We propose a new method for calculating total energies of systems of interacting electrons, which requires little more computational resources than standard density-functional theories. The total energy is calculated within the framework of many-body perturbation theory by using an efficient model of the self-energy, that nevertheless retains the main features of the exact operator. The method shows promising performance when tested against quantum Monte Carlo results for the linear response of the homogeneous electron gas and structural properties of bulk silicon.

The series resistance in an industrial screen-printed monocrystalline silicon PV module is known to be one of the key factors which need to be considered in order to increase the module efficiency. A model has been built for the series resistance of the module which is based on sub-models for the screen-printed solar cell and the solder interconnects of the structure. The theoretical results of the model have been verified by diode curve fitting of IV measurements, both for the cell and the module. The model can be used to analyse the distribution of the series resistance related to the different parts of the cell, to optimise the front metal grid structure for a specific number of solder spots on the busbar of each cell and the thickness of the interconnection ribbons

The degradation of two amorphous silicon‐based photovoltaic (PV) modules, namely, of single junction amorphous silicon (a‐Si) and of micromorph tandem (a‐Si/ ‐Si), after 11 years of exposure in the south of Spain is analyzed. Their I‐V curves were measured outdoors to study the changes of the electrical parameters in the course of three different periods: during the initial days of exposure, during the first year, and in the subsequent 10‐year period. The translation of the curves to an identical set of operating conditions, which enables a meaningful comparison, was done by the different correction procedures described in the standard IEC60891:2021, including the procedure 3, which does not require the knowledge of module parameters, whose values are typically not available. The annual power degradation rates over the entire 11‐year period are 1.12% for the a‐Si module, which is 3.02% for the first year, and 0.98% for the a‐Si/ ‐Si, which is 2.29% for the initial year.