Download Presenting a Technical Report - OKE

PV-wirefree versus
conventional PV-systems:
detailed analysis of difference in energy yield
between series and parallel connected PVmodules
Henk Oldenkamp
OKE-Services, The Netherlands
8 June 2004
Web: www.pv-wirefree.com
19th European Photovoltaic Solar Energy Conference and Exhibition
Overview presentation
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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 PVmodules 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: 30-400%
Conclusions: measurement results
Overview shading effects
Condition Very lightly Lightly
shaded
shaded
Moderately
shaded
MPP range shunt
[% of Voc]
MPP range string
[% of Voc]
Shunt power gain
minimum [%]
80 – 82
80 – 83
82 - 84
75 - 87
67 – 85
46 - 76
2-5
10 - 20
0 - 50
Shunt power gain
practical [%]
5 - 25
10 - 40
30 - 400
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
Finally: shunts = PV-wirefree
• 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