3. Parabolic Trough Collector Concepts

Figure 27 Reflector facets [43]

2. 
   Vacuum insulated receivers, with stainless steel tubes and respective selective coating, are usually of a maximum length of 4 m. Modern receivers are suitable for other heat transfer fluids at higher temperatures and pressures.
   
3. 
   Heat transfer fluid and operating temperatures ranging up to 300°C with mineral oil and 400°C with silicon and synthetic oil. Further adaptation of some collectors for steam can reach up to 500°C (at high pressures ~100 bar) and others with nitrate molten salts up to 550°C.
   
4. 
   Hydraulic or geared drive system with a tracking axis bellow the vertex of the parabolic cross-section. The rotary axis is built coaxial to the centre of mass axis as an optimisation, to reduce the loads on the drives.
   
5. 
   Flexible interconnection elements such as ball-joints or flex-hoses. These elements suffer from frequent breakdowns during operation and tend to have low resistance against high pressure.
   
6. 
   Central torque unit, from which further arms extend to support the mirrors and the heat collector elements supports (HCE) in the case of torque box and tubes. Other alternative or well optimized structures like space frame came to use to minimize the assembly costs,
   

achieve lightweight structures with standardized frame components.