Detailed nonlinear transient modeling of the photovoltaic (PV) system enables an accurate study of the host integrated AC/DC grid. In this article, the parallel architecture of the graphics processing unit (GPU) catering to a massive number of PV modules is utilized in conjunction with CPU for efficient transient simulation. To reflect the exact operation status of the solar power system subjected to various temperatures and nonuniform solar irradiance in the electromagnetic transient (EMT) simulation, all necessary panels are modeled individually, and therefore, a scalable PV array model with a flexible level of aggregation is proposed in addition to its fully detailed discrete counterpart so as to improve the computational efficiency. The single-instruction multiple-thread implementation mode of the GPU enables up to 10 million PV panels, regardless of the size or type, to be computed concurrently, and noticing that the hybrid AC/DC grid has a significant irregularity, the CPU is also adopted to tackle systems with inadequate parallelism. Meanwhile, since the AC grid dynamic interaction has a distinct tolerance on the time-step to that of the remaining part, a multi-rate scheme is employed to expedite the heterogeneous CPU-GPU computation for dynamic-EMT co-simulation, whose results are validated by the commercial off-line tools MATLAB/Simulink and DSATools/TSAT.