A lot of surface area in the built environment is suitable for the generation of solar energy. Optimal use of the facades and roofs for energy generation on buildings is paramount to reach our climate goals. To date, various pv solutions are on the market or under development for the opaque parts of buildings. However, a largely unexploited surface area are the windows of a building, offering a huge largely unexploited potential. Developing pv products that combine the aspects of a window with energy generation is a challenge. TNO has joined efforts with academics and industry to develop a new pv window concept. This resulted in a prototype that we want to develop together with construction companies and the glass industry into a market-ready product.

Creating an energy producing window, without affecting its prime functions is a technical challenge. This is the reason that this potential has largely been neglected over the years. A window needs to provide an unhindered see through and allow enough light to penetrate, while a pv panel ultimately utilises most of this light. Balancing these contrasting requirements will result in a slightly tinted pane that nevertheless generates significant amounts of solar energy.

Spot on the horizon

A flexible and translucent perovskite module

Perovskite as an upcoming thin film technology is specifically suited for the application in pv windows. It has the potential to homogeneously cover surfaces with a neutral hue. Creating a microscopic pattern of a thin layer of opaque perovskite will result in transparent surface that is relatively easy to manufacture. In this way we can tweak the amount of sunlight that penetrates and the energy that is generated.

Energy-neutral buildings

We have demonstrated this concept on ten by ten centimetre laboratory sample with an efficiency of five percent. A prototype with 50% perovskite coverage was shown to retain 40% of the efficiency. Within two years we aim to improve the five percent efficiency to ten percent without compromising aesthetics and transparency.

Using glass facades as solar windows

Glass curtain walls are important architectural features and widely applied on office buildings. If we can make these suitable for energy generation it opens a huge, to date unexploited surface area. We estimate that in the Netherlands alone 110 square kilometre is available, amounting to 11 gigawatt peak (GWp) of power generation.

Together with partners we want further develop this technology into a market-ready product for Dutch business and industry. The aim is to develop glass that lets in at least 20% of the sunlight while converting at least 10% into solar power (10% efficiency). In this way, PV windows can make a substantial contribution to making buildings energy-neutral.

Products on the market

In this relatively new field, there are high expectations about innovative products that will appear on the market in a few years. These windows will likely contain solar cells that cannot be seen by the naked eye. Unfortunately, these products are not yet on the market.

What is already on the market are windows in which the solar cells are incorporated into the window as thin stripes. The solar cells are visible when close to the window, but less visible from a distance. Many people do not find these stripes annoying and therefore consider these so-called semi-transparent solar windows.

As far as we know, there are currently three manufacturers offering such a product; in alphabetical order:

Cooperate with TNO on the development of solar windows?

Please contact Roland Valckenborg

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