# A Novel Hybrid CSP-PV Power Plant Based on Brayton Supercritical CO\({}_{2}\) Thermal Machines
## 1 Introduction  
To stay on track to limit the global temperature rise to 1.5 \({}^{\circ}\)C above pre-industrial levels, the world needs a significant increase in renewable energy. By the end of 2022, renewables comprised 40% of the global installed power capacity. This represents the largest increase in renewable energy capacity to date, adding nearly 295 GW and boosting the renewable energy stock by 9.6%, with solar energy contributing almost two-thirds [1]. Integrating large-scale storage systems becomes crucial to ensure a stable and reliable energy supply as the world seeks to reduce carbon emissions and move towards cleaner energy sources. Storage systems enable the capture and efficient use of excess energy generated by intermittent renewable sources, such as photovoltaic (PV) and wind power. In concentrated solar power (CSP) systems, thermal energy storage (TES) technology has proven particularly effective in converting intermittent solar power into a manageable source. Hybridizing CSP technology with other energy sources enables even better performance by balancing supply and demand, reducing intermittent generation, and lowering the cost of electricity. Thus, integrating storage systems in renewable energy plants, such as hybrid CSP plants, is vital in creating a sustainable and resilient energy infrastructure,supporting decarbonization goals and providing a cost-effective, reliable, and manageable energy source. CSP has traditionally been considered more suitable than PV for baseload generation because thermal storage is more economical than battery storage. However, the solar fields used in CSP technology are usually relatively expensive. In addition, PV plants without storage supply electricity at a much lower cost than CSP plants of comparable capacity without storage. Therefore, the integration of these two technologies is presented as an attractive approach to achieve baseload solar generation with an affordable levelized cost of electricity (LCOE). Figure 1 shows a standard hybridization scheme between a PV and a CSP system [2]. The key idea is to maximize power generation and reduce the LCOE by ensuring coverage over a significant portion of the day. To accomplish this goal, the PV plant, characterized by its low LCOE [3], is strategically designed to generate power during hours of solar radiation. On the other hand, the CSP system captures and stores the thermal energy produced by the solar field. This stored thermal energy is then converted into electricity during hours when solar radiation is unavailable. This innovative approach eliminates the need for expensive battery storage [4] and avoids the necessity of oversizing the solar field. This is because it only needs to generate enough thermal energy to be converted into electricity during periods without solar radiation. Heating resistors might be placed into the thermal energy storage system (typically a molten-salt two-tank configuration), powered by the PV plant, ensuring that excess energy is utilized. However, it is important to emphasize that the efficiency of the heat engine significantly impacts the power recovery from the stored PV energy. In the best-case scenario, approximately half of the stored power is typically recovered. The optimal design of highly integrated CSP-PV power plants was addressed in [5]. A comparison was made between grid-level integration and the inclusion of electric heaters to convert excess PV electricity into heat by storing it in the CSP. The results concluded that the hybrid CSP-PV technology achieved a lower cost of electricity for dispatch levels above 50% and that designs with electric heaters had a 3.6% to 10% lower LCOE compared with grid integration. In [6], it was shown that the hybridization of CSP plants with PV systems could significantly increase the overall plant capacity factor, which contributes to achieving a fully dispatchable solar electricity production system. The study found that CSP-PV plants can achieve capacity factors of 80% or more while reducing the size of the CSP solar field.