A dye-sensitized solar cell including ZnO nanowire arrays grown of a flat substrate for harvesting solar energy is integrated with a piezoelectric nanogenerator for harvesting ultrasonic wave energy. The two energy harvesting approaches work simultaneously or individually and can be integrated in parallel or serial for raising the output current, voltage or power, respectively. A solar cell employs an optical fiber and semiconductor nanowires grown around the fiber. A p-n junction based design, organic-inorganic heterojunction, or a dye-sensitized structure is built at the surfaces of the nanowires. Light entering the fiber from a tip propagates through the fiber until it enters a nanowire where it reaches a photovoltaic element. Light entering the fiber cannot escape until it interacts with a photovoltaic element, thereby increasing the solar conversion efficiency. The fiber can transmit light, while the nanowires around the fibers increase the surface area of light exposure.