Inflatable solar collector provides carbon-free energy
Mirrors or lenses can concentrate a large area of sunlight onto a small area to generate heat and electricity. This technology, known as concentrated solar power (CSP), offers enormous potential for commercial energy production in North Africa, the Middle East and the southern regions of the United States and Europe, where the evening peak in power consumption cannot be effectively covered by photovoltaic cells. One obstacle, however, is that current CSP technology is too expensive to make up the shortfall. The HELIOtube project rejected conventional CSP technology requiring heavy and expensive glass-mirror parabolic troughs. Instead, they focused on developing a cheap and light-weight alternative that uses large inflatable cylinders to concentrate the sun’s rays. These are held in position by metal rings, which are part of a modular design and help rotate the tube to track the sun. Project manager Christoph Schnabel says: “The team produced a full-scale HELIOtube, 220 metres in length and 9 metres in diameter, which we installed and operate in a real-world demonstration plant.” A new approach to solar power A highly durable, flexible, lightweight and recyclable material was used to create the cylinder. The cylinder comprises three plastic films; a base film, a transparent film and a mirror film. The mirror film divides the concentrator into two air-tight chambers that run the length of the tube. Small differences in pressure between the top and bottom chambers arch the mirror film downward to create a mirror channel. This concentrates the sun rays by a factor of 100 and heats the thermal fluid running through the receiver in the upper chamber to a temperature of up to 400o C. Each HELIOtube produces around a megawatt of thermal energy and they can be connected to form a solar-thermal power station. The energy produced is used directly in various industrial processes or converted to electricity by a steam turbine. Therefore, the system can be applied at small-scale, such as for industrial heating, or at the utility-scale for large-scale generation of electricity. The rolled HELIOtube weighs 90 % less than a comparable parabolic trough and can be easily transported in a standard 40-foot shipping container and then inflated at the designated site. This significantly reduces production, transport, and installation costs. A significant bonus, the innovative material used to create the cylinder dramatically reduces the need for precious freshwater in cleaning activities. Particles like sand and dust can be blown away with compressed air, lowering water consumption. A validated technology Researchers conducted detailed wind load studies on a scale-model to identify what size of wind protection devices were needed and to determine and test the final tube geometry and field configuration. “We were able to analyse an incredible amount of data,” observes Schnabel. “It allowed us to understand and optimise the system and showcase it to potential clients, thereby putting us on the international map as a technology provider.” The large-scale HELIOtube pilot conducted in Spain demonstrated that this cheaper and less resource-intensive collector technology for CSP plants can set the standard for a reduced carbon footprint in power plants. According to Schnabel: “Our technology is probably the most flexible on the market right now and can cater to nearly every possible customer application.” HELIOtube will become an important driver in the use of eco-friendly CSP for industrial applications and electricity generation. “The ultimate goal is to increase renewables in the global energy mix and extend the use of CSP to a larger customer base and raise overall acceptance,” Schnabel concludes.
Keywords
HELIOtube, concentrated solar power (CSP), film, thermal receiver, power station
