Page 14 - North American Clean Energy September/October 2019 Issue

solar energy
Gear Set Reset
How double-enveloping worm technology
“Heliostat” combines the Greek words for sun (“helios”) and stationary (“stat”)—in other words, a device that tracks the sun from a stationary point.
is driving heliostat dependab
by Jacob Randall
The Ivanpah project in the Mojave Desert uses 173,000 heliostats and is the world’s largest concentrated solar power facility, generating an estimated 940,000 megawatt-hours of clean energy a year.
For azimuth drives, many heliostat makers have come to favor a double- enveloping worm gear design, where the worm and gear wrap around each other. This design offers greater contact between the worm thread and the
gear teeth than a standard cylindrical worm gearing. In a double-enveloping design, the curved profiles of the gear teeth match the circular profile of the worm thread, allowing full engagement between the thread and the teeth. Single enveloping worm gear designs can only achieve partial engagement between the thread and the teeth.
Figure 1: The mesh of common cylindrical worm gearing (left) provides one to 1 1⁄2 gear teeth in contact with the worm while the double-enveloping design (right) provides greater tooth contact—up to eight times more than cylindrical worms.
When the average person thinks about solar power, it is likely they will
picture a classic photovoltaic (PV) solar panel installation. While less familiar, concentrated solar power (CSP) also has an important role, as countries embrace alternative energy production as a means to address emerging challenges. While building a CSP facility requires far more time and expense than constructing a PV array, CSP facilities can produce a tremendous amount of energy and, most importantly, can store it far more efficiently than PV systems. As a result, CSP facilities tend to offer distinct advantages over classic PV, especially in locations close to the equator with high solar radiation.
The efficient operation of a CSP facility goes beyond the collection tower. A successful CSP installation requires well-constructed heliostats that precisely track the sun throughout the day and reflect its rays onto the heat exchanger atop the tower. While heliostats may appear as little more than large mirrors affixed to support poles, they are actually complex devices that require careful engineering to function effectively over a 30-plus-year life span. Precise movement of each heliostat is essential. They key to this precision? The gear set.
Aiming for Extreme Accuracy
Two types of drive systems are used to position heliostats for optimal reflection throughout the day: an azimuth drive that allows for east to west rotation, and an actuator for the vertical elevation of the mirror. Heliostats rotate 270 degrees or
more a day along the azimuth drive. These movements—with rotation speeds as slow as .009 RPMs—must be extremely precise
to maintain proper alignment. To achieve a proper angle of incidence (where the light rays strike the mirror exactly so) a robust gear design is required, one that employs the same type of technology used to point and position satellite systems and surgical tables.
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SEPTEMBER•OCTOBER2019 /// www.nacleanenergy.com
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Cylindrical worm gearing Double-enveloping worm gearing