Researchers have unveiled a new self-adjusting ‘solar window’ design that is able to adapt to different light conditions, allowing for solar energy to be captured during the day, but for extra light to pass through as it gets darker in the evening or early mornings.
Using a new generation of dye-sensitised solar cell design, researchers in France and Spain have developed a new type of solar module that is able to become more transparent in low light conditions, creating the potential for solar cells embedded in windows that avoid inadvertently blocking too much natural sunlight from entering a building.
Previous designs for solar windows were unable to adjust the amount of light they let pass through into buildings like offices and homes, making it difficult to balance natural lighting and heating in buildings with an ability to generate solar power.
When there are low levels of sunlight, windows with embedded solar cells could leave the interior of a building darker, as the embedded solar cells blocked what little light there was from passing into the building.
However, in a new scientific research published in the journal Nature Energy, research led by Dr Renaud Demadrille of the University Grenoble Alpes, has utilised next generation ‘dye sensitised’ solar cells that are activated by sunlight, to develop a new solar module design that can adjust is transparency based on the amount of available light.
“Semi-transparent photovoltaics only allow for the fabrication of solar cells with an optical transmission that is fixed during their manufacturing resulting in a trade-off between transparency and efficiency. For the integration of semi-transparent devices in buildings, ideally solar cells should generate electricity while offering the comfort for users to self-adjust their light transmission with the intensity of the daylight,” the research paper says.
The researchers utilised the ‘dye sensitised’ solar cells, which are a type of thin-film solar cell that is able to convert sunlight into electricity through the layering of certain chemicals. The cells can also be tuned to a particular colour on the visible spectrum, allowing windows to change colour as the amount of available sunlight increases.
As the chemicals themselves create exhibit the necessary semiconductor properties to work as a solar cell, the technique avoids the need for the opaque silicon wafers used in conventional solar panels and makes the dye-sensitised cells suitable for embedding into surfaces like windows.
“For the development of smart photovoltaic windows and their massive integration in buildings, variable and self-adaptable optical properties would be very valuable. The ultimate aim would be that solar cells, transparent under low-light conditions, could tune their absorption under more intense illumination to produce energy without any external manipulation,” the research paper says.
Currently, the conversion efficiencies of dye-sensitised solar cells are comparatively low, often below 10 per cent in many commercially available cells, but the technology has some promise due to the prospect of substantially lower production costs.
The new solar cell designs allow for more light to pass through the ‘solar window’ when there is less sunlight available, and use more of the sunlight to produce power when it is very sunny, allowing the windows to balance both the amount of natural light passing into the building and the amount of energy captured.
The design, developed by Dr Demadrille and the research team, allows for around 60 per cent of the light hitting a window to pass through when it is dark. However, during daylight hours when the amount of available sunlight is significantly higher, this drops to 27 per cent as the embedded solar cells activate.
The researchers say that further work is required to improve the long-term stability of the dye-sensitised cells, which are prone to degradation over time.
The current designs were able to achieve a stable conversion efficiency of up to 4.17 per cent over a 50-day period, but further work on improving this reliability, and the conversion efficiency, will be needed before the solar windows are deployed on a large-scale.
In May, researchers at the University of Sydney announced that they had successfully demonstrated the long-term durability of perovskite solar cell designs, another form lower cost of next-generation solar cells which also have the potential to be embedded in surfaces of buildings, or even vehicles.
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