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What do you mean by saying that the solar station has a nominal power of “W” kilowatt?
This means that the total power of the panels is exactly “W”, i.e. let’s say, if the station consists of N panels of power w, then W = N × w. But how is determined the power of the single panel “w”, i.e. power specified in its technical characteristics? The power indicated on the panel’s datasheet is obtained from the testing at the standard test conditions ( STC, when the power of incident radiation is 1000 W/m², temperature 25°C, AM 1.5).

Here “s” is the panel’s area in sq.m. and “η” – its efficiency %. In fact, as a result of the testing, when the panel receives radiation at an intensity of 1000 W/m², its IV performance and power output are registered, and knowing the area of it’s surface (i.e. its dimensions) is calculated it’s efficiency η (%). It is very important to understand, that:

If we assume that S = N × s – is the total area of all panels, then for the whole station consisting of N panels we have:

I.e. useful station area multiplied on its efficiency on the numerical value is always equal to the installed capacity in kilowatts (but the dimension of the sq.m.)
But now let’s think about what annual energy output in kilowatt-hours will has this station. Useful (i.e. “working”) area of the station is S = N·× s – this is the area which is involved in the conversion of solar energy into electrical energy.
The average annual capacity of a solar station depends on the insolation of the area where the panels are installed, the orientation of the solar panels and the tilt angle of panels. The average annual insolation I (kWh / m²) is the amount of energy (for example, in kilowatt-hours kWh) that falls per square meter of the earth’s surface in a given location. It is usually defined as a result of long-term monitoring and in free access they perform various tabular data, for example, the data of the US space agency NASA.

Where “I” is the value of the insolation in kilowatt-hours per square meter, “S” is the total area of all Panels in square meters.

Substituting this two expression, we get the following formula for the average annual energy yield of the station:

i.e. in numerical value:

As you can see, the average annual output (yield) of the station is completely determined by the installed capacity and insolation in a given location, and by numerical value it is equal to their mathematically production.
Of course, higher productive panels will have less surface area, but when we assume that capacity of the station is already known, in fact it means that we know the production of total area of all panels on their efficiency. And you can choose more productive panels that will occupy less space or less productive (cheaper) panels if there are no restrictions for the occupied space, but the result will not change from that.
Thus, 1kW solar station has an average annual output of energy in kilowatt-hours (kWh) equal to the numerical value of insolation (in kWh/ per square meter) in a given location.
For example, if in given location insolation is equal to 1700 kWh/m², then the station with a capacity of 1 kW will have an average annual output of about 1700 kWh.

V.Sharafyan