This work presents a multi-stage stochastic optimization model to analyze price dynamics and reliability of supply in a 100% renewable power system. The stochastic framework captures uncertainty arising from the intermittency of weather-dependent renewable energy sources and compares three market design options for a future fully renewable German electricity market: an energy-only market without capacity reserve, an energy-only market with a capacity reserve, and a centralized capacity market with overprocurement of dispatchable capacity. The results indicate that all market design options ensure a sufficiently reliable power supply. In comparison, an oversized capacity market reduces price volatility but leads to a relatively small increase in system costs. While all options perform similarly from an efficiency perspective, the choice of mechanism has important implications from a distributional perspective.