Two-stage concentration for broadband solar energy transmission: Theory and experiment of high-energy-density fiber optical coupling

Optical fibers are ideal for transmitting high-energy-density sunlight because they are lightweight, have low energy loss, and flexibility. To achieve high concentration ratios and efficient coupling in a wide-spectrum two-stage concentrating solar optical fiber power transmission system, theoretical analysis and simulation were conducted to study the effects of crucial lens parameters on the focal spot diameter and convergence angle. The results show that the convergence angle of the primary concentrator lens initially increases and then decreases with the F-number; it is directly proportional to both the wavelength and the edge ring’s tilt angle. The convergence angle of the secondary concentrator lens is inversely related to the lens's radius of curvature and directly proportional to the focal length. In contrast, the focal spot diameter of the secondary lens is directly proportional to the curvature radius and thickness. A principle based on the synergistic adjustment of the focused wide-spectrum's convergence angle and spot diameter was conducted, optimizing them because they are optical structures and crucial parameters. An experiment is proposed to couple the concentrated spot of 520-1064 nm wide-spectrum into a single optical fiber, achieving a minimum focal spot diameter of 0.73 mm and a transmission efficiency of 87.8%.