High efficiency evacuated flat-plate solar collector for process steam production

A flat-plate solar collector for process steam production was developed. Th e operating temperatures are in the range between 100 and 150 degrees C. Th e boiling collector can be used for process heat supply in the industry and for solar cooling applications as well. It operates as a system with contr olled influx of liquid. instabilities of the two-phase Bow in the internal evaporator have been successfully suppressed and the design of the system h as been investigated. We constructed a prototype collector based on a comme rcially available evacuated flat-plate collector. To realise high thermal e fficiencies at temperatures up to 150 degrees C, the thermal losses of the absorber have been drastically reduced using an ultra low emissive Selectiv e absorber, a low pressure krypton filling (50 hPa) in the collector casing , and a highly reflecting aluminium foil between absorber and rear side. Th e prototype collector was dynamically tested at our outdoor test facility a nd showed very high efficiencies of more than 60% at 100 degrees C steam te mperature and of 45% at 150 degrees C steam temperature (T-amb = 15 degrees C). The operation behaviour of the prototype was always stable and the ste am mass quality showed excellent values of nearly 100%. (C) 1999 Elsevier S cience Ltd. All rights reserved.