Solar collectors that are safer, simpler and more efficient

Background 

Parabolic trough solar collectors harvest the sun’s energy by focusing its radiation onto a receiver containing a heat transfer medium, typically either steam, thermal oil or liquid salt. However, in the event of a fault, this system may pose a danger to people and the environment, given the high pressure at which the medium circulates through the receiver. This is a significant risk, not least because a 50 MW solar power plant may use up to one million litres of thermal oil, for example. 

Airlight Energy Manufacturing SA, headquartered in Biasca, Switzerland, has prototyped an innovative parabolic trough solar connector that eliminates this risk whilst also improving efficiency and reducing costs, based on a simple, elegant solution. By using air as the transfer medium, this novel system achieves two key benefits: Air can be heated to temperatures upwards of 600 °C, and it can also be transferred to a pebble-bed storage unit. At night, the heat flow direction is simply reversed to deliver the solar energy as and when it is required. 

Solar power is collected by means of a parabolic pressure chamber enclosed by two membranes. The first is a silicon fibreglass membrane that is pulled over the base structure. The cover membrane is made from transparent, low-refractive ETFE (ethylene tetrafluoroethylene), a lightweight material that also offers high UV transmittance. The chamber is pressurised to a few millibars using a variable-speed fan, which gives the parabolic reflector a perfect curvature and ensures a very high radiation concentration on the receiver. 

Airlight Energy also designed an innovative support structure for the trough collector using lightweight, pre-cast concrete. Rotating the reflector on the fixed foundations thus requires very little energy, enabling it to track the sun’s course and to collect a maximum of solar energy. In addition, this also makes it possible to move the collector to a safe position during high winds. 

Challenge 

The solar collectors are intended for desert regions with strong sunlight, such as those found in more remote parts of Africa, Mexico, the Arabian Peninsula, India or Australia. In these challenging environments, the electronic and electrical equipment installed in each collector, including the power distribution system and the switchgear, needs to be especially robust. Maintenance interventions are costly and time-consuming, and finding appropriately qualified local staff may also be an issue. Another issue that needed to be addressed is the possible lack of locally available spare parts. 

Solution 

Eaton not only met Airlight Energy’s switchgear requirements, but also provided the right kind of technical and logistical support. The company thus chose Eaton’s miniature circuit breakers and FAZ and FRCmM residual current devices, as well as the EMR4 measuring and monitoring relays and the NZM2 circuit breaker, which is used as a master switch. The devices are primarily used to protect the cables and systems against overcurrents or short circuits. Airlight Energy was impressed by the overall package that Eaton had to offer, especially in terms of product and material quality, which made it the right fit for this demanding application. 

What’s more, the busbar system used for mounting the xEffect devices made the installation of the miniature circuit breakers and the residual current devices in the plant’s control panel significantly easier. The quick and easy installation, together with the versatile range of application options, reduced manufacturing costs whilst also simplifying any future on-site maintenance. Additionally, the FAZ miniature circuit breakers, which are rated to 63 A, also come with a number of on-board features that further simplify maintenance. These include a red-green contact position indicator, guides for secure terminal connection, a protective cover and a 3-position DIN-rail clip. The FRCmM residual current circuit breakers meanwhile also come with a contact position indicator and offer a wide range of rated currents. 

Thanks to their comprehensive international approvals, the devices also support Airlight Energy’s export plans, ensuring that its solar power plants can be installed anywhere in the world. Add to this Eaton’s global presence and local support services, which enable the company to obtain spare parts quickly and have them delivered to solar power plants even at remote locations. 

Results

The project is supported by the Swiss Federal Office of Energy. Technical support for the project comes from University of Applied Sciences and Arts of Southern Switzerland (SUPSI), the Swiss Federal Institute of Technology in Zurich (ETH) and the Paul Scherrer Institute. The third prototype is currently undergoing a series of on-site tests in Biasca, Switzerland, to collect the necessary data and validate the underlying mathematical models. As part of these tests, Airlight Energy is recording, documenting and visualising all essential indicators, including the collector temperature and the energy being stored in the pebble bed.

Eaton is proud to supply Airlight Energy with its flexible, rugged and globally certified range of circuit protection devices. The two companies will continue their partnership in order to further develop the technology and install solar capacity where it is most needed and effective, anywhere in the world.