East - West Split - How many invertors???

[NoodleNoggin]

Sorry to bump an old thread but im doing a little research on the whole E/W how many invertors subject.

This thread makes for interesting reading, I also found this article which basically concludes that a single invertor is the way to go:

InterPV.net - Global PhotoVoltaic Business Magazine

"The investigations on both PV systems have demonstrated that in an east-west orientated PV system, with a single inverter for the east and west generator, mismatching losses occur. As expected, these losses are very small and are partially compensated by the fact that the single inverter operates in a higher efficiency range. In contrast to minimal yield losses, the following costs can be reduced significantly: firstly the number of inverters can be reduced and secondly the nominal power of the single inverter can be reduced by up to 35% - depending on the inclination angle of the installed solar modules. Furthermore, installation costs can be minimized.
If one considers basic installation rules, the inclination angle of the solar modules and module technology, installing a single inverter in an east-west orientated system can be cheaper than installing a system with separate inverters. Finally, installing a single inverter has no disadvantages compared to installing an inverter with two MPP Trackers. "

 

[Joker]

Have a read of this research paper from Fronius... it doesnt copy and paste well but the words give you enough.

EFFICIENT EAST-WEST ORIENTED PV SYSTEMS WITH ONE MPP TRACKER

ABSTRACT: A willingness to install east-west orientated photovoltaic (PV) systems has lacked in the past. Nowadays,
however, interest in installing PV systems on east-west roofs is steadily increasing. Although south orientated systems are
better, east-west oriented PV systems can also generate substantial earnings. Moreover, due to the sharp drop in module
prices, increased demand for east-west systems are expected for the future. From the perspective of grid operators, eastwest
oriented PV systems are preferable to south orientated ones, as the energy is fed-in more evenly throughout the day,
therefore reducing power peaks thus relieving the grid. Up to now it was assumed that
east-west orientated PV systems require separate inverters for each orientation, or at least one inverter with multiple MPP
Trackers (Maximum Power Point), to avoid mismatching losses. This paper will show an analysis of east-west orientated
PV systems connected to one MPP Tracker and demonstrate the high performance of such systems.

1 INTRODUCTION
Based on theoretical analysis, the behaviour of the
MPP of an east-west orientated PV system was
investigated and then verified by comparing results. For
the practical results two east-west arrays were installed –
one PV array with thin film modules and one PV array
with crystalline modules. These arrays were then split
and put into operation as separate systems – the first with
one inverter for the east roof and one inverter for the west
roof, and the second with a single inverter for both roofs.
The thin film modules were installed with an azimuth
angle of -67.5° for the east generator, 112.5° for the west
generator, and an inclination angle of 30°. The crystalline
modules, on the other hand, were mounted with an exact
orientation of -90° for the east generator, 90° for the west
generator, and an inclination angle of 15°.
Measurements of the ‘IV’ characteristic were taken to
obtain accurate results and possible inverter deviations
were monitored by installing energy meters.

