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Technologies for solar steam generation with high performance can help solving critical societal issues such as water desalination or sterilization, especially in developing countries. Very recently, we have witnessed a rapidly growing interest in the scientific community proposing sunlight absorbers for direct conversion of liquid water into steam. While those solutions can possibly be of interest from the perspective of the involved novel materials, in this study we intend to demonstrate that efficient steam generation by solar source is mainly due to a combination of efficient solar absorption, capillary water feeding and narrow gap evaporation process, which can also be achieved through common materials. To this end, we report both numerical and experimental evidence that advanced nano-structured materials are not strictly necessary for performing sunlight driven water-to-vapor conversion at high efficiency (i.e. ≥85%) and relatively low optical concentration (≈10 suns). Coherently with the principles of frugal innovation, those results unveil that solar steam generation for desalination or sterilization purposes may be efficiently obtained by a clever selection and assembly of widespread and inexpensive materials.Developing sustainable technologies is fundamental for mitigating the anthropogenic impact on environment 1 : global warming and clean water scarcity are progressively impacting our economies and societies [2][3][4] . Therefore, international collaborative efforts have taken place to limit global temperature rise (up to 2 °C respect to pre-industrial levels 5 ) and address clean water scarcity in the most water-stressed areas, where nearly two-thirds of global population will live by the year 2025 6 . Several filtration or distillation processes have been developed for the generation of fresh water from either brackish or sea water. Most of these processes are highly energy intensive and powered by fossil fuels 7 , whereas more sustainable alternatives have been recently investigated to couple clean water generation with renewable energy 8 . Among these methods, solar distillation appears as one of the most economical and practical solutions for small scale desalination, particularly in remote and off-grid areas [8][9][10][11] . Steam generation by solar energy (solar steam) has been also recently investigated in a broad variety of other applications, for instance enhanced oil recovery 12,13 , power generation 14 , sterilization 15 , separation processes 16 or evaporation-driven engines 17 . The present challenge in solar steam generation is to develop robust and cost-effective technologies with enhanced solar-to-vapor conversion efficiencies 18,19 . Currently, large plants for steam generation from solar thermal energy rely on a cavity or surface absorbing solar radiation 20,21 , being the absorbed heat then used to evaporate water directly or by means of a carrier fluid. These solutions suffer from large surface heat and optical losses 18 ; therefore, nanofluid volumetric receivers have been rece...

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