Integration of wave-energy converters with coastal structures provides a way to make wave-energy utilization economically viable. This theoretical study examines a piezoelectric membrane system that serves as a breakwater and a wave-energy harvester. The system is in the form of a piezoelectric layer built into a flexible membrane wave barrier. Series resistor-inductor-capacitor electric circuits are used to obtain electrical output power from ocean waves through the piezoelectric layer. This type of piezoelectric membrane system is proposed for providing harborage and wave-energy extraction at marinas and small boat harbors. Use of an eigenfunction expansion method, solutions to the wave-scattering problem, the calculation of the deflection of the piezoelectric membrane, and an analytical expression for the electric-power output per unit surface area of the piezoelectric layer (output power density) are described. The output power density can reach its maximum value at an optimum resistance, which increases with the thickness and surface area of the piezoelectric layer and decreases with wave frequency. At the optimum resistance, the maximum power output density and the minimum transmission coefficient occur at the same critical frequency, which is controlled by the dimensions and initial tension of the piezoelectric membrane. The surface area and the inductance of the piezoelectric layer have little effect on the output power density, which increases with the thickness of piezoelectric layer nearly linearly.