Inflatable Concentrated Solar Power (CSP) Prototype Concept — Project Summary & Lessons Learned

This project explored an unconventional approach to Concentrated Solar Power (CSP) using inflatable lightweight reflectors based on Cassegrain optics. Inspired by historical and modern patents (see References), the design aimed to provide a low-cost, scalable, and lightweight solar collection system capable of delivering heat energy for domestic or industrial use.

Concept Overview

  • The system features an inflatable Cassegrain reflector suspended inside a larger external balloon filled with CO₂ or another transparent, dense gas.

  • The reflector assembly includes a primary parabolic mirror and secondary convex mirror to focus sunlight onto a central absorber.

  • A heat pipe system transfers thermal energy from the absorber to a radiator or heat exchanger, enabling either direct heat usage or potential conversion to electrical power.

Control System

  • Orientation of the floating reflector is achieved via servo-driven strings, operating as an inverted marionette or zeppelin-like system.

  • A minimum of 3 strings (with corresponding motors) enables full 2-DOF control (roll and pitch). A 4-string variation was also considered to reduce motor count while maintaining stability.

  • Microcontrollers manage string lengths and coordinate reflector positioning via kinematic transformation.

Key Advantages

  • Lightweight construction: Inflatable mirrors reduce weight and material cost compared to traditional Ag-glass mirrors.

  • Modular and scalable: The system design allows easy upscaling from prototypes to larger industrial units.

  • Minimal energy for actuation: Small servo motors suffice for positioning, reducing system power needs.

  • Flexibility in gas usage: Using an external CO₂-filled balloon enables better control and environmental resistance compared to helium or hydrogen.

Challenges & Lessons Learned

  • Lower reflectivity: Inflatable mirrors typically offer reduced optical efficiency.

  • Environmental sensitivity: Wind, pressure changes, and weather can destabilize the system; additional protection or gas containment strategies are needed.

  • Complex control architecture: Accurate reflector control requires precise motor coordination and string actuation—adding technical overhead.

  • Shifting market economics: The dramatic drop in PV panel costs during the 2010s made thermal CSP approaches economically uncompetitive for small-scale use.

  • Deployment complexity: Ensuring durability, pressure integrity, and mirror alignment posed significant engineering challenges.

Conclusion

While technically innovative and mechanically elegant, the inflatable CSP system was ultimately discontinued due to the economic dominance of photovoltaic technologies. However, it served as a rich learning opportunity in lightweight structure design, solar thermodynamics, and robotic soft-body control. The concept remains archived as an example of how market shifts can reshape the viability of alternative energy innovations, even when technically feasible.

References

  • R1. H.P. Sleeper, Jr., Inflatable solar energy collector (US Patent)

  • R2. Vedanta Society of Western Washington, Apparatus using a balloon supported reflective surface for reflecting light from the sun, US 5,404,868 (1995.04.11)

  • R3. Cassegrain Reflector: https://en.wikipedia.org/wiki/Cassegrain_reflector

  • R4. John H. Culling, Solar Energy Heating Apparatus, US 3,182,654 (1965.05.11)

  • R5. Winger et al., Inflatable solar energy collector apparatus, US2009260620A1 (2009.10.22)

  • R6. Heliovis AG, Inflatable Solar Collector, US2010186733A1 (2010.07.29)

  • R7. Harry Hahn, Lightweight low-cost solar concentrator, US2011162637A1 (2011.07.07)

  • R8. Ric Enterprises, Inflatable heliostatic solar power collector, US7997264B2 (2011.08.16)