Solar Panels - Temperature and Irradiance effect

Solar panel main parameters

As discussed in a previous article about solar cells, the solar cell is defined as a device that converts solar energy to electricity. We said that it can be used during the daylight or used with an energy storage element like a battery to use at the time of bad weather or shading where the sunlight is not enough to generate electricity or during the night time.

In this article, we will continue with the next step of the electricity from solar panels. We will discuss and explain the main parameters that affect the performance of the solar cell/panels, and we will also explain the panel specifications to understand all about the solar panels. Let’s start.

What is the definition of the solar panels?

A solar panel is a group of solar cell arrays connected to produce electricity to power certain loads or applications or be stored in storage devices like batteries. The dimensions of the solar panel vary based on the number of cells included.

The standard solar cell size is 156mm X 156mm. the number of cells per panel that are known are 32, 36, 48, 60, 72, and 96 cells/panel. The output voltage of the solar panel will be the summation of the voltage of each solar cell (the solar cell output voltage is about 0.5 volts). The power range of the solar cell is from 1 to 1,5 watts.

What are the general parameters that affect the solar panels production?

Before explaining the solar panels' data sheet, we should know some very important parameters that affect the generation of electricity from solar cells and panels. Knowing that these parameters will enable us to easily read and understand the datasheet these parameters are Solar irradiance and Temperature.

What is the Solar irradiance?

The solar irradiance (it is also called insolation) is the main parameter of the solar cell which determines the amount of the electrical power generated from the solar cell. it is defined as the power of the sunlight per unit area with unit W/m2 and the energy of the sunlight also is represented as J/m2.

The value of the solar irradiance that reaches the earth outside the atmosphere is about 1360 W/m2 this value when reaches the surface of the earth and is measured at sea level its value is about 1000 W/m2 during clear days.

When huge numbers of photons in the sunlight hit the electrons in the solar cell, they excite the electrons and give them the Energy that they are carrying to be free and moved outside the cell because of the existence of the depletion layer of the internal P-N junction. the value of the solar irradiance is varied according to the whither condition and the position of the place of measuring.

The below map shows the distribution and the variation of solar irradiance and solar energy around the world. It shows that the areas that have a high solar irradiance are the areas at and around the 30 latitudes north and 30 south. These areas are reached by the sun's energy. Hence, the power generation in those areas is high unlike the other regions that have low irradiance values and as a result low power generation.

Solar Panels - Solar energy distribution

What is the effect of the solar irradiance on the solar power system?

The power generated from the solar power system is directly proportional to the solar irradiance. If the 1000 W/m2 value is affected by the angle of the sunlight which must be perpendicular and the clouding and shading of the weather, the total power generated will be decreased.

The solar irradiance is measured by pyranometers or pyrheliometers these devices are used in the tracking system and usually support the solar power system to optimize the overhaul system by getting the maximum irradiance value for the solar panels.

What is the effect of the temperature on the solar power system?

In the world of solar panels, the temperature increase is considered the killer of the efficiency of the solar panels where the efficiency is negatively affected by increasing the temperature. The increase in temperature causes an increase in the electron's energy and a decrease in the energy band gap.

At this high energy, the depletion layer and the barrier potential will be decreased, enabling electrons to be diffused through the depletion layers instead of moving out to the load. The potential difference of the solar cell will decrease and as a result, the total power will decrease.

What is the temperature coefficient?

The temperature coefficient is the ratio between the power lost measured at STC divided by the number of degrees over 25 ^oC. So we can calculate the lost power which is equal to the temperature coefficient multiplied by the degrees over 25. for example, if we have a solar power system of 400 W installed at 55 o C with a solar panel temperature coefficient of about 0.36%, the power loss % is equal to 10.8% which means that the 400 w will be 365.8 W.

What is the solar panel efficiency?

The efficiency of the solar panel is the ratio between the output electrical power from the panel to the total sun power absorbed by the panel. Let us say a solar panel with an area of about one square meter (1m2) at 1000 W/m2 radiance value and 30% panel efficiency will produce 300 watts (excluding all the other parameters affecting the solar panel output including the active area of the 1 m2 area used).

The maximum efficiency reached is 39.46. All manufacturing companies do their best with their R&D departments to improve the efficiency of solar panels by improving the semiconductor materials and the P-N junction manufacturing.

What is the effect of dust on the PV panels?

When dust accumulates on the surface of the PV panels, the amount of solar radiation that excites the electrons in solar cells to produce electricity will be decreased and as a result, the short circuit current and the open circuit voltage will be reduced causing the output power of the panel to be reduced.

The efficiency of the solar panel is indirectly proportional to the dust accumulated on the surface (could be reached 25 % based on the dust quantity). The dust can cause scratches, corrosion, and cracks in the PV panels. That is why the surface of the panels should be cleaned periodically.