Abstract
Sodium hypochlorite (NaClO) is a chemical commodity widely employed as a disinfection agent in water treatment applications. Its production commonly follows electrochemical routes in an undivided reactor. Powering the process with photovoltaic (PV) electricity holds the potential to install stand-alone, independent generators and reduce the NaClO production cost. This study reports the comparative assessment of autonomous, solar-powered sodium hypochlorite generators employing different photovoltaic (PV) technologies: silicon hetero-junction (SHJ) and multi-junction (MJ) solar cells. For Si hetero-junctions, the series connection of either four or five SHJ (4SHJ and 5SHJ, respectively) cells was implemented to obtain the reaction potential required. MJ cells were illuminated by a novel planar solar concentrator that guarantees solar tracking with minimal linear displacements. The three solar-hypochlorite generators were tested under real atmospheric conditions, demonstrating solar-to-chemical conversion efficiencies (SCE) of 9.8% for 4SHJ, 14.2% for 5SHJ and 25.1% for MJ solar cells, respectively. Simulations based on weather databases allowed us to assess efficiencies throughout the entire model year and resulted in specific sodium hypochlorite yearly production rates between 7.2–28 gNaClO cm−2 (referred to the PV surface), depending on the considered PV technology, location, and deployment of electronics converters. The economic viability and competitiveness of solar hypochlorite generators have been investigated and compared with an analog disinfection system deploying ultraviolet lamps. Our study demonstrates the feasibility of off-grid, solar-hypochlorite generators, and points towards the implementation of SHJ solar cells as a reliable technology for stand-alone solar-chemical devices.
Highlights
The recent developments in solar technologies have paved the way for the autonomous operations of independent, off-grid installations, which employ renewable energy sources as primary feedstock
We report a comparative analysis of solarpowered sodium hypochlorite generators employing two different PV technologies: (i) silicon hetero-junction or (ii) multi-junction GaAs solar cells under solar concentration (Fig. 1)
Three solar-hypochlorite devices were tested outdoors under real solar illumination, powered by 4SHJ solar cells, 5SHJ solar cells and MJ solar cells illuminated by a solar concentrator, respectively
Summary
The recent developments in solar technologies have paved the way for the autonomous operations of independent, off-grid installations, which employ renewable energy sources as primary feedstock. Electrochemical processes are intrinsically inclined to PV integration, as they require direct electricity to aSchool of Engineering, Ecole Polytechnique Federale de Lausanne (EPFL), Station 18, 1015, Lausanne, Switzerland. A solar-powered, stand-alone, electrochemical device requires the following conditions to be met, in order to work at high efficiencies and represent an economic appealing alternative: (i) a discontinuous commodity demand (mitigated by storage, potentially); (ii) decoupling of PV source and electrochemical device – this route is likely more amenable for short-term implementation than a monolithic, fully integrated device;[1,2] (iii) a comprehensive design of the components, whose dimensioning needs to be correlated and aimed at maximizing chemical throughput and conversion efficiency.[1,3]
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