Experimental observations on hot-spots and derived acceptance/rejection criteria

Abstract

The hot-spot phenomenon is a relatively frequent problem occurring in current photovoltaic generators. It entails both a risk for the photovoltaic module's lifetime and a decrease in its operational efficiency. Nevertheless, there is still a lack of widely accepted procedures for dealing with them in practice. This paper presents the IES-UPM observations on 200 affected photovoltaic modules. Visual and infrared inspection, as well as electroluminescence, peak power rating and operating voltage tests have been carried out. Thermography under steady state conditions and photovoltaic module operating voltage, both at normal photovoltaic system operating conditions, are the selected methods to deal in practice with hot-spots. The temperature difference between the hot-spot and its surroundings, and the operating voltage differences between affected and non-affected photovoltaic modules are the base for establishing defective criteria, at the lights of both lifetime and operating efficiency considerations. Hot-spots temperature gradients larger than 20°C, in any case, and larger than 10°C when, at the same time, voltage operating losses are larger than the allowable power losses fixed at the photovoltaic module warranties, are proposed as rejecting conditions for routine inspections under contractual frameworks. The upper threshold of 20°C is deduced for temperate climates from the basic criterion of keeping absolute hot-spot temperatures below 20°C.

Efficiency analysis of PV power plants shaded by MV overhead lines

“…The results reveal a hot spot temperature between 10 and 20°C, and a small current reduction. This is in agreement with [18]. In fact, not all the modules presenting a hot spot with a higher temperature than the average temperature of the module between 10 and 20°C have an effective power loss (measured as a decrease in the operating voltage in relation to a non-defective/ shaded module of the same string).…”

Quantitative assessment of the power loss of silicon PV modules by IR thermography and its dependence on data‐filtering criteria

“…To obtain a precise correlation, great care was taken choosing the used temperature difference. The difference between mean temperatures or an equivalent yields results that show a correlation between module power and temperature, in contrast to, for example, the use of a difference between maximum temperatures …”

“…The difference between mean temperatures 7 or an equivalent 8 yields results that show a correlation between module power and temperature, in contrast to, for example, the use of a difference between maximum temperatures. 4,12 In order to deduce an appropriate correlation between the IR data and the electrical performance of the modules, an integral energy balance of a solar module in transient state is formed:…”

An ode to polyethylene

“…Highly conductive polyethylene materials have already been successfully used in conduction cooling of superconducting magnets and can help in mitigating formation of hot spots in photovoltaic solar cells, which decrease the cells' lifetime and decrease their operational efficiency. [75][76][77][78] High thermal conductivity of composite polyethylene particle films has also been demonstrated, which promotes lateral heat spreading away from the locally heated area and allows making use of the larger area for passive cooling through radiation. 48 Wearable technologies can benefit from integrating such thermally conductive films and fibers into clothes to either deliver thermal energy to toes and fingers in cold environments or to remove heat from the armpit areas when the temperature rises.…”