Abstract: A modular energy accumulator system using compressed air. The system comprises a plurality of bladder modules disposed underwater for subjection to a hydrostatic ambient pressure. The plurality of bladder modules include a first bladder module and at least a second bladder module, each of the bladder modules being oriented substantially longitudinally about a vertical axis when made buoyant by ingress of compressed air. An interconnection pipe assembly is configured to facilitate ingress of compressed air into the bladder modules to a pressure level substantially equal to the hydrostatic ambient pressure, and also to facilitate egress of air from the bladder modules at the hydrostatic ambient pressure. The bladder modules are tethered for being maintained in the underwater disposition.