Studies of the direct input of solar energy to a fossil-fueled central station steam power plant

Abstract

Seven possible methods of absorbing solar energy as direct thermal input to an 800 MW, fossil-fueled, central station steam power plant have been studied. Irrespective of method, the solar heat is first collected by an array of flat mirrors and concentrated on a tower-mounted absorber where it is transferred into the power cycle. The heat absorbing methods studied were heating of feed-water, evaporation of water, superheating of steam, combined evaporation and superheating, reheating of steam, air preheating, and combined air preheating, and feedwater heating. Factors considered were relative capital cost, energy conversion efficiency and complexity of design, operation and control. Combined evaporation and superheating proved to be the preferred method because of its high utilization of solar energy, relatively low indicated capital cost and only moderate complexity in design, operation and control. Feedwater heating also has very desirable capital cost, design and operating aspects, but suffers from the drawback that over 30 per cent of the solar energy absorbed is, in effect, lost because of degradation of the steam cycle efficiency.