## 3 Results
### Varying Lamp Input Power and Temperature  
The solar simulator was operated at 20%, 50% and at 90% of its rated current. Running the simulator often results in the generation of heat due to the nature of the light source used. The response of the crystalline silicon (c-Si) reference cell under test for over a minute, with its corresponding irradiance, irradiance percentage difference and cell surface temperature, are shown in Figure 9.  
Figure 8: AM1.5 and Xenon arc lamp spectrum.  
Figure 9: Solar simulator operated at varying set points of its rated current.  
As the solar simulator is kept running for a longer period (180 s) in Figure 9, the silicon reference cell's temperature increases beyond the recommended 25 \({}^{\circ}\)C for conducting experiments under standard test conditions (STC). The slight fluctuations in irradiance, as seen in region C of Figure 9, are higher than region A because the simulator is operating at a higher input power, in order to attain the set point of 1000 Wm\({}^{-2}\). There is an increase in the percentage difference of the irradiance in region C, compared to that of areas A and B. The amount of electrical energy transferred as heat from the solar simulator onto the surface of the reference cell is shown in Figure 10.  
The lamp's input power in Figure 10 fluctuates due to a slight change in the lamp's voltage. However, the lamp's input power becomes stable after 120 s of operating the solar simulator. This is because the irradiance set point is reasonably maintained at a lower input power. Because temperature control is not part of the setup for the ADAS, the temperature of the reference cell continues to increase gradually until the solar simulator is switched off, or until thermal equilibrium is reached.  
To determine the amount of energy required to remove the heat imparted onto the surface of the reference cell in Figure 10, Equation (1) is utilised to keep the cell temperature at 25 \({}^{\circ}\)C. It is assumed that the outdoor temperature does not significantly affect the ambient temperature while conducting the experiment.  
\[Q=mc\Delta T \tag{1}\]  
where \(Q\) is the heat energy transferred (Joules), \(m\) is the mass of the silicon reference cell, \(c\) is the specific heat capacity of the silicon solar cell (joule per gram degrees Celsius), and \(\Delta T\) is the change in temperature. The specific heat capacity for the silicon reference cell (710.08 J/kg K), if \(c\) is made the subject in Equation (1), is expressed as:  
\[c=\frac{Q}{(m~{}\Delta T)} \tag{2}\]  
In order to determine the total energy imparted on the reference in Figure 11, and what quantity of heat must be expelled in order to maintain the cell temperature of 25 \({}^{\circ}\)C at 1000 Wm\({}^{-2}\) for carrying out an indoor test on photovoltaic (PV) modules, as recommended by [8]. The total power generated by the solar simulator, total energy exerted by the solar simulator on the reference cell, and the total heat is given by Equations (3)-(5).  
\[P_{total}=G\times A \tag{3}\]  
where \(P_{total}\) is the total power of the simulator (W), \(G\) is the irradiance (Wm\({}^{-2}\)), and \(A\) is the area of the reference cell (m\({}^{2}\)).  
Figure 10: Energy generated by the solar simulator.  
Also, the energy exerted on the reference cell by the solar simulator is expressed in Equation (4).  
\[E_{total}=P_{total}\times t \tag{4}\]  
where \(E_{total}\) is the total energy exerted on the reference cell (k), \(P_{total}\) is the total power of the simulator (W), and \(t\) is time (s).  
The total heat required to maintain a cell temperature of 25 \({}^{\circ}\)C at 1000 Wm\({}^{-2}\) is represented by Equation (5).  
\[Q=\rho Atc(T_{f}-T_{i}) \tag{5}\]  
where \(Q\) is the total heat (k), \(\rho\) is the density of silicon g cm\({}^{-3}\), \(A\) is the area of the reference cell (m\({}^{2}\)), \(t\) is the thickness of the reference cell, \(T_{f}\) is final temperature (\({}^{\circ}\)C) and \(T_{i}\) is the initial temperature (\({}^{\circ}\)C).