26 FuturEnergy | Noviembre November 2019 Fotovoltaica | PV www.futurenergyweb.es irradiadores más en la parte superior e inferior de la cara posterior del módulo, para registrar la irradiancia reflejada desde el lado posterior. También se colocan termopares en el medio y borde del módulo posterior de cada matriz para medir la temperatura real de funcionamiento. Influencia de la reflectancia y altura del módulo en la ganancia energética de los módulos bifaciales La ganancia de energía diaria promedio por módulo desde septiembre 2018 hasta abril 2019 se muestra en las Figuras 3 y 4. Los is installed on the front of the module to record the oblique incidence irradiance. Two further irradiators are installed at the top and bottom of the rear module to record the irradiance reflected from the rear side. Thermocouples are also installed in the middle and at the edge of the rear module of each array to test the actual operating temperature. Influence of surface reflectance and module height on the bifacial modules’ energy gain The average daily energy gain per module from September 2018 to April 2019 is shown in Figures 3 and 4. The data shows that, compared with the monofacial PERC modules, the energy gains of bifacial PERC modules with an installation height of 1.5 m are 10.1%, 15.82%, 14.5% and 20.59% in the grass, sand, cement and white painted environments respectively. This is in line with the trend that the higher the surface reflectance, the higher the energy gain. The energy gain is as high as 20.59% on the white painted surface, with a reflectivity of 67.21%, and 10.1% on grass, which is higher than the expected value. Figure 4 shows that when the installation height is increased from 1 m to 1.5 m, the energy gain of the bifacial modules significantly increases, with energy gains on grass and sand increasing by 2.23% (absolute value) and 3.4% respectively, thereby meeting the expectation that a higher surface reflectance, improves the energy gain. Experience shows that the energy gain of the bifacial modules is generally slightly higher in summer compared to winter, because of the periodic variation of the solar elevation angle and the long length of summer mornings and evenings (the scattered light ratio is relatively high). Figure 5 illustrates the energy gain of themonthly bifacial modules and shows the same trend for grass and cement surfaces at low latitudes such as Hainan. In higher latitudes, the energy gain in January and February 2019 is over 5% lower than in other months, mainly as a result of the change in solar elevation angle: the lower solar elevation in the winter means that the array is standing in its own shadow,making the high reflectance of the white painted surface less prominent compared to summer. Based on the data collected from September 2018 to April 2019, the annual energy gain will be higher than the average gain over the previous eight months, taking into account the impact of seasonal factors on the energy gain. Difference in module operating temperature With two temperature sensors on the rear side of the modules, the operating temperature difference between bifacial and monofacial modules can be studied. Theoretically, the light received on the rear side of the bifacial modules will increase the operating current of the component and create a higher module temperature. In addition, the transmittance of the bifacial PERC cell to the infrared radiation is higher than that of the monofacial cell and the lower thermal effect produced by the infrared radiation reduces the module operating temperature. Figure 6 shows that the operating temperature of all the bifacial modules on the different surfaces (at the edge and in the middle of the modules) is lower compared tomonofacial modules. The average operating Figura 2. Instalación en las diferentes superficies probadas durante el proyecto Hainan. Figure 2. Field installation of the different surfaces tested during the Hainan project. Figura 3. Ganancia de energía diaria promedio para módulos en diferentes superficies | Figure 3. Daily average energy gain for modules on different surfaces Figura 4. Ganancia de energía diaria promedio para módulos a diferentes alturas de instalación Figure 4. Daily average energy gain for modules at different installation heights
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