Roberto de Luca and Aniello Fedullo from the University Salerno of Italy invented a new solar concentrating device they say is inspired by the Ear of Dionysus. According to the legends, Doinysus’s ear had an elliptical cave so he could hear even the weakest whispers of a prisoner in one of the cave’s foci.

The Sunlight Trap, as they have called it, faces two parabolic mirrors. The light coming from the Sun falls on the larger parabolic mirror and reflects to the smaller mirror. From there, it is reflected back onto the larger mirror, but focused in the middle of it, trapped inside a small dark space – the black body, or the accumulator. “Through a sunlight trap system, solar radiation is first concentrated in a small region of space and then sent into a blackbody, where it can be stored (not for an arbitrary long time, though) for a variety of uses,” De Luca told physorg.com.

Several applications can derive from this invention. The simplest to imagine is that the small black space accumulating heat could be used to boil water, create steam, and spin a turbine to produce electricity. Other uses could be water desalination, water heating or anything you could imagine that you could use that heat for.

The Ear of Dionysus is The Classic Cassegrain system, which has a parabolic primary mirror and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary. The Ritchey-Chrétien design is a variety of Cassegrain system and good development stage of Cassegrain lens. Ritchey-Chrétien lens has hyperbolic primary and hyperbolic secondary mirrors. As Sun moves in the sky the light falls onto the receiver under different angles and a hyperbolic mirror provides a larger field of view compared to a conventional configuration. Reflecting Ritchey-Chrétien in particular is free of third-order coma and spherical aberrations. It is free of chromatic aberrations as well. Although it does suffer from astigmatism, field curvature and aberrations of high orders.

The advantage of this design – compact lens. The limitation of the lens – high cost of primary mirror. This failing could be overcome by using the technology of mass production.

When you want to concentrate a larger flow of sun light - the alternative to conventional Cassegrain system is the linear cylindrical optics. The linear cylindrical optics is more rational to concentrate light and to construct powered thermal – electrical stations. Another alternative – using holograms, synthesized or fabricated by means of writing of two wave fronts: plane and aspherical.

About applications. After first concentrating stage the solar radiation is «sent into a blackbody, where it can be stored» and, as inventors told, the solar radiation heat could be used to boil water, create steam, and spin a turbine to produce electricity.

It is very interesting theme, what is blackbody? Is it a «black box» filled by flowing water or by molten salt? Or the walls of this blackbody are covered by PV-cells for direct receiving of electricity? There are perspective researches in using nanostructures to convert the ionized and thermal properties of photons into electricity.  

Solar concentrators are beginning to speed up their development because they’re low tech, simple to build and cheaper to use. Indeed it is so. But it is necessary to know as Harvesting of Sunlight with the use of optical concentrators is developing, so PV methods and devices are perfected as well. Optics and Quantum-electronics go parallel in solar renewable tech.

Vasil Sidorov after www.physorg.com

18.07.2009

E-mail: sidorovvasil@gmail.com