We describe an open-source simulation tool for the modeling of photovoltaic devices with equivalent circuit networks. Our SpiceGUI interconnects devices with known current voltage characteristics and calculates the current density-voltage curve of the combined device. The SpiceGUI is written as hybrid Octave/MATLAB code and has a flexible graphical user interface. It supports batch simulations with the SPICE tools LTspice, NGspice, and SMARTspice. The available postprocessing functions include convenient batch parameter plots and power loss analysis diagrams. We present two simulation examples. The first example simulates a solar cell with front contact fingers. It assists the reader in understanding the SpiceGUI unit tree and serves as starting point for the development of custom models. This first example also shows that the SpiceGUI yields reliable results, even for very demanding models that exceed 4 GB working memory. The second example models back-contacted thin-film silicon solar cells. We use measured Jsc-Voc curves as input data for the current sources of the network. Additional resistive elements complete the network. The simulated JV curves of the combined device agree well with the measured JV curves. The distributed nature of the resistances is essential to describing the shape of the measured JV curves.