The lead-free nanocomposite generator device for high-output energy harvesting using piezoelectric alkaline niobate-based particles (KNLN) and copper (Cu) nanorods filler is reported. To produce the piezoelectric nanocomposite (p-NC), lead-free KNLN particles synthesized using a solid-state method and the Cu nanorods are distributed in a polydimethylsiloxane (PDMS) matrix. The lead-free flexible nanocomposite generator (NCG) made by a simple spin-casting method successfully converts mechanical energy to electricity up to 12 V and 1.2 A. These are higher than previously reported outputs from other lead-free and composite-based nanogenerators. The harvested energy is utilized to directly turn on white light emitting diodes (LEDs) without external circuits and to operate a complex circuital liquid crystal display (LCD). A large-area NCG device (30 cm x 30 cm) is also fabricated using the bar-coating method to obtain maximum output up to 140 V and 8 A (approximate to 0.5 mW). This NCG technology has substantial advantages as a simple, cost-effective, scalable, and high-throughput approach for practical flexible electronics, bio-eco-compatible self-powered systems, and body sensor networks (BSN).