Performances et limites de chaudières à gaz de centrales solaires
Production of electricity from solar energy is mainly achieved by means of solar cells or by central receiver power plants. These plants are driven by vapor turbines where the fluid temperature is about l000°F or by gas turbines in which gas temperature exceeds 1500°F. The geometry and optical properties of heliostats are used to modelize their behaviour. Thus the field of mirrors can be optimized by considering shadowing and blocking effects. The flux distribution is computed in order to determine the aperture area and how much flux reaches the cavity interior. The tube geometry of the heat exchanger is adjusted relatively to the walls. Improvements due to selective coatings is examined. On the basis of these information, unsteady local temperatures of heat exchanger tubes are computed for good weather and typical clowdy days. Daily and weekly simulations are performed in order to predict the life-time and the mechanical damage mainly resulting from high temperature creep. A continuous creep computation allows to extrapolate preceding results in order to know the final damage. Considering mechanical behaviour, as well as energy efficiency, some options are evaluated such as higher temperatures, pressure increase, other flux patterns, alternative alloys… to determine heat exchanger limit. Gas receivers are technologically feasible with usual materials. By stress-strain analysis it can be deduced that the damage is kept at a low value with the open cycle but is higher with a closed cycle. The final efficiency of such installations is about 20%.