2 MISMATCHING
At first glance, the installation of a single inverter in
an east-west oriented PV system leads to the expectation
of large mismatching losses. Due to the different
orientations in an east-west PV system, the solar modules
are exposed to various irradiation levels. For this reason,
different module currents occur between the east and
west strings, depending on the time of day. In contrast to
large current differences between the east and west
generator, the MPP voltages are nearly identical, as can
be seen in Figure 1. Since the total voltage of the east
generator is similar to the total voltage of the west
generator, very small mismatching losses are expected if
these strings are connected in parallel to a single inverter
(one MPP Tracker).
The mismatching losses differ according to the
inclination angle of the installed solar modules and the
module technology used. The greater the inclination
angle of the solar modules, the higher the mismatching
losses. Essential to understand the losses from the
module technology are the fill factor and the change of
the MPP voltage as a function of irradiation.
Figure 1: IV characteristic of a crystalline module at
different irradiation levels [1]
The fill factor - which is usually higher for crystalline
modules than for thin film modules – is crucial, since it
determines how steeply the power curve drops before and
after the MPP. Figure 2 shows the typical characteristics
of a crystalline module and a thin film module. It can be
seen that the power curve of the crystalline module drops
more steeply around the MPP than the power curve of the
thin film module. Therefore, it is likely that crystalline
modules lead to higher mismatching losses in east-west
orientated PV systems than thin film modules.
Another important point, however, is the change of
the MPP voltage as a function of irradiation [see Figure
1]. A small change of the MPP voltage over a wide
irradiation range causes the fewest losses. The change in
MPP voltage is mainly affected by the module
temperature. A low temperature coefficient and good
ventilation of the solar modules therefore results in better
performance in east-west orientated PV systems.
Moreover, a high low-light performance of a solar
module can also improve the power output. Since all
these variables differ with every module, no general
conclusion can be drawn about which technology is more
favourable for east-west oriented PV systems.
Crystalline module - Fill factor ≈ 80%
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
0 10 20 30 40 50 60 70
Voltage [V]
Current [A]
0
50
100
150
200
250
300
Power [W]
V/I - Characteristic MPP V/P - Characteristic V/P - Characteristic
Thin film module - Fill factor ≈ 60%
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
0 20 40 60 80 100 120 140
Voltage [V]
Current [A]
0
20
40
60
80
100
120
Power [W]
V/I - Characteristic MPP V/P - Characteristic V/P - Characteristic
Figure 2: Characteristic curves of a crystalline module
and a thin film module

3 RESULTS
3.1 Low mismatching losses
As explained in section 2, the installation of a single
inverter in an east-west orientated PV system necessarily
results in mismatching losses. However, these losses are
minimal and are partially compensated by other positive
effects. For example, an east-west orientated PV system
with a single inverter operates in a higher effiency range
for more of the time when compared to an installation
with separate inverters. The figures shown in section 3.1
use data from the
east-west orientated PV system with the crystalline
modules [see section 1].
DC Voltage
200
300
400
500
04:48 07:12 09:36 12:00 14:24 16:48 19:12 21:36
Time
Voltage [V]
DC Voltage: East-Generator
DC Voltage: West-Generator
DC Voltage: East/West-Generator
Irradiation and Temperature
0
200
400
600
800
1000
04:48 07:12 09:36 12:00 14:24 16:48 19:12 21:36
Time
Irradiation [W/m2]
0
20
40
60
80
100
Temperature [°C]
Irradiation: East-Generator Irradiation: West-Generator
Temperature: East-Generator Temperature: West-Generator
Figure 3: Comparison of the measured DC voltages with
the corresponding irradiation and temperature profile on
a sunny day
Figure 3 shows the DC voltage of the east/west
generator with a single inverter compared to the DC
voltages of the east/west generator with separate
inverters. As can be seen, the voltages of the east and
west generator are different. In the morning, the voltage
of the west generator is generally higher than the voltage
of the east generator, whereas the reverse is true in the
afternoon. This is a result of the irradiation and
temperature behaviour of solar cells, since the DC
voltage remains nearly constant at a global irradiation
level above ~180 W/m2 and increases/decreases with
decreasing/increasing module temperature.
The east/west generator produces mismatching losses
because the DC voltage of that generator is not identical
with the DC voltage of the west generator in the morning.
The same applies to the DC voltage of the east generator
in the afternoon. Although the DC voltage of the
east/west generator deviates by up to 5% from the
voltages of the generator with separate inverters, the
energy losses are very small, as can be seen in Figure 4.
This is because the DC voltage of the east/west generator
follows the voltage of the east generator in the morning
and the voltage of the west generator in the afternoon. An
additional point to note is that a deviation of 5% from the
optimal MPP voltage does not lead to the same
percentage of power losses, since a lower/higher MPP
voltage also causes a higher/lower MPP current.
Energy
201,14 201,34
0
50
100
150
200
Sunny day
Energy [kWh]
East/West-Generator East- + West-Generator
AC power
0
4
8
12
16
20
24
04:48 07:12 09:36 12:00 14:24 16:48 19:12 21:36
Time Power [
kW]
East/West-Generator East- + West-Generator
Figure 4: AC power comparison with the corresponding
energy yield on a sunny day. ~ 0.1% energy losses of the
east/west generator with a single inverter compared to the
east/west generator with separate inverters
As shown in Figure 4, the AC power curve of the
east/west generator with a single inverter overlaps the
combined AC power curve of the east/west generator
with separate inverters for the whole day. The different
DC voltages of the generators lead to approximately
0.5% mismatching losses but the final energy losses are
just 0.1% - within the accuracy of measurement of the
energy meters of ±1%. As mentioned before, the
mismatching losses are partially compensated due to the
east/west generator with a single inverter operating in a
higher efficiency range. The energy losses are highest on
a sunny day because the lower the irradiation difference
between the east and west strings, the lower the deviation
of the DC voltages. The result is that energy losses are
even lower on a cloudy day or on days with diffuse
irradiation.

