| Work Detail |
Researchers from both companies have built a lightweight, flexible heterojunction silicon (HJT) photovoltaic panel that measures 563 mm x 584 mm and weighs just 218.5 g.
Japanese investment holding company Softbank is developing a wide range of technologies for its planned ultralight High Altitude Platform Station (HAPS), a solar-powered aircraft intended to operate at an altitude of 20 km above the Earths surface carrying telecommunications base stations as payload.
One of its research projects, completed in March this year, aimed at a silicon PV panel of less than 700 g/m2, inspired by the high-efficiency silicon PV modules used in solar car racing. It was described in an R&D paper titled “ The Challenge of Ultra-Lightweight Solar Modules for HAPS,” published on Softbank’s website.
In the paper, the team explained why they pursued silicon photovoltaic technology: “The lightest and most efficient solar cell currently available is the composite solar cell for space applications, but it is expensive and time-consuming to manufacture,” they said. “For this reason, we selected high-efficiency crystalline silicon cells, which are available at about 1/1000 the price.”
The project, which involved Japanese company Fujipream Corporation and Chinese module manufacturer Longi, achieved a silicon heterojunction panel weighing 665 g/m2, even lighter than the project target of 700 g/m2.
Manufactured using Longi cell technology – the same 80µm HJT technology used to build a record-breaking cell introduced in 2022 – the encapsulated modules measured 563mm x 584mm and weighed 218.5g. The maximum output power of 71.1W was measured using the AM 1.5 standard spectrum for a module efficiency of 22.2% over effective area.
To achieve the target weights, all materials were much thinner than conventional panels. The front cover, cells, encapsulants and backsheet measured 25 µm, 80 µm, 150 µm and 50 µm, respectively.
Connections of this size were a challenge. “For direct cell-to-cell connections, a thin copper wire with a diameter of 250 µm was selected and connected using low-melting solder,” explain the researchers, who point out that a manual process was used.
Further research is planned to achieve the 500 g/? target. “To achieve this goal, we will continue to develop modules with the aim of making each component of the module even thinner and more efficient, as well as improving the wiring and lamination technology,” the researchers said.
In fact, Softbank’s spokesperson confirmed to pv magazine that a new project is underway. “Solar module manufacturer Fujipream Corporation is our partner for this research project,” they said, adding that they are not limiting themselves to one particular solar cell manufacturer for the work.
Softbank has been working with external partners from industry and academia since 2017 toward solving technological challenges on the path to achieving its HAPS goals. For example, this month it announced the successful second field test of its Sunglider HAPS aircraft with US aerospace and defense technology company AeroVironment in the state of New Mexico. |
