Advancements and development pathway of a nascent domain: Underwater solar energy utilization

Underwater solar energy is a compelling renewable resource, primarily due to its notable abundance and sustainability. Currently, the attention paid to capture underwater solar energy for underwater or near-water energy requirement scenarios is insufficient. This review provides a comprehensive analysis of the theoretical framework for underwater solar energy utilization. It encompasses an examination of various aspects, including light-water interaction, such as reflection at the air-water interface, and water’s attenuation due to absorption and scattering. Given the challenge in accurately and conveniently evaluating underwater solar spectrum, this work proposes a potential and straightforward methodology to ascertain the solar spectrum in any water clarity conditions by examining the spectral attenuation coefficients of Formazine standard turbidity solution through spectrophotometry. After the comprehensive understanding of the underwater solar spectrum, the spectrum matched underwater solar cells with optimal energy gaps can be designed. The current research status of wide bandgap solar cells (≥1.8 eV), including perovskite solar cells, organic solar cells, and dye-sensitized solar cells are reviewed. Furthermore, this work highlights the potential of underwater solar concentration as a new pathway toward efficiency underwater solar energy utilization. Due to the distinct optical properties between water and air, the terrestrial-based solar concentrator cannot be used underwater. Consequently, developing water-based solar concentrators is recognized as a pivotal domain for future. Naturally, the advancement of suitable underwater concentrating photovoltaic technology and the underwater concentrating photovoltaic-thermal integrated systems are regarded as valuable avenues for research.