# Indoor PV Modeling Based on the One-Diode Model
## 2 Methodology
### Experimental and Validation Procedures
The equation used to convert the measured spectral irradiance to spectral illuminance is expressed as [46]:  
\[\text{IIluminance }(\text{lux})=\int_{390}^{830}V(\lambda)E(\lambda)d\lambda \tag{21}\]  
where \(V(\lambda)\) is the measured spectral irradiance value. The 7 W LED and 12 W CFL light sources were chosen, since LED and CFL light sources outperform the other lights sources, such as xenon and incandescent lamps [47], in terms of efficiency. Therefore, their usage is expected to increase in the near future. The same methodology can also be used for any other light source. The impact of different light sources and their respective spectra on conversion is mainly due to their efficiency, as most of their spectra fall within the wavelength range of 390-830 nm considered for illuminance. For example, Figures 7 and 8 show that the power of the 12 W CFL is around 71% higher than that of the 7 W LED, but its illuminance is only 36% higher (1691.637 lux/1237.093 lux, respectively). This reflects the lower efficiency of CFL light when compared to LED light. Also, the values of 1691.637 lux and 1237.093 lux corresponds to 4.72 W/m\({}^{2}\) and 4.05 W/m\({}^{2}\), respectively. For the experimental measurements, a total of 10 different illuminance levels are used to illuminate both PV panels (kx0b22\(-\)12x1 and kx0b22\(-\)04x3f). Illuminance levels range from 1000 lux to 100 lux with a 100 lux step size. To reduce measurement error, each illuminance level is measured 10 times, and the average is taken. As shown in Figure 9, a Keithhey 2450 source measurement unit (SMU) is also used to record the panel's I-V curve [48; 49]. To eliminate the effects of lead resistance, a four-wire connection is established. The connections shown in Figure 6 are made as close as possible to the PV panel to avoid affecting the measurement accuracy due to the resistance of the probe cables. The results of the spectrometer and SMU are then exported to MATLAB to validate the proposed model's accuracy. Figure 8: 7 W LED spectrum. Figure 9: SMU connection with the PV panel. Both the characteristic point translation and parameter extraction techniques are implemented as MATLAB functions, which yield a set of model parameters for the corresponding PV panels depending on the measured reference values. During parameter extraction, the \(R_{s}\) value is increased at each iteration so that the maximum-power point of the corresponding I-V curve is as near as possible to the translated maximum-power point. Hence, it is expected that the sequence and combination of both the translation and parameter extraction techniques will be able to enhance the model's accuracy. The characteristics of the PV panels are given in Table 1. PV panel kx0b22\(-\)12x1 has one solar cell. On the other hand, kx0b22\(-\)04x3f consists of three solar cells. These three solar cells are connected in series. The solar cells used in both the PV panels are made of monocrystalline semiconductor material [50; 51]. The table shows the PV panels' STC datasheet values. However, the manufacturers did not provide the reference values under indoor illuminance conditions due to the low light intensity. Therefore, the experimental measurement at 1000 lux is used as the input values for the translation technique described in the previous section to translate the characteristic points to different illuminance levels. An overview of the experimental methodology and results is presented in Figure 10. The first and second steps are repeated for each artificial light source, whereas the third to fifth steps are repeated for each artificial light source and each PV panel.