The folding photovoltaic charging system powering stratospheric balloons

High-altitude balloon© CNES/PRODIGIMA/GABORIAUD Romain, 2021

A robust, reusable, sustainable solar charging system

The stratosphere is a critical but challenging zone of exploration. As a result, stratospheric balloons have emerged as indispensable platforms for scientific and technological exploration in this altitude spectrum. However, the scientific balloon community at CNES, the French Space Agency, has been searching for a sustainable and reusable energy generation solution for the instruments in its gondolas (the containers that carry the equipment). This is where CSEM’s innovative photovoltaic (PV) Stratstore technology comes into play. Stratstore’s ingenuity lies in its robust, high-performing, retractable, PV panels that open and close like venetian blinds, protecting them during landing.

Solar module system with a unique design

CNES gondola with its retractable, high-performance PV panels CNES gondola with its retractable, high-performance PV panels.

“We have engineered a bespoke encapsulant, a special coating, for the solar modules that can withstand harsh conditions, such as very high or low temperatures and strong UV exposure” reveals Pierrick Duvoisin, Lightweight Module Line Specialist, from CSEM. “The design of this system is also unique for this type of application—it has a solar tracking feature allowing 360 degrees of movement and which follows the Sun’s trajectory even at altitudes exceeding 40 kilometers. The system has also been designed to retract into a protective enclosure upon landing, ensuring the integrity of the system and facilitating its reuse,” he adds. With CNES’s support, CSEM has been able to continuously refine Stratstore’s design by deploying the charging system on preliminary real-world missions. These involve deploying the charging system at an altitude of 35,000 meters before retrieving and reusing it. This process has qualified the system for further use.

Triggering a leap in energy autonomy

Jean-Marc Nicot, Expert in Onboard and Ground Systems of Stratospheric Balloons at CNES, highlights that: “Stratstore combines high-quality materials with innovative design to provide significant cost savings and energy efficiency for our gondolas. By using Stratstore, we can reduce the energy constraints of our gondolas and increase their energy autonomy. This allows us to reduce the weight and number of onboard batteries, which also extends the duration of our missions from days to months. Moreover, Stratstore is a fully reusable system aligned with our sustainability strategy.”

Powering future stratospheric exploration and Europe’s PV domain

The Stratstore solar charging system has been successfully completed, but CNES and CSEM will maintain their collaborative relationship and continue to develop and refine the system’s design through successive test missions over the coming years. This evolution is driven by a commitment to enhancing performance, addressing observed limitations, and ensuring optimal functionality in response to real-world operational needs. Switzerland may be a small country, but it plays a significant role in the European PV technology sector. One of CSEM’s strategies is to focus on developing high-value, highly specialized PV products that stand out in the market and showcase its expertise. Stratstore is an example of this strategy in action, changing the ways we think about and use solar energy.

📣Congratulations to CNES on the successful TRANSAT mission!

News update, June 27, 2024. We are honored to have contributed by providing the solar panels that powered the scientific instruments. Our PV panels ensured a constant supply of renewable energy throughout the balloon's transatlantic journey. This mission marks a significant milestone in sustainable high-altitude exploration.

To the CNES press release (in French): Successful first flight of the TRANSAT 2024 campaign

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