# A Novel Hybrid CSP-PV Power Plant Based on Brayton Supercritical CO\({}_{2}\) Thermal Machines
## 1 Introduction
However, in promising future scenarios focused on cost reduction (around USD 60/kWh), the advantages of batteries become evident, and a PV plant with batteries shows a higher competitiveness than a plant with TES. This was also discussed in [17]. Different scenarios were explored in [18] to identify the dominant technology in a hybrid solar power plant providing sustainable and programmable energy by 2050. It was concluded that CSP with TES is currently the most affordable technology. Still, a shift towards PV with BESS is expected, mainly due to both systems' significant reduction in costs. This paper introduces an innovative integration scheme that combines PV and CSP (based on PTC solar field technology) systems. In this proposed scheme, both solar resources operate synchronously, providing low-temperature heat (PTC) and power (PV) to a novel high-temperature heat pump. This heat pump efficiently transfers high-temperature heat to the power cycle (heat engine), simulating the output that would have been generated by a central receiver system with heliostats, but now with a parabolic trough collector field. To ensure the system's dispatchability, a two-tank molten-salt TES is strategically positioned between the thermal output of the heat pump and the power cycle. This integration through a heat pump instead of electrical resistors allows the recovery of all the power supplied by the PV, thereby enhancing the thermal supply from the PTC. This fact constitutes a key aspect of the proposal, enabling two main benefits. On the one hand, it enhances both the thermal level and the overall quantity of thermal energy derived from the PTC field. This avoids the need for a central receiver system with a heliostat field to achieve high temperatures and eliminates the necessity for field oversizing. Instead, these functions are fulfilled by the PV field. On the other hand, the coefficient of performance (COP) of the heat pump compensates for the efficiency-related penalty imposed by the power cycle. Consequently, the proposal enables the retrieval of all power supplied by the PV field, a feat not achieved in conventional hybridization, where electrical resistors are used to store PV surplus. Lastly, it is worth noting that the proposed hybridization ensures that all power injected into the grid comes from a synchronous generator, contributing its rotational inertia. This characteristic offers stability advantages compared with direct injection from the PV field. Figure 2 illustrates the concept of the proposed hybrid plant. The PV power drives the mechanical consumption of the heat pump, while the thermal solar field provides the low-temperature heat input. The heat pump efficiently integrates and converts both energy sources into a high-temperature heat output, which can be either stored or directly converted into electricity by the heat engine. The implementation employs a parabolic trough collector (PTC) solar field to leverage well-established technologies. A two-tank thermal energy storage system, filled with molten solar salt (with a weight composition of 60% NaNO3 and 40% KNO3), operates at temperatures of 589 \({}^{\circ}\)C/405 \({}^{\circ}\)C. This temperature range aligns with the current state-of-the-art in CSP technology, particularly with central receiver systems [19]. Consequently, this system is anticipated to avoid corrosion and material-related issues, different from those currently reported in CSP plants with storage. The role of the heat pump is to effectively convert the PTC solar field into a virtual heliostat/central tower receiver system, thereby enhancing the overall efficiency of the heat engine. Figure 2: Conceptual scheme of the proposed novel hybrid CSP-PV plant. The core component of this integrated system is a heat pump based on a reverse Brayton cycle, using supercritical CO2 as the working fluid.