Device for cleaning solar modules, of both the photovoltaic and solar thermal type, by projection of a cleaning liquid onto the surface of said modules in the form of spray, is described. The device is of the towed type, for mounting on a tractor vehicle or similar, and is implemented based on an articulated unit which comprises a coupled parallelogram structure, having the possibility of pivoting around a support structure solidarily joined to the carrier vehicle, joined by the opposite end to a telescopic arm which articulately includes a projection bar on its distal end, with variable positioning, integrating a multiplicity of nozzles for projecting cleaning liquid. The projection bar includes mechanical sensors for positioning thereof on the surface. The different movements are carried out in a controlled manner by actuation of hydraulic cylinders and the articulated joint between the projection bar and the telescopic bar includes a means for adjusting the maximum inclination angle of the projection bar.