Power loss due to temperature in photovoltaic panels

The loss of power of solar panels due to temperature is one of the great enemies of photovoltaic installations. Up to nearly 15% of the energy generated by the photovoltaic module can be lost.

When planning a photovoltaic installation, it is necessary to take into account the consumption that will be made and thus be able to know how many photovoltaic panels will be necessary to cover all the energy demands. In these studies, there is usually oversizing to cover possible increases in specific consumption or decreases in production due to external factors.

These calculations are usually made on the basis of the parameters indicated by the manufacturer and which can be found both in the data sheets and on the back of the solar panels. Although the first we usually look at is the maximum power of the panel, it will also be important to look at other parameters such as efficiency. Efficiency is usually found in percentages and is the ratio between the electrical power delivered by the panel and the power of the radiation falling on it.

Parameters in perfect standard conditions

The parameters of the solar modules were extracted after different tests carried out on the equipment, always under perfect standard conditions. These conditions include an incident irradiance of 1000 W/m2, an ambient temperature of 25 degrees Celsius and an air mass of 1.5 (AM1.5) on the spectrum. This implies that when the conditions are different from those marked in the tests, the efficiency, voltage and final power of the photovoltaic module vary.

One of the factors that most influences this efficiency is the ambient temperature. Or by excess, as can happen during the summer months, when the hours of sunshine are greater and also the temperature, factors that will heat the panels well above the standard 25 degrees. Or by default, during the winter months, where in higher regions or in the north, temperatures can drop very low and cold air can cool the panels well below the standard 25 degrees. Hence the importance of the value, and the differences between the panels, of the power loss due to the temperature coefficient, which gains relevance when examining the technical data of the module.


Power loss coefficient due to temperature.

The power loss coefficient due to temperature will be the one that tells us how much power we are going to lose as the temperature increases. It will normally be expressed as a percentage per degree, for example -0.34%/ºC. What it says is that for every degree raised or lowered from the 25°C the solar panel was tested in, 0.34% of the panel’s power will be lost.

In the following table you can see how the power varies as the temperature increases by one degree and in ranges of five degrees. The most efficient and resistant panels are generally around -0.26%/ºC of coefficient while the least resistant are around -0.38%/ºC. These differences can add up to almost 1W of lost power for every degree of difference in the most powerful panels and 0.5W in average panels.

As an example, suppose we have an installation of five 640W panels, with a thermal power loss coefficient of -0.38%/ºC, at an average temperature of +/- 10ºC, something that happens during most of the summer, the losses of the installation will be 121.6W. If we extrapolate it to industrial installations, where there can be 30 modules installed, we speak in the case of panels with losses of 729.6W. In the case of higher temperatures, something that can easily happen in summer, since it is the temperature of the panel, if the ambient temperature is +/- 10ºC, the module that spends long hours in the sun will reach very high temperatures. high. With a panel temperature of +/- 35 ºC, 85.12W per module would be lost, with five panels we would lose 425.6W and with thirty panels 2,553.6W.

The difference between the coefficient of power loss due to temperature is reflected all the more as the installation is larger. For example, in a 5kW residential installation with a temperature variation of +/- 10ºC, the difference between the panel with the least resistance to temperature changes and the one with the best resistance will be almost 80W, the first losing 190W while that the second would lose 111.72W. This in a 50kW industrial installation, the difference is even greater, this being almost 500W, with 1,520W against 1,040W. In a commercial installation of 2mW, the installation with a higher coefficient, the power losses would be 76,000W and with a lower coefficient, the losses would be 52,000W, a difference of 24,000W.

Just as there is a temperature coefficient for power, it can also be found for current and voltage. With the first, the increase in temperature will not produce a great variation, the increase in intensity being minimal, whereas in the case of voltage if there is a decrease in it, which ends by producing a drop in the power of the solar panel.

In summary, when choosing the photovoltaic module for our installation, and its sizing, it is necessary to take into account the usual climatic conditions, and the most extreme, where the panels will be located to calculate and oversize the installation if necessary, and thus be sure that the energy production will always be optimal.

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