# Virtual Power Plant Optimization in Smart Grids: A Narrative Review
## 5 Discussion  
Many different strategies are reported in the literature for the creation of VPPs. They aim to integrate renewable energy and increase its usage to address current sustainability issues generated by natural fossils. VPPs can be used to offer energy services in different energy markets, to increase the local energy system autonomy, and to support the implementation of energy communities considering the local socio-economic context. Each application case provides advantages for different smart grid management scenarios. Most of them are studied, researched, and applied to pilot infrastructures. All VPP alternatives are characterized by the same model structure and energy assets. The services are offered not only in energy markets but also to different energy operators responsible for the safe and reliable distribution of energy. An example, in this case, is the distribution system operator that manages the energy of a low-voltage grid. The distributed energy resources are the most important components of a VPP. They are the entities that generate, store, and consume energy. Additionally, in the case of energy communities, the citizens or energy prosumers play an important role. The VPP may coordinate the energy resources to provide different energy services depending on the market type. Among the offered services by VPP, the most important ones covered in the research literature are imbalance prevention, storage for excess power, peak-cut, load management, energy trading, backup and stability, congestion management, and frequency regulation. For charging energy storage systems when energy prices are low, VPPs can buy energy in the wholesale electricity market. On the other hand, VPPs can decide to sell energy that is a surplus and discharge power from the energy storage systems when the prices are growing in order to match the demand of flexible assets. For the balancing market, when a power plant cannot reach its commitment, VPPs can sell replacement capacity on short notice and may be able to increase/decrease production/consumption during a period. In the ancillary services market, VPPs can offer frequency regulation services such as, for example, committing unused capacity. At the same time, a VPP can provide energy management towards the DSO. VPPs can manage all involved resources to deal with the intermittent generation (uncertainty) in smart grids by offering services to the DSO and at the same time optimizing the profit of its participants. VPPs are used to assure the energy autonomy of local energy systems that may operate decoupled from the main grid. The researched literature deals with VPPs as a solution to provide support for energy autarky. They coordinate the energy generation with the storage and the demand so that the local microgrid energy imports or exports are minimized. In this case, the grid can benefit from the power supply stability at the edge, while the VPP can work fully or partially powered by renewables. Islands are reported as a positive example of a local energy system that is facing technical, environmental, and socioeconomic challenges related to its energy supply that may be addressed using VPPs. The energy supply of islands often relies on high yet costly dependency on imported fossil fuels, suffers from energy supply constraints due to the lack of interconnections among electricity and gas, and is significantly affected by the high seasonality of demand due to tourism. In this case, the VPP simplifies the distribution of energy for that region and uses local resources to the benefit of the community. Batteries, water-based systems, PV, and wind farms are the RES that needs to be available fully or partially for achieving autonomous VPP in islanding conditions.