## 3 Use Case. CEDER-CIEMAT Microgrid
### Characterising the Efficiency of the Elements of the Microgrid
#### 3.3.1 Hydraulic System  
The hydraulic system consists of a Pelton turbine connected to a 60 kW electric generator, four pumps of 7.5 kW each, and two water storage tanks with a total capacity of 2000 m\({}^{3}\) and a difference in level of 70 m between them.  
In order to characterise the turbine, a series of tests were carried out by operating them at different power levels and checking the consumption of the resource (in this case, water stored in the tanks) for each one of them. The results obtained are shown in Table 1:  
The powers at which the turbine has been characterised are 7.5 kW, 15 kW, 22.5 kW, and 30 kW, since these are the powers at which we can operate the pumping system (four pumps of 7.5 kW each). The system will return the turbined water that is collected by the lower reservoir to the upper reservoir.  
The water consumption per kW produced is lowest in the 30 to 35 kW range, where less than 9 m\({}^{3}\) of water is needed for each kW of power generated by the turbine. Therefore, as far as possible, the turbine should ideally operate in this power range.  
In order to characterise the pumping system, it is necessary to know the amount of water that the pumps are capable of lifting to the upper reservoir and their levels of electricity consumption. To accomplish this, water was pumped from the lower tank to the upper tank at the four possible power levels (7.5 kW, 15 kW, 22.5 kW, and 30 kW), i.e., using one, two, three, or all four pumps simultaneously. The results obtained are shown in Table 2:  
To calculate the efficiency of the hydraulic system, we will use Formula 1 described in the previous section, obtaining the results shown in Table 3.  
The efficiency increases as the power increases due to the fact that the nominal power of the turbine is 30 kW, and therefore, its efficiency is higher at values close to that value, dropping significantly at lower values (7.5 kW). We can estimate the efficiency of the installation to be close to 32%, given that the turbine will not be used at power levels lower than 15 kW, as its efficiency decreases significantly within this range of values.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Turbine Energy (kWh)** & **Water Consumption (m\({}^{3}\))** & **m\({}^{3}\)/kWh** \\ \hline
7.5 & 100.6 & 13.4 \\
15 & 147.3 & 9.1 \\
22.5 & 202.2 & 9.0 \\
30 & 265.1 & 8.8 \\
35 & 311.7 & 8.9 \\
40 & 441.8 & 11.1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Turbine water consumption at different operating powers.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Pumps/Power (kWh)** & **Water Rising (m\({}^{3}\))** & **m\({}^{3}\)/kWh** \\ \hline
1 Pump/7.5 & 21.6 & 0.231 \\
2 Pumps/15 & 43.3 & 0.232 \\
3 Pumps/22.5 & 64.9 & 0.231 \\
4 Pumps/30 & 86.5 & 0.230 \\ \hline \hline \end{tabular}
\end{table}
Table 2: m\({}^{3}\) of water lifted to the upper tank with one, two, three, and four pumps.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Power (kW)** & **Performance (\%)** \\ \hline
7.5 & 21.5 \\
15 & 29.4 \\
22.5 & 32.1 \\
30 & 32.6 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Performance of the hydraulic system at different operating powers.