This paper investigates small-scale decentralised markets in the German electricity system. In our case decentralised markets are defined as regions in which regional electricity demand is met primarily by regional generators. The research question is twofold. Firstly, how does the size of decentralised markets have an impact on indicators like CO2 emissions, variable costs or transmission grid extension. Secondly, which effects on these indicators can be observed if only power plants of a certain size or technology are allowed to take part in the decentralised markets.