Self-tracking phase change concentrator device demonstrator
Concentration photovoltaic systems uses free-space optics to concentrate sunlight onto photovoltaic cells, using mechanical trackers to accurately track the sun's position and keep the focal spot on the PV cell. We recently proposed and demonstrated a proof-of concept of a self-tracking mechanism using a phase-change material to greatly extend the acceptance angle of the concentration device. The light responsive mechanism allows for efficient waveguide coupling and light concentration independent of the angle of incidence inside its angular range of acceptance. The system uses a lens pair to achieve a flat Petzval field curvature over the acceptance angle range. A waveguide slab acts as the concentrating device. The use of a dichroic prism membrane separates the solar spectrum into two parts, lower wavelengths (<750nm) are coupled into the waveguide, while the energy of higher wavelengths (>750nm) is used to power the self-tracking mechanism. The energy in this part of the spectrum is absorbed by a carbon black paraffin wax mixture that undergoes a phase change and subsequently creates a coupling feature due to thermal expansion which allows the lower wavelength part to be coupled into the waveguide. We show the extension of our proof-of concept to a device-like demonstrator, featuring the extension to a lens array and much larger dimensions. All parts of the proof-of-concept device have been upscaled to meet the requirements of a larger scale demonstrator. The demonstrator has an acceptance angle of +/- 16 degrees and can achieve an effective concentration factor of 20x. We present experimental and simulation results of the demonstration device.