Luminescent solar concentrators
Encyclopedia
A luminescent solar concentrator (LSC) is a device to generate solar power
.
It uses luminescent plates either impregnated by luminescent substances or fluorescent thin films on transparent plates. The plates absorb solar light
which is converted to fluorescence
guided to plate edges where it emerges in a concentrated form. The concentration factor is directly proportional to the plate surface and inversely proportional to the plate edges. Such arrangement allows to use small amounts of solar cells as a result of concentration of fluorescent light. The fluorescent concentrator is able to concentrate both direct and diffuse light which is a specially important in cloudy days. The theoretical basis of concentration performance and other recent advances have been the subject of research.
. The resulting luminescence
emitted at the longer wavelength
part of the spectrum should have high yield. Repeated reflections of the fluorescent light in a transparent matrix should carry the radiation
to the edges of the plate where the light will emerge in a concentrated form. The concentration factor is the ratio of the plate surface
to the plate edge. Theoretically about 75–80 % of the luminescence would be trapped by total internal reflection in the plate having a refractive index
of about 1.51. Photovoltaic cells can be coupled to the edges and receive the concentrated light. Such an arrangement should substantially decrease the amount of photovoltaic cells needed to produce a given amount of electricity
and thus reduce the cost of the system. If all these ideal conditions could be realized calculations show the collecting efficiency
, which is the amount of energy reaching the photovoltaic cell divided by the energy
falling on the plate should be about 20%. This result is obtained by taking into account the overall absorption
of the colorants in the plate, their fluorescent efficiency, the trapping efficiency (depending of the refractive index of the plate medium), and the Stock efficiency (which is the ratio of the average energy emitted to the average energy absorbed).
The efficiency of LSC was never above 7%; one of the main reasons for the relatively low efficiency is the self-absorption of the luminescent dyes as a result of overlapping of the absorption and luminescence of the dyes. Another difficulty is the escaping of the luminescence emitted beyond the critical angle. The advantages and disadvantages of the different colorants: organic dyes vs. rare earth elements and other inorganic species, trapping media glass
or polymer, bulks vs. thin films deposited on transparent
plates have to be considered. Use of photonic systems as a band gaps preventing the escape of the trapped radiation is recommended. Using materials in which the absorption of light and the emission arise from different electronic levels prevents self-absorption. Utilizing solar cells with their sensitivity
matching maximum emission of the colorants is beneficial. A possible solution to the problems is a luminescent material in which the excitation and emission arise from different electronic levels. Interaction of the colorants with surface plasmons increase their transition probabilities from the ground to the excited state
and efficiency of absorbed solar light.
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
.
It uses luminescent plates either impregnated by luminescent substances or fluorescent thin films on transparent plates. The plates absorb solar light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
which is converted to fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
guided to plate edges where it emerges in a concentrated form. The concentration factor is directly proportional to the plate surface and inversely proportional to the plate edges. Such arrangement allows to use small amounts of solar cells as a result of concentration of fluorescent light. The fluorescent concentrator is able to concentrate both direct and diffuse light which is a specially important in cloudy days. The theoretical basis of concentration performance and other recent advances have been the subject of research.
Theory
The theory of internal reflection of fluorescent light which is subsequently concentrated at the edges, has been discussed in detail for inorganic materials and organic dyes incorporated in bulk polymers. For optimum performance a transparent plates doped by fluorescent species should absorb the major part of solar spectrumSpectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
. The resulting luminescence
Luminescence
Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...
emitted at the longer wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
part of the spectrum should have high yield. Repeated reflections of the fluorescent light in a transparent matrix should carry the radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
to the edges of the plate where the light will emerge in a concentrated form. The concentration factor is the ratio of the plate surface
Surface
In mathematics, specifically in topology, a surface is a two-dimensional topological manifold. The most familiar examples are those that arise as the boundaries of solid objects in ordinary three-dimensional Euclidean space R3 — for example, the surface of a ball...
