Delft startup Physee puts energy producing PowerWindows to the test
5 March, 2021 by
Delft startup Physee puts energy producing PowerWindows to the test
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After achieving great results in the lab, Delft-based solar startup Physee is now starting a pilot project to test energy producing windows in a real life environment. StartupJuncture talked with Willem Kesteloo, co-founder of Physee.

Physee and PowerWindow

In 2014, Ferdinand Grapperhaus and Willem Kesteloo participated in the research group of Dr. Eric van der Kolk at Delft University of Technology. After discovering a transparent substance with interesting deflective properties, they decided to start their own company PowerWindow in 2014 and began developing energy-producing windows. Grapperhaus and Kesteloo participated in startup competitions like New Venture and PowerWindow was named ‘Europe’s best energy startup’ at the Generate15 event in Groningen.

Starting from March 30 2016, the Delft-based startup operates under the new name Physee and is housed in the YES!Delft incubator of the Delft University of Technology. PowerWindow will be Physee’s first product.

Coating and competitors

Unlike some of its competitors, like Greek startup Brite Solar (who participated in Startupbootcamp HighTechXL in 2015), Physee’s PowerWindow doesn’t rely on high-tech solar cells inside the glass. Instead, the solar cells of a PowerWindow are located in the window panes. What makes PowerWindow different, isn’t the solar cells or the glass itself; it’s the coating on the glass.

“The coating itself concentrates the light and sends it to the sides, something which sets us apart from our competitors.” Indeed, the job of this coating is to absorb just the right amount of solar light, concentrate it, and deflect it to the sides, where strips of solar cells in the window panes transform the light into electricity. All of this is achieved with windows who look exactly the same as ‘normal’ windows.

Niche market

After careful market validation, Physee concluded that there is one niche market that is perfect as a testing ground for the implementation of PowerWindows. Kesteloo: “The co-called DBFMO-contracts, projects which integrate all aspects of construction: design, building, finance, maintenance and operation. This in combination with BREAAM certification.”

BREAAM certified buildings are usually constructed with sustainability and energy efficiency in mind and as such could benefit a lot from a product like PowerWindow. The people who construct projects like this are also more willing to invest in energy efficient technology, which is important as PowerWindows will cost 30 to 60 percent more than normal windows.

Pilot project in Eindhoven

Recently, Physee received a 350.000 euro investment from the Netherlands Enterprise Agency (Rijksdienst voor Ondernemend Nederland, RVO), intended for innovative early-stage companies. Kesteloo: “After seeing promising results in the lab, this early-stage investment enables us to make our product market ready and to expand our team.”

The investment enabled Physee to start a pilot project to test the PowerWindows in a real-life environment. Up until now, Physee has been testing the PowerWindows in the lab, using the solar lamps made by fellow YES!Delft startup Eternal Sun.

In June, together with their partners OVG Real Estate and Rabobank, Physee will install thirty square meters of PowerWindows during the renovation of the Fellenoord office building in Eindhoven, a BREEAM certified DBFMO-project. PowerWindows will be installed on every floor of the building, and in every direction, making it possible to test them in a range of different conditions.
The project will start in June and will run until December 2016. Sometime during the pilot project, the official launch of Physee will take place.

Goals and growth

The main goal of the pilot project is to optimize the coating. Ultimately, Physee wants to produce a window that looks like… a window. Kesteloo: “A normal window has between six and nine coatings, that combined give the window certain set light-, heath- and isolation characteristics. We want our PowerWindows to have exactly the same characteristic as a normal window.” This gives them the unique business case of having a normal window, with the invisible capability of producing energy. Kesteloo: “I think the days of single-purpose materials are gone. PowerWindow will be a multi-purpose window.”

A secondary goal is to improve the efficiency of the windows. This is also dependent on the coating. If the pilot project is successful, Physee will be needing additional money for further growth. Kesteloo: “Then we will need around 1 to 2 million euro. This could be achieved either through partners or through investors, a strategy we will decide on after the pilot project is finished.”


PowerWindow will be Physee’s first product, but Kesteloo also has other uses for the technology in mind: “We might develop a stand-alone product, a PowerWindow that is not connected to the grid and which is able to directly power an electrical appliance. Also, we might use our coating in other transparent products, such as car windows, greenhouses or glasses. Eventually we might even use our coating in non-transparent products, such as walls and roofs.”

For now, the main focus of Physee’s activities will be on the Dutch market and the aforementioned real estate projects. After that, expansion to the rest of Europe and the world is a possibility, with a special focus on places with a high population density and a lot of sun hours. Dubai could be such a place.

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