Solar hydrogen is a promising long-term global energy option for the post-fossil fuel era. On the other hand, solar hydrogen may have already found an early commercial application in the form of seasonal energy storage for remote stand-alone photovoltaic (PV) applications. In a stand-alone solar hydrogen energy system, the photovoltaic array is coupled with an electrolyser to produce H-2 which is stored to be later converted back to electricity in a fuel cell. The system setup comprises several subsystems which have to be controlled in an optimal way. Numerical simulations are used to get a closer insight into the transient response behavior of these elegant, but rather complicated systems during variable insolation conditions and to estimate the overall system performance accurately over extensive periods of time. The simulations are performed with the H2PHOTO program which has been successfully used for the design of a solar hydrogen pilot plant. It has also shown good accuracy against experimental data.