Water disinfection using the Electrochlorination process requires electricity. This power is usually supplied from power plants close to the treatment facilities. However, for mini-plants within areas of long and hot days, the sunlight could be the source. It's free, available, and considering the current innovations even reliable.
Solar disinfection takes in the electricity generated by photovoltaics and delivers an electric current to electrolytic processes to produce the disinfectant that is Sodium Hypochlorite in this case.