Combined Storage System Developments for Direct Steam Generation in Solar Thermal Power Plants
Abstract
Solar thermal power plants are a key technology for electricity generation from renewable energy resources. Thermal energy storage (TES) is indispensable for solar thermal power plant applications. It makes it possible to meet the intermediate load profile with dispatchable power, a benefit that has a high value to power utilities and that gives concentrating solar power (CSP) technology an edge over photovoltaic and wind power. The major high temperature collector technologies are parabolic troughs, linear Fresnel collectors (line focusing systems), power towers and dish collectors (point focusing systems). Most systems utilize a steam cycle that drives a turbine for electrical energy production. The primary heat transfer fluids (HTF) in the absorbers differ between these technologies. HTFs include water/steam, thermal oil, molten salt and air. Each HTF has its own unique properties and characteristics. This paper focuses on storage designs using water/steam as the HTF in the absorber. This so-called direct steam generation (DSG) has some major advantages. These advantages of the HTF include the following: low costs, low freezing temperature, non- flammable and non-hazardous to ground water. Also, the DSG design results in a comparably low number of heat exchangers and it has a high upper temperature limit (Eck and Hennecke 2009). DSG is utilized today in parabolic trough collectors (e.g. Solarlite), linear Fresnel collectors (e.g. Solar Power Group) and solar tower receivers (e.g. Abengoa PS10, eSolar, Bright Source). The technologies differ in terms of the temperature and pressure levels, as well as the enthalpy ratios for preheating to phase change and to superheating.