This paper proposes a Simulated Annealing based Global Maximum Power Point Tracking (GMPPT) technique designed for photovoltaic (PV) systems which experience partial shading conditions (PSC). The proposed technique is compared with the common Perturb and Observe MPPT technique and the Particle Swarm Optimization approach to GMPPT. The performance is assessed by considering the time taken to converge and the number of cases where the technique converges to the GMPP Simulation results indicate the improve performance of the Simulated Annealing based GMPPT algorithm in tracking to the Global maxima in a multiple module system experiencing PSC.