Renewable Energy Communities (RECs) are anticipated as key means to restructure the energy system in the European Union. However, there are still many open questions regarding the needed conditions that would allow their extensive roll-out. Here we propose a techno-economic model to assess the conditions needed by RECs to operate in an economic beneficial way in the Belgian context. The results indicate that while user type, user consumption and electricity tariff design are important, they are not as important as the amount of installed flexible technology, e.g. heat pumps or electric vehicles, to reduce operational costs. In scenarios with high penetration of flexible technologies the annual operational costs of the REC can be up to 17 % lower than the operational costs of the business-as-usual situation.