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PV Mismatch loss study using flash test datasets
1. Confidential | ยฉ 2016 SunPower Corporation
Quantification of System
Level Mismatch Losses
using PVMismatch
Flash test results
Mismatch at STC
Annual Energy Loss due to Mismatch
Authors:
Chetan Chaudhari
Gregory M. Kimball
Raymond Hickey
Ben Bourne
2. 2Confidential | ยฉ 2016 SunPower Corporation |
Introduction
โข What is Mismatch loss ?
โDifferences in the current-voltage characteristics of photovoltaic (PV)
modules connected in series and parallel combinations lead to a loss in the
system level power referred to as โmismatch lossโ or โelectrical mismatch
lossโ.
โข Pmpp@system < Pmpp@module
3. 3Confidential | ยฉ 2016 SunPower Corporation |
Contributing factors to mismatch loss
โข Manufacturing variability
โข Shading
โข Operating temperature non-uniformity
โข Varying DC wiring lengths
โข Uneven degradation
4. 4Confidential | ยฉ 2016 SunPower Corporation |
Contributing factors to mismatch loss
โข Manufacturing variability
โข Shading
โข Operating temperature non-uniformity
โข Varying DC wiring lengths
โข Uneven degradation
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Need
โข Literature survey shows guidance on mismatch loss from 0.01% to 2%
โข Mismatch loss typically used as a flat derating factor for system capacity
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Goal
โข Create a framework that can be utilized to model various factors that contribute to
mismatch loss for
โa given population of flash test results
7. 7Confidential | ยฉ 2016 SunPower Corporation |
Goal
โข Create a framework that can be utilized to model various factors that contribute to
mismatch loss for
โa given population of flash test results
โsystem configuration
8. 8Confidential | ยฉ 2016 SunPower Corporation |
Goal
โข Create a framework that can be utilized to model various factors that contribute to
mismatch loss for
โa given population of flash test results
โsystem configuration,
โsite location
9. 9Confidential | ยฉ 2016 SunPower Corporation |
Goal
โข Create a framework that can be utilized to model various factors that contribute to
mismatch loss for
โa given population of flash test results
โsystem configuration,
โsite location
โimpact on annual Energy
10. 10Confidential | ยฉ 2016 SunPower Corporation |
Quick overview of PVMismatch
โข Core framework for the study
โข An explicit IV curve calculator
โข Written in Python
โข Go Open Source! (https://github.com/SunPower/PVMismatch)
โข PVMismatch Model chain
โCell > Cell string > Module > String > System
โCapability to set โSunsโ and temperature for each cell (individually or
collectively)
โCapability to configure cell string layout and bypass diodes
โข Former work using PVMismatch
โ Accurate Modeling of Partially Shaded PV Arrays [2]
โ A fast parameterized model for predicting PV system performance under partial shade conditions. [3]
11. 11Confidential | ยฉ 2016 SunPower Corporation |
Datasets behind the study
โข Dpvmod1 represents normal distribution
from factory data
โข 1000+ unique IV curves from modules
โข Dpvmod2 represents a synthesized
multimodal distribution
โข 1000+ representative IV curves
25. 25Confidential | ยฉ 2016 SunPower Corporation |
Mismatch loss at STC across system sizes
โข With non-normal distribution of module characteristics, the mismatch
increases
โข Case for importance of binning methods
26. 26Confidential | ยฉ 2016 SunPower Corporation |
Concluding remarks
โข P95 mismatch loss decreases with system size
โข Annual energy loss > STC mismatch loss
โข Mismatch loss calculated agrees with other lower estimates found in the
literature
โข and is << 1-2% industry practice
27. 27Confidential | ยฉ 2016 SunPower Corporation |
Future scope
โข Introducing other contributing factors to the mismatch model
โOperating temperature non-uniformity
โVarying DC wiring lengths
โUneven degradation
28. Thank You
Letโs change the way our world is powered.
Confidential | ยฉ 2016 SunPower Corporation
30. 30Confidential | ยฉ 2016 SunPower Corporation |
References
1. J. W. Bishop, โComputer simulation of the effects of electrical mismatches in photovoltaic cell interconnection circuits,โ Sol. Cells, vol. 25, no.
1, pp. 73โ89, Oct. 1988.
2. Meyers, B., & Mikofski, M. (2017). Accurate Modeling of Partially Shaded PV Arrays. In 44th IEEE Photovoltaic Specialists Conference.
3. Meyers, B., Mikofski, M., & Anderson, M. (2016). A fast parameterized model for predicting PV system performance under partial shade
conditions. In Conference Record of the IEEE Photovoltaic Specialists Conference (Vol. 2016โNovember, pp. 3173โ3178). Institute of
Electrical and Electronics Engineers Inc. https://doi.org/10.1109/PVSC.2016.7750251
31. 31Confidential | ยฉ 2016 SunPower Corporation |
Method โ Mismatch loss at STC
โข Select Ns * Nm count of modules from the flash test distribution (Ns = number of strings, Nm = number of
modules in a string)
โข Using PVMismatch, generate IV curves for each of the flash test results
โข Configure a PV system of desired configuration with Ns strings of Nm modules each
โข Calculate mismatch loss at STC using equation 1 and 2
โ ๐๐๐๐ = 0
๐๐ โ๐๐
๐ ๐๐๐๐๐ 1
โ ๐๐๐ถ ๐๐๐ ๐๐๐ก๐โ ๐๐๐ ๐ =
๐ ๐๐๐ ๐ฆ๐ โ ๐ ๐๐๐
๐ ๐๐๐
ร 100 (2)
โข Pref is the sum of module level powers each at its maximum power point
โข Pmpsys is the system level power of the configuration at the systemโs maximum power point
โข Repeating this method for 1000 unique scenarios yields a distribution of mismatch losses for
each PV system configuration