Painted panels to harvest solar heat
Over sixty percent of all the energy we use comes in the form of heat. Why not use the façades of buildings to harvest that heat directly from the sun? That is the vision Calosol, a spin-off from TNO and building company Emergo, wants to realize. While the start-up is entering the market with its plug and play façade panels, plenty of fundamental research questions remain, explains co-founder and CTO Bart Erich.
It was a radical change in thinking that ultimately led to the façade panels Calosol is now commercializing recollects Bart Erich, who also is a researcher at TNO and TU/e. ‘AkzoNobel had developed a coating to cool buildings by reflecting sunlight. At a trade fair where they were presenting their innovation, I asked them “Why not turn this idea around and absorb the energy to heat the building instead?”’
‘AkzoNobel had developed a coating to cool buildings by reflecting sunlight. I asked them “Why not turn this idea around and absorb the energy to heat the building instead?”’
Capturing the invisible
This idea led to the RVO projects FITS and FITS4E in which AkzoNobel together with Emergo and TNO proved the principle. These projects were followed by the Horizon 2020 project ENVISION in which the team developed a coating that efficiently absorbs an important yet invisible part of the solar spectrum: the near infrared, which makes up about fifty percent of all radiated energy. ‘We apply this coating to specifically designed panels to be attached to building façades. The biggest advantage of the coating is that it can be produced in a wide range of colors and still absorbs enough of the energy. This is an important feature if you want to apply it in the built environment,’ explains Erich. The heat is transported via fluid in the back of the panels and acts as a heat source for a heat pump allowing it to be used for heating or warm tap water.
In the series of joint projects, the three partners further developed the panels. ‘We have tested several different set ups and colors at the SolarBEAT facilities located on top of the Vertigo building. In 2019, we applied the panels on the façade of a sports hall in Almere, where they provide heat to the showers, the floors and radiators. After that project, we have combined our panels with heat pumps in two renovation projects for social housing companies here in the region, namely Trudo in Eindhoven and Compaen in Helmond.’ The panels turned out to do an excellent job. ‘In case of a renovated row dwelling we only need to install about 15 square meters of panels to make it energy positive when combined with PV on the roof. At the moment, we are building a catalogue of the different products that are available now,’ says the entrepreneur.
Challenging research
At the same time, also in his role as an academic researcher both at TNO and at TU/e Erich is working on fundamental questions that still remain. ‘People tend to think that research into something as concrete as our panels cannot be scientifically challenging, but I strongly dispute that. For example, we are currently involved in various projects about intelligent heat management. As more components for heat capture, storage and distribution are being developed, the challenge is to find out how to combine them into smart energy systems. For example, students are now experimenting with our panels, a heat pump and a heat battery provided by Cellcius to heat and cool the offices of the Eindhoven Engine (Smart Heat Shed project). And in several RVO MOOI (Missiegedreven Onderzoek Ontwikkeling en Innovatie) projects, we are investigating associated topics like model predictive control, dynamic pricing, how to best combine our panels with heat pumps, heat batteries, and heat vessels to search for the optimal way of storing the heat harvested during the day for use during the night, weeks or seasons, and how we should control such a heat management system at level of a building, a district, and the grid.’
Besides at systems level, also at the level of the panels themselves there are ample challenges to be researched, Erich says. ‘What heat flow profiles can we expect as a result of wind? How does the energy flow in and out of the panels? How do parameters like orientation or humidity influence the efficiency of the heat transfer? In order to accurately model and control the panels, we need to know how they perform under every conceivable circumstance. Not only to harvest heat, but in case of cooling it is all about the reversed process releasing the heat. Although we have already solved many of these questions especially related to heating, for cooling questions are still open. Some involve some pretty fundamental questions. For example, we are also looking into the possibility to switch the coating between absorption and reflection, in order to use the same panels both for heating and cooling.’
"In order to accurately model and control the panels, we need to know how they perform under every conceivable circumstance."
Test village
Erich’s first priority now is to make the spin-off fly commercially. ‘At the moment, we are focusing on large projects in the range of 1000 m2 of panels or more. The minimum for projects is about 200 m2 . We are optimizing our panels to fit within the energy system of different types of buildings. My dream would be to have a small test village built here on campus where we can experiment with these kinds of technologies for energy harvesting, conversion and storage in a true everyday setting, at a real life scale. Why not build student housing where you can demonstrate and test the latest in energy solutions, and use the entire campus as a living lab for energy solutions? When you are applying new solutions at real scale, you will encounter problems you cannot foresee in the lab. The challenges are not only on the fundamental level but all the way up to the level of application. We need to address all issues on all levels in an integral approach in order to make a real difference.’