Stagnation of Large-Scale Thermal Solar Systems
Abstract
Among the large scale solar plants realized so far, the occurrence of stagnation is generally rare so that no special precautionary measures were taken to re-start the plants quickly and maintenance free. However, when it comes to large scale plants with industrial and commercial applications which in the future will probably be set up increasingly - frequent cases of stagnation can be expected (e.g. standstills over the weekend, holidays,…) and special, system oriented measures are required to achieve a smooth stagnation behaviour for the plant operator. A concept, many times proven with small scale plants, was adapted to large scale plants. In order to keep significant and temporary steam generating capacities (up to about 130 kW per 1000 m2 collector surface) in large scale plants under control, an efficient stagnation cooler which runs without auxiliary power was developed and causes a complete condensation of the vaporous heat carrier occurring in case of stagnation. The condensate is temporarily stored in a collecting container and can be pumped back into the system automatically and pressure controlled as soon as the stagnation process is finished. An already existing large scale plant (500 m2) was later retrofitted with a suitably dimensioned prototype of this stagnation cooler, together with the necessary system adjustment and a measuring system was installed. The measurements showed the efficiency of this cooler principle. Nevertheless, special focus must be put on the arrangement of pipes of the feed and the return lines, as severe steam hammering might occur during the refilling procedure.