Internet of Things (IoT) has revolutionized the way future cities are planned. The concept of embedding intelligence into spaces and objects makes it possible to build all sorts of smart and distributed systems that automate and improve everyday operations in the fields of health, energy, manufacturing, and transport, amongst others. One of the most significant visions to come out of the IoT revolution is Smart Cities. Equipped with sensing and communication technologies and powered by renewable energy sources, Smart Cities could be the key to protecting environmental resources and ensuring sustainable urbanization as the world population continues to grow. Of the various available renewable energy sources, solar is one of the most popular and promising. However, solar energy is a function of its environment, and sudden changes in meteorological conditions can cause intermittency and disrupt power generation. In desert regions where solar energy is the most plausible option for renewable energy, dust-based soiling remains the biggest obstacle. The accumulation of dust particles on the surface of PV modules can obstruct the absorption of radiation by the module, effectively reducing its output. One common method to measure soiling loss is to perform Current-Voltage (IV) Tracing; where the characteristics of a PV module are used to evaluate the performance of the module. However, solar facilities in smart cities are often distributed in the form of small farms, rooftop installations, and parking lot shades in order to make use of the available space and reduce power lines. This represents a challenge to monitoring and maintaining soiled panels due to the scale and distribution of the installations. In this paper, we present the design and implementation of an IoT-based solar monitoring system for city-wide, large-scale, and distributed solar facilities in smart cities. The system uses low-cost hardware and IoT networking technologies to remotely perform and communicate IV curves from individual modules or strings in a remote facility. A prototype was implemented and used to evaluate soiling loss in Sharjah, UAE, over the period of two months under harsh summer weather conditions. The prototype was able to successfully and reliably collect IV tracing and communicate it back to a cloud-based server for researchers to view and analyze. The obtained results show that soiling has a major impact on PV modules efficiency with up to 40 % power loss after two months of soiling. The PV soiling index and PV soiling loss are evaluated to allow solar facility operators to reduce cleaning costs, optimize power output, and enable preventative maintenance in city-wide distributed solar facilities.