ADVANTAGES OF EAST-WEST SYSTEMS
IN THE COMMERCIAL SECTOR
Increased yield and cost savings with one MPP tracker
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© Fronius International GmbH
Version V1.0 11/2021
Peter Schmidhuber, Jasmin Gross
Solar Energy
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equally to the male and female form
.
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TABLE OF CONTENTS
1 Introduction .....................................................................................................................................4
2 Types of alignment .........................................................................................................................5
3 East-west system construction .....................................................................................................6
4 Choosing the inverter .....................................................................................................................7
5 Energy yield according to orientation ..........................................................................................9
5.1 Factors influencing the PV yield .................................................................................................... 10
6 East-west with 1 MPP tracker ..................................................................................................... 14
6.1 Lower costs with one MPP tracker ................................................................................................ 15
6.2 Positive impact on efficiency .......................................................................................................... 15
7 Calculation example .................................................................................................................... 17
7.1 Example A: without oversizing ....................................................................................................... 17
7.2 Example B: oversizing of 120% ..................................................................................................... 19
7.3 Example C: Oversizing of 140% .................................................................................................... 21
8 Simulation results ........................................................................................................................ 23
9 Conclusion ................................................................................................................................... 24
10 Appendix ....................................................................................................................................... 25
11 List of figures ............................................................................................................................... 34
12 List of tables ................................................................................................................................. 34
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1 INTRODUCTION
When planning a commercial photovoltaic system, it is necessary to adapt to local conditions in order to
generate the maximum yield at a low cost. First of all, along with the classic system design, it is necessary to
decide the direction of alignment for the system.
In this document, different system alignments for commercial photovoltaic systems are explained and
compared with one another – based on the expected yield and their individual advantages. The east-west
orientation in the commercial sector is also discussed in detail: specifically, the impact of implementing eastwest systems with a single MPP tracker per inverter.
PV*SOL calculations are used to show that different alignments on one MPP Tracker – such as the classic
east-west orientation – have no effect on the total energy yield of the commercial system, but do have many
advantages.
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2 TYPES OF ALIGNMENT
Commercial photovoltaic systems can be aligned in different directions. The most useful alignments are
south, east, or west. Combinations of these three alignments are also possible and commonplace (such as
south-east, east-west, south-west).
The east-west alignment makes more room for more power
One common variation is the so-called "east-west system", where the PV system modules partly face east
and partly face west.
This mounting system is a very efficient method, especially on flat roofs, as firstly more can be squeezed
onto the roof surface, and secondly, you do not have to worry about the modules themselves potentially
casting a shadow. With a south-facing system on the other hand, you have to take into account that modules
may be shaded by other modules.
Because of this reciprocal shading in south-facing systems, adopting an east-west orientation allows almost
twice as many modules on the roof surface as when mounting them aligned to the south.
Figure 1: PV modules aligned to the south
Figure 2: East-west PV module orientation
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3 EAST-WEST SYSTEM CONSTRUCTION
An east-west system on a flat roof of a business
enterprise usually has row upon row of modules, with a
maximum tilt of 10 degrees. There is no need to worry
about the modules shading one another, as they are
positioned back-to-back. On sloping roofs, such as on a
gable roof, modules are conventionally installed "parallel
to the roof" in classic module mounting systems, or
"integrated into the roof".
Mounting PV modules on a flat roof is usually less onerous, because the area exposed to the wind is
smaller, meaning that less ballast and fixing are needed than for a south-aligned support system on a flat
roof. In many cases, this can also be a crucial deciding factor in opting for this orientation. On older roofs, the
additional load caused by the ballast needed for a south-facing system is not always possible for structural
reasons, either.
A distinction is made between a centralized and a de-centralized system design for positioning the inverters.
Depending on local circumstances, the inverters for the commercial PV system can be placed close to the
modules, or close to the distribution box.
Figure 3: Flat roof mounting arrangement for an east-west
system
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4 CHOOSING THE INVERTER
Once the orientation of the commercial PV system has been decided, the main components necessary for
the project are defined in principle. The essential element of a PV system is the inverter(s). Once you have
decided on the type of inverter, it is necessary to address the question of the power category for each
device.
Lower initial costs in an east-west system
The required inverter power category is based primarily on the total generator output of the PV system.
There is a fundamental difference between a south and east-west alignment here, however. With an eastwest orientation, for example, the same generator output can be achieved using a lower power category
inverter than for a south orientation. Considerable cost savings can be made for the project as a result.
The differences in the required power category stem from the maximum power of the inverter. Despite the
same generator output, this maximum power varies in accordance with the type of alignment. This is clear to
see in a comparison of the PV yield curves for the two alignment types.
