250
M. Pravettoni
Obviously, the answer is «No» again. The reason is the following: with solar PV
installations the power rating of power plants is related to their energy rating by a
remarkably more complex relation than the simple and “naïve” Equation
energy = power × time.
Therefore, let us look here at all the factors that influence, in a PV plant, the
relationship between power rating and energy rating.
In the previous chapter the physical parameters that influence the module power
have been described, together with the Standard Test Conditions (STC) at which the
module power can be rated. Power rating at STC is an important tool in comparing
various products from different manufacturers. Indeed, performance at STC can be
reliably assessed, even artificially indoors on solar simulators, with a high degree of
reproducibility within laboratories and between different laboratories. (The differences are typically of the order of 2–3% in most laboratories worldwide.) However,
STC refer to idealized conditions, which hardly reflect the variety of physical and
environmental conditions that modules experience outside the laboratory in the field
and which reduce the power generation during operation. Therefore, energy rating
is needed to give more confidence to the estimated energy yield during the lifetime
of modules within power plants.
This chapter is on module deployment in real installations and explores what are
the factors that transfer the module power at STC to the energy that the module is
expected to produce in one year: these factors are analysed in Sect. 10.2. However,
there are at least three important cases where the calculation procedure of Sect. 10.2
cannot be applied easily, and which are worth noting: these are the cases of installations on trackers, either for flat-plane modules (1) or for concentrating photovoltaics
(2), and of bifacial modules (3); these three cases are presented in Sect. 10.3. Furthermore, certain loss mechanisms occur when transferring electricity from the module to
the grid. Also, certain failure modes can occur when modules are put into operation:
these failure modes can be “recoverable” (either partially or fully) or “unrecoverable”. Together with the loss mechanisms they will be explained in Sect. 10.4, with
some examples of failure modes on modules from real installations.
Finally, Sect. 10.5 is dedicated to the tools (hardware and software tools) that may
be needed to correctly perform energy rating of PV power plants.
10.2 From Power Rating to Energy Rating
In this section we will guide the reader through the various physical and environmental effects that affect energy generation of PV modules in the field. The result will be
remarkably different than the naïve expectation that energy is simply the power times
the duration of exposure to sunlight. Because of this, a 3 kW power plant cannot be
expected to produce 3 kWh of energy for every hour of sunlight.
M. Pravettoni
Obviously, the answer is «No» again. The reason is the following: with solar PV
installations the power rating of power plants is related to their energy rating by a
remarkably more complex relation than the simple and “naïve” Equation
energy = power × time.
Therefore, let us look here at all the factors that influence, in a PV plant, the
relationship between power rating and energy rating.
In the previous chapter the physical parameters that influence the module power
have been described, together with the Standard Test Conditions (STC) at which the
module power can be rated. Power rating at STC is an important tool in comparing
various products from different manufacturers. Indeed, performance at STC can be
reliably assessed, even artificially indoors on solar simulators, with a high degree of
reproducibility within laboratories and between different laboratories. (The differences are typically of the order of 2–3% in most laboratories worldwide.) However,
STC refer to idealized conditions, which hardly reflect the variety of physical and
environmental conditions that modules experience outside the laboratory in the field
and which reduce the power generation during operation. Therefore, energy rating
is needed to give more confidence to the estimated energy yield during the lifetime
of modules within power plants.
This chapter is on module deployment in real installations and explores what are
the factors that transfer the module power at STC to the energy that the module is
expected to produce in one year: these factors are analysed in Sect. 10.2. However,
there are at least three important cases where the calculation procedure of Sect. 10.2
cannot be applied easily, and which are worth noting: these are the cases of installations on trackers, either for flat-plane modules (1) or for concentrating photovoltaics
(2), and of bifacial modules (3); these three cases are presented in Sect. 10.3. Furthermore, certain loss mechanisms occur when transferring electricity from the module to
the grid. Also, certain failure modes can occur when modules are put into operation:
these failure modes can be “recoverable” (either partially or fully) or “unrecoverable”. Together with the loss mechanisms they will be explained in Sect. 10.4, with
some examples of failure modes on modules from real installations.
Finally, Sect. 10.5 is dedicated to the tools (hardware and software tools) that may
be needed to correctly perform energy rating of PV power plants.
10.2 From Power Rating to Energy Rating
In this section we will guide the reader through the various physical and environmental effects that affect energy generation of PV modules in the field. The result will be
remarkably different than the naïve expectation that energy is simply the power times
the duration of exposure to sunlight. Because of this, a 3 kW power plant cannot be
expected to produce 3 kWh of energy for every hour of sunlight.