Control of decentralised solar district heating

The purpose of decentralised solar district heating plants is to feed solar heat directly into district heating networks. This decentralised heat supply has to consider two major output conditions: a stable required feed-in supply temperature and a feed-in heat power equal to the heat output from the solar collectors. However, many installations cannot achieve the second output condition, since severe oscillations appear in the feed-in heat power. 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. One main conclusion is that a robust control system is characterized by the ability to provide required flows and temperatures. 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