Clusters are an organisational and economic phenomenon. This paper attempts to answer what an energy cluster actually is and whether it meets the requirements of a cluster in the classical approach of economic sciences. The Act of 20 February 2015 on renewable energy sources (Ustawa OZE 2015) introduced the concept of an ‘energy cluster’. It was aimed at, among others, increasing energy security and environmental protection through an efficient use of renewable energy sources. In the literature on the subject, there is no single universally applicable definition of a cluster, it can only be considered in its various aspects. The concept of a cluster has so many applications, associations and meanings that in many respects it has become a ‘chaotic idea’ due to flattening and equalising different types, processes and spatial scales of economic location within one universal concept. However, the main doubt concerns the very definition of a cluster.