Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-05-28
2001-08-14
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C359S015000, C136S259000
Reexamination Certificate
active
06274860
ABSTRACT:
TECHNICAL FIELD
The present invention relates to optics, particularly to the field of optical concentrators for gathering optical radiation. The optical concentrator made by the subject of the present invention may be used in all technical areas where concentrated optical radiation is utilized. It can be used for optical radiation spanning the spectrum from the ultra-violet to the infrared.
BACKGROUND ART
Luminescent solar concentrators are known in the art and act to trap and collect light from luminescent centers dispersed in a planar sheet. Luminescent concentrators utilize the total internal reflection in the wave-guide to trap a portion of the light emitted from the luminescent centers. The luminescent centers reradiate longer wavelength light in a 360 degree solid angle and so are inefficient in directing light to one edge of the plate or to a small region of the edge.
One example of a solar concentrator known in the art utilizes a hologram and a prism or plate; see, e.g., U.S. Pat. No. 4,863,224, issued to Afian et al. However, this solar concentrator needs to be aligned to the sun and does not provide for any passive solar tracking ability.
Also known in the art is a light gathering device comprising a hologram and a total reflection surface for a collecting monochromatic light at a single angle of incidence; see, e.g., U.S. Pat. No. 5,268,985, issued to Ando et al. However, Ando et al employ a single angle of incidence and a single wavelength, and thus require a tracking mechanism and cannot utilized the entire solar spectrum.
Yet another concentrator known in the prior art is an electromagnetic wave concentrator; see, e.g., U.S. Pat. No. 4,505,264, issued to Tremblay. The electromagnetic wave concentrator utilizes a multidielectric guiding plate to concentrate electromagnetic energy. This invention has the disadvantage of multiple reflection losses in the guiding plate and high absorption losses in some of the more cost effective embodiments. Also this invention posses difficult optical fabrication problems and hence is more expensive to fabricate.
U.S. Pat. No. 5,877,874, issued Mar. 2, 1999, to the present inventor, discloses a device for concentrating solar radiation, which employs a hole graphic planar concentrator (HPC) for collecting and concentrating optical radiation. The HPC comprises a planar, highly transparent plate and at least one multiplexed holographic optical film mounted on a surface thereof. The multiplexed holographic optical film has recorded therein a plurality of diffractive structures having one or more regions which are angularly and spectrally multiplexed. Two or more of the regions may be configured to provide spatial multiplexing, While the teachings of that patent are certainly useful for its intended purpose, improvements thereover are sought; the present invention represents such an improvement.
There remains a need for a solar concentrator that decreases energy losses in the concentration of solar radiation and that utilizes a substantial portion of the solar spectrum while reducing or eliminating tracking requirements.
DISCLOSURE OF INVENTION
Accordingly, it is an object of the present invention to provide a spectrally selective solar concentrator in which different spectral components of sunlight can be concentrated for use as different forms of energy such as electricity, light and heat.
It is a further object of the present invention to reduce or eliminate tracking requirements for solar concentrators.
It is another object of the present invention to simplify the design and manufacture of solar concentrators.
It is a still further object of the present invention to provide a light concentrator which can have its spectral selectivity designed for the desired application. Each application disclosed herein has a unique spectral requirement to work effectively.
It is a yet further object of the present invention to provide a solar concentrator which acts as a passive filtering device for UV and IR in light gathering illumination systems.
Further objects and advantages of the present invention will become apparent from a consideration of the drawings and ensuing description thereof.
In accordance with the present invention, a holographic planar concentrator for collecting and concentrating optical radiation is provided. The holographic planar concentrator comprises (a) at least one planar highly transparent plate, (b) at least one multiplexed holographic optical film mounted on a surface thereof to form a light guiding structure, and (c) at least one photovoltaic cell secured beneath the multiplexed holographic optical film, on a side opposite to that upon which solar radiation is incident. Each photovoltaic cell is bounded laterally by at least one such holographic optical film. Further, multiple (at least two) such films may be formed in the Z (vertical) direction.
The multiplexed holographic optical film has recorded therein a plurality of diffractive structures having two or more regions which are angularly and spectrally multiplexed. The multiplexed hologram is adapted to couple optical radiation into the planar highly transparent plate such that the optical radiation is not lost and travels through both the planar highly transparent plate and the multiplexed holographic film. The multiplexing of the hologram serves to reduce recoupling losses in the holographic planar concentrator.
The highly transparent plate is multifunctional and performs in the following manner. First, it acts as a structural support for the holographic material. Second, it provides environmental protection to the holographic material. Third, it provides high optical transmission in the wavelength range of 350 to 1400 nanometers, which is important to the total efficiency of the holographic planar concentrator. Fourth, the higher refractive index of the glass relative to the air surrounding it functions to compress the incoming angular acceptance angles from a full angle of 160 degrees to approximately 80 degrees for daily sun angle variations; this reduces the angular performance requirements on the holographic structure. Fifth, the highly transparent plate acts as a total internal reflection (TIR) secondary concentrator for the holographic planar concentrator device.
The higher refractive index of the highly transparent plate relative to air provides TIR confinement in the highly transparent plate, thus limiting the divergence of the collected light to the thickness of the plate and causing an increase in concentration. The highly transparent plate thickness can also be adjusted to reduce the number of bounces that occur as the confined light propagates down the highly transparent plate by TIR. This is an important feature, since the primary limiting factor in the distance that the light can travel in the highly transparent plate is the recoupling or replay of the light by the same holographic structure. The reversibility of optical systems comes into play and requires that the holographic optical elements making up the HPC have different spectral and angular performance across the surface as the light advances towards the edge of the highly transparent plate.
In addition to the spatially multiplexed holographic optical elements, recoupling losses in the HPC may be reduced by launching the optical radiation from the film into the highly transparent plate at a small trapping angle of less than about 5 degrees. As used herein, small trapping angles are measured from the plane of the holographic film and are considered to be less than 5 degrees. A combination of small trapping angles and the thickness of the highly transparent plate will further reduce the recoupling losses and allow for the HPC to be scaled to a practical size for energy collection.
Without these features to avoid recoupling, the HPC cannot be made to function effectively.
The holographic planar concentrator of the invention is fabricated by:
(a) mounting the multiplexed holographic optical film on one surface of the highly transparent plate; and
(b) recording the plurality of diffractive str
Collins David W.
Lee John R.
Pyo Kevin
Terrasun, LLC
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