves, solenoid valves, pumps, cylinders, seals and wear bands, and pre-bent tubing/fitting assemblies.

The hydraulic actuators each drive 12 panels that weigh over 900kg and have a total of 240 curved mirrors. The actuators enable these panels to track the sun in extremely small increments, with small, low-speed displacement pumps providing two short pulses from the reservoir to the unit’s motor three times per minute. Furthermore, the system is designed to withstand backlash from high winds, by allowing the solar trough to slip and rotate in a controlled fashion, without damage to the motion control mechanics. This designed “clutching action” is inherent in hydraulic systems, with the use of pressure relief valves, and allows the solar collector to realign and begin tracking the sun again when the wind subsides.

At the end of each day, the actuators move the arrays in large intervals by engaging high-speed pumps to increase motor speed and return the solar panels to their home position for the following day’s tracking of the sun. At this point the hydraulic system’s duty cycle, the mechanical locking mechanism, featuring Parker 2H cylinders, stows the parabolic troughs for the night. The Parker actuators provide lockdown capabilities with wind load control up to 84mph to protect the solar arrays against hurricane winds while in stow.

Using Parker technology, the Nevada Solar One plant is able to provide Nevada Power Company and Sierra Pacific Power Company, and ultimately the people of Nevada, with a viable alternative to fossil fuel powered electricity, helping to ensure a more sustainable future.