Researchers at Ecole Polytechnique Federale de Lausanne (EPFL) school of engineering in Lausanne, Switzerland have developed a way to combine antennas with solar panels. The technology is the first step towards developing more compact and lightweight satellites. It could also be deployed in autonomous antennas systems used to restore communications after a natural disaster.
One of the problems the researchers faced is that solar cells are not particularly efficient reflectors. To solve the problem they modified a “reflectarray” (RA) antenna. A typical reflectarray antenna has a resonator mounted on top of a substrate above a ground plane. For the combined solar cell/antenna, resonators are placed on top of the solar cells, allowing the cells to maintain up to 90 percent of their photovoltaic efficiency.
“It is not the first time that scientists try to merge solar cells and antennas,” said Julien Perruisseau-Carrier, project supervisor. “But the advantage of our method is that it allows preserving good performances for both the antenna and the photovoltaic system, while leaving intact the solar cell's original structure. You just have to take existing solar cells, and to add a conductive layer.”
By changing the material used for the resonator, RF efficiency can be traded for improved photovoltaic efficiency (or vice-versa). A copper resonator gives high RF efficiency, but blocks light from reaching the part of the solar cell behind it. A transparent conductor, like those used with LCDs, lets light through but is less efficient at RF.
Reflectarray antennas have been called “the technology of the future”. Several papers about it can be found on ieeexplore.ieee.org (Google “Reflectarray” for links) and I found more papers listed on Hindawi's International Journal of Antennas and Propagation. NASA is planning to launch an Integrated Solar Array and Reflectarray Antenna (ISARA) in late 2014. Julien Perruisseau-Carrier said: “NASA selected a satellite with these antennas and solar panels for a technology demonstration mission planned for 2014. For this mission, NASA is using a platform with solar panels on one side and antennas on the other. Being able to combine these two devices would have saved on surface area, for example.”
More details are available in the paper Copper and Transparent-Conductor Reflectarray Elements on Thin-Film Solar Cell Panels . I need to do some more research on Reflectarray antennas, but if they can be used at TV broadcast frequencies this technology could make it easier to deploy future (very) low-power broadcast TV boosters to fill in coverage in terrain shadowed areas. I could also see potential uses for low power mesh networks.
Will the first application of the EPFL work will be on the ground or in space?
Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.
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