This is a guest post written by Giuseppe Masanotti, a Construction Engineer specialized in structural engineering. He is a member of the Urban planning Commission and of the Structural Safety Commission of the Turin Order of Engineers.
Transparent photovoltaics: glass and façades that generate energy
In the not-too-distant future, we can imagine that windows, doors, roofs and façades will no longer be passive elements, but intelligent surfaces capable of producing energy: invisible to the eye, but fundamental to the energy transition of cities.
Transparent photovoltaics and, more generally, BIPV (Building Integrated Photovoltaics) are the key to this transformation.
It is not a question of adding solar panels to roofs and façades, but of integrating energy production into the very heart of the building, transforming windows and surfaces into discreet and sustainable electricity generators.
From early research to the new generation of photovoltaic glass
The first concrete demonstrations date back to 2014, when researchers at Michigan State University developed the first prototype of a completely transparent photovoltaic panel.
The technology used organic molecules capable of absorbing invisible wavelengths (UV and near-infrared), allowing visible light to pass through and conveying the collected energy to the edges of the panel, where thin conventional cells converted it into electricity.
Initially, efficiency was very low, around 1%, but research has made great strides: today, similar modules reach 10%. This is not yet at the level of traditional silicon, but it is more than enough to pave the way for widespread adoption, especially on large glass surfaces.
One of the most promising innovations comes from South Korea, where a group of researchers has developed a moulded glass for BIPV applications.
Its unique feature lies in its surface morphology and optimised vertical orientation to the south, which overcome some of the typical limitations of transparent modules.
The test compared two modules: one made of conventional glass (3.2 mm) and one made of moulded glass (5 mm). Despite its greater thickness and a slight loss of efficiency (0.5% due to lower open-circuit voltage), the result was surprising: the moulded glass module guaranteed high performance without compromising aesthetics, making it the ideal solution for integrated vertical photovoltaic façades.
How transparent photovoltaics work
Transparent panels are modules that allow visible light to pass through but absorb UV and IR rays, converting them into electrical energy. They can be:
- Glass-glass (sandwich), with integrated photovoltaic cells
- Active solar glass, in which the material itself produces energy
The second type is the most interesting and is based on different types of transparent modules:
- With silicon gel – production up to 100 W per square metre
- Organic-based – production up to 300 W per square metre
- Graphene-based – very promising but still under study and refinement
Current efficiencies reach 10%, but their strength lies not so much in the performance of the individual cell as in their ability to cover large vertical surfaces that cannot normally be used with conventional systems. Potentially, all the glass façades of a skyscraper could be used.
Real-world applications: Takanawa Gateway Station
Although these technologies are still in their infancy, the first applications are beginning to be installed and tested on functioning buildings, where it is possible to verify the effectiveness, durability and visual impact of these new panels.
Takanawa Gateway Station in Tokyo, a busy railway station is trialling a new application for solar photovoltaics. With its large windows covering almost the entire façade, this building is the ideal prototype for this type of application: large surfaces, large electricity production.
The technology, currently under development, involves a transparent coating, invisible to passers-by, that can generate electricity from exposure to sunlight.
Challenges and prospects of an invisible revolution
Transparent photovoltaics is currently one of the most promising innovations for sustainable architecture: it preserves aesthetics and transparency, transforms previously passive surfaces into energy generators, reduces air conditioning loads by filtering UV and IR rays, and increases property values and energy certifications for buildings.
There are still challenges to overcome: efficiency is still lower than standard panels, costs are up to three times higher per square metre, and the durability of emerging technologies needs to be tested over the long term.
However, scientific advances and concrete examples of integration show that we are facing a change that is already underway. In the coming years, thanks to the push for NZEBs (Nearly Zero Energy Buildings) and urban smart grids, windows and façades will no longer be simple barriers between inside and outside, but invisible energy generators, an integral part of self-sufficient and resilient cities.
The future of architecture will not only be made of glass and steel, but of intelligent surfaces that capture sunlight and transform it into electricity: the silent revolution of energy-producing glass has only just begun.
Photos: Leo Okuyama & Patrik Bloudek
