Technical assessment of Brayton cycle heat pumps for the integration in hybrid PV-CSP power plants

Abstract

The hybridization of Concentrated Solar Power (CSP) and Photovoltaics (PV) systems is a promising approach to reduce costs of solar power plants, while increasing dispatchability and flexibility of power generation. High temperature heat pumps (HT HP) can be utilized to boost the salt temperature in the thermal energy storage (TES) of a Parabolic Trough Collector (PTC) system from 385 °C up to 565 °C. A PV field can supply the power for the HT HP, thus effectively storing the PV power as thermal energy. Besides cost-efficiently storing energy from the PV field, the power block efficiency of the overall system is improved due to the higher steam parameters. This paper presents a technical assessment of Brayton cycle heat pumps to be integrated in hybrid PV-CSP power plants. As a first step, a theoretical analysis was carried out to find the most suitable working fluid. The analysis included the fluids Air, Argon (Ar), Nitrogen (N2) and Carbon dioxide (CO2). N2 has been chosen as the optimal working fluid for the system. After the selection of the ideal working medium, different concepts for the arrangement of a HT HP in a PV-CSP hybrid power plant were developed and simulated in EBSILON®Professional. The concepts were evaluated technically by comparing the number of components required, pressure losses and coefficient of performance (COP).

Techno-Economic Evaluation of CSP–PV Hybrid Plants with Heat Pump in a Temperature Booster Configuration

“…There are several possible configurations for a CSP-PV system with a heat pump. Madhi et al [9] investigated three different concepts combining parabolic trough collectors with oil as heat transfer fluid, a PV field, molten salt thermal storage, and a heat pump. In the first configuration, the molten salt was preheated by the CSP field and further heated by the HP using ambient air as the heat source.…”

“…The CSP field provides the heat source for the heat pump. The medium of the heat pump is air, as the results are similar to N2 (best fluid in [9]) and it is easier to obtain. The PV field supplies the heat pump with electricity.…”

“…Numerous studies have analyzed hybrid plants [1][2][3][4][5][6][7][8][9][10] and some plants have already been constructed [11][12][13]. Different levels of hybridization are possible [1].…”

“…Therefore, payback periods of around 5-10 years could be achieved. Mahdi et al [9] analyzed the use of high-temperature heat pumps to boost the salt temperature in the thermal energy storage of a parabolic trough collector system from 385 °C up to 565 °C. Different heat transfer fluids (HTF) for the heat pump were simulated and compared.…”

Carnot Battery Based on Brayton Supercritical CO2 Thermal Machines Using Concentrated Solar Thermal Energy as a Low-Temperature Source

“…Footprint estimation of selected configurations was included in the analysis. Mahdi et al [28] proposed a reverse Brayton heat pump integrated with a steam Rankine power plant, using molten salts as a thermal energy storage system. Different gases were analysed as working fluid for the heat pump, whereas environment and PTC were combined to supply low thermal energy to the heat pump, which is driven by PV.…”