# Energy Efficiency Improvement in Reconfigurable Photovoltaic Systems: An Evaluation of Team Systems
## 1 Introduction  
As stated by the Energy Department of the European Commission, energy is the commodity that fuels the economy, and the prosperity and security of the EU depend on a stable and affordable energy supply [1]. The changes driven by the EU's energy policies have led to a significant reduction in the use of the most polluting fuels, with consumption shifting towards natural gas and renewables. The decrease in gas production in the EU in recent years (a 2.5% drop over the last 10 years [2]) has resulted in a greater dependence on gas imports. To reduce this dependence on foreign resources, it is necessary to increase energy production using domestic resources. In this regard, the intensive use of renewable energies and high-efficiency systems will play a crucial role. Regarding renewables, photovoltaic (PV) solar energy has shown the highest growth in Europe in the last 10 years, reaching 186 GW installed by the end of 2021, an increase of close to 150% [3]. While this is a step in the right direction, it is important to also consider increasing the efficiency of PV systems. Inverters used in grid-connected PV (GCPV) systems are highly efficient (typically 92-98% in commercially available inverters [4; 5]), with some room for improvement, but the industry is currently focused on increasing the efficiency of solar panels. According to data published by the National Renewable Energy Laboratory (NREL), the currently highest confirmed conversion efficiency for PV modules ranges between 14% and 25% [6], depending on the PV technology considered, values that coincide with those previouslycollected in the [7]. Another approach worth exploring is the improvement of energy efficiency through the use of reconfigurable PV systems in grid-connected applications. The plant-oriented (PO) configuration is the most prevalent architecture used in large-scale GCPV systems due to its simplicity and low cost per kW [5]. This architecture is based on a single set of series-parallel electrically interconnected PV modules, known as a PV generator (PVG), which can be considered as the energy capture subsystem. Additionally, the PVG is connected to the grid through a single central inverter, which acts as the energy processing subsystem. The central inverter is responsible for extracting the maximum power from the PVG and transferring it efficiently to the grid. Making GCPV systems more competitive requires maximizing the energy injected into the grid, which in turn requires finding the optimal relationship between the power capacities of the different subsystems. The optimal sizing of a GCPV system based on a PO configuration (as is shown in Figure 1) involves determining the optimal relationship between the nominal or peak power of the energy capture subsystem (\(P_{PVG(STC)}\)) and the nominal power of the used energy processing subsystem (\(P_{INV}\)). The output power of the central inverter (\(P_{AC}\)) is obtained from the inverter efficiency (\(\eta_{INV}\)) and the PVG output power (\(P_{DC}\)). The PVG output power is obtained from the PVG efficiency (\(\eta_{PVG}\)), the irradiance (\(G\)), and the PVG operating temperature (\(T_{PVG}\)). Finally, the PVG operating temperature is obtained from the incident irradiance (\(G\)), the ambient temperature (\(T_{A}\)), and other features related to the construction of the PVG. Therefore, the design of this kind of GCPV system firstly addresses the appropriate choice of both the PVG peak power given in standard test conditions--STC (\(P_{PVG(STC)}\)) and the rated power of the central inverter (\(P_{INV}\)). The ratio between these two values is usually known as the sizing ratio (SR) and constitutes one of the main design parameters of the GCPV systems based on PO configuration. The first references on this topic date back to the 90s, and since then many authors have focused their research on this subject to obtain criteria that allow for determining of the optimal value of this parameter.