# Investigation of a Solar-Driven Organic Rankine Cycle with Reheating
## 1 Introduction  
The utilization of renewable energies is an important weapon in order to face the increasing price of electricity, the greenhouse effect, and the depletion of fossil fuels [1]. Solar-driven power cycles are interesting ideas for producing significant amounts of electricity from a small to great scale [2]. The advantage of this idea is the possibility of using thermal storage for storing thermal energy and using it when there is electricity demand [3]. This fact makes possible the avoidance of batteries that are used in configurations with photovoltaics [4]. The most usual choice is sensible storage, while in the last years there are ideas about latent storage and thermochemical storage designs. One of the most usual power cycles for combination with solar thermal collectors is the organic Rankine cycle (ORC), which is an ideal choice for low and medium temperature levels, usually up to 300 \({}^{\circ}\)C [5]. ORC is a cycle like the conventional water/steam Rankine cycle but it works with organic fluids and generally is a less complex unit than the water/steam Rankine cycle [6]. The typical design of the ORC consists of a heat recovery system (HRS), an expanding device, a condenser, and an organic fluid pump. A critical issue about ORC is the selection of the expanding device. For low capacities up to 10 kW, the most usual choice is the scroll expander for capacities up to 100 kW, while for higher capacities, axial turbines can be used [7]. An idea for improving the performance of the ORC is the incorporation of a recuperator after the expanding device in order to recover heat and to reduce the energy need in the HRS, something that improves the thermodynamic efficiency. [PERSON] et al. [8] found that the use of a recuperator increases the ORC efficiency from 5.23% to 6.49% which means anenhancement of around 25%. In another investigation, [PERSON] et al. [9] found 9% enhancement with the use of a recuperator in off-design conditions of an ORC. Another idea is the use of a double-stage ORC, an idea that uses two different ORCs. [PERSON] et al. [10] found that this configuration is able to improve the ORC efficiency by 8% to 12%. Furthermore, [PERSON] et al. [11] studied a double-stage ORC driven by solar energy. They conducted a geospatial analysis in order to evaluate this technology properly and they found the overall system performance to be ranged from 2.2% to 2.8% on an annual basis. In the literature, there are plenty of papers about solar-fed ORC, but they usually investigate the conventional ORC. [PERSON] et al. [12] performed a thermodynamic analysis of a solar-driven organic Rankine cycle with flat plate collectors and concluded that system efficiency can be up to 7.8%. In another paper, [PERSON] et al. [13] investigated a simple ORC driven by flat plate collectors and found a global maximum efficiency of 14.6%. [PERSON] et al. [14] studied the idea of incorporating evacuated tube collectors with an ORC for electricity and hydrogen production. They concluded at 5.92% energy efficiency and 18.21% exergy efficiency. [PERSON] et al. [15] investigated a solar-driven regenerative ORC with parabolic trough solar collectors for Greek climate conditions. They found that the payback period of the investment is close to nine years and the yearly system efficiency is 15.1%. In a similar configuration, [PERSON] and [PERSON] [16] concluded that the utilization of nanofluids in the solar field and in the storage system can improve the efficiency up to 1.75%. The use of linear Fresnel reflectors for driving an ORC has been studied by [PERSON] et al. [17]. They concluded with maximum system efficiency at 19.65% at steady-state conditions. The previous literature summary makes clear that there is a high interest in the domain of solar-driven ORCs. Different solar collectors have been tested, and different configurations of ORC can be found in the literature.