Voltage and angle stability of power systems with renewable power supply and the corresponding region of attraction are analyzed jointly. First, the power system model is derived that consists of algebraic power network equations and differential power generator equations. The renewable power generators like photovoltaic inverters or wind turbines are modeled with first order dynamics. Second, power system stability is analyzed for two kinds of power networks: high-voltage networks with purely inductive power lines and medium-/low-voltage networks with homogeneous resistive-inductive power lines. For both cases, decoupling droop controllers are presented and the stability of this power system including these controllers is analyzed. The analysis is based on contraction arguments that have been used before to prove consensus in multi-agent system. However, due to the particular structure of the power system model, conventional contraction arguments have to be adapted for this analysis.