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Transparent Solar Panels

Solar panels are becoming increasingly popular, thanks to their ability to generate electricity using free and abundant sunlight.

However, one of the factors preventing widespread adoption of solar panels is the limited space for installation, particularly in densely populated areas like cities where land and roof space are scarce. To address this issue, transparent solar panels are being introduced as a potential solution to capture solar energy in more areas.

What Are Transparent Solar Panels?


The idea of a transparent solar panel may seem counterintuitive. We know that solar panels need to absorb light to generate electricity, yet transparency implies that light can pass straight through.

Transparent solar panels generate electricity using photovoltaic (PV) cells (also known as solar cells). These are similar to the cells that make up traditional solar panels. The difference is in how light is directed towards these PV cells.

Traditional solar panels consist of multiple PV cells arranged in a grid pattern. These cells collect solar energy directly from the sun and must be placed at an angle to maximise their exposure to sunlight.

Transparent solar panels, however, are mostly made up a transparent material. This material captures invisible wavelengths of sunlight and redirect them towards thin strips of PV cells positioned at the panel's edges. This allows transparent solar panels to be placed vertically, expanding the range of potential installation locations.

How Do Transparent Solar Panels Work?


Visible light (the light that we can see) makes up only a small portion of the total energy our sun produces. Light from the sun is made up of lots of small particles of energy called photons. A photon's energy level will determine its position on the electromagnetic (EM) spectrum.

Traditional solar panels absorb as many visible and infrared photons as possible to produce the maximum amount of energy. Therefore, traditional solar panels are often opaque. Transparent solar panels, however, make use of a different part of the EM spectrum.

Transparent solar panels absorb photons of infrared and ultraviolet (UV) light whilst allowing photons of visible light to pass through. Infrared and UV wavelengths of light are not visible to our eyes. This means that we do not notice they have been absorbed so the panels appear almost perfectly transparent to us.

The working principle of transparent solar panels. Visible light from the sun is able to pass through, but infrared and ultraviolet light is absorbed by particles and refracted towards photo voltaic cells at the edge of the panel.
The working principle of transparent solar panels.

Thin Film Luminescent Solar Concentrator

The main component of some transparent solar panels is a transparent luminescent solar concentrator (TLSC). This is a thin slab of highly refractive material containing small light-absorbing particles (usually organic salts).

These particles absorb photons of infrared and UV light, which causes them to glow. The light that these particles glow with is not visible to our eyes and is made up of photons of low-energy infrared light. This process of shifting photons down the EM spectrum is called down shifting photoluminescence.

The high refractive index of the TLSC allows the emitted infrared photons to be guided and concentrated on thin PV cells at the edges of the panel. These PV cells are where the electricity is generated.

Semi-Transparent Solar Panels

Semi-transparent solar panels are different from fully transparent solar panels as they are only around 60% transparent. Semi-transparent solar panels work in the same way as traditional solar panel. However they are very thin to achieve a partially see-through appearance.

Alternatively, semi-transparent solar panels can be made through segmentation. Here which gaps are left in between adjacent solar cells to provide some transmission. This technique is not ideal however because the solar panel active area (the total area that can absorb solar energy) decreases as the transparency increases. The semi-transparent solar cells there is always a tradeoff between transparency and efficiency.

The semi-transparent nature of these solar panels means that their efficiency is lower than traditional opaque solar panels. To improve the efficiency of transparent solar cells, research is focused on developing higher efficiency semiconductors including amorphous silicon, organic semiconductors and perovskite materials.

Transparent Solar Panels vs Opaque Solar Panels


As transparent solar panels continue to improve, is it possible that they will replace our traditional solar panels entirely?

Traditional, opaque solar panels are are able to capture much more solar energy and are also significantly more efficient. Installation of these panels is limited in densely built areas, but they a great option for rural and residential areas where land and roof space is widely available.

That doesn't mean that we should discount transparent solar panels. Although their efficiency is low, they can be installed into spaces where glass is already present. It's thought that a skyscraper built using transparent solar panels in place of glass could generate a quarter of its energy needs via solar energy.

Traditional, semi-transparent, and transparent solar panels each have advantages which make them suited to different applications.

Solar Panel Type Advantages Disadvantages
Opaque Solar Panel
  • Currently the most efficient solar panel available (up to 22% efficiency).
  • The technology is more established, hence they are currently much cheaper to buy and install.
  • Should be placed at an angle to capture as much solar energy as possible - this requires a lot of space to use.
  • Current solar panels are rigid, thick and opaque. There are some situations where opaque solar panels can't be installed.
  • Limited space for applications, especially in cities with many muitple storey buildings.
Semi-Transparent Solar Panel
  • Higher efficiency than fully transparent solar panels.
  • Can use same materials as opaque solar panel technology, hence efficiency is improving quickly.
  • Usually slightly tinted, which may be off-putting when used in place of windows.
  • Trade off between transparency and efficiency - the more transparent the solar panel, the lower its efficiency.
Transparent Solar Panel
  • Panels still work when placed vertically, providing more options for use.
  • Better aesthetics as panels can be integrated into existing glass surfaces.
  • Ideal for use in densely built areas where open space is limited.
  • Low efficiency, with the maximum efficiency thought to be around 5%.
  • Transparent solar panels are more fragile than opaque solar panels, and may not have as long of a lifespan due to the organic materials they are made with.

The Future of Transparent Solar Panels


Being able to use transparent solar panels opens a wide range of potential applications. Any outdoor object that currently uses glass could be installed with transparent solar panels to generate electricity.

One of the most anticipated uses of transparent solar panels is with building integrated photovoltaics (BIPV). Transparent solar panels could be installed into the windows, facades, and skylights of new and existing buildings. Imagine cities where skyscrapers are able to generate electricity through their glass exteriors. It is thought that in the U.S, transparent solar panels have the potential to provide 40% of the country’s energy demand when applied to every building’s glass surfaces.

For individuals, transparent solar panels could also have a big benefit. For example, transparent solar panels could be used to charge the battery of your mobile phone or other portable electronic devices. We might also see them being used in the windshields and sunroofs of our cars to generate energy to power electric vehicles.

Transparent solar panels are currently expensive and further technological development is needed before we start to see them in our everyday lives. Until then, traditional solar panels will continue to provide us with an affordable way to harvest solar energy.

Further Reading


Foldable OLED technology is expensive Flexible Solar Panels and Solar Cells

The development of flexible solar panels and solar cells has opened new avenues for the use of solar technologies. As a source of clean and renewable energy, solar power is a key solution to tackling climate change

Read more...
OLED device Solar Cells: A guide to Thoery and Measurement

A solar cell is a device that converts light into electricity via the ‘photovoltaic effect’. They are also commonly called ‘photovoltaic cells’ after this phenomenon, and also to differentiate them from solar thermal devices.

Read more...

Contributors


Written by

Caitlin Ryan

Scientific Writer

Diagram by

Sam Force

Graphic Designer

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