TU Delft student of Sustainable Energy Technology Stefan Roest has developed a new type of hybrid solar collector with a higher efficiency and a longer lifespan than the hybrid panels on sale today.

A hybrid solar panel combines a photovoltaic solar cell that converts sunlight into electricity with a thermal solar collector to harvest infrared energy for heat.  So far neither the electricity production or heat production efficiency has been especially interesting for consumers.  The research trend instead has been to find ways to use infrared for electricity production.

Basically a hybrid solar collector is a combination of a photovoltaic solar panel and a thermal solar collector. The residual heat from the photovoltaic cells is used to heat a circulating fluid. Customarily the fluid flows through a system of tubing on a copper or aluminum sheet.

A great deal of infrared energy is needed to heat the fluid in the tubes and the supporting structure. The structure is why the solar collector needs to be fitted with a transparent cover that helps to retain the heat.  This design gets quite hot and the materials used in the photovoltaic solar cell degrade quickly under temperatures of around 120º C. When the design heats up the efficiency is reduced.  At 120º C the efficiency loss get to around 20 per cent and the lifespan is cut to between five and ten years.

Roest’s graduation research as part of a Master’s degree in Sustainable Energy Technology developed a new type of hybrid solar collector with increased electrical efficiency and a longer lifespan.

Roest’s design doesn’t require a transparent cover. The fluid flows through a large number of small aluminum channels directly under the solar panel instead of through a built up tubing on a support sheet. Thus, less heat is required to heat the water sufficiently for household use. Roest then chose not to use a crystalline silicon PV solar panel, opting instead for a thin film solar cells because it’s easier to draw heat from this type of solar cell. Getting rid of the cover meant that the heat of the solar panel would be reduced to around 80º C.

Roest Hybrid Solar Panel from TU Delft. Click image for the largest view.

The design reminds one more of a “heat sink” than an “infrared absorber”.

Using thin film photovoltaic cells exploits their performance.  Thin film cells perform relatively well at high temperatures. At an operating temperature of 80 degrees the efficiency loss is down to 10%, instead of the 20% of crystalline silicon photovoltaic cells. This will more extend  Roest’s hybrid solar collector to an estimated lifespan of 15 to 20 years.

Miro Zeman, professor of Photovoltaic Materials and Devices at TU Delft, who oversaw Roest’s work commented saying, “This innovative design could play an important role in the development of affordable and efficient hybrid systems for household use.”

The second half of the story is Roest needed a means to test his new design.  So Roest also built an actual solar simulator that he used to test the efficiency of his prototype hybrid solar panel.  This prompted considerable commercial interest in the solar simulator, which motivated Roest and a partner to start the TU Delft spin-off company Eternal Sun, so they could quickly put the solar simulator on the market. Eternal Sun recently came out on top at the European finals of the BE.Project, a competition for student-entrepreneurs.

Roest Solar Simulator at TU Delft

TU Delft quickly patented the relevant technology and The Eternal Sun team has now grown to include six students and recent graduates, with five solar simulators sold since January.

Roest has been at this awhile. In 2007, he was the team leader of the Nuon Solar Team that won the World Solar Challenge in Australia with the solar car Nuna4.

That’s two new products out of one project.  Interested parties can find contact information for Roest at the end of the TU Delft press release page and the Eternal Sun link.

Roest has taken hybrid panels to a new level, but this isn’t over yet.  More is sure to come.  But the young team at Eternal Sun has a great start with the simulator selling now and the simulator will help every researcher that has one to speed up their work.


Name (required)

Email (required)


Speak your mind