Use of a Geothermal-Solar Retrofit Hybrid Power Plant to Mitigate Declines in Geothermal Resource Productivity

摘要

Many, if not all, geothermal resources are subject to decreasing productivity manifested in the form of decreasing production fluid temperature, flow rate, or both during the life span of the associated power generation project. The impacts of resource productivity decline on power plant performance can be significant; a reduction in heat input to a power plant not only decreases the thermal energy available for conversion to electrical power, but also adversely impacts the power plant efficiency. The reduction in power generation is directly correlated to a reduction in revenues from power sales. Further, projects with Power Purchase Agreement (PPA) contracts in place may be subject to significant economic penalties if power generation falls below the default level specified. This paper evaluates the retrofit of existing air-cooled binary geothermal power plants with concentrated solar heat input to mitigate the effects of geothermal production fluid temperature decline. The evaluation includes analysis of several declining geothermal production fluid temperature scenarios and identification of the ranges of solar collector capital cost and electrical power sales price where solar thermal retrofit of the base geothermal power plant could improve project economics. It is concluded that solar thermal retrofit of a geothermal power plant with declining production fluid temperature can increase net power generation, especially during periods of high ambient temperature when air-cooled binary plant output is typically lowest. Power plants with higher production fluid design temperatures can achieve higher efficiency, which allows these plants to generate a greater quantity of power from each unit of solar energy input. The quantity of additional power generation attributed to each unit of solar heat input increases as the production fluid temperature decreases from its design point temperature.