 

[Joker]

... continued from above...


3.2 Energy yield comparison – Part I
The following energy yield comparison shows the
result of the east-west orientated PV system with thin
film modules. As can be seen in Figure 5, the energy
losses of the east/west generator with a single inverter are
very low over a long period.
Energy yield - 3 Months
107,96 115,53
137,61
361,10
109,07 117,06
138,47
364,60
0
50
100
150
200
250
300
350
400
May 09 Jun 09 Jul 09 May 09 - Jul 09
Month
Energy [kWh/kWp]
East/West-Generator East- + West-Generator
Figure 5: Energy yield comparison of the east-west
oriented PV system with thin film modules over a period
of 3 months. ~1% energy losses of the east/west
generator with a single inverter compared to the east/west
generator with separate inverters
Based on the results from May to July, it can be
expected that the annual energy losses of the east/west
generator with a single inverter will be less than 1%. The
east/west generator with a single inverter therefore has a
clear advantage compared to an installation with separate
inverters. It is also superior to an installation of a single
inverter with two MPP Trackers. In fact, the east/west
generator with a single inverter is the cheaper solution
whilst generating almost the same energy yield, as only
one inverter is needed. In addition, the single inverter can
have a lower nominal power than the sum of the nominal
power of the separate inverters. This is because the power
peaks of the east and west generator are time-shifted, as
shown in Figure 6. The nominal power reduction
depends on the inclination angle of the solar modules –
the higher the inclination angle, the lower the nominal
power of the single inverter. As explained in section 1,
the thin film modules were installed with an inclination
angle of 30°, allowing the nominal power of the single
inverter to be reduced by approximately 15%.
AC power profile
0
0,5
1
1,5
2
05:31 07:55 10:19 12:43 15:07 17:31 19:55
Time
Power [kW]
East-Generator [1,013 kWp] West-Generator [1,012 kWp]
East/West-Generator [1,711 kWp]
Figure 6: Example of the AC power profile of the
east-west orientated PV system with thin film modules. A
nominal power of ~85% of the sum of the nominal power
of the separate inverters is sufficient for the single
inverter
From these results it can be concluded that the cost
savings are greater than the energy losses. This means
that the payback time of the east-west PV system with a
single inverter is shorter.

3.3 Energy yield comparison – Part II
The results in section 3.3 are the energy yield
comparison of the east-west orientated PV system with
crystalline modules. Since the inclination angle of the
solar modules is just 15°, there is very little energy loss,
as can be seen in Figure 7. The mismatching losses are
between 0.3% and 0.5%, but they are compensated due to
the higher efficiency operation of the single inverter.
Energy yield - 3 Months
121,10 127,51
149,48
398,09
121,15 127,49
149,54
398,18
0
50
100
150
200
250
300
350
400
May 10 Jun 10 Jul 10 May 10 - Jul 10
Month
Energy [kWh/kWp]
East/West-Generator East- + West-Generator
Figure 7: Energy yield comparison of the east-west
orientated PV system with crystalline modules over a
period of 3 months. The energy yield of the east/west
generator with a single inverter is nearly the same as that
of the east/west generator with separate inverters
In this case, the east/west generator with a single
inverter is the lower-cost option. The cost savings are
obvious and roughly the same as set out in section 3.2.
Firstly, only one inverter is required. Secondly, the
nominal power of the single inverter can be reduced by
approximately 5%, as shown in Figure 8. The nominal
power reduction of 5% results from the 15° inclination
angle of the crystalline solar modules, as explained in
section 3.2. At this point, it should be mentioned that a
single inverter with twice the nominal power of one
separate inverter is always cheaper than two smaller
inverters.
AC power profile
0
5
10
15
20
25
04:48 07:26 10:04 12:43 15:21 18:00 20:38
Time
Power [kW]
East-Generator [11,35 kWp] West-Generator [11,5 kWp]
East/West-Generator [21.8 kWp]
Figure 8: Example of the AC power profile of the
east-west orientated PV system with crystalline modules.
A nominal power of ~95% of the sum of the nominal
power of the separate inverters is sufficient for the single
inverter
Consequently, the payback time of the east/west
generator with a single inverter is shorter than that of the
east/west generator with separate inverters.
4 BASIC INSTALLATION RULES
The following rules must be observed in order to
ensure that an east-west orientated PV system with a
single inverter operates optimally:
Shading must be avoided
The number of solar modules must be identical
in all strings
Within a single string, the inclination angle and
orientation of the solar modules must be
identical

