CORDIS - EU research results

Advanced Lightweight and Flexible Array with Mechanical Architecture

Periodic Reporting for period 2 - ALFAMA (Advanced Lightweight and Flexible Array with Mechanical Architecture)

Reporting period: 2019-11-01 to 2021-10-31

More and more missions require power supply > 25 kW such as solar electrical propulsion and high throughput satellites. However, the restricted volume between the fairing and the spacecraft sidewall limits the number and the dimension of rigid solar panels during launch. Therefore, the answer for this growing power demand lies neither in stacking more rigid solar arrays, nor by marginal efficiency improvements on III-V multi-junction solar cells, but rather in innovative/disruptive photovoltaic solutions.

To answer this challenge, more solar capacity per volume are needed in stowed configuration, and flexible solar arrays are the only answer for this high-power challenge.

In this context, ALFAMA project brings answers for the mass, the cost and the power challenge, with ambitions at each level of the solar array:
- The mechanical architecture of a lightweight modular deployment system
- The photovoltaic assembly fabrication process, with printed harness & lamination for easier integration, manufacturing and high voltage protection
- The photovoltaic array structure, with thin flexible layers for high power/mass & power/volume ratio
- The solar cells, with the development of highly efficient and ultra-thin lightweight III-V cells using inverted metamorphic and epitaxial lift-off processes.

ALFAMA's drastic improvements will enhance the EU space sector competitiveness, enable new missions and build synergies between space and non-space activities.

ALFAMA brings together a team of 8 partners, leaders in their field, from 3 EU-member states, who will join their efforts towards the realization of a disruptive solar array technology.
Here is an overview of the tasks performed from the beginning of the project.

WP01: Project’s specifications have been made to lay the foundations of the project and to move forward the project goals. These specifications concern:
- Lifetime requirement
- Performance requirement
- Environmental requirement
- Design and manufacturing requirement
- Technical requirement, such as :
- solar cells architectures (dimensions, grid layout, metal contacts, etc.)
- photovoltaic array flexible design (electrical & mechanical)
- mechanical structure and deployment mechanism,
- system-level to analyze ALFAMA’s technology impact (satellites and launchers levels).

WP02: Epitaxy (ISE), Epitaxial Lift-Off (ELO) (TF2) and thin-film processing (TF2) have all been optimized for the production of ultra-thin IMM3J ELO solar cells, with a thickness <20 um and an areal mass density of ~13 g/cm2. An AM0 efficiency of 30.2% and power-to-mass ratio of 3.0 kW/kg were demonstrated, far surpassing the project targets of >26% and >1.27 kW/kg. Electron irradiation and thermal tests were performed on the cells at ISE, AZUR and TF2. A batch of 25 dummy and 25 functional ultra-thin IMM3J ELO solar cells with a areas of ~20 cm2 was manufactured for the subsequent manufacture of flexible PVAs (see WP3).

WP03: Flexible photovoltaic modules processes development. Different tasks were conducted :
- Design & test of new interconnector solutions for space flexible solar array
- Adaptation of standard terrestrial lamination process and materials selection for spatial flexible PV module
- Development of a printed harness module with specific bill of material and interconnections processes
- Fabrication of intermediate size PVA coupons, characterizations, and testing in representative environment

WP04: Realization of rolling/folding mechanical structure:
- Deployment mechanisms have been defined, built and tested
- An aluminum mast and pressure plates have been designed and procured.
- The deployment mechanisms, mast and pressure plates have been integrated to form a complete prototype wing.
- Interfaces of the prototype wing are made fit to be combined with the flexible PVA built by CEA.

WP 5: Flexible solar array breadboards
- A 5 m2 flexible PVA populated by functionnal and dummies cells has been designed and built by CEA
- A breadboard PVA based on 12 high efficiency ultra-thin IMM cells was fabricated by CEA
- 0g ground support equipment is designed, built and tested to be able to simulate a zero gravity situation during deployment of the prototype wing
- The flexible PVA is combined with the prototype wing
- A succesfull deployment test has been performed on the prototype wing including flexible PVA in combination with the 0g ground support equipment

WP06: A website and social media have been created as well as flyers and posters related to ALFAMA project, to facilitate the dissemination of the project first results. The website and social networks are updated with the news of the project.
The web site and LinkedIn were used to disseminate the results of the project all along the action.Evens publications and news were collected and registered on the project website, whereas the main activities performed were detailed on twitter and LinkedIn with pictures to illustrate the work that has been done. A video as also been recorded during the last consortium meeting. In this video, the partners present the actions implemented and the results obtained. This video will be published on the web site, twitter and LinkedIn as a conclusion of the project highliting the main results.
The ambitious specifications showed the progress compared to the state of the art of the ALFAMA structure.
The progress beyond state of art was initiated by the partners with their work on the design and the first prototypes. Many advances have been made, particularly with the first thin and ultra-thin lift-off solar cells. In conjunction with this, the development of the first flexible substrate with printed conductive tracks adapted to innovative cell geometry was achieved. All these advances are aimed at achieving several KPIs:
1/ Power/mass ratio increased by ≥ 50% with III-V lift-off solar cells and a novel mechanical architecture
2/ Cost reduction with high throughput the assembly process
3/ Power density increased more than 3 times with compact stowed configuration
4/ Relevant roadmaps for space

ALFAMA's drastic improvements will enhance the EU space sector competitiveness, enable new missions and build synergies between space and non-space activities.
Flyer and Poster