Hans-Eggenberger-Prize 2014 for innovative solar technology
The mechanical engineer Thomas Cooper developed for his PhD thesis a solar power system of cost-effective parabolic trough concentrators coupled to high-efficiency photovoltaic cells. He was awarded the Hans-Eggenberger-Preis 2014.
Thomas Cooper has been awarded the Hans-Eggenberger-Prize 2014 (prize money: 10'000 CHF) for his PhD thesis entitled “High-concentration solar trough collectors and their application to concentrating photovoltaics.” Now a postdoctoral researcher in the Renewable Energy Carriers lab of Professor Aldo Steinfeld, Cooper began his PhD in 2010 in the same lab. Since then, his PhD research has pioneered technologies which can drastically increase the efficiency while simultaneously reducing the cost of solar power. The principle, known as concentrating photovoltaics (CPV), consists of using tracking mirrors to focus the sunlight before it reaches the solar cell. By concentrating solar radiation more than 500 times, the same amount of electricity can be produced using much less solar cell material. Moreover, the concentrated light allows the solar cell to operate more efficiently. But it’s not enough to use conventional mirrors to concentrate the light; in order to be cost-competitive the mirror material must be as cheap as possible.
Pneumatic multilayer trough mirror
This is where the first major innovation comes into play: a novel thin polymer foil reflector which is precisely inflated to form the shape of four tangentially connected circular arcs. Remarkably, this shape can always be designed to match the performance of a parabolic mirror, which was previously thought to be the ideal shape for a solar reflector. In addition to its superior optical performance, the inflated mirror also provides an enclosed balloon which protects the solar cells and other electrical equipment.
The degree by which the light is focused, called the concentration ratio, is a key parameter in the design of the system. In order make use of triple-junction solar cells, with efficiencies now surpassing 40%, concentration ratios of greater than 500 times are required. Such high concentrations were previously only possible with point-focus mirror systems, which are typified by expensive-to-produce three-dimensional shapes. The problem is that the cheaper and more robust alternative line-focus mirror systems have a theoretical concentration limit of around 200 times.
Groundbreaking secondary concentrator
This is where the second major breakthrough of this work comes in: a secondary non-imaging concentrator that can break the concentration limit of a line-focus based system and boost it well above 500 times. This novel secondary concentrator is specifically optimized to work in conjunction with the inflated primary mirror.
The research of Prof. Steinfeld’s lab was carried out in collaboration with Airlight Energy - a Swiss cleantech provider focusing on unique solutions for solar power - and the University of Applied Science of Southern Switzerland, and was financed by the Swiss Commission for Technology and Innovation. A full-scale prototype of the system was constructed at the headquarters of Airlight Energy in Biasca, Switzerland. The first test of the prototype witnessed the highest solar concentration ever measured on a parabolic-trough-based system. Furthermore, a maximum solar-to-electricity efficiency of 20.2% was measured: a world record efficiency for a trough-based PV system.
The multidisciplinary work has fused together aspects of mechanical, electrical and civil engineering sciences to achieve a robust design. A novel construction based on a cast concrete frame offers superior stiffness, wind-resistance, and a long lifetime. Futhermore, this resource is widely available resource even in remote areas of developing nations, and the vast majority of the structure can be constructed on site using local labor content. The mirrors, which would represent a significant weight and cost of a conventional system, are polymer membranes less than one tenth of a millimeter thick, which can be transported in rolls; a clear advantage for remote locations, and also advantageous at the end-of-life of the system. The solar cells themselves, are more than 500 times smaller than for a conventional system with the same power output, implying a significant reduction in raw material requirements.
The design represents a paradigm shift in solar photovoltaics towards lower-cost structures which are capable of spanning large areas and thus producing large power outputs. Ultimately, the methods and general design concepts presented in this work open new avenues for concentrating solar collectors, reducing their cost, increasing their efficiency, and widening their range of potential applications.
