262
M. Pravettoni
global AM1.5 or the direct component of AM1.5 spectra) and the direct measured
spectral irradiance has generally a stronger effect on energy rating than for flat-plane
non-concentrating modules.
The last remarkable differences with respect to the list in Sect. 10.2.5 is that,
due again to the sensitivity of CPV cells only to the direct component of irradiance,
CPV systems strictly operate only in clear-sky conditions and are therefore subject
to huge variations of operating irradiance depending on weather. As a consequence,
CPV can be deployed only in regions where the DNI is high and weather conditions
very stable all over the years, such as arid desert climates, to minimize the loss of
energy production due to high diffuse component of irradiance.
10.3.3 Energy Rating for Bifacial PV Modules
So far we have always neglected the albedo (the component of irradiance reflected
from the ground and surroundings). The reason was that at the optimal tilt, PV
modules are always oriented towards the sky and the albedo is unlikely to make a
significant contribution to the global in-plane irradiance on top of the module, which
is during most of the sunny hours dominated by the other two components (the direct
and the diffuse).
However, the albedo will make a relevant contribution to the global in-plane
irradiance for bifacial modules. Bifacial PV modules (see [5]) are typically doubleglass modules in which bifacial cells are able to absorb light also from their rear
side: as a consequence, at optimal tilt the rear side of bifacial modules is largely
illuminated by the in-plane albedo component R(t), as illustrated in Fig. 10.7. This
is even more relevant when bifacial modules are installed on trackers.
Energy rating for bifacial modules is still missing a protocol at the time of writing,
but is receiving great interest from the PV community, as it is foreseen that bifacial
modules will become more and more relevant in the PV market share, in the near
future. With reference to Sect. 10.2.5, a future protocol for the energy rating of bifacial
modules will need to take into account at least the following additional information:
• the global in-plane irradiance is now G(t) = [B(t) + D(t)][1 + R(t)];
• the albedo needs also to be corrected for the angle of incidence effect, using an
appropriate formula that can be found in the work by Martin and Ruiz [3];
• the effect of spectral mismatch described in Sect. 10.2.4 needs now to be quantified
for both the front and the rear side. It will depend on the tilt of the installation and
also now on the spectral albedo (for which a standard is undefined at the time of
writing).
M. Pravettoni
global AM1.5 or the direct component of AM1.5 spectra) and the direct measured
spectral irradiance has generally a stronger effect on energy rating than for flat-plane
non-concentrating modules.
The last remarkable differences with respect to the list in Sect. 10.2.5 is that,
due again to the sensitivity of CPV cells only to the direct component of irradiance,
CPV systems strictly operate only in clear-sky conditions and are therefore subject
to huge variations of operating irradiance depending on weather. As a consequence,
CPV can be deployed only in regions where the DNI is high and weather conditions
very stable all over the years, such as arid desert climates, to minimize the loss of
energy production due to high diffuse component of irradiance.
10.3.3 Energy Rating for Bifacial PV Modules
So far we have always neglected the albedo (the component of irradiance reflected
from the ground and surroundings). The reason was that at the optimal tilt, PV
modules are always oriented towards the sky and the albedo is unlikely to make a
significant contribution to the global in-plane irradiance on top of the module, which
is during most of the sunny hours dominated by the other two components (the direct
and the diffuse).
However, the albedo will make a relevant contribution to the global in-plane
irradiance for bifacial modules. Bifacial PV modules (see [5]) are typically doubleglass modules in which bifacial cells are able to absorb light also from their rear
side: as a consequence, at optimal tilt the rear side of bifacial modules is largely
illuminated by the in-plane albedo component R(t), as illustrated in Fig. 10.7. This
is even more relevant when bifacial modules are installed on trackers.
Energy rating for bifacial modules is still missing a protocol at the time of writing,
but is receiving great interest from the PV community, as it is foreseen that bifacial
modules will become more and more relevant in the PV market share, in the near
future. With reference to Sect. 10.2.5, a future protocol for the energy rating of bifacial
modules will need to take into account at least the following additional information:
• the global in-plane irradiance is now G(t) = [B(t) + D(t)][1 + R(t)];
• the albedo needs also to be corrected for the angle of incidence effect, using an
appropriate formula that can be found in the work by Martin and Ruiz [3];
• the effect of spectral mismatch described in Sect. 10.2.4 needs now to be quantified
for both the front and the rear side. It will depend on the tilt of the installation and
also now on the spectral albedo (for which a standard is undefined at the time of
writing).