This report, prepared by CE Delft on behalf of Eneco, discusses the market design for CO2-free electricity. It serves as a discussion paper for a workshop in September 2023 and focuses on ensuring CO2-free electricity by 2035 while maintaining security of supply. The paper discusses challenges and solutions, including investments in solar and wind energy, flexible power and controllable CO2-free power. Key questions are raised regarding policy, self-sufficiency, security of supply and price spikes. The paper also highlights the increasing influence of weather-dependent energy sources on electricity prices, incentives for investment in flexible power and the need for controllable CO2-free power, specifically focussing on extreme situations. Finally, the paper indicates that additional market rules and promising options will be explored in more detail after the workshop to ensure electricity supply.