Characterization of Transients of Direct Solar Insolation Based on One-Minute Data 929180
Direct solar insolation transients caused by clouds can impose variations on the operating temperatures of solar thermal systems. Dish-Stirling systems buffer solar transients through the use of liquid metal heat transport systems between the absorber and the engine. While the temperature difference across the absorber dome is affected by any transient, the engine control system will maintain the liquid metal temperature as long as there is sufficient energy for the engine to operate. Otherwise, the liquid metal temperature will vary without control, and off-tracking from the sun may be desired. These temperature variations cause thermal stresses that may reduce the life of the heated components.
120 days of data were collected over a 6-month period for Richland, Washington, and then analyzed. The transients were categorized in terms of duration and average direct insolation values. Limitations of the data and the analysis techniques are described. An average of 1.2 full temperature transients occur per day for a 25 kW dish-Stirling system with a liquid metal pool boiler.