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Short abstract

Based on interviews with PEC experts and an analysis of European hydrogen initiatives, this article shows how epistemic residues inherited from fossil based logics shape which solar hydrogen futures are deemed viable, relegating more alternative pathways to the background.

Long abstract

Hydrogen has recently attracted strong political and industrial interest as a key solution for decarbonizing energy systems. While electrolysis‑based hydrogen remains embedded in infrastructures and economic logics inherited from fossil fuel systems, emerging solar‑based pathways - such as photoelectrochemical (PEC) technologies - may be associated by some actors with alternative imaginaries of autonomy and decentralization. Drawing on work on innovation residues (Felt, 2025), our fieldwork shows that these speculative possibilities are often absorbed into dominant discourses, revealing epistemic residues that shape which futures are considered viable.

Based on interviews and observations with PEC experts and actors involved in European hydrogen initiatives, this paper examines how such residues constrain possible trajectories for solar hydrogen. Our findings show that PEC technologies tend to inherit fossil‑based logics: market dynamics and expectations of large‑scale deployment, echoing how inherited configurations can shape present choices (Pottin and Felt, 2025). As a result, alternative imaginaries are overshadowed by standardized visions of innovation.

The European consortium SUNER‑C illustrates this dynamic. By prioritizing solar fuels as the main future of solar hydrogen, it sidelines other plausible pathways, such as solar chemicals, despite expert support. These exclusions reflect not only explicit strategic decisions but also accreted epistemic residues (Boudia et al., 2018) that shape how innovation is framed and valued, making some futures appear more aligned with dominant logics while others become residual or difficult to articulate.

By foregrounding these residues, the paper shows how certain energy futures become obscured or dismissed and argues for rethinking innovation through sidelined possibilities.