Abstract
The concept of a geothermal-solar power plant is proposed that provides dispatchable power to the local electricity grid. The power plant generates significantly more power in the late afternoon and early evening hours of the summer, when air-conditioning use is high and peak power is demanded. The unit operates in two modes: a) as a binary geothermal power plant utilizing a subcritical Organic Rankine Cycle; and b) as a hybrid geothermal-solar power plant utilizing a supercritical cycle with solar-supplied superheat. Thermal storage allows for continuous power generation in the early evening hours. The switch to the second mode and the addition of solar energy into the cycle increases the electric power generated by a large factor—2 to 9 times—during peak power demand at a higher efficiency (16.8%). The constant supply of geothermal brine and heat storage in molten salts enables this power plant to produce dispatchable power in its two modes of operation with an exergetic efficiency higher than 30%.
Highlights
The rate of heat flow from the core to the surface of the earth is 44 TW (44*1012 W)
The following parts of this paper introduce the concept of the proposed geothermal-solar unit and its operation in the two modes
A geothermal-solar power plant that operates with low-temperature geothermal brine is capable to supply two to nine times more power than an optimized subcritical Organic Rankine Cycles (ORCs) unit
Summary
The rate of heat flow from the core to the surface of the earth is 44 TW (44*1012 W). A hybrid ORC geothermal-solar mode with thermal energy storage, which is converted to electricity during the higher electric power demand of the late afternoon hours. The two-mode operation allows the power plant to continuously utilize the brine from the geothermal well(s) and to utilize solar irradiance to significantly increase its output during the high electric demand hours. Most of the studies on hybrid systems pertain to geothermal-solar units that use PV for the production of excess electric power during the peak demand period or use the geothermal fluid for heating, while [18] uses a subcritical ORC cycle with very limited superheat. This study pertains to a hybrid geothermal-solar power plant that operates in two modes and utilizes a supercritical ORC with solar superheat to take advantage of a higher temperature supercritical thermodynamic cycle that does not have the limitations of common supercritical cycles without superheat. The conclusions on the two modes of operation are succinctly presented in the final section
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