Photovoltaic solar-energy conversion is a well-known promising technology to produce renewable energy. Unfortunately, cells used for converting light into electricity are expensive. One way of investigating into the field of PV consists in increasing cell efficiency and expanding the working wavelength range, but this technology is even more expensive!
Solar concentration seems therefore to be the perfect solution. The general idea of a PV concentrator is to use optical devices that focus sunlight onto a receiving solar cell - the smaller the cell, the smaller the cost. This means that the cell surface is replaced by lenses (or mirrors) and no additional light is collected - a manner of reducing costs. The main challenge of this technology consists in efficiently tracking the sun: as Earth rotates, the angle of incidence of the sunbeams changes, resulting in a moving focal point. If the focal point moves, sunbeams will rapidly miss the cell (especially with high-concentration cells), making the system useless. So, solar concentrators need a tracking system to operate the whole day long.
Finally, the optical system must avoid making an image of the sun on the cell and spread out incoming light over the full cell to get maximum efficiency.
Our research here in Hololab focuses on:
High diffraction efficiency on broadband wavelength thanks to multilayer diffraction gratings Hybrid (refractive/diffractive) lenses to eliminate chromatic aberration Non-imaging Fresnel lenses Plane tracking system
Left: Typical design of lens concentrating system. Right: Sun tracking problem.
For a summary, you can download this document (in english): pdf
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