This work, written in 2008, is on a photovoltaic field simulator that is a power electronic device which produces direct voltages and currents. These simulate the behaviour of a photovoltaic field working in arbitrary conditions of solar irradiance and temperature. The most important application of the simulator is the testing of inverters. This work also introduces a new model describing the behaviour of photovoltaic modules of any generation. This is particularly useful to scientists and plant designers as it is based only on the electrical parameters that are always reported in a photovoltaic module’s datasheet.