Yield of photovoltaic panels. How is it calculated?

You have certainly heard about the performance of photovoltaic panels. In this article we briefly explain what it is and how it is calculated, so that photovoltaics are within everyone’s reach and not just professionals.

Yield of photovoltaic panels. How is it calculated?

The power of the photovoltaic panels, in order to have identical references for all manufacturers, is calculated under the STC conditions (Standard Test Condition), i.e. an irradiation of 1000W / m2, temperature of 25 ° C, spectral distribution = 1.5.

Without going into details, it is sufficient to understand that all manufacturers test their panels, in order to define the power of the same, under the same conditions, in order to have a unique data. The efficiency of a panel is the amount of solar energy that a panel is able to convert into electrical energy per unit of surface, and it is always the maximum efficiency under the STC conditions mentioned above.

The calculation of the efficiency of a photovoltaic panel is quite simple knowing the peak power and the dimensions (the dimensions of the panel including the frames are used, ultimately the maximum size of the module).

The formula for the calculation (simplified in symbols for non-experts) is the following:

Efficiency% = (Power / Surface / 1000) * 100

The power is the peak power expressed in W, the surface is the surface of the panel in square meters including the frame, 1000 is the irradiation of 1000W / m2, 100 is used to obtain the efficiency in percentage.

Let’s take a practical example, using a 230W peak panel, with dimensions in meters of 1.650 × 0.98 and therefore 1.617sqm of surface area and apply the formula:

Yield % = (230 / 1.617 / 1000) * 100 = 14.22%

The peak efficiency of the panel is 14.22%, this means that at a time of day with ground irradiation of 1000W / m2 and a temperature of 25 ° C, our panel will convert 14.22% of solar radiation into electricity. The dimensions and the peak power can be found on the technical data sheets of the panels or on the labels of the same.

It should be noted that we are only talking about the peak efficiency at STC conditions (Standard Test Condition) and how to calculate it, we are not talking about the productivity of photovoltaic systems which depends on much more complex factors.

We also add that if there are no space problems, the efficiency of the panel is a relatively important datum, while it must be taken into account more importantly when it is necessary to create systems with the maximum possible power in the available surface. In the latter case, the peak power per unit area cannot be neglected.

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