Rotary actuators play key role in solar panels

Powerful hydraulic actuators from Parker Hannifin play an integral role in the world's third largest concentrated solar power plant, Nevada Solar One.

The rotary actuators are used to rotate and tilt a series of parabolic mirrored troughs, allowing them to track the sun's motion for maximum efficiency and protect the arrays from high winds and dust storms.

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.

The plant is creating interest because it uses parabolic trough systems, which employ a different technology to the photovoltaic solar panels common on rooftops.

These parabolic trough systems use concentrated sunlight 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 and 260C.

This fluid produces steam that drives a generator system to produce electricity.

Acciona needed a dependable precision actuator system to capture maximum sun exposure and the 760 solar collector assemblies make this possible.

The electromechanical systems used in other solar fields were unable to deliver the combination of control and robust construction Acciona was looking for.

Parker's hydraulic system is powerful enough to track the sun accurately during the day and provide safe, secure stowing of the panels at night.

Parker's self-contained hydraulic system uses the same fluid to power and lubricate the system.

This design will deliver virtually maintenance-free operation for over 20 years.

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.

By allowing the solar trough to slip and rotate in a controlled fashion, the system can withstand backlash from high winds without damage to the motion control mechanics.

This 'clutching action' and pressure relief valves allow 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 in 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.

The Nevada Solar One plant provides Nevada Power Company, 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.

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