19 th European Photovoltaic Solar Energy Conference and Exhibition
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Transcript of 19 th European Photovoltaic Solar Energy Conference and Exhibition
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PV-wirefree versus conventional PV-systems:detailed analysis of difference in energy yield between series and parallel connected PV-modules
19th European Photovoltaic Solar Energy Conference and Exhibition
Henk OldenkampOKE-Services, The Netherlands8 June 2004
Web: www.pv-wirefree.com
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Overview presentation
• Definitions• What is PV-wirefree?• PV-wirefree claims …• Focus of this presentation• Test setup• Explanation of the graphs• Measurement results• Conclusions• Finally
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Definitions
• PV-string: series connection of PV-modules of which all cells are connected in series
Duality of a PV-string is:• PV-shunt: parallel connection of PV-modules
of which all cells are connected in parallel
But all cells of a PV-module connected in parallel is not practical due to high currents and its associated losses
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Definitions
• PV-string: series connection of PV-modules of which all cells are connected in series
• PV-shunt: parallel connection of PV-modules of which all cells are connected in series
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What is PV-wirefree?PV-wirefree = PV-shunt(s)
• Large numbers of PV-laminates connected in parallel using a current carrying mounting frame (= mounting bus)
• Each group of PV-laminates connected to one set of mounting busses has its own inverter, and is called a subsystem
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What is PV-wirefree?PV-wirefree = PV-shunt(s)
• Large numbers of PV-laminates connected in parallel using a current carrying mounting frame (= mounting bus)
• Each group of PV-laminates connected to one set of mounting busses has its own inverter, and is called a subsystem
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What is PV-wirefree?PV-wirefree = PV-shunt(s)
• Large numbers of PV-laminates connected in parallel using a current carrying mounting frame (= mounting bus)
• Each group of PV-laminates connected to one set of mounting busses has its own inverter, and is called a subsystem
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PV-wirefree claims
• Increase of annual energy yield especially in suboptimal conditions
• Considerable decrease of costs
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Focus of this presentation
• This presentation proves the first claim: a significant increase of annual energy yield
How?
• By measuring the full P versus V curves of nine PV-modules continuously switched between shunt and string under varying shading conditions, excluding any other influences on the array power
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Test setup
Every minute the lower 9 pv-modules are connected in shunt and in string, and a photo is taken. A 1000 points power versus voltage sweep takes 7 seconds
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Explanation of the graphs
Red line = average shunt power per module versus shunt voltage
Purple line = irradiation during the 7 seconds sweep time
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Explanation of the graphs
Red dot marks maximum power point of the shunt
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Explanation of the graphs
Blue line = average string power per module versus average module voltageGreen line = irradiation during the 7 seconds sweep
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Explanation of the graphs
Blue dot marks maximum power point of the average string module
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Explanation of the graphs
Black dot marks maximum power point of the string when loaded at 81.5% of Voc (expected MPP)
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Measurement resultsDefinition of three types
• Very lightly shaded: the shade covers roughly the area of one cell
• Lightly shaded: the shade covers several cells
• Moderately shaded: the shade covers several modules
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Measurement resultsVery lightly shaded
P shunt/string = 0.3% P shunt/string at V=81.5% Voc = 0,4%
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Measurement resultsVery lightly shaded
P shunt/string = 4.9% P shunt/string at V=81.5% Voc = 9.6%
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Measurement resultsVery lightly shaded
P shunt/string = 2.4% P shunt/string at V=81.5% Voc = 8.7%
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ResultsVery lightly shaded
• Minimum gain: 2-5%• Expected gain in practice: 5-25%
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Measurement resultsLightly shaded
P shunt/string = 1.5% P shunt/string at V=81.5% Voc = 2.0%
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Measurement resultsLightly shaded
P shunt/string = 10.8% P shunt/string at V=81.5% Voc = 12.0%
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Measurement resultsLightly shaded
P shunt/string = 10.6% P shunt/string at V=81.5% Voc = 27.0%
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ResultsLightly shaded
• Minimum gain: 10-20%• Expected gain in practice: 10-40%
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Measurement resultsModerately shaded
P shunt/string = 3.8% P shunt/string at V=81.5% Voc = 53.9%
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Measurement resultsModerately shaded
P shunt/string = 0.4% P shunt/string at V=81.5% Voc = 226.6%
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Measurement resultsModerately shaded
P shunt/string = 23.9% P shunt/string at V=81.5% Voc = 176.0%
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Measurement resultsModerately shaded
P shunt/string = 49.6% P shunt/string at V=81.5% Voc = 174.2%
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ResultsModerately shaded
• Minimum gain: 0-50%• Expected gain in practice: 30-400%
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Conclusions: measurement resultsOverview shading effects
Condition Very lightly shaded
Lightly shaded
Moderately shaded
MPP range shunt[% of Voc]
80 – 82 80 – 83 82 - 84
MPP range string[% of Voc]
75 - 87 67 – 85 46 - 76
Shunt power gain minimum [%]
2 - 5 10 - 20 0 - 50
Shunt power gain practical [%]
5 - 25 10 - 40 30 - 400
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ConclusionsShunts always perform better
Since:• The MPP voltage nearly constant• And simple and efficient MPP tracking
possible
Additional advantages of shunts • Inverters can have significantly narrower
input voltage windows, which will reduce costs and/or increase efficiency of inverters
• MPP tracking efficiency will always be significantly better
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• More information available at– Stand T22– www.pv-wirefree.com
• Partners PV-wirefree– Bear, ECN, OKE, OJA, Oskomera. TNO– Connector: Multi-Contact,
• Acknowledgements– Nico van der Borg, ECN
Finally: shunts = PV-wirefree