Strategy of operation and theme for control of a solar-fossil hybrid electric plant

Abstract

The Crosbyton Solar Power Project has proposed a design for a solar-fossil hybrid electric power plant. This plant will utilize ten Solar Gridirons and a fossil fuel boiler to produce 5 MWe on a steady and reliable basis. Before the final design for this plant can be made, detailed operational procedures must be defined. This study considers strategies, methods, and procedures for operating and controlling the Solar Gridiron. Specifically, two elements of sclar boiler operation were investigated.

The first effort was to develop a basis for selecting the solar boiler operation modes for use under various conditions. A mode is defined by the state of the fluid exiting the boilers. A criterion for switching from one mode to another, in order to improve plant performance, is referred to as a solar boiler operational strategy. For this study several strategies were investigated in an effort to find procedures which provide the most effective capture and utilization of solar energy for the plant. Several strategies were found which improve the expected plant performance. However, the final decision between these strategies must ultimately incorporate economic considerations beyond the scope of this study.

The second effort related to boiler operation, considered in this study, dealt with control of the fluid through the boilers. A control system providing rapid, yet safe, control of the solar boilers is fundamentally different than a control system for a fossil boiler. For fossil boilers, an operator can control the firing rate to produce the amount and q u a l i t y of steam desired. For solar boilers, solar availability directly influences the boiler output, and there is no way to effectively control the solar power reaching the Gridiron. An effective and versatile control scheme for the solar boilers, developed daring this study, is described in detail.