This paper presents a methodology for the analysis and simulation of the effect of operating large photovoltaic(PV) plants, in coordination, as static synchronous compensators (STATCOM). The goal is to improve voltageprofiles at different load nodes and reduce power losses in transmission lines. The proposed approach takes intoaccount the varying reactive power capacity in PV inverters, which depends on weather conditions.To implement the proposed method, proper Internet of Things (IoT) hardware and software solutions arerequired. In this context, the grid status and weather data need to be transmitted continuously, via wirelesscommunication technology, to an edge computer. Based on the transmitted data, and using the system mathe-matical model, an optimization algorithm is then responsible for finding out the optimal reactive power setpointfor each plant in real time.The proposed method is implemented and tested successfully using MATLAB platform with the MATPOWERIEEE 30-bus test grid model. When only five 20 MW PV plants are connected to different locations in the gridwith a penetration rate lower than 25 percent, the simulation shows the effectiveness of the optimal coordinationof PV plants to deal with the effect on the transmission grid of instantaneous operation of multiple loads. In thiscontext, a daily load profile of heat pumps, operating in winter scenario in multiple households, is approved. Animprovement up to 68 percent in the global voltage profiles in the load buses for one-day scenario is achieved.Furthermore, total accumulated active and reactive power losses are reduced by 24.1 percent.