Spaceframe and Tracker

Rehnu’s mechanical system is unique in using a large spaceframe structure to hold reflectors and receivers in a rigid, elongated array. The spaceframe acts structurally as a long beam with a large hexagonal cross section. This design achieves, with a minimum of steel, the high stiffness needed to avoid bending under gravity and the high strength needed to withstand very high wind gusts.

The nodes are the strong points of the spaceframe structure. Two central nodes provide the mounting points for the elevation bearing. The system balances about these nodes to minimize drive power and the turning load of the wind. Other nodes at the top and bottom of each cell of the structure provide mounting points for the reflector assemblies and the receiver supports. The design illustrated above with eight reflectors in a 2 x 4 array is currently being prototyped at the University of Arizona. REhnu will build longer generators with twelve reflectors in a 2 x 6 array.

Turning well clear of the ground

The spaceframe structure turns on a pedestal with a minimum of 8-foot ground clearance, so vegetation and wildlife remain largely undisturbed. The high clearance also minimizes soiling of the reflectors. The pedestal foundation is built with a minimum of steel and no concrete, disturbing only a small ground area.

Low mass per watt of output power

The two-axis tracker can easily become the most expensive single item of any high-concentration photovoltaic system. Hence, the overriding consideration in REhnu’s patented tracker design is to minimize its mass and cost per kilowatt of output power, while constraining the energy consumed and carbon emitted during manufacture. On this basis, steel was chosen over aluminum, and is configured in the lightest possible structure. The total mass of steel in the spaceframe, pedestal, and foundation of the REhnu design amounts to 100 kg per kW of peak power. This is less than for most two-axis trackers and for single-axis solar thermal trough systems. It is also less than for most wind power turbines.