With almost all the new products (both cells & modules)
being introduced in the market are bifacial, the technology is all set to
dominate the PV market by the next decade. With such an advent, it is important
for an end user to understand how optimally a bifacial module can be utilized
for enhanced commercial returns. We in our previous blog titled “Designing
bifacial PV power plants – Getting the details right! Part 1” introduced you to
factors affecting the
output of bifacial module & further also suggested the comprehensive range of
those factors which can result in desiredoutput from a bifacial power plant. This part would introduce our end
readers on the simulation study we carried out for bifacial power plant. It
would educate its readers on the methodology we followed and assumptions we
considered. In addition to it, this article would also point out the albedo
dilemma in PVSyst and how can it be deciphered.
There are lot of recorded studies which detail the
performance of bifacial module around the world however only a few of them have
India as a focus. India is amongst the fastest growing PV market in the world.
Further it is also the 7th largest country & houses almost all
the type of climatic conditions. Such varied conditions packed in a single
country makes it a suitable choice for studying performance of any solar power
plant. In order to clearly distinguish the performance of a power plant, we
carried out a simulation study by considering a power plant of a fixed capacity.
6 different location each based in the 6 different climatic zones (refer Figure 1) were selected for simulation.
·Hot & dry climatic zone
·Warm & humid climatic zone
·Moderate climatic zone
·Composite climatic zone
·Cold & sunny climatic zone
·Cold & cloudy climatic zone
For further details on the description of climatic zones,
kindly refer to our article “Mono vs Poly – An introspective simulation study!
– Part 1”
Albedo as we discussed in the last article has direct impact
on the bifacial gain. Thus it is important to have a power plant which utilizes
ground with high albedo values. While there are studies citing the bifacial
gain at a given albedo, they may not always factor in all the components
correctly. It is important to note, albedo is not constant but it changes considerably
as the season varies throughout the year. This makes it important to simulate
the power plant with correct albedo factored in. While simulating any power
plant in PVSyst, location of the plant is recorded at initial steps. The
associated climatic conditions of the location can be very well approximated
from the software. Albedo can be very well associated with the climatic
conditions as the ground type utilized in a bifacial power plant gets a cover
(water in rains, snow – both fresh & old during winter, etc.). However when
we use PVSyst specifically for a bifacial power plant, it only considers a
fixed albedo throughout the year. Further while there is input of manually
entering the albedo and changing it, the effects of climate & its
associated considerations in the software clearly seem to lack.
In our study we considered the ground to be of concrete
which has an albedo of 30% ± 5% under clear climatic conditions. Taking
example of cold & sunny climatic zone, the site located in this area has
fairly clear weather from May to September & the concrete ground remains
exposed most of the times. The winter here starts in October where one can
experience drop in temperature, however the ground cover doesn’t change. From
November to January (sometimes even February) the location receives heavy to
very heavy snowfall and hence the ground has a fresh snow cover which requires
the albedo values to be updated for those months. For the next 3 months, the
location may receive occasional snowfall and the ground would mostly have old
snow cover which requires the albedo of the ground to be updated again to lower
values. A similar exercise was done for each location selected in the
particular climatic zone which enables us to be close to the actual energy
production from a power plant (refer Figure 2).
The input to zone wise season variations were collected from various open
source platforms. The associated albedo for a particular zone were further
calculated from various open source reports (PVSyst database, NREL, ARL-NOAA
Research Laboratories).
Figure 2: Graphical
comparision of albedo variation between PVSyst and various climatic zones
While we detailed the methodology of the simulation study we
carried out, it is important to understand the assumptions & considerations
we made. Firstly we carried out this study for both bifacial plants with fixed
tilt & with trackers. This can be understood from the fact that utilizing
bifacial modules with trackers lead to significant gain in energy output (when
comparing it to bifacial power plant installed at fixed tilt). Further the
market for bifacial trackers is expected to grow at a CAGR of 12%~30% in next
decade which makes it a strong contender for the next decade (GTM Insights,
Grand View Research). Secondly, as we mentioned earlier the ground was
considered to be made up of concrete. Concrete was considered because it is
easily available, has fair albedo and can very well have a power plant built
upon. Further the varying seasons and its effect on albedo values was also
considered as mentioned above. Next for easing the calculations on GCR &
land requirements the bifacial module was considered to be in 1P orientation
for both fixed tilt & tracker based power plants.
Specific to mounting, for trackers we have considered
trackers with backtracking option. The tracks the sun for the entire day which
enables energy boost. However there may be times when there is mutual shading
of tracker due to position of sun. Thus when the mutual shadings begin, the
tracker does no more follow the sun, but it goes back to its original position
so that no more further shading occurs. Further as the module are in 1P
orientation, there would be structure shading specifically on trackers onto the
module. We have considered the structure shading factor of 5% in our study
(Soltec). The shed transparency factor represents the amount of light that
passes through cells and in between modules. With the current module technology & the 1P
tracker, the shed transparency factor is considered at PVSyst default of 0%.
While
this part gave you an outline to our study, the albedo dilemma & the
important assumptions we considered in the study, the next part of the study
would give detailed analysis of gains (both technical & commercial) one can
expect when installing a bifacial plant throughout the country. Keep looking
onto this space for out next article.
Let
us all pledge to make solar energy the primary source of energy in the near
future.
RAHE
ROSHAN HAMARA NATION
