The Advanced Geothermal Powerplant produces energy using steam. Geothermal energy production is constant, but it can only be built on top of steam vents on each map. This one is the underwater variant.

Seize control of nearby steam vents to take advantage of reliable energy.

They're often the most metal-efficient source of energy on a map—but when destroyed, the resulting explosion is enough to annihilate most of your fleet. The water offers modest protection from attack and detection, but be wary of torpedo bombers and explosive AoE-equipped units targeting the water directly above.