Cell and substrate temperatures of glass/glass and glass/polymer PV modules

Performance of photovoltaic (PV) modules decrease as the operating temperatures increase. In hot climatic conditions, the operating temperature can reach as high as 85°C for the rooftop modules. Considering a typical power drop of 0.5%/°C for crystalline silicon modules, a performance decrease of approximately 30% could be expected during peak summer seasons due to the difference between module rated temperature of 25°C and operating temperature of 85°C. Therefore, it is critical to accurately predict the temperature of the modules so the performance can be accurately predicted. The module operating temperature is based not only on the ambient and irradiance conditions but is also based on the thermal properties of module packaging materials. One of the key packaging materials that would influence the module operating temperature is the substrate, polymer backsheet or glass. In this study, the thermal influence of three different polymer backsheet substrates and one glass substrate has been investigated through five tasks:

1. Determination and modeling of substrate or module temperature of coupons using four different substrates (three backsheet materials and one glass material).

2. Determination and modeling of cell temperature of coupons using four different substrates (three backsheet materials and one glass material)

3. Determination of temperature difference between cell and individual substrates for coupons of all four substrates

4. Determination of NOCT (nominal operating cell temperature) of coupons using all four substrate materials

5. Comparison of operating temperature difference between backsheet substrate coupons.

All these five tasks have been executed using the specially constructed one-cell coupons with identical cells but with four different substrates. For redundancy, two coupons per substrate were constructed and investigated. This study has attempted to model the effect of thermal conductivity of backsheet material on the cell and backsheet temperatures.