5 CONCLUSION
The investigations on both PV systems have
demonstrated that in an east-west orientated PV system,
with a single inverter for the east and west generator,
mismatching losses occur. As expected, these losses are
very small and are partially compensated by the fact that
the single inverter operates in a higher efficiency range.
In contrast to minimal yield losses, the following costs
can be reduced significantly: firstly the number of
inverters can be reduced and secondly the nominal power
of the single inverter can be reduced by up to 35% -
depending on the inclination angle of the installed solar
modules. Furthermore, installation costs can be
minimised.
If one considers basic installation rules, the
inclination angle of the solar modules and module
technology, installing a single inverter in an east-west
orientated system can be cheaper than installing a system
with separate inverters. Finally, installing a single
inverter has no disadvantages compared to installing an
inverter with two MPP-Trackers.
6 REFERENCES
[1] Fraunhofer Institute for Solar Energy Systems ISE,
How fast does an MPP Tracker really need to be, 24th
European Photovoltaic Solar Energy Conference,
Germany, 2009

 

[sundown]

have just had east west split fitted 10 panels on east and 5 on west . west with shading issues. sunnyboy 3000tl-20
having read this thread, because of unequal strings , seems to me i should have 4000tl with 2 mppt. any comments please

 

[wstevew]

have just had east west split fitted 10 panels on east and 5 on west . west with shading issues. sunnyboy 3000tl-20
having read this thread, because of unequal strings , seems to me i should have 4000tl with 2 mppt. any comments please

I would say you need 2 trackers or inverters.

I'm not expert enough to say if the 4000TL is suitable as each tracker needs 150v. But I'm sure others on here can advise.

I have an e/w split 22.5 degrees incline, eight 240kWp panels on each orientation and my installer has wired the two strings into a single tracker on the 4000TL Its working fine but I have arranged for them to come out and move the strings onto the seperate trackers. I have no shading and identical strings. 3.7kWh generated today 10th December. (Sunny)

 

[sundown]

on the 10 th i harvested 2kw. with my 3000tl on 1 mppt. seems i should have 2 mppt inverter

 

[man]

Hi
I have a system of 3.45 kW with 20 photovoltaic panels (LG 235 M1C-C2 ) and two strings; one oriented to the East and other one to West (10 panels E and 10 panels W). The slope of my roof is + / - 25º. I have a Sunny Boy 3300 with one MPPT. I consider a hypothesis to change to another one that has two MPPT (but I have I have many doubts about this). I started my production only 20 days ago. I live in northern Portugal.
Someone told me that is possible to use in each string, a Schottky diode of at least 10A and 600V to isolate the two strings together (diode in series) to improve my system with my Sunny boy (in this way one string (in the shade) not absorb the energy that the other one is producing).
I would like to know more about this. Anyone can help me in this matter?

 

[cbw]

Sorry to dig up an old thread!

However it does show that I have looked before asking..............

On the SMA 4000TL Can I put 6 panels south and 10 west, or do they have to be equal on each tracker?????

Cheers,

James

 

[SolarCity]

The SMA 4000TL is dual tracker inverter so the strings do not need to be equal.

 

[babba]

Glad you asked was a question i was wondering about i know power one no probs and assumed the same.... thanks men