New-Tech Europe Magazine | Aug 2018

The big rim drives at the back of the mirror act as a counterbalance to the mirror itself, balancing out the entire structure. Besides the benefit of stabilizing the heliostat structure, this counterbalancing also allows lower energy consumption from the moving parts. Also, the large diameter of the rims means that precise movement can be achieved using low-cost gears and motors, contrary to a linear actuator, which requires more precise and expensive motors to achieve the same accuracy levels. In addition to this counterbalancing function, the two rims can also be used as encoders when machined correctly (see Figure 2). This not only makes them lighter but also reduces BOM costs, as external encoders are no longer necessary. Taking all these improvements into account, the heliostat's power requirement is reduced to the point where it can rely on PV cells mounted on the heliostat itself as a power source, in combination with battery storage, which increases its autonomy. This overall design enables a fairly simple hardware architecture using the following components: Two motion control drives that control both axes of the heliostat's rims (the HelioDrive). A photovoltaic panel, battery, and energy and battery management unit (the HelioEBMU) that harvests energy out of the PV panel, charges the battery, and supplies the energy to the autonomous system. A wireless module (the HelioNode) that communicates with the centralized field control system through a mesh network made of similar devices. All components are connected together with a wired bus within each autonomous heliostat. The master drive communicates with the centralized field control system and with other devices using wireless technology, while at the same time running the heliostat's

Figure 3: Components of the AutoR (autonomous rim) drive heliostat system.

lifetime of the spring. If needed, the spring can simply be replaced, reducing the technical skills required to maintain this part of the heliostat. Also, with belt drive systems the rims can be easily kept in place using self- locking gearboxes, which are both efficient and easy to implement. An additional locking pin to secure the

heliostat during storms can be easily slid into place when needed, preventing too much strain to be put on the small drives. Both rims are designed the same to ensure both drivers have the same power requirements to move the mirror pane, which also reduces the number of different components required.

Figure 4: Assembling the sandwich-like structure. By tightening the nuts, the mirror is forced into the concave shape of the wooden frame.

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