The EPFL researchers have managed to merge antennas and solar cells in a mixed device that promises unprecedented efficiency. It is a first step towards the development of more compact and lighter satellites, but also to the improvement of mobile communication systems used in case of disaster.
Traditionally, telecommunication antennas and solar cells do not mix. They must function independently to not interfere. This constraint has such an impact on the weight and size of satellites: they must have an area large enough to accommodate both an antenna system - for transmitting and receiving data - and solar panels for the electricity supply.
As part of his master project carried out within the Perruisseau-Carrier Group, Philippe Dreyer proposes to merge antennas and solar cells. In collaboration with Transparent Conductive Oxides (TCOs) group of the photovoltaic Laboratory (PV -LAB), he has developed a joint surface, which helps maintain excellent performance from the antenna and from the photovoltaic cell.
It will substantially reduce the volume, weight and cost of satellites. Portable and autonomous communication stations, which are often used to establish contacts in natural disasters, could also benefit from this new discovery. With this new technology, they could become lighter and therefore move more easily. 'Our approach is compatible with flexible implementations. It is possible to bend our device, so that it unfolds once arrived in the disaster areas' illustrates Professor Perruisseau-Carrier, who oversaw the project.
A simple 'layers' structure
For their study, researchers have favored the use of so-called “reflectarray” (RA) antennas, which have the advantage of being flat, inexpensive and highly efficient. They combined these antennas with thin solar cell made of amorphous silicon layers, developed by the Photovoltaic and Thin Film Electronics Laboratory (PV -Lab).
The device is composed of solar cells on which a set of conductors (resonators) is tabled. This structure “in layer' preserves up to 90% of the photovoltaic performance. 'This is not the first attempt to merge antennas and solar cells. But our method is special as it provides good performance for both the antenna and both the photovoltaic device, all without affecting the structure of the solar cell. From a technological point of view, it is just taking a solar cell and adding a conductive layer'
Two variants of antennas have been developed: one with a copper resonator, which does not pass of optical beams where the metal is deposited, but which ensures high performance of the antenna , and another with a transparent conductor, which emphasizes the performance of the solar cell.
Thus, for future applications, one will use either method, depending on whether one wants to enhance the operation of the antenna, or the solar panels. 'We are especially pleased that these results are the fruit of a single master thesis, which has been extended to a few months' says Julien Perruisseau-Carrier.
Antennas and solar cells of tomorrow
Still unusual, the devices selected for this study were not randomly chosen: they are promising materials for space. Developed over 20 years in the PV- Lab, thin solar cells made of amorphous silicon layers have the advantage of being lightweight and resistant to radiation. 'With a yield of 10 to 11%, they are not as effective as traditional cells III- V multijunction' concede Christophe Ballif and Monica Morales Masis from PV-Lab. 'However, they allow a better power to weight ratio (in terms of W/kg).'
RA antennas are considered part of tomorrow's technologies. 'The NASA will send a satellite equipped with this type of antennas and solar panels in a technology demonstration mission in 2014' says Julien Perruisseau-Carrier. For this mission, the NASA will use a platform with side panels and antennas on the other. The possibility of merging the two devices in this case would already save some space.
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