Abstract:

Objective Interfacial solar steam generation (ISSG) has emerged as a promising eco-friendly and low-carbon emission technology to address the global water scarcity. However, most current studies have focused too much on evaporation materials, ignoring the real bottlenecks are in the low-cost, scalable production and low fresh water yield in seawater desalination. In order to solve the above problems, this paper proposes a novel strategy to construct a water-electricity synergistic generator (WESG) by combining interfacial evaporation technology with photovoltaic generation.

Method The WESG containing a solar cell, thermoelectric generator, viscose fiber based nonwoven fabric and a copper condenser from top to bottom. The device skillfully uses the waste heat generated during the work of photovoltaic cells to facilitate interface evaporation, and solves the problem of low power generation efficiency caused by high temperature generated during the operation of the photovoltaic cells. The structure and wicking effect of the viscose fiber based nonwoven fabric, evaporation and electricity performance of the WESG was characterized.

Results The viscose nonwoven fabric is twisted, staggered, and interconnected to form a porous structure, resulting in good air permeability. The water droplets on the surface of viscose nonwovens fabric completely is diffused within 0.2 s, indicating that the water quickly reaches the gas-liquid interface and continuously supplies water to the evaporation interface. Assisted with evaporation process, the temperature of the photovoltaic cell is decreased from 62 ℃ to 48 ℃ under the simulated irradiation of 1 kW/m², and the evaporation rate reaches 1.36 kg/(m²·h). According to the voltammetry characteristic curve of the photovoltaic cell, the photovoltaic conversion efficiency is increased from 8.8% to 9.6% after cooling. The results show that the combination of photovoltaic power generation and interfacial water evaporation technology can effectively reduce the working temperature of photovoltaic cells and improve the photoelectric conversion efficiency of photovoltaic cells. The thermoelectric generator sheet can release 84 mV voltage, and the maximum power density is 28.12 μW/cm²during evaporation. The outdoor performance experiment of the WESG is able to generate 2.23 kg/m² of water and 37.3 (kW·h) /m²electricity in one day. The photoelectricity conversion efficiency and solar to vapor conversion efficiency are maintained at 9.5% and 82%, respectively during 144 h of cycle operation, suggesting that the excellent working stability of WESG. After purification, the ion concentration of salt water is decreased by 2-4 orders of magnitude, reaching the drinking water standards of the World Health Organization and the United States Environmental Protection Agency, implying that the WESG has a good water purification effect.

Conclusion In summary, this work provides a WESG with minimized energy loss and passive cooling condensation. The WESG cleverly uses the waste heat generated during the work of photovoltaic cells to realize interface evaporation, and solves the problem of low power generation efficiency caused by high temperature generated during the operation of the photovoltaic cells. The results show that the evaporation of water transported by viscose nonwoven fabric can effectively decrease the temperature of photovoltaic cells, and improve the photoelectric conversion efficiency of photovoltaic cells. This paper preliminary verifies the potential of utilizing traditional nonwoven materials and photovoltaic power generation to realize water-electricity synergistic generation and large-scale application.

Key words: interfacial steam generation, photovoltaic power, nonwoven material, viscose, desalination, synergistic water-electricity generation.