Disclosed is an energy-accumulation apparatus including an accumulator body assembly defining a pneumatically-pressurizable chamber. The pneumatically-pressurizable chamber is configured to communicate with a pneumatic-pressure source. The pneumatic-pressure source is positioned on a shore and being located away from a body of water. The energy-accumulation apparatus also includes an outer surface extending from the accumulator body assembly. The outer surface is configured to securely contact a sloped floor zone of a body of water at a position being spaced apart from a shore.