Fig. 6: Solar efficiency limits and costs for feasible PEC separations using low-solar-efficiency single-junction semiconductors.

Viable solar efficiencies for water treatment at the municipal scale (a) and resource extraction involving enrichment (b), with minimum solar efficiency (solid blue/purple lines) and maximum solar efficiency (orange) limits fully corrected for losses. Dashed lines (avoidable losses) indicate the minimum solar efficiency requirements if the system is not appropriately designed and manufactured to eliminate avoidable losses through pathways such as contact resistances. Shaded regions, bounded by the minimum and maximum solar efficiency curves, indicate the regime of thermodynamically viable PEC separations, spanning those concentrations for which the minimum required efficiency (blue/purple) is lower than the maximum attainable efficiency (orange). Black vertical lines indicate the maximum concentration at which water treatment is viable (a) or minimum concentration at which resource extraction is viable (b). Water treatment spans numerous applications with varying initial concentrations, shown here as in Fig. 2 and Supplementary Table 1^42,53,54,55. Resource extraction applications involve the enrichment of species across a wide range of concentrations spanning multiple unit operations, shown here as in Fig. 2 and Supplementary Table 1)^{36,56,57,58,59,60,61}. Capital costs of PEC and PV+EC separations systems for municipal-scale water treatment to eliminate a contaminant with c_initial = 10 ppb (c) or c_initial = 1 g/L (d). Bars on the left show contributors to overall system cost, and those on the right show contributors solely to the photoactive components of the PEC and PV + EC systems (BoS Balance of system costs); see Supplementary Note 10 and Supplementary Tables 5–6. Source data for (c, d) are based on Supplementary Data 1 and also provided as a Source Data file.