# State of the Art of Telecommunication Systems in Isolated and Constrained Areas
## 5 The Tethered Balloon Solution
### Ecological Energy Supply  
As seen in Figure 18, flexible photovoltaic panels will achieve the autonomy of the balloons in electrical energy. This technology underwent a major boom when a research project carried out in 2012 made it possible to create thin-film photovoltaic cells a few micrometers thick. [PERSON] carried out this study at Stanford University in the United States [85]. Thanks to their small thickness, these structures have the advantage of being flexible and light. However, they must be built on the same substrate, which was the study's main problem.  
Nevertheless, the scientific team managed to create a reusable substrate, which was very complicated because the substrate had to, among other things, have a homogeneous surface, resist very high temperatures, and not react with certain chemicals used in the manufacturing of photoelectric cells. The solution was to make the thin film photoelectric cells on a rigid substrate consisting of a wafer of silicon dioxide (SiO\({}_{2}\)) on which was deposited a layer of nickel 300 nm thick. Then, the different layers constituting the current producing unit were deposited conventionally. As part of the proof of concept, the deposited layers were made of hydrogenated amorphous silicon.  
Figure 17: Illustration of the Schefferville radio coverage.  
The layers were then covered with a protective polymer on which was fixed a transparent and heat conductive transfer sheet used to transport the cell. In a second step, the still-rigid product elements were immersed in water at room temperature. Slight traction was exerted on the transfer sheet allowing the water to penetrate between the wafer and the nickel until the separation of these two layers. The cells were then extracted from the water and heated to 90 \({}^{\circ}\)C to make them flexible. They could then be pasted anywhere (telephone, electronic business card) using double-sided adhesive or glue. After, the sheet was removed, and the silicon wafers could be reused to manufacture new cells. The conversion efficiency obtained during this experiment remains unchanged after the transfer. It was 7.7% on the rigid substrate and remained identical after transfer. Using other types of cells (CIGS) composed of copper, indium, gallium, and selenium, the efficiency achieved was 22.6%. The photovoltaic panels' arrangement on the balloon envelope will optimize their performance because as the sun makes its way around, the photovoltaic cells capture the sunlight all day. This solution is deployable very quickly. It suffices to carry the balloons on-site to set up the ground-fixing system and the batteries and then launch the balloon. The balloon is operational 24 h a day. Depending on its size, it can carry loads of up to 250 kg. Its operating cost is less than 100 CAD per hour. The side that will require improvement is flight autonomy. Currently, captive balloons with this type of structure (PET-PA-PET) and the inherent helium leaks last approximately ten days in the air. It is then necessary to readjust the volume of helium. The fleet of balloons deployed on-site can respond to occasional problems such as during a sudden environmental event when communications are broken and there is no longer any energy supply, or when one wishes to carry out a measurement campaign over an isolated and vast territory.  
On the other hand, if a new combination of materials makes it possible to increase the flight time to one month, the fleet of tethered balloons constituting the telecommunication system in an isolated and constrained environment may be used permanently. It would not be absurd to send a person, once a month, equipped with helium refills in a remote environment to re-inflate the balloons. From then on, it would be possible to follow trains carrying passengers or iron ore, as the Tshuetin railroad company in Northern Quebec does, and all the company's rolling stock. This would provide significant additional safety. Likewise, mining companies operating in Northern Quebec could monitor their production sites remotely.