# Virtual Power Plant Optimization in Smart Grids: A Narrative Review
## 4 VPP Applications in Smart Grids
### Local Energy Autonomy
As renewable energy is unstable, a ramp rate limitation is computed to decrease any issues that may occur in case of a spike of energy, where the gradient is out of the limits [94]. The authors of [81] describe both analytical and experimental infrastructure used on the island of Bornholm. The approach is focused on modeling a low-voltage microgrid for  
Figure 5: VPP for local energy autonomy. providing grid services and achieving energy autonomy. The potential of a renewable-driven VPP is analyzed considering different energy domains such as electric, heat, gas, transportation. The constraints impacting the energy autonomy, such as the power flow, the dependency on batteries, and the system flexibility are considered. Another island that took steps toward assuring the local energy autonomy using a VPP configuration is Porto Santo Island [82]. The aim is to use all the available renewable resources to generate energy and meet the demand while avoiding the import of energy from the continental energy network, which is expensive. The potential energy that could generate an alternative solution can be taken from wind and sun, the only available resources. An action plan was created, and the characteristic is to increase the system efficiency by using VPP aggregators as load dispatchers that will balance the supply and the demand. Other studies focused on the energy for households using photovoltaic generation and controllable loads [84]. The objective is to model a system that controls the energy provided, since solar energy is considered cost-effective but at the same time unstable and not secured, but without storing it, since that is an expensive procedure. To accomplish this, the system architecture plays a role. The energy distribution must be managed with controllable loads, and the strategy is computed with quadric interpolation. The model simulation demonstrates the possibility of achieving energy autonomy without the necessity of storage resources. The authors of [83] describe a model for a grid-connected VPP that collects solar and wind and produces renewable energy with low costs targeting the optimization of transportation. To understand the energy demand necessary for a full trip, some factors are considered. For example, the number of passengers is computed using stochastic methods because the number is not distributed uniformly during the entire day. Another factor is the minimum redistribution of vehicles from the origin to the distribution on a specific hour. Multiple cases were simulated with 100 iterations, indicating a reduction of costs by 20% on a dataset from Tokyo city. The authors of [85] discuss VPP energy autonomy and its usage for integrating energy resources, considering the demand on the market. The mathematical methods need to be correlated with the techniques that manage the distribution of the network. The model offers a structure that can handle the diversity of requests, being flexible, but at the same time effective. The authors also accentuate that the geographical position is important even for renewable energy. Energy autonomy can be reached [86] with a stochastic model that is heavily optimized with multiple levels of scheduling. A day-ahead prediction in a VPP that can provide increases on the income is modeled with a bi-level optimization. It creates the first schedule plan, goes over it again, and analyzes the ratio of costs and improvements. In this type of model, the need of a backup is necessary because the predictions can change based on special events induced by the consumers. The demand curve is analyzed and flattened as much as possible. The system output can be coordinated using the VPP over which charging\(-\)discharging power is applied. The model was simulated in the easter China micro-grid, assuring some levels of energy autonomy and a decrease in costs. Another country that created a model for energy autonomy is Portugal. The goal is to fully operate on renewable energy over 30 years [88].