Gavin D. J. Harper

A window on thefuture of solar glazing

Welsh Energy Sector Training (WEST) Conference,Liberty Stadium, Swansea, Wales,

16th September 2014

g.harper@glyndwr.ac.uk@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 Harperg.harper@glyndwr.ac.ukwww.gavindharper.com

http://www.cser.org.uk/

https://www.westproject.org.uk/

@gavindjharper

@CSER_PV

@LCRI_WEST

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