Efficiency and performance of photovoltaic panels

This article discusses the efficiency and performance of modules, as well as the optimum conditions of their operation. We will show you the ideal temperatures to operate them in, and we will discuss the STC factor.

PV panel efficiency and performance

 

Weather conditions, including high (air) temperatures influence the operating efficiency of photovoltaic panels. Temperature fluctuations cause changes in the temperature of PV panels and the accompanying materials. This in turn influences the physical and chemical properties of the entire photovoltaic module. This also translates into its performance efficiency. Photovoltaic panels are made of silicon, a semiconducting material. As the temperature changes, the module changes its electrical and physical properties, such as:

  •  solar radiation absorption

  • charge mobility and energy gap width

  • resistance (electric conductivity) of the semiconductor itself and concentration of charge carriers

The above properties influence the nominal power produced by the PV generator.

From this article, you will find out the following: 

  • PV panel efficiency and performance in various climate conditions
  • Efficiency of photovoltaic modules
  • Electric insulation film – longer usable life of PV panels
  • Optimum operating conditions for photovoltaic panels

PV panel efficiency and performance in various climate conditions 

Photovoltaic panels are designed in such a way that they are able to operate in ambient temperatures between -40 °C and +85 °C. Thanks to this, they can be installed practically anywhere on our planet.

 

Highest cell efficiency

Photovoltaic cells operate at highest efficiency on sunny days, when they are reached by the greatest possible stream of light. However, the high temperature of the solar cell, primarily influenced by ambient temperatures, contributes to changes in the voltage on the panels, also translating to drops in generated energy.

Inasmuch as intense insolation provides the opportunity for high light absorption, high temperatures contribute to voltage drops in PV modules. Voltage drops cause reduced electric energy production efficiency in warmer climates. See also the entry: Is photovoltaics worth it?

 

Photovoltaic module efficiency 

However, assessing the efficiency of photovoltaic modules over the course of the year, beside the temperature, one needs to take into account the number of sunshine days in the year, and their average length. High insolation (exceeding 2000 W/ m2) in warmer climates and the presence of the sun over decidedly the majority of the year (as compared to e. g. the moderate climate) compensates the lower performance resulting from temperatures over +25 °C. It is significant to note that in lower temperatures, on sunny days PV panels are able to generate the same or even more electric energy than in warmer climate zones. In Poland, highest efficiency of PV power stations is found in the Spring months.

 

Electric insulation film – longer usable life of PV panels 

Continuous presence of photovoltaic modules in high temperature environments carries with itself also reduced operating lifetime. In equatorial and tropical climate zones, they are able to operate on average for 15-25 years. Longer-term operational lifetimes are achievable by the use of reinforced electric insulation film or panes of glass. The operating lifetime in moderate and cold climate zones reaches 30-40 years.

 

Optimum operating conditions for photovoltaic panels

The main parameter of PV cells is their nominal power, expressed in Watts (W). The higher this value, the more electric energy is a photovoltaic module able to generate on a unit basis. The nominal power of a PV module is determined under laboratory conditions described by the STC (Standard Test Conditions).

  • insolation: 1000 W/ m2,
  • internal PV module temperature: +25 °C
  • air mass coefficient 1.5 AM.

 

STC – favourable panel operating conditions 

The SC describe the most favourable operating conditions for photovoltaic panels, under which they are able to achieve peak power. When the cell temperature of +25 °C is exceeded, photovoltaic panel performance drops.

The temperature of solar cells under normal working conditions is in turn described by the NOCT (Normal Operating Cell Temperature) value, corresponding to:

  • insolation of 800 W/ m2,
  • a sunlit panel temperature of +20 °C, whereby the internal module temperature may be between 42 °C and 45 °C (depending on the model)
  • a wind speed of 1 m/ s
  • an air mass coefficient of 1.5 AM – determined for Europe.

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