to the plate edge. Theoretically about 75–80 % of the luminescence would be trapped by total internal reflection in the plate having a refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
of about 1.51. Photovoltaic cells can be coupled to the edges and receive the concentrated light. Such an arrangement should substantially decrease the amount of photovoltaic cells needed to produce a given amount of electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
and thus reduce the cost of the system. If all these ideal conditions could be realized calculations show the collecting efficiency
Efficiency
Efficiency in general describes the extent to which time or effort is well used for the intended task or purpose. It is often used with the specific purpose of relaying the capability of a specific application of effort to produce a specific outcome effectively with a minimum amount or quantity of...
, which is the amount of energy reaching the photovoltaic cell divided by the energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
falling on the plate should be about 20%. This result is obtained by taking into account the overall absorption
Absorption (electromagnetic radiation)
In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy for example, to heat. The absorption of light during wave propagation is...
of the colorants in the plate, their fluorescent efficiency, the trapping efficiency (depending of the refractive index of the plate medium), and the Stock efficiency (which is the ratio of the average energy emitted to the average energy absorbed).
The efficiency of LSC was never above 7%; one of the main reasons for the relatively low efficiency is the self-absorption of the luminescent dyes as a result of overlapping of the absorption and luminescence of the dyes. Another difficulty is the escaping of the luminescence emitted beyond the critical angle. The advantages and disadvantages of the different colorants: organic dyes vs. rare earth elements and other inorganic species, trapping media glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
or polymer, bulks vs. thin films deposited on transparent
Transparency and translucency
In the field of optics, transparency is the physical property of allowing light to pass through a material; translucency only allows light to pass through diffusely. The opposite property is opacity...
plates have to be considered. Use of photonic systems as a band gaps preventing the escape of the trapped radiation is recommended. Using materials in which the absorption of light and the emission arise from different electronic levels prevents self-absorption. Utilizing solar cells with their sensitivity
Sensitivity
Stimulus|Sensitivity may refer to:* Sensitivity , the ability to react to a stimulus* Sensitivity , the strength of physical or emotional reaction in people* Sensitivity , variations in process dynamics and control systems...
matching maximum emission of the colorants is beneficial. A possible solution to the problems is a luminescent material in which the excitation and emission arise from different electronic levels. Interaction of the colorants with surface plasmons increase their transition probabilities from the ground to the excited state
Excited state
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....
and efficiency of absorbed solar light.
See also
- Solar cells
- LuminescenceLuminescenceLuminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...
- Thin films
- Rare earth elements
- Surface plasmons
Further reading
- Strong emitting sol–gel materials based on interaction of luminescence dyes and lanthanide complexes with silver nanoparticles
- Theoretical and experimental analysis of photonic structures for fluorescent concentrators with increased efficiencies
- Optimized excitation energy transfer in a three-dye luminescent solar concentrator
- High-Efficiency Organic Solar Concentrators for Photovoltaics
- Efficiency limits of photovoltaic fluorescent collectors
- A luminescent solar concentrator with 7.1% power conversion efficiency
- Maximising the light output of a Luminescent Solar Concentrator
- Characterization and reduction of reabsorption losses in luminescent solar concentrators
- Controlling Light Emission in Luminescent Solar Concentrators Through Use of Dye Molecules Aligned in a Planar Manner by Liquid Crystals
- The effect of photonic structures on the light guiding efficiency of fluorescent concentrators
- Increasing the efficiency of fluorescent concentrator systems
- Strongly modified [2,2′-bipyridyl
-3,3′-diol (BP(OH)2): a system undergoing excited state intramolecular proton transfer as a photostabilizer of polymers and as a solar energy collector] - Plasmon-controlled fluorescence: a new paradigm in fluorescence spectroscopy
- Innovative materials based on sol–gel technology
- Organic–Inorganic Sol–Gel Composites Incorporating Semiconductor Nanocrystals for Optical Gain Applications