I. Introduction
Due to the worsening environmental problems caused by fossil fuels, renewable energy, especially solar photovoltaic (PV) energy, has undergone significant development over the last several decades and is becoming an essential source of energy harvesting. As the cost plummets and regulative incentives keep growing, PV system penetration is boosting [1]. Nonetheless, the intermittent PV power mainly attributed to the movement of clouds often leads to rapid power fluctuations in grid. When utility-scale or aggregate PV systems are considered, these fluctuating power can result in large power ramp-rates, eventually leading to significant grid frequency deviations even blackouts [2]. In order to address the above challenges, many grid operators have imposed standards to limit the large PV power ramp-rates, e.g., Germany and Puerto Rico have required a maximum PV ramp-rate of 10%/min [3], [4], while Denmark has enacted a more strict regulation with 100 kW/s [5]. As an immediate solution, energy storage systems have been widely adopted to compensate the PV power variations. In most cases, the storage capacity needs to be doubled to cope with the worst-case scenario of PV power going from full to almost no production in a very short period of time [6]. As a result, the capital cost of the PV generation is substantially raised, especially for utilityscale systems. Essentially, the energy storage system that reacts to the erratic solar PV output power fluctuations is referred to as a reactive approach. On the other hand, solar forecasting enables a proactive approach. By forecasting the solar irradiance and projected PV generation in the near future, the ramp-down function can be initiated sufficiently prior to the actual cloud shading occurs. Therefore, upon the incidence of the ramp event, the PV generation will not experience severe fluctuation. This proactive approach has been proved to significantly improve the performance of reactive approaches by shrinking the required energy storage capacity and offering remarkable reliability and flexibility to the PV system [7]–[9].