Background and scope:

There are currently quite mature technologies tested on industrial pilot scale to provide synthetic fuels and chemicals from renewable energy sources via a sequence of independent energy and chemical conversion steps (Power-to-X or Carbon Capture and Utilization technologies). However, energy losses during the different steps (e.g., electricity production or thermochemical conversion) make the process highly energy intense. Also, the provision of affordable, renewable electricity at the needed scale is challenging. A potential workaround to this bottleneck is the development of devices which directly convert solar energy and abundantly available molecules (such as water or carbon oxides) into liquids and gases – within a single device. These so-called solar-to-X technologies avoid the beforehand conversion of solar energy into electricity and reduce the complexity of the process by a complete integration of the different steps. 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. The objective is to make progress towards synthetic fuels and chemicals technologies which integrate all necessary conversion steps into a single device, and which are solely and directly driven by solar energy. Devices which are driven by electricity or heat are not the focus of this Challenge – except for radically new electrolyzer designs beyond incremental R&D on mature electrolyzer designs. Partially integrated systems, where the overall balance of plant is not significantly simplified (e.g., PV-assisted photoelectrochemical devices) are not within the scope of this Challenge. The use of sacrificial agents has to be avoided and the desired product has to go beyond hydrogen and carbon monoxide. To summarize, this Challenge focusses on: i) Novel electrolyzer designs showing a significantly simplified balance-of-plant compared to mature electrolyzer designs; ii)Fully-integrated PV-EC devices, with electrochemical conversion (EC) and photovoltaic unit (PV) combined in a single device; iii)Photosynthetic devices converting directly sunlight and simple feedstock molecules into a fuel or chemical (e.g., Photoelectrochemical devices, Particulate systems, Biohybrid photosynthetic devices, Thermally-integrated photosynthetic devices, etc.); iv)Solar-driven biological conversion devices (e.g., solar cell factories).

This Challenge is directly relevant to the objectives of the European Green Deal and Repower EU.

Specific objectives:

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.

Expected outcomes and impacts:

This Challenge addresses the development of devices - their enabling technologies and use cases - that store sunlight directly on the long term in the form of fuels and chemicals to enable a decentralized energy, transport and production system.

The portfolio of projects selected under this Challenge is expected to collectively:

• cover Areas 1,2 and 3: There is a strong need to go from the pure concept to next maturity level by developing devices running at elevated timeframes and efficiencies (Area 1). To ensure a fair and honest comparison between the developed devices, common metrics, key performance indicators and standardised protocols must be developed and tested (Area 2). At the same time, fundamental mechanisms that are common to the different device architectures are not fully understood and require dedicated exploration (Area 3). Combining these three aspects in a single portfolio of different projects with close interaction and a commonly developed vision is expected to significantly speed up innovation in the field of solar-to-X.
• identify the most impactful end products and application cases (both on an environmental and economic level): Renewable fuels and chemicals provide the opportunity to couple diverse sectors, including the energy, chemical and transport sector, construction, agriculture or the food and feed sector. By choosing a specific material, chemical or fuel, diverse application scenarios can be addressed by the different projects. Future application scenarios may include remote locations (f. ex. ammonia synthesis for precision farming), single buildings, energy communities in cities or off-grid communities (e.g., devices integrated in architecture), etc.

Concerning environmental and economic impacts:

• The overall system must be cost-efficient and show a simplified balance-of-plant compared to current solutions, e.g., the combination of photovoltaics and an electrolyzer unit.
• The feedstock for the desired product must be sourced locally, preferably valorizing waste streams and solar energy.
• Projects should promote the use of abundant and sustainable resources in the fabrication of solar-to-X devices, minimizing the reliance on rare or expensive materials.
• Proposals should clearly identify a (future) market need and address it with the proposed technology.

Portfolio composition: The applicants of Area 1 should specifically mention to which of the technological areas their technology belongs (Novel electrolyzer designs, Fully-integrated PV-EC, Photosynthetic devices, Solar-driven biological conversion devices).

Specific conditions

Technologies starting from an energy-rich feedstock, such as biomass, and proposals that only address parts of the full solar-to-X chain (e.g., half reactions) will not be considered.