2.2.2. Automated Installation and Maintenance Maneuvers

In this section, we propose a procedure with which to carry out the automated installation and maintenance maneuvers for gravity-based first generation TECs by controlling the inner ballast water inside the device in order to place the TEC at the desired depth. In the procedure proposed, it will be noted that the degree of complexity of the maneuvers is substantially reduced, as are the means required, which will translate into a substantial reduction in costs. As in the previous section, the installation of the TECs can be divided into the installation sequence of the structure of the TECs and the installation sequence of the gondolas. The following steps have, therefore, been defined in order to perform the automated installation tasks:

	- **–** Once the base structure that supports the gondola is completely installed, the gondola is moved using a tugboat. The tugboat will move one gondola per trip (see Figure 9a).
	- **–** When the tugboat arrives in the position in which the gondola will be placed, the guide cables connected to the structure of the TEC are recovered by using an acoustic signal (see Figure 9b).
	- **–** In the following step, the gondola is lowered onto the seabed. The inner ballast water inside the device is controlled, signifying that the gondola starts filling with water and its inner ballasts permit the gondola to descend. If the difference between the weight of the gondola and the buoyancy force is small, the descent process will be performed slowly. The descent velocity is completely controlled by changing the amount of water inside the inner ballasts (see Figure 9c,d). The gondola descends to a depth close to the base structure that will support the gondola.
	- **–** When the gondola is at the desired depth, but not in a vertical position as regards the base structure owing to the tidal currents, the guide cable will help install the gondola on the base (see Figure 9e).
	- **–** When the gondola is on the structure of the TEC, the inner ballasts of the gondola are filled with water in order to achieve an adequate coupling with the base structure. The installation of the TEC is, therefore, completed (see Figure 9f).

**Figure 9.** Automated installation maneuver of the gondola (immersion sequence): (**a**) movement of the device with maneuver control in closed loop; (**b**) connection between the cable wire and the gondola; (**c**) immersion maneuver in closed loop; (**d**) immersion maneuver in closed loop (cont.); (**e**) immersion maneuver finished; and (**f**) installation maneuver in closed loop finalized.

The maneuvers that are necessary to perform the maintenance tasks (recovery of a submerged gondola) in a closed loop follow an inverse order to that described for the installation of the gondola. The steps required to perform maintenance maneuvers are the following:

	- **–** When the gondola is on the structure of the TEC (see Figure 10a), water begins to empty out of the inner ballasts of the gondola until the structure of the TEC and the gondola separate (see Figure 10b).
	- **–** The controlled emersion process of the gondola now begins. Water is emptied out of the inner ballast of the gondola in a controlled manner in order to obtain a smooth emersion movement (see Figure 10c,d). A guide cable is used during the emersion process.
	- **–** When the gondola is on the surface of the sea, the inner ballast is completely emptied in order to increase the buoyancy of the gondola, after which, the control system is disconnected.
	- **–** The maintenance tasks are carried out on the gondola (see Figure 10e). When these tasks have been completed, the control system is connected and the gondola starts filling its inner ballasts with water, thus allowing the gondola to descend automatically (see Figure 10f).
	- **–** All the steps explained for the installation of the gondola (immersion maneuver) are repeated to achieve the connection between the base structure of the TEC and the gondola.

**Figure 10.** Automated maintenance maneuver of the gondola (emersion sequence): (**a**) the water begins to be emptied out of the gondola; (**b**) separation between the TEC structure and the gondola and start of emersion process; (**c**) emersion maneuver in closed loop; (**d**) emersion maneuver in closed loop (cont.); (**e**) emersion maneuver finalized, the inner ballasts are completely empty and are disconnected from the control system; and (**f**) start of maintenance tasks.
