KEYWORDS: GRIN lenses, Spherical lenses, Solar concentrators, Lenses, Sun, Near field optics, Refractive index, Near field, Optics manufacturing, Photovoltaics
We present the design and simulation of first-ever planar single-element solar lenses (modified hemispherical gradientindex structures) for concentrator photovoltaic applications, with high collection efficiency and liberal optical tolerance at averaged cell irradiance levels exceeding 1000 suns. These compact lens designs satisfy the severe constraints of the refractive indices of viable polymeric materials and fabrication techniques, for visible and near-infrared radiation. The planar hemispherical gradient-index lens for a far-field (solar) source is created from a near-field unit magnification spherical gradient-index lens. Our new solutions incorporate a constant-index core (crucial for manufacturability). Simulations include a polychromatic and extended sun. A sample design for an f/1.40 solar lens is provided, where planar lenses comprise a concentrator module's protective glazing, with loss-less packing due to a square lens entry allowed by the modified truncated (non-full aperture) design, without incremental optical losses.
Novel solutions for realistic gradient-index (GRIN) lenses are presented, that create the possibility of nominally
stationary photovoltaic concentrators capable of daylong averaged flux concentration levels of order 103. One transfers
the burden of precision solar tracking from massive units on which numerous solar modules are mounted, to
miniaturized mechanical components inside modules that are completely stationary. The best optical properties for this
aim would appear to be perfect imaging - a case where imaging and nonimaging objectives coalesce because perfect
imaging is non-trivially synonymous with attaining the fundamental limit to concentration. Our GRIN profiles surmount
limitations of classical Luneburg solutions that resulted in GRIN lenses being deemed physically unattainable
idealizations for sunlight. To wit, while preserving perfect imaging, our GRIN profiles eliminate the need for refractive
indices near unity, markedly reduce the range of refractive indices required, and permit arbitrary focal length. They are
also amenable to realistic materials and fabrication technologies. Raytrace simulations confirm that they offer an
unprecedented solution to this problem - even accounting for chromatic aberration and misalignment. Eliminating
massive precision tracking of large photovoltaic arrays in favor of precision cm-scale lens tracking inside the modules
opens the possibility of rooftop CPV. The perception that high solar concentration is inseparably linked to massive
trackers is supplanted here by a different paradigm.
Certain classes of gradient-index lenses can achieve both perfect imaging and flux concentration at the fundamental
limits. Although useful in microwave technology, eponymous Luneburg lenses have been viewed as esoteric
idealizations for visible and near-infrared radiation due to the paucity of suitable materials and fabrication methods. We
show that the classic Luneburg problem was constrained in subtle, implicit ways that can be relaxed. With the extra
degrees of freedom, we demonstrate new gradient-index profiles that can accommodate both realistic, readily available
materials and existing manufacturing technologies, while compromising neither perfect imaging nor maximum
concentration (confirmed by raytrace simulation) - thereby opening new vistas for solar concentration and other visible
and near-infrared applications. Specifically, the broader genres of solutions identified here permit a far smaller range of
refractive indices than previously believed, with minimum required refractive index values well above unity, at arbitrary
lens f-number, with less sensitivity to dispersion losses than conventional lenses.
This paper presents a novel approach regarding the design of stationary, non imaging, refractive lenses with
high acceptance angles. A lens lies on a stationary aperture and as the sun moves throughout the day, the
concentrated focal spot is tracked by a moving solar cell. The purpose of this work is to replace the 2-axis
tracking of the sun with internal motion of the miniaturized solar cell inside the module. We show families of
linear lenses with wide acceptance angles 60. and 30. achieving moderate concentrations of 10 - 30 suns. The
lens is designed with a variation of the simultaneous multiple surface (SMS) technique which is combined with
a genetic algorithm to optimize the free variables of the problem.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.