PV-wirefree versus conventional PV-systems: detailed analysis of difference in energy yield between series and parallel connected PV- modules 19 th European Photovoltaic Solar Energy Conference and Exhibition Henk Oldenkamp OKE-Services, The Netherlands 8 June 2004 Web:

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 voltage Green 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 results Definition 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 results Very lightly shaded  P shunt/string = 0.3%  P shunt/string at V=81.5% Voc = 0,4%

Measurement results Very lightly shaded  P shunt/string = 4.9%  P shunt/string at V=81.5% Voc = 9.6%

Measurement results Very lightly shaded  P shunt/string = 2.4%  P shunt/string at V=81.5% Voc = 8.7%

Results Very lightly shaded Minimum gain: 2-5% Expected gain in practice: 5-25%

Measurement results Lightly shaded  P shunt/string = 1.5%  P shunt/string at V=81.5% Voc = 2.0%

Measurement results Lightly shaded  P shunt/string = 10.8%  P shunt/string at V=81.5% Voc = 12.0%

Measurement results Lightly shaded  P shunt/string = 10.6%  P shunt/string at V=81.5% Voc = 27.0%

Results Lightly shaded Minimum gain: 10-20% Expected gain in practice: 10-40%

Measurement results Moderately shaded  P shunt/string = 3.8%  P shunt/string at V=81.5% Voc = 53.9%

Measurement results Moderately shaded  P shunt/string = 0.4%  P shunt/string at V=81.5% Voc = 226.6%

Measurement results Moderately shaded  P shunt/string = 23.9%  P shunt/string at V=81.5% Voc = 176.0%

Measurement results Moderately shaded  P shunt/string = 49.6%  P shunt/string at V=81.5% Voc = 174.2%

Results Moderately shaded Minimum gain: 0-50% Expected gain in practice: %

Conclusions: measurement results Overview shading effects ConditionVery lightly shaded Lightly shaded Moderately shaded MPP range shunt [% of Voc] 80 – 8280 – MPP range string [% of Voc] – Shunt power gain minimum [%] Shunt power gain practical [%]

Conclusions Shunts 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 – Partners PV-wirefree –Bear, ECN, OKE, OJA, Oskomera. TNO –Connector: Multi-Contact, Acknowledgements –Nico van der Borg, ECN Finally: shunts = PV-wirefree