# A Methodology for Exploiting Smart Prosumers' Flexibility in a Bottom-Up Aggregation Process
## 5 Performance of the Bottom-Up Aggregation Process  
The aggregation process is tested for various situations to assess the time required for the creation of the aggregates.  
The VAE and the prosumers' population is emulated using three computers with processor Intel CORE i5 7 th generation: one PC with Windows 10 OS and 8 GB RAM for emulating the VAE and four prosumers (HP PC) and two PCs with Windows 7 OS and 4 GB RAM, for simulating other 40 prosumers (Fujitsu PC 1 and 2). The PCs need Java SE SDK v8.x, Tomcat v9.0.x, MySQL v8.0.x, Eclipse Mosquito v1.6.x. Figure 15 shows the deployment diagram of the test environment.  
Various simulations were conducted to test the algorithm. Firstly, it was assumed that the DSO asks for a load reduction between 20,000 W and 75,000 W with a tolerance of \(\pm\)1000 W to 44 residential and commercial prosumers. Since it is not possible that a single prosumer can satisfy the request from the DSO, the 44 prosumers start the aggregation policy in the VAE, creating aggregates able to totally or partially respond to the DSO request for a given price.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \(\Delta\)**P [W]** & **Price [€]** & **Devices Involved** \\ \hline \(-\)4455.19 & 2.52 & Battery \\ \hline \hline \end{tabular}
\end{table}
Table 4: Winner offer at 12:00.  
Figure 15: Deployment diagram of the test environment.  
Various simulations were conducted to evaluate the time needed for the aggregation process. The results of the simulations are reported in Figure 16, showing the elaboration time and the number of aggregates as a function of the required power variation. The results of the simulations show that, according to the algorithm operation described in Section 3, the number of aggregates is between 1 and 7 and that the elaboration time for all the considered cases is between 20 and 29 min depending on the required power variation.  
A second test was conducted by repeating the process of request and formulation of offers six times, keeping unchanged the variation in power required (20,000 W \(\pm\) 1000 W) by varying the number of users involved in the process from time to time. The latter varied from a minimum of 26 to a maximum of 44. The elaboration time varies between 7 and 11 min in this case and is reported in Figure 17.  
In all examined cases, the elaboration time is compatible with the needs of the power systems. Indeed, since the aggregation process was performed  
Figure 16: Elaboration time and number of aggregates as a function of the required power variation.  
Figure 17: Elaboration time and number of aggregates as a function of the number of prosumers participating in the aggregation process.  
for flexibility, such elaboration times are acceptable and do not cause issues to the flexibility management.  
Once the process has been completed, the VAE publishes in the \"Offers Selection\" page all the offers received, showing for each of them the total power variation in the aggregate, the requested price (including the surcharge due to the service provided by VAE), the overall reliability and score of the aggregate, an identification code of the offer and the number of aggregate users with the subdivision by type. The DSO is given the opportunity to select the offer it feels best suits its needs. Multiple criteria can be used to select the \"best\" bid, for example, selecting the bid with the lowest price/reliability ratio.