TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Structure: In the piezoelectric-photovoltaic structure, the piezoelectric substrate is interposed between a top electrode and a bottom electrode. The photovoltaic layer is interposed between an outer anode layer and an inner cathode layer. The anode and cathode layers are metallic, the anode layer having a higher work function than the cathode layer. The material of the anode layer is distributed to only partially cover the photovoltaic layer. The material of the anode layer is distributed over the photovoltaic layer in the form of a lattice or comb structure. An insulating layer separates the piezoelectric substrate and the top and bottom electrodes from the photovoltaic layer, cathode and anode. The cathode layer and the photovoltaic layer are separated by an interposed layer of lithium fluoride. Photovoltaic layer comprises an outer sub-layer of a transparent electron blocker (hole extractor) polymer and an inner sub-layer of electron donor and electron acceptor (donor-acceptor) polymers. Electron donor-acceptor polymer layer comprises dispersed carbon nanotubes. The piezoelectric-photovoltaic structure comprises an elongate substantially cylindrical body with the layers superposed concentrically. The substantially cylindrical body is a fiber. The piezoelectric-photovoltaic structure comprises fibers that are woven, braided or otherwise arranged in the form of a textile or cord. It comprises a planar body having the layers superposed substantially parallel to it. The planar body is a sheet or film. The piezoelectric substrate comprises a polymer. Piezoelectric substrate comprises dispersed piezoelectric ceramic particles. The photovoltaic layer comprises dye-sensitized photovoltaic cells. Preferred Method: Forming piezoelectric-photovoltaic structure comprises depositing a top electrode and a bottom electrode onto the piezoelectric substrate prior to superposing the photovoltaic layer. The top and bottom electrode are metallic and are deposited onto the piezoelectric substrate by thermal evaporation. The method also comprises superposing an insulating layer over the substrate prior to superposing the photovoltaic layer. Superposing the photovoltaic layer includes the steps of overlaying a cathode layer, overlaying a layer comprising electron donor and electron acceptor polymers over the cathode layer, depositing a layer of a transparent electron blocker (hole extractor) polymer onto the electron donor-acceptor polymer layer, and depositing an anode layer onto the transparent electron blocker polymer layer. The method comprises depositing a layer of lithium fluoride onto the cathode layer prior to depositing the electron donor-acceptor polymer layer. The cathode layer is metallic and is deposited by thermal evaporation. The anode layer is metallic and is deposited onto the transparent electron blocker (hole extractor) polymer layer by thermal evaporation. The layer of electron donor-acceptor polymer is formed by depositing a coating of a polymer solution using a spin coating, dip coating, casting, screen printing, doctor blading, or inkjet printing method. Electron donor-acceptor polymer layer is formed from a polymer solution comprising a mixture of poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM), or poly(p-phenylenevinylene) (PPV) and poly(2-methoxy-5-propyloxy-sulfonate-1,4-phenylenevinylene) (MPS-PPV), or poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and PCBM, or poly(2-methoxy-5-(3',7'-dimethyloctyloxyl))-1,4-phenylenevinylene (MDMO-PPV) and PCBM, or PPV and fullerene (C60), or poly(3-octylthiophene) (P3OT) and PCBM, or PCBM and poly(2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta(2,1-b;3,4-b')dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)) (PCDTBT), or poly(N-dodecyl-2,5-bis(2'-thienyl)pyrrole-(2,1,3-benzothiadiazole)) (PTPTB) and PCBM, the mixture being dissolved in chlorobenzene or 1,2-dichlorobenzene or chloroform. Electron donor-acceptor polymer layer is formed from a polymer solution comprising a mixture of P3HT and PCBM in a ratio of 1:1 by weight. The electron donor-acceptor polymer layer is formed from a polymer solution comprising dispersed carbon nanotubes. The method also comprises annealing the electron donor-acceptor polymer layer. The electron blocker (hole extractor) polymer layer is formed by depositing a coating of a polymer solution using a spin- or dip-coating method. Electron blocker (hole extractor) polymer layer is formed by depositing a coating comprising a solution of a poly(3,4-ethylenedioxythiophene) (PEDOT):polystyrenesulfonate (PSS) or poly-tetrafluoroethylene (PTFE). The method further comprises annealing the electron blocker polymer layer. Providing a piezoelectric substrate includes forming the substrate by an extrusion process. The piezoelectric substrate is extruded from a feed that comprises composite granules containing dispersed piezoelectric ceramic particles in a polymer matrix. Preferred System: In power conversion system, the first circuit includes a rectifier. The second circuit includes a charge controller. One or both of the first and second circuits is/are connected to the terminals of an energy storage device. The piezoelectric-photovoltaic structure is the piezoelectric-photovoltaic structure above. The first circuit includes a rectifier, where the rectifier is an integrated chip or a part of an integrated chip. The first circuit is connected, in parallel with a storage capacitor, to DC-DC converter, where the DC-DC converter is a step-down converter. The DC-DC converter is an integrated chip or a part of an integrated chip. A single integrated chip comprises both the DC-DC converter and the rectifier. The second circuit is connected, in parallel with the storage capacitor, to the DC-DC converter. The second circuit is connected, in parallel with a second storage capacitor, to a second DC-DC converter. It includes a voltage regulator, where the voltage regulator is a diode connected in series with the photovoltaic element. The diode is a Shottky diode. The first circuit comprises the piezoelectric elements and the rectifiers, where one or more piezoelectric elements are connected to each rectifier, and where the rectifiers are connected in parallel. The second circuit comprises the photovoltaic elements connected in series. At least one DC-DC converter is connected to an output smoothing circuit. At least one smoothing circuit comprises a reservoir capacitor and an inductance. A bypass diode connects a pair of output terminals of the, or each, DC-DC converter, or connects a pair of output terminals of the, or each, output smoothing circuit. Each bypass diode is a Shottky diode. Preferred Array: In the power conversion array, the set of series-connected power conversion systems is connected to a final DC-DC converter. The final DC-DC converter is a step-up converter. The power conversion array comprises final DC-DC converters, each having an input terminal connected to a respective set of series-connected power conversion systems and an output terminal connected to a power line bus. The set of series-connected power conversion systems is connected to DC-AC inverter. The power conversion array comprises inverters, each having an input terminal connected to a respective set of series-connected power conversion systems and output terminals connected to a power line bus.