## 3 Results and Discussion  
### Solar Radiation, Electricity Generation, Temperature and Relative Humidity  
Solar radiation and electricity generation, along with temperature and relative humidity of ambient, inside the ISD and during sun drying, are shown in Figure 3. The solar panel generated a stable voltage between 19 and 21 V, even when solar radiation fluctuated. The highest solar radiation recorded in batch 1, 2 and 3 was 580.6, 788.2 and 673.5 W/m\({}^{2}\) at 13:53, 11:42 and 11:13, respectively. In batch 1, it was a cloudy and slightly rainy day. It can be seen that the stability of energy generation seemed not to be strongly affected by the fluctuation of solar radiation. Figure 3: Solar radiation and photovoltaic (PV) voltage (**top**), and temperature and relative humidity of the inflatable solar dryer (ISD), compared to conventional sun drying and the ambient condition (**bottom**) during three drying batches (20, 22 and 23 November, 2017). The temperatures in the ISD were generally higher than for sun drying. Moreover, the highest temperatures recorded in the ISD were 46.9, 60.0 and 51.5 \({}^{\circ}\)C at 13:55, 14:11 and 10:52 in batch 1, 2 and 3, respectively. Similar results were also reported from paddy rice drying using an ISD in the Philippines [22]. Hence, the temperature in the ISD was around 10 to 13 \({}^{\circ}\)C higher than the ambient temperature. The surface of the solar panels could also easily become dusty. Therefore, the panels should be cleaned regularly, in order to prevent a greater loss of energy generation from the panels. Moreover, a high risk of a short circuit on the solar charge controller was observed due to faulty insulation and wiring. Any loose connection between the cables and wires should be avoided. The wire insulation at the plugs of the charge controller should be improved. The shadow effect on the surface temperature of paddy rice is shown in Figure 4. High cover and round shape of the black plastic film blocked the sunlight and created a shade area on the right or left side of the ISD drying area. Temperature of the paddy rice in the shade was around 10 \({}^{\circ}\)C less than the paddy rice exposed to the sunlight. This could be one of the explanations for the low drying performance of the dryer [31; 32]. The air velocity at each outlet was 5.05 \(\pm\) 0.25 m/s. It could be estimated that the air velocity in the ISD was between 0.3 and 0.5 m/s. Since the fans were connected to the solar battery and therefore supplied with a nearly constant current, no substantial difference in the air velocity was observed among all batches. In contrast to the study of [PERSON] et al. [22], in this study, condensation of water in the lower layers of the paddy rice did not occur in the ISD. Figure 4: Thermal image (**top**) and real image (**bottom**) inside the inflatable solar dryer (ISD). Temperature and relative humidity in the ISD at different distances from the ISD inlets at a particular time in each batch, where the ISD inlets were represented as 0 m, are presented in Figure 5. A rapid increase of temperature from the collector to half the length of the ISD was detected in all batches. For instance, in batch 2, the temperature increased from 40.8 \({}^{\circ}\)C at the collector to 55.3 \({}^{\circ}\)C in the middle at a distance of 12.4 m. Subsequently, the temperature was slightly lower near the outlet (about 1-2 \({}^{\circ}\)C) than the temperature in the middle of the ISD. On the other hand, the relative humidity was relatively constant along the ISD. Figure 6 presents the temperature change of the paddy rice during a mixing process with the roller bar. It can be seen that temperature of the paddy rice in the upper layers was higher than in the lower layers. The bulk height of the paddy rice prevented a heat transfer from the top to the bottom layer, and therefore the temperature on the top was about 5 \({}^{\circ}\)C higher than on the bottom layer.