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Is the Power of Solar Panels Real?

Solar panels are sold with a power output rating, typically between 260-340-400 and up to 500W peak watts (Wp). This is the maximum power that a panel could have in STC (Standard Measurement Conditions).

Is the Power of Solar Panels Real?

When manufactured, each solar panel is tested at the end of each production line so that a manufacturer knows the actual power output of each panel .

Therefore, one of the first questions we can ask is:

Do you really get the Watts you are paying for?

Until recently there has been no possibility to test the power of the panels (external measurements are not precise enough) and the artificial, and fraudulent, increase in the nominal power is an easy way for an unscrupulous manufacturer to do something wrong. free money .

In other words, there are manufacturers that sell us a 270 Watt solar panel, when its real power can be perfectly around 260-265W.

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A simple look at some statistics shown in the following graph shows that there is a serious  problem of quality and veracity in the panels that reach our hands.

Deviation in % from the power indicated on the label

Is the Power of Solar Panels Rea

The graph shows in % the deviations (positive or negative) in two cases:

  • On the one hand, those marked with the “x” are measurements made on solar panels that the manufacturer knew  that those measurements were going to be made.
  • On the other hand, those marked with a red dot are measurements made on panels that  the manufacturer did not know  that the measurements were going to be made.

To determine the % deviation, the power output of each panel has been compared to the rated power output, so a score of 0% means the panel produced exactly what it promised.

The results are variable and the worst panel is 12% less than the promised power. Most of these panels that have been used for measurements are new.

It is true that saying that a panel has 12% less power than it should may not sound too important, but it is, as this will affect the energy production every day of the life of the installation.

But this is not the most serious, but the fact that the manufacturer, by  falsifying the real power,  implies that:

  • You are getting rich at the expense of a product that does not perform as it should.
  • It is deceiving us with the falsification of the real power, so without a doubt it will also be doing it with the quality of other parts that make up the solar panel.
  • It damages the image of the sector, since an owner who is dissatisfied with the production of his installation can spread the already widely heard idea: “Solar energy does not work”.

You may be interested in this report on Electroluminescence Degradation and Test carried out by the IEEE.

What is the power of usual solar panels?

In today’s market there is a wide variety of solar panel power, for example:

panel power  panel size Yield (Efficiency %)
250W Solar Panel 1.7m x 1.0m 14.7%
260W Solar Panel 1.7m x 1.0m 15.2%
270W Solar Panel 1.7m x 1.0m 15.8%
280W Solar Panel 1.7m x 1.0m 16.4%
300W Solar Panel 1.7m x 1.0m 17.6%
310W Solar Panel 1.7m x 1.0m 18.2%
320W Solar Panel 1.7m x 1.0m 18.8%
330W Solar Panel 1.7m x 1.0m 19.4%
330W Solar Panel 2.0m x 1.0m 16.5%
340W Solar Panel 2.0m x 1.0m 17%
350W Solar Panel 2.0m x 1.0m 17.5%
370W Solar Panel 2.0m x 1.0m 18.5%
380W Solar Panel 2.0m x 1.0m 19%
390W Solar Panel 2.0m x 1.0m 19.5%
400W Solar Panel 2.0m x 1.0m twenty%
410W Solar Panel 2.0m x 1.0m 20.5%

How much energy (kwh) does a solar panel produce?:

As we see in the table above, the usual power of solar panels is between 350W to 450W or even more in the case of solar farms. For homes, they are usually used with powers between 350W and 400W, because they are smaller and more “adjustable” to the roof of a house, and for large installations, larger and more powerful models are used.

In the case of having a 400W solar panel at home, you should know that those 400W are nominal, that is, they are only obtained in very specific conditions and that they will rarely occur.

To know how much energy a solar panel produces, it must be related to the peak sun hours (hours per day with a radiation of 1000W/m2), so, in the South of Spain for example, we would have that the energy generated in a sunny day, in spring, it would be:

400W x 5 hours of sun per day = 2000Wh per day.

Well, if it happens to you that your panels are like the ones mentioned at the beginning of the article, of low quality and that they produce less than what they promise, your profitability plan will be seriously affected.


Always try to use solar panels of recognized brands and with experience in the manufacture of panels. Failure to do so can lead to a situation where your panels produce much less than what you paid for them.

Therefore, if you are a photovoltaic installer, or even a homeowner who is thinking of putting solar panels at home, you must be very aware of how important it is to buy good quality solar panels , so that your investment is not compromised or even that you have supply problems if you are disconnected from the grid and only depend on solar panels (with batteries).

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