# Energy Efficiency Improvement in Reconfigurable Photovoltaic Systems: An Evaluation of Team Systems
## 3 GCPV Systems with Adaptive Sizing Ratio
### Team Concept  
The term \"team\" was introduced in 2002 by the company SMA Solar Technology AG to designate the reconfiguration strategy adopted in some series of grid-connected PV inverters. Since then, the application of this concept to the line of central inverters can be found in several company publications [45; 46]. In team systems, the modification of the sizing ratio is achieved by adjusting the nominal power of the PVG connected to a single inverter, whose maximum power is constant. In this case, the PVG consists of a set of PV arrays. The architecture supporting this reconfiguration principle is based on the use of an initial number of PV arrays (\(n\)) and the same number of inverters. The PV arrays can be dynamically grouped or divided to increase or decrease the nominal power of the resulting PV generators that will finally be connected to one or more of the available inverters. The grouping or division of the PV generators will depend on the available power at the output of the PV arrays and on the rated power of the used inverters. To simplify the analysis of this kind of system, two hypotheses concerning the team architecture are assumed as follows:  
1. The \(n\) PV arrays have the same nominal power (it is noted as \(P_{PVG}\)). 2. The \(n\) used inverters have the same rated power; that is, \(P_{INV1}=P_{INV2}=\ldots=P_{INVn}=P_{INV}\). As an example, the structure of a team-based GCPV system based on four PV arrays and four inverters (\(n=4\)) is shown in Figure 5.  
The configuration shown in Figure 5a is used in periods of low insolation (lower energy production). In this case, the team system is constituted by a single PVG, formed by the union of the four available basic PV arrays, connected to a single inverter. This configuration has the highest value of \(R_{S}\). When the energy production of the PVG increases and exceeds a certain threshold, the system configuration is changed to the configuration shown in Figure 5b. In this case, the team-based system is constituted by two equal PV generators, each formed by the union of two basic PV arrays. Each new PVG is connected to one inverter, so this new configuration has two equal sizing ratio factors, but half the value obtained in the previous configuration. Finally, Figure 5c shows the configuration to be used during periods of highest insolation. In this configuration, the team-based system consists of four PV generators, with each generator corresponding to a single basic PV array. Each PVG is connected to a single inverter, forming four subsystems with equal \(R_{S}\) factors (the smallest value when compared with the two previous configurations). Analytical expressions (from Figure 5) can be derived to determine the power thresholds required for grouping (changing from configuration (c) to (b) or from configuration (b) to (a)) or dividing (changing from configuration (a) to (b) or from configuration (b) to (c)) the PV generators. These expressions will depend on the model used for the inverter'sefficiency, as shown in Equations (5) and (6), the rated power of the used inverters (\(P_{INV}\)), and the condition that the PVG will always be divided into two parts of equal power or two parts of equal power will always be grouped. In this way, the value of the threshold power (denoted as \(P_{UG}\)) to transition from a PVG formed by two equal PV arrays to a PVG formed by only one PV array with double the power will be calculated from the intersection of the curves of efficiency of the power processor involved, as shown Equation (7).