Solar-to-X technologies, also called artificial photosynthesis or solar fuel technologies, support the vision of a decentralized, local energy and production system with a local provision of the needed resources. In this vision, communities become not only prosumers of electricity, but also of fuels, chemicals and materials.

In this Challenge, solar-to-X technologies must address societal needs not already sufficiently covered by other energy technologies. The developed technologies should demonstrate how they can be embedded in the full functional value chain from generation to use, be self-sustaining in the long-run and provide a win-win opportunity for prosumers and the environment.

Project proposals should address one (and only one) of the following three areas:

Area 1: Standalone solar-to-X device development

Projects should address all of the following specific objectives:

• Develop standalone solar-to-X devices, converting sunlight and simple, low-energy molecules such as water, carbon oxides or N2 (non-exhaustive list) into fuels, chemicals and materials.
• Enable simplified production chains where one directly goes from simple feedstock to complex products, beyond hydrogen or carbon monoxide.
• Design solar-to-X systems that can operate independently, allowing communities and remote areas to have access to reliable and sustainable energy sources and a local production and utilization of chemicals and fuels.
• The developed devices have to reach at least TRL 4 within a 3-4 year project runtime.

Area 2: Benchmarking and common metrics development for solar-to-X devices

Projects should address all of the following specific objectives:

• Develop common metrics, protocols and equipment to enable a fair and standardized comparison between technologies within the same class, as well as between different technology classes in the field of solar-to-X (see Area 1 for the different technology categories).
• Develop a holistic framework by identifying key performance indicators common to the different categories, while considering unique features of each category. It is required to develop metrics, protocols and equipment for multiple solar-to-X device architectures (aligned with Area 1).
• Devices stemming from area 1 should serve as a portfolio-own testbed to validate the developed methodologies, protocols and equipment in practice. Standards for solar-to-X devices can (and should) build on existing ones.
• Acceptance of the developed metrics and protocols by a broad range of stakeholders within the diverse research communities must be ensured from the beginning, by e.g., co-creation workshops, extensive outreach activities, etc.

Area 3: Understanding fundamental mechanisms by means of computational materials science

Projects should address all the following specific objectives:

• Explore fundamental phenomena crucial to multiple device architectures to enable next-generation solar-to-X devices.
• Drive forward the one-to-one comparison between theory at the atomistic level and experiment. Developing more accurate and less resource-demanding quantum mechanical methods is highly encouraged.
• Bridge the scales from describing properties at the atomic, mesoscopic up to the macroscopic device level within a multiscale approach.
• Adopt a holistic approach to exploring phenomena applicable to multiple solar-to-X device architectures (aligned with area 1). Devices stemming from area 1 should serve as a portfolio-own testbed to validate the developed theoretical models.