Additive-enhanced solar distillation: Mechanisms, performance, and practical limitations

Solar distillation offers a simple and renewable method for decentralized freshwater production, but its practical application remains constrained by low evaporation rates, limited solar-energy utilization, and substantial heat losses. Numerous studies have investigated nanofluids, surfactants, dyes, salts, alcohols, phase change materials, and hybrid formulations; however, previous reviews have generally examined these approaches separately or as part of broader solar-still enhancement strategies, making their comparative assessment difficult. This review critically evaluates additive-assisted solar distillation through a unified framework that links material type with the governing heat- and mass-transfer mechanism, operating conditions, performance reliability, environmental safety, and practical feasibility. Relevant studies were systematically identified, screened, and classified according to additive category, still configuration, concentration, basin-water depth, climatic conditions, reference system, reported productivity, thermal performance, stability, and implementation limitations. Reported results were interpreted using standardized and evidence-qualified comparisons rather than direct ranking by maximum productivity enhancement. The analysis shows that additives can improve solar absorption, basin-water heat transfer, interfacial evaporation, thermal-energy storage, or combinations of these mechanisms. Nanofluids and carbon-based materials generally provide strong photothermal enhancement, whereas surfactants primarily modify interfacial behavior and phase change materials extend heat availability beyond peak irradiance. Hybrid systems frequently report the largest improvements, but many of these values reflect combined effects from thermal storage, cover cooling, modified absorbers, or other simultaneous interventions. Representative effective ranges reported in the reviewed studies were approximately 0.01–0.20 wt% for oxide nanofluids, 50–300 ppm for commonly investigated surfactants, 5–15 wt% for microencapsulated PCMs, and 0.05–0.10 wt% nanofluid combined with 5–10 wt% PCM in hybrid systems. The practical effectiveness of all additive classes is limited by concentration sensitivity, sedimentation, agglomeration, photodegradation, foaming, fouling, leakage, cyclic deterioration, water quality concerns, and material-recovery requirements. The principal contribution of this review is the integration of technical performance with stability, reusability, environmental implications, and techno-economic constraints within a single comparative structure. The findings indicate that no additive class is universally superior and that long-term performance retention, safe containment, recovery capability, and standardized testing are essential for meaningful comparison and scale-up. This framework provides a more reliable basis for selecting additive systems and for developing durable, environmentally responsible, and economically viable solar-distillation technologies.