## 2 Methods
### Curve-Shape Measurements and Indoor Tests
After determining the position of the module, the angle-adjustment function of the holder is used to adjust the angle such that the supporting surfaces of the holder and module are approximately parallel. This is repeated two times to fix the module position and holder angle. Subsequently, the upper pressed portion is tightened using a specified tightening torque. First, the coordinates of the curved surface are measured using the CMM (Figure 4). The detailed procedure is as follows. This step is also essential for determining the offset value in the indoor performance tests in the next step. * The framed module is placed on a CMM surface plate (attached to the frame to prevent bending deformation). * To verify the reference plane of the surface plate, a stylus is dropped on the surface plate near the four corners of the frame, and the height of the surface plate is measured (at four points; the \(Z\) value). Two points where the height of the surface plate is at the minimum and maximum are selected. The inclination of the line connecting the two points from the \(XY\) plane of the CMM coordinate system is calculated. No problems occur when the inclination is less than \(0.1^{\circ}\). * The X- and Y-axes are defined with the vertex closest to the mechanical origin of the CMM as the origin within the envelope surface of the approximately rectangular area covered by the cell (Figure 4 and the active zone defined in Figure 5). In addition, the \(Z\)-axis in the vertical direction (upward) is considered, and the \(X\)-, \(Y\)-, and \(Z\)-axes are left-handed. * The height is measured from the plate surface of the origin. Let this be dimension \(A\). * Let \(N\) and \(M\) be the number of rows and columns, respectively, of cells in an approximately rectangular area. The \((2N+1)\) and \((2M+1)\) measurement points are divided uniformly, including the edges of the rectangular region. All the \((2N+1)\)\(\times\)\  
The position of the reference plane for the indoor measurement is given by the center of gravity of the active zone of the PV module parallel to the mechanical contact points of the module (Figures 5 and 7), rather than by the mechanical contact points of the module or the peak position of the module. The coordinate point of the average value of the \(X\) and \(Y\) coordinates in the cell coordinate measurement by the CMM was set as the center point of the module on the reference plane. The optical axis of the solar simulator was aligned accordingly. The envelope surface of the approximately rectangular area covered by the cell should not protrude from the uniformly illuminated area of the reference surface. In the case of a module in which the cells are arranged at equal intervals, the center point of the enveloping surface of the approximately rectangular area covered by the cells  
Figure 5: Definition of the active area and positional relationship to the mechanical contact points. Figure 6: Coordinate measurement of the curved PV modules. Figure 7: Indoor tests with the carrier. is regarded as the center point of the module. Even if it is not calculated from the CMM measurement values, the optical axis of the solar simulator may be aligned with this. That the envelope surface of the approximately rectangular area covered by the cell should not protrude from the uniformly illuminated area of the reference surface. This measurement is analogous to that of single-junction PV devices. For the solar simulators, the only adjustment is that of the total irradiance intensity (considering the associated variation in the spectral irradiance). After the indoor test with the solar simulators, the actual output power was compared using the monitored power output (Figure 8). First, an outdoor testbed was set at a given orientation angle, and the reference plane was adjusted horizontally. The carrier (holding fixture) was then placed on the reference plane while maintaining angles equal to those in the coordinate measurement and indoor performance test.