The growing use of wireless sensors and autonomous electronic systems, e.g. for structural health monitoring or the Internet of Things, increases the demand for sustainable and maintenance-free power sources. Piezoelectric energy harvesters convert ambient mechanical vibrations into electrical energy, enabling self-powered operation in environments where battery replacement is impractical. Hybrid pyro-piezoelectric energy harvesters further enhance this concept by additionally exploiting temporal temperature variations, which are often present alongside mechanical excitations. Energy harvesters are often beam-shaped structures made of piezoelectric material that oscillate due to external mechanical vibrations (ideally in the resonance range). This piezoelectric structure is attached to an electric circuit, which is needed to rectify the electric signal and store the harvested energy. The electromechanical behavior of the piezoelectric structure is influenced by the electric circuit and vice versa. In this contribution, we introduce a Finite Element (FE) simulation framework to analyse the efficiency of piezo- and pyro-piezoelectric energy harvesters [1,2]. The underlying continuum model is based on the coupled set of mechanic, electro-static and thermal equations. The constitutive description focuses mainly on linear behavior (linear piezoelectricity and pyro-piezoelectricity). The connection to various electric circuits is realized via nonlinear boundary conditions or by coupling to an electric circuit simulator. The FE simulation framework allows to analyse the efficiency of piezo- and pyro-piezoelectric energy harvesters for different mechanical and thermal excitations and various electric circuits. Several numerical examples are discussed and partly compared to experimental results.