The purpose of decentralised solar district heating plants is to feed solar heat directly into district heatingnetworks. This decentralised heat supply has to consider two major output conditions: a stable required feed-insupply temperature and a feed-in heat power equal to the heat output from the solar collectors. However, manyinstallations cannot achieve the second output condition, since severe oscillations appear in the feed-in heatpower. This problem can be solved by two different control concepts with either temperature- or flow-control.Detailed measurements from two reference plants are provided for these two different control concepts. Onemain conclusion is that a robust control system is characterized by the ability to provide required flows andtemperatures. The major difference between robust and less robust control is that the supply temperatures and/or flows do not fluctuate even if the input conditions are unfavourable. © 2019 Elsevier Ltd. All rights reserved.