SunPower Shading Study
Comparison of SunPower and Yingli PV Module Performance
Under Real-World Shading Conditions Due to
Vent-Pipes, Leaves, and Trees
Report by:
Matthew Donovan, Staff Engineer – [email protected]
Jason Forrest, Test Engineer – [email protected]
Number of pages: 9
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Report # 6-29-4
415.320.PVEL
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Abstract
PVEL operates an outdoor PV system testing facility at PV-USA, a grid-connected research site
located in Davis, CA. PVEL has installed five (5) independent systems for the purpose of
comparing the shaded performance of SunPower modules to that of Yingli modules. The
experimental setup is designed so that one system acts as a control that is never shaded while
the other four test systems are exposed to shading conditions designed to be similar to realworld conditions. The systems are identically arranged and monitored with revenue-grade AC
power meters.
The results of this test show that the percentage of energy lost due to shading was significantly
less on SunPower systems than Yingli systems with both systems on transformer-less (TL) string
inverters. The SunPower systems on TL string inverters lost significantly less energy due to
shading than the Yingli system on microinverters. The Yingli system on microinverters
performed marginally better than the Yingli system on a TL string inverter
Figure 1: Picture of the combination shading from Leaves + Vent Pipes + Tree
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System Description
Group1
(Control)
Group2
Group3
Group4
Group5
Yingli
Yingli
YL240P-29b
YL240P-29b
SunPower SunPower SunPower
Module Type
X21/343
Inverter Type
X21/343
E20/327
Enphase
M215
SPR-3000p-TL-1
# of Modules
Eight (8) per system
DC Capacity (W)
2,744
2,744
2,616
1,920
1,920
20o
Tilt
180o (south)
Azimuth
Table 1: Description of the systems evaluated in this report
Measurement
AC power and energy
Plane-of-array irradiance
Wind speed
Wind direction
Ambient temperature
Precipitation (rain, hail)
Relative humidity
Barometric pressure
Module temperature
(2 per module type)
Sensor
Shark 100 revenue grade meter
(2x) Eppley PSP secondary
standard thermopile
pyranometer
Vaisala WXT520
Vaisala WXT520
Vaisala WXT520
Vaisala WXT520
Vaisala WXT520
Vaisala WXT520
Type-T thermocouples
Uncertainty
± 0.2%
±2%
Greater of ± 0.3 m/s or ± 3 %
± 3°
± 0.3° C
±5%
±3%
± 0.5 hPa
± 1.5° C
Table 2: Description of the measurement equipment – each system is identically outfitted
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Experiment and Analysis Methods
Quantifying Un-shaded Performance
A baseline of performance was established for each system by measuring energy production on
one clear day near the start of each test. This was used to establish a normalization factor
(βunshaded) for each system. βunshaded represents the energy yield of a test system relative to the
control system in un-shaded conditions and is used to normalize results of the shading tests.
Equation 1
(over 24 hours in un-shaded conditions)
Quantifying the Impact of Shading
For each test, we measured energy produced over a full 24-hour period using a Shark 100
revenue-grade production meter with 0.2% accuracy in energy measurement. Equation 2 is
used to determine the energy lost due to shading.
Note that the term
represents the energy the system will be expected to produce on
that day if there were no shade.
Equation 2
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Test Results (Combination: Leaves + Vent Pipes + Tree)
The Combination Shade Test has one leaf placed directly over one cell in half of the modules,
and in addition has an artificial tree placed to the west of the array and two vent pipes placed
just south of the array, as shown in Figure 1. The SPR-3000p-TL-1 inverters used in this test
have an “MPPT Scan” feature which comes disabled by default. This scan feature ensures that
the inverter finds the maximum operating power even in the case of a “lumpy” IV curve. The
MPPT Scan feature was enabled for this test, and therefore we calculate the normalization
factor, βunshaded, for a clear day with the MPPT Scan activated. Normalization factors are
included in the appendix.
kWh Produced
Energy Loss Due
to Shading
Group 1:
SunPower
X-series on
TL String
Inverter
(Control)
12.24
Group 2:
SunPower
X-Series on
TL String
Inverter
Group 3:
SunPower
E-Series on
TL String
Inverter
Group 4:
Yingli
on TL String
Inverter
Group 5:
Yingli
on Microinverters
11.15
9.67
5.94
6.13
0.0%
-7.8%
-13.8%
-28.9%
-28.3%
Table 3: Results of the Combination Shade Test from Leaves + Vent Pipes + Tree
Figure 2: Results of the Combination Shade Test from Leaves + Vent Pipes + Tree
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Test Results (Leaves only)
The Leaves Shade Test has one leaf placed directly over one cell per module for each of the
modules in each group. This is the same configuration as the Combination Shading, shown in
Figure 1, except with no tree or vent pipes, and with twice the number of leaves. The MPPT
Scan feature was left disabled for this test. Therefore we calculate the normalization factor,
βunshaded, for one clear day near the time of the test with the MPPT Scan feature also disabled.
kWh Produced
Energy Loss
Due to
Shading
Group 1:
SunPower
X-series on
TL String
Inverter
(Control)
18.45
Group 2:
SunPower
X-Series on
TL String
Inverter
Group 3:
SunPower
E-Series on
TL String
Inverter
Group 4:
Yingli
on TL String
Inverter
Group 5:
Yingli
on Microinverters
17.19
15.13
5.91
7.68
0.0%
-6.3%
-11.3%
-52.2%
-37.9%
Table 4: Results of the Leaves Shade Test
Figure 3: Results of the Leaves Shade Test
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Conclusion
The SunPower modules lost less energy due to shading than the Yingli modules by a significant
margin in both shading tests. It is particularly noteworthy that the SunPower groups
outperformed both Yingli test groups despite the fact that one Yingli test group used
microinverters, which are typically believed to mitigate the impact of shading. Additionally, we
note that any inverter that has a MPPT Scan feature should have the feature enabled to ensure
best performance of the inverter in shaded conditions.
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Appendix: Baseline Data and Normalization Factors
Group 1:
SunPower
Group 2:
SunPower
Group 3:
SunPower
Group 4:
Yingli
Group 5:
Yingli
X-series on TL
String
Inverter
X-Series on TL
String
Inverter
E-Series on TL
String
Inverter
on TL String
Inverter
on Microinverters
(Control)
kWh
Produced
16.61
16.51
15.35
11.13
11.14
β
1.000
0.994
0.924
0.670
0.671
Table 5: Baseline data for the Leaves Shade Test – this data was taken on September 4, 2012, with the MPPT Scan
feature of the inverters disabled
Group 1:
SunPower
Group 2:
SunPower
Group 3:
SunPower
Group 4:
Yingli
Group 5:
Yingli
X-series on TL
String
Inverter
X-Series on TL
String
Inverter
E-Series on TL
String
Inverter
on TL String
Inverter
on Microinverters
(Control)
kWh
produced
12.14
12.00
11.14
8.29
8.48
β
1.000
0.988
0.917
0.683
0.699
Table 6: Baseline data for the Combination Shade Test – this data was taken on November 2, 2012, with the MPPT
Scan feature of the inverters enabled
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