A new hybrid solar system designed to be directly integrated into windows and glass surfaces comes from an international study. While the efficiency is still minimal, it can produce hot water at 50°C
Photovoltaic-Thermal Windows for nZEB Buildings
Photovoltaic and solar glass facades are slowly making their way into sustainable architecture, paving the way for new energy solutions in nZEB buildings. In the ongoing quest for highly integrated solutions to reduce energy consumption in buildings, some are focusing on harnessing the full potential of the sun. This led to the creation of an innovative photovoltaic-thermal window by Francesco Polito, Gan Huang, and Christos N. Markides.
The researchers from Imperial College London and Karlsruhe Institute of Technology developed a hybrid system capable of using sunlight to generate both electricity and heat. This solution is particularly ideal in situations where roof or building space is limited.
The approach is somewhat similar to hybrid solar collectors (PV-T), modules that combine photovoltaic cells with a solar thermal panel. Most of these collectors are used in residential systems and can heat domestic hot water up to 60-70°C. Many manufacturers have brought this technology to both national and international markets, and the latest research focuses on PV-T collectors integrated with phase change materials (PCMs) or spectral division systems, concentration optics, etc., to further improve the application. However, hybrid solar panels still require significant roof space.
The new photovoltaic-thermal window could meet this need, allowing previously unused parts of the urban environment to generate both electricity and hot water simultaneously. The research team behind the innovation calls their solution the first semi-transparent PV-T window for building integration.
The innovative system uses semi-transparent solar glass supplied by Onyx Solar. The glass has micro-strips of amorphous silicon cells spaced apart to partially cover the surface. The heat emitted by the photovoltaic cells is captured along with the infrared heat from the incident light by a 4mm thick layer of water placed behind the solar glass. Behind that, there is a standard low-iron glass. All components are held together by two polycarbonate frames.
The system was tested under environmental conditions in London with different tilt angles of 30°, 60°, and 90°. The researchers found that at a 30° tilt, the photovoltaic-thermal window could simultaneously generate electricity with an electrical efficiency of 3.6% and provide hot water at around 50°C, with a thermal efficiency of 10.7%, on a typical summer day in London. The water temperature decreased by around 7°C, while the thermal efficiency improved to 17.6% as the tilt angle increased to 90° (vertical), with a slight reduction in electrical efficiency (3.3%). The study was published in Advanced Science.
