This paper analyzes the impact of renewables on the resource adequacy in German electricity market. A system dynamic model is proposed to model the electricity market by considering the uncertainty of renewable generation. The aim is to investigate the impact of the increasing renewables generation and its intermittency on the profitability of new installed capacity and long term investment decisions in an electricity market with a very tight reserve margin. It is assumed that the share of renewables generation will increase up to 60% in 2050. The results show that the investment in new conventional capacity will be profitable if the share of intermittent generation by solar and wind is at least 12% of total renewable generation in each year. The reason is that higher intermittency of renewables leads to more frequent scarcity situation and more profit for new capacity. The results prove that higher share of renewables leads to higher mean and variance of loss of load. Also, increasing share of renewables could result either ascending or descending average prices and it depends on the intermittency percentage of renewables' generation. Increasing share of renewables leads to a higher price variance and higher intermittency results a steeper increase of price variance.