Performance of Solmacs, a High PV Solar Concentrator With Efficient Optics

in CPV-8 conference proceedings (in press)

Study of a solar concentrator for space based on a diffractive/refractive optical combination

Poster (2013, April 16)

This paper presents a new design of a planar solar concentrator for space applications focusing on two spatially separated PV cells, allowing independent control of output power of each cell. It has the ... [more ▼]

This paper presents a new design of a planar solar concentrator for space applications focusing on two spatially separated PV cells, allowing independent control of output power of each cell. It has the advantages of both spectral splitting and solar concentration by the combination of a blaze transmission diffraction grating and a flat cylindrical Fresnel lens. An optical optimization has been realized and two variations of configuration have been developed to improve tracking tolerance: first, a design completed by secondary reflective concentrators and second, a symmetrical configuration composed of two lenses. First numerical results are presented, highlighting the possibility to design a concentrator at about 10×, with an electrical output power about 290W/m² lens and less than 10% losses for tracking errors lower than ±0.9°. [less ▲]

Achromatization of nonimaging Fresnel lenses for photovoltaic solar concentration using refractive and diffractive patterns

Doctoral thesis (2012)

In the field of concentrated photovoltaics, the main disadvantage of lenses compared to mirrors lies in their chromaticity: Snell's law is related to the refractive index which is wavelength dependent ... [more ▼]

In the field of concentrated photovoltaics, the main disadvantage of lenses compared to mirrors lies in their chromaticity: Snell's law is related to the refractive index which is wavelength dependent. Consequently, even for purely collimated beams under normal incidence, the maximum concentration achievable with typical lenses made of PMMA is limited to ~1000×. This maximum value becomes even lower when considering Sun's angular aperture. Since the law of reflection is not wavelength dependent, mirrors can theoretically achieve the thermodynamic limit of concentration which is about 46'000×. This thesis aims at the design and the manufacturing of an achromatic Fresnel lens suitable for photovoltaic solar concentration, i.e. combining high concentration, low production cost and tolerance to manufacturing errors. Firstly, we investigated a hybrid lens made of a refractive lens and a diffractive lens. The investigations showed that the concentration ratio could be multiplied by 4. A full chapter is dedicated to the optimisation of blazed diffraction gratings to finally achieve the design of the diffractive lens. Nevertheless, a bilayer diffractive lens is needed to obtain a high diffraction efficiency which makes the diffractive lens highly sensitive to manufacturing errors and consequently not suitable for photovoltaic solar concentration. Purely refractive achromatic Fresnel doublets were then investigated and several designs were compared. They allow for very high concentration ratios in the case of collimated beams under normal incidence, higher than 100'000×. Therefore, contrary to singlets, Fresnel doublets are much more affected by the angular size of the source than by the chromatic aberration. Moreover, it was shown that they are tolerant to manufacturing error, change of temperature and uncertainty on the refractive index. It emerges from this thesis that the concept of achromatic doublets is a tolerant and low-cost production solution to achieve a highly concentrated white flux. Although bilayer diffractive lenses are not suitable for concentrated photovoltaics, the combination of refractive with diffractive structures seems to be promised to a bright future for spectrum splitting applications, including spectrum splitting for concentrated photovoltaics. [less ▲]

Hybrid Lens for Solar Concentration: Optimization of the Multilayer Diffractive Lens

Poster (2012, November 12)

Manufacture process degrades the ideal shape of multilayer diffractive lens due to draft angle, half radius tool and slope error. We show some shape improvements using an extended scalar theory.

Experimental Results of Flat Fresnel Doublets made of PMMA and PC

Conference (2012, April)

To reduce the chromatic aberration lots of imaging systems like cameras and telescopes turn to achromatic doublets. On the other hand, to be cheaper, lighter and thinner, more and more systems like ... [more ▼]

To reduce the chromatic aberration lots of imaging systems like cameras and telescopes turn to achromatic doublets. On the other hand, to be cheaper, lighter and thinner, more and more systems like projectors and headlights use Fresnel lenses. To combine high performances and low cost, the use achromatic Fresnel doublets has been investigated. [less ▲]

Hybrid Lens for Solar Concentration: Optimization of the Multilayer Diffractive Lens

Poster (2012)

Flat Fresnel doublets made of PMMA and PC: combining low cost production and very high concentration ratio for CPV

in Optics Express (2011), 19(S3), 280-294

The linear chromatic aberration (LCA) of several combinations of polycarbonates (PCs) and poly (methyl methacrylates) (PMMAs) as singlet, hybrid (refractive/diffractive) lenses and doublets operating with ... [more ▼]

The linear chromatic aberration (LCA) of several combinations of polycarbonates (PCs) and poly (methyl methacrylates) (PMMAs) as singlet, hybrid (refractive/diffractive) lenses and doublets operating with wavelengths between 380 and 1600 nm – corresponding to a typical zone of interest of concentrated photovoltaics (CPV) – are compared. Those comparisons show that the maximum theoretical concentration factor for singlets is limited to about 1000 × at normal incidence and that hybrid lenses and refractive doublets present a smaller LCA increasing the concentration factor up to 5000 × and 2 × 106 respectively. A new achromatization equation more useful than the Abbé equation is also presented. Finally we determined the ideal position of the focal point as a function of the LCA and the geometric concentration which maximizes the flux on the solar cell. [less ▲]

Achromatization of solar concentrator using diffractive optics

Poster (2009)

Photovoltaic energy suffers from payback time. High solar concentration (above 500 suns) is a very interesting way to reduce production cost. The use of lenses allows more flexibility to make light flux ... [more ▼]

Photovoltaic energy suffers from payback time. High solar concentration (above 500 suns) is a very interesting way to reduce production cost. The use of lenses allows more flexibility to make light flux more uniform. In addition lenses are less prone to errors of manufacture and can be easily duplicated. Unfortunately, optical materials are very dependent on the wavelength which causes important chromatic aberrations. One can think about achromatic doublets but doublets are thick, heavy and require exotic glasses which make them expensive. During the conference, I would like to present an innovative way to achromatize solar concentrators using hybrid (refractive/diffractive) lenses. Indeed, an hybrid lens is as thin as a Fresnel lens and is made in only one glass. But diffractive lenses suffer from limited broadband diffraction efficiency due to spurious orders. To overcome the lake of efficiency we are investigating the use of multi-layer diffractive optical element. This technique allows to achieve an efficiency greater than 97% over the full visible spectrum using only three components (e.g. two optical elements + air). [less ▲]