Spaceframe & Tracker

REhnu’s mechanical system is unique in its use of a large, lightweight spaceframe structure to hold reflectors and receivers in a rigid, elongated array.

The basic tracker unit of REhnu’s system consists of a 2×4 array of eight dish reflectors and receivers (eight modules) mounted in a spaceframe structure and pointed at the sun. Above, a prototype tracker generates electricity from one completed module.

The lightweight spaceframe structure is optimized for high stiffness and extremely low mass. The structure consists mostly of large cube frames, each holding in coalignment a dish and receiver.

The spaceframe also serves as the complete azimuth structure for sun tracking. It includes two stiff, widely spaced nodes near its center of gravity that support the elevation bearing, and a cut-away allowing for elevation motion. In this way, the added motion for 2-axis sun tracking requires only a pedestal with a vertical axis azimuth bearing. The spaceframe acts structurally as a 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.

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 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, the entire structure is made of lightweight high strength low alloy (HSLA) steel, 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 most two-axis trackers and single-axis solar thermal trough systems. It is also less than for most land-based wind power turbines, and half that for offshore wind power.

Turning well clear of the ground

The spaceframe structure sits 8 feet above the ground, leaving vegetation and wildlife largely undisturbed. The high clearance also minimizes soiling of the reflectors. The pedestal foundation installation uses no concrete and disturbs only a small ground area.