Figure 4: Utilization of inverter capacity in east-west and south-facing systems
In an east-west aligned system, daily production in the PV system begins at first light in the early hours of the
morning, increases rapidly, and is typically almost at maximum production by late morning, maintaining this
level until the early afternoon. The curve falls again in the late afternoon/evening, but production only stops
on the west side late in the evening. This results in a broad, but nevertheless flat PV yield curve.
In a south-aligned PV system on the other hand, production starts somewhat later in the morning, and then
rises sharply. A south-facing system tends to briefly record the greatest yield around noon, although this
decreases again in the afternoon. South-facing systems typically produce a steeper, but more narrow PV
yield curve.
In the south-facing yield curve, the inverter is most frequently called upon around midday, and is utilized at
up to 100% capacity for the majority of the time. In the flatter east-west alignment, on the other hand, the
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inverter capacity is more evenly utilized throughout the day, with the maximum power never usually reaching
100%. Inverters can therefore be significantly oversized in east-west systems.
Opting for a low power category for the inverters also has a positive effect on the initial cost, which means
that the impact on the overall system cost is also positive.
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5 ENERGY YIELD ACCORDING TO ORIENTATION
An east-west PV module orientation is possible both on a flat roof and on conventional sloping roofs, and is
extremely useful in many cases. In general, an east-west system produces energy for longer throughout the
day. As already mentioned, production in an east-west system begins earlier in the morning and stops later
in the evening, compared to a south-facing system. This results in a broader, but flatter PV yield curve. A
south alignment on the other hand creates a higher but narrower yield curve, because this generates more
energy than an east-west system, especially around midday.
Figure 5: Typical shape of the energy yield curve in relation to the orientation of the PV system
Higher self-consumption in east-west systems
A broad (east/west) PV yield curve is generally a sound basis for a high self-consumption rate, as overall,
energy is produced for longer and most importantly, production is more evenly spread throughout the day,
which tends to keep the temporary PV surplus to a minimum. As a result, companies that rely on an eastwest system orientation for their PV system benefit from a high self-consumption rate. The higher the selfconsumption, the faster the investment in the PV system pays for itself.
If you compare the two alignment types on the basis of the expected yield, and assuming the same
generator output, a south-facing system usually generates more than an east-west system.
But: If you look at the respective proportions of roof surface being used in each case, east-west orientations
will always achieve a better yield than south alignments, as the roof surface can be used more efficiently,
and more PV modules can be installed. In turn, more PV modules mean that the PV generator itself is larger.
The larger the PV generator, the greater the anticipated PV yield.
The utilization of the individual inverters is also usually higher in an east-west system, as the alignment in
two directions reduces the peak load. This means firstly, better utilization of inverter capacity, and secondly,
operating the inverter in a better efficiency range. Most inverters are at their most efficient if they are not
operating at full capacity.
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5.1 Factors influencing the PV yield
The energy yield of a PV system basically depends on the different, external factors acting on the PV
modules. These include the outside temperature, the insolation, and the use of an MPP solar tracker with the
inverters.
Effect of temperature
The ambient temperature has a major effect on the PV modules and thus on the PV yield. High temperatures
have a negative effect on the PV yield, as is obvious from the graphic below.
Figure 6. Energy yield in relation to outside temperature
As you can see, the temperature primarily affects the voltage (V), not the current (A). The higher the
temperature, the lower the voltage. In an east-west system, this effect would be indirectly proportional. In the
morning, the first rays of sunlight on the east side cause the temperature to rise, which causes a drop in
module array voltage. On the west side, on the other hand, the temperatures in the shade are even lower,
which causes the voltage to rise. On the shaded side, so the voltage is higher, but the power on the shaded
side is still low due to the lack of solar radiation. For this reason, the inverter sets the optimal operating point
to the east modules in the sun. On the shaded west side, however, no significant losses occur, even though
they are not in the ideal operating point.
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Effect of insolation
Along with outside temperature, direct insolation has the most influence on the PV modules, and thus on the
PV yield. The direct insolation on the module array differs, depending on the location, time of day, and
weather conditions. The more intense the irradiance, the higher the anticipated PV yield.
The graphic below shows a module characteristic diagram in relation to insolation.
Figure 7: Energy yield in relation to insolation intensity
It is easy to see that the voltage level is high, even when there is little sunlight. This only changes slightly
right up to maximum irradiance, as irradiance primarily affects current (A) and not voltage (V) – as is the
case with temperature.
This effect impacts positively on an east-west orientation, because if sunlight is already present on the east
side in the morning, the voltage level is nevertheless similar to that on the west side. The resultant mismatch
losses are therefore marginal and can be ignored.
Effect of module tilt
Due to the major impact insolation has on the total energy yield of a PV system, the tilt angle chosen for the
PV modules should be one that makes optimum irradiance possible. The ideal tilt angle differs according to
alignment and location.
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