PHYSEE was founded by Willem Kesteloo and Ferdinand Grapperhaus in September 2014. It is a spin-off from research conducted at the department of Radiation, Science & Technology (RST) at the Delft University of Technology on Luminescent Solar Concentrators led by Erik van der Kolk.

PHYSEE believes that sustainable innovations will only become and remain successful if they are without compromise. Meaning that the innovation should be non-intrusive and cost-efficient. It is from that believe PHYSEE developed PowerWindow.


PowerWindows are patented and transparent windows that convert light into electricity. Conventional glass reflects about 30% of the incoming light, PowerWindows instead collect this light with a coating on the outside windowpane, transport it through the glass to the edges of the window, and convert it at solar cell strips inside the window frame. Combined with a thermal storage system, PowerWindows can save up to 50% of the total energy demand (electricity and heating) when renovating conventional commercial buildings, and up to 100% of new constructed commercial buildings, with a payback time of 3-5 years. PowerWindow is the Ecological, Economical, and Aesthetical innovation to make the built environment energy neutral.

Company Profile
Incorporation 2014
Website Ferdinand Grapperhaus
Willem Kesteloo
Employees 16


Company history and milestones
September 2016 Physee wins the Postcode Lottery Green Challenge
January 2017 Physee joined the Dutch trade mission to CES 2017 in Las Vegas
June 2017 First PowerWindows are installed in Amsterdam
June 2017 Awarded as Technology Pioneer by World Economic Forum
September 2017 PHYSEE is B Corp certified by meeting rigorous standards of social and environmental performance, accountability, and transparency
March 2018 One of the winners of the NIPIM World Start-up Competition
May 2018 Physee raises 1.5 million Euros to accelerate development of smart and sustainable building facade solutions


Physee PowerWindow from Ruben Hamelink on Vimeo: