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

Overview presentation

• Definitions• What is PV-wirefree?• PV-wirefree claims …• Focus of this presentation• Test setup• Explanation of the graphs• Measurement results• Conclusions• Finally

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

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

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

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

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

PV-wirefree claims

• Increase of annual energy yield especially in suboptimal conditions

• Considerable decrease of costs

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

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

Explanation of the graphs

Red line = average shunt power per module versus shunt voltage

Purple line = irradiation during the 7 seconds sweep time

Explanation of the graphs

Red dot marks maximum power point of the shunt

Explanation of the graphs

Blue line = average string power per module versus average module voltageGreen line = irradiation during the 7 seconds sweep

Explanation of the graphs

Blue dot marks maximum power point of the average string module

Explanation of the graphs

Black dot marks maximum power point of the string when loaded at 81.5% of Voc (expected MPP)

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

Measurement resultsVery lightly shaded

P shunt/string = 0.3% P shunt/string at V=81.5% Voc = 0,4%

Measurement resultsVery lightly shaded

P shunt/string = 4.9% P shunt/string at V=81.5% Voc = 9.6%

Measurement resultsVery lightly shaded

P shunt/string = 2.4% P shunt/string at V=81.5% Voc = 8.7%

ResultsVery lightly shaded

• Minimum gain: 2-5%• Expected gain in practice: 5-25%

Measurement resultsLightly shaded

P shunt/string = 1.5% P shunt/string at V=81.5% Voc = 2.0%

Measurement resultsLightly shaded

P shunt/string = 10.8% P shunt/string at V=81.5% Voc = 12.0%

Measurement resultsLightly shaded

P shunt/string = 10.6% P shunt/string at V=81.5% Voc = 27.0%

ResultsLightly shaded

• Minimum gain: 10-20%• Expected gain in practice: 10-40%

Measurement resultsModerately shaded

P shunt/string = 3.8% P shunt/string at V=81.5% Voc = 53.9%

Measurement resultsModerately shaded

P shunt/string = 0.4% P shunt/string at V=81.5% Voc = 226.6%

Measurement resultsModerately shaded

P shunt/string = 23.9% P shunt/string at V=81.5% Voc = 176.0%

Measurement resultsModerately shaded

P shunt/string = 49.6% P shunt/string at V=81.5% Voc = 174.2%

ResultsModerately shaded

• Minimum gain: 0-50%• Expected gain in practice: 30-400%

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

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

• 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