A window on the future of solar glazing
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Transcript of A window on the future of solar glazing
Gavin D. J. Harper
A window on thefuture of solar glazing
Welsh Energy Sector Training (WEST) Conference,Liberty Stadium, Swansea, Wales,
16th September 2014
[email protected]@gavindjharper
www.gavindjharper.comhttp://orcid.org/0000-0002-4691-6642
Solar Concentrators
• Solar concentrators collect sunlight from a very wide area, and concentrate it down to a much smaller area.• A smaller quantity of photovoltaic material can be
located at the smaller area.• This makes more efficient use of the photovoltaic material.• This could potentially lead to cost reductions in photovoltaic
devices.
• There are “large scale” solar concentrator technologies – e.g. “mirrors in the desert”, but technologists are also investigating whether the principle could apply on a smaller scale for BIPV.
Organic SolarConcentrators(OSC’s)• A variation on
this technology developed at MIT is known as “luminescent solar concentrators” (LSC’s)
Organic Solar Concentrators
• OSC’s consist of a sheet of plastic, surrounded by photovoltaic devices on their edges.• The plastic is “sprayed” with a dye.• The combination of dye and plastic act as a
“waveguide”.• A waveguide is a device which captures light and
directs it along a path to a particular location.• The edges of the sheet appear bright as the light
is concentrated.• It is this concentrated light that the photovoltaic
device captures.
Organic Solar Concentrators
• OSC’s consist of a sheet of plastic, surrounded by photovoltaic devices on their edges.• The plastic is “sprayed” with a dye.• The combination of dye and plastic act as a
“waveguide”.• A waveguide is a device which captures light and directs it
along a path to a particular location.• The edges of the sheet appear bright as the light is
concentrated.• It is this concentrated light that the photovoltaic device
captures.
Organic Solar Concentrators
• Light hits the plastic, the dye absorbs the light.• The energy is thereby transferred to the dye, causing the electrons in
those molecules to jump to a higher energy level.• When the electrons fall back to a lower energy level, the dye
molecules release that energy into the plastic sheet, where it gets stuck.• The light can’t escape the plastic, this is known as total internal
reflection.• (This is the same principle used to transmit data using light over fibre optic
cables).
• It just bounces around in the material, ultimately making its way to the outer surface. At the outer surface, the solar cells are waiting to absorb the light and generate electricity.
Organic Solar Concentrators
• Approximately 80% of the re-emitted photons are trapped within the waveguide by total internal reflection for ultimate collection by a PV device mounted on the substrate edges.
• Photon loss (dashed lines) occurs via non-trapped emission or absorption by other dyes.
• Light transmitted through the first OSC can be captured and collected by a second OSC whose dyes absorb and emit light at lower energies for electrical conversion at a second, lower bandgap PV device.
• Alternatively, the bottom OSC can be replaced by a low-cost PV cell or used to heat water in a hybrid PV thermal system.
Image & Text from: M.J. Currie, J.K. Mapel, T.D. Heidel, S. Goffri, M.A. Baldohttp://softsemi.mit.edu/Research/photovoltaic-devices/organic-solar-concentrators
Drawbacks to OSC’s
• While the light energy bounces around in the plastic, it sometimes gets reabsorbed into the dye molecules and ends up emitted as heat. This energy, then, never makes it to the solar cells.
Luminescent Solar Concentrators• Luminescent Solar Concentrators are an
evolution of the Organic Solar Concentrator.
• The plastic of an Organic Solar Concentrator is replaced with a sheet of glass coated with a dye.
• A type of aluminum called tris(8-hydroxyquinoline) is added to the dye molecules.
• These aluminum molecules cause the dyes to emit light waves at frequencies the dyes can't absorb.
• This stops light loss through re-absorption as the light makes its way to the solar cells at the concentrators edge.
An image of a Luminescent Solar Concentrator under test.Image: Viktoria Levchenkohttp://www.researchgate.net/profile/Levchenko_Viktoria/publications
Device Duraability• At the moment, this technology is one to consider for the
future.• The challenge is that the dyes used within the device are
unstable and over a period of three months or so degrade.• Work is ongoing to improve the performance of these
devices.
Pythagoras Solar Windows
Image from: Pythagoras Solar, www.pythagorassolar.com
Pythagoras Solar Windows
Image from: Pythagoras Solar, www.pythagorassolar.com
Pythagoras Solar Windows
• Stacked its solar cells.• Appears like venetian blinds inside a window pane, so
you can still see the view while generating electricity.
SolarWindows
Images from:Pythagoras Solar
Dye SensitisedSolar Cells
The modern version of a dye solar cell, also known as the Grätzel cell, was originally co-invented in 1988 by Brian O'Regan and Michael Grätzel at UC Berkeley
Dye Sensitised Solar Cells
• Simple to make using conventional roll-printing techniques• This could allow for “continuous” rather than “batch” production.
• Semi-flexible and semi-transparent which offers a variety of uses not applicable to glass-based systems• Utilises many low cost materials.
• HOWEVER, uses small amounts of platinum and ruthenium which are expensive and have proven very hard to eliminate from the process.
• Challenges with dye stability / degradation mechanisms.• European Photovoltaic Roadmap suggests that these degradation
mechanisms can be overcome and DSC’s will make a significant contribution to the solar generation mix by 2020
Honeycomb Patterned Thin Film Devices• Honeycomb patterned thin film devices capture some
sunlight from PV material deposited in a “honeycomb” pattern, but allow light to pass through the middle of the hexagons.• The material blends “Fullerenes” (carbon) and
semiconductor materials.
Images Brookhaven / Los Alamos National Laboratory
Honeycomb Patterned Thin Film Devices• “The material stays transparent because the polymer
chains pack densely only at the edges of the hexagons, while remaining loosely packed and spread very thin across the centers…The densely packed edges strongly absorb light and may also facilitate conducting electricity…while the centers do not absorb much light and are relatively transparent.”• “Combining these traits and achieving large-scale
patterning could enable a wide range of practical applications”
Lead scientist Mircea Cotlet, Brookhaven’s Center for Functional Nanomaterials
Standalone Window for Low Voltage DC• Developed by Nihon
Telecommunication System Inc.• ‘Stand Alone’ does not require
interconnection with circuits in building.• Growing use of low voltage DC in
consumer electronic devices.• Avoids the losses associated with
converting DC-AC with an inverter, and then back from AC-DC.
StandaloneWindow for Low Voltage DC• Many portable
electronic devices have converged around USB as a charging standard.
Gavin [email protected]
http://www.cser.org.uk/
https://www.westproject.org.uk/
@gavindjharper
@CSER_PV
@LCRI_WEST
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