WP4 – Deliverable 4.3 IMPACT OF PHOTOVOLTAIC … · IMPACT OF PHOTOVOLTAIC GENERATION ON POWER...

PV in Urban Policies- Strategic and Comprehensive Approach for Long-term Expansion EIE/05/171/SI2.420208

WP4 – Deliverable 4.3 IMPACT OF PHOTOVOLTAIC GENERATION ON POWER QUALITY IN URBAN AREAS WITH HIGH PV POPULATION Results from Monitoring Campaigns Authors: Sjef Cobben (Continuon), Bruno Gaiddon (Hespul), Hermann Laukamp

(Fraunhofer ISE) Version: 1 Version date: 2008-07-14 Reviewer(s): Estefanía Caamaño (Universidad Politécnica de Madrid – Instituto de Energía

Solar, Spain), Donna Munro (Halcrow, United Kingdom), Tomoki Ehara (Mizuho Information & Research Institute, Japan), Jim Thornycroft (Halcrow, United Kingdom) Esther Allen, Fraunhofer ISE (Germany)

Revision date: 2008-07-08 Status: approved

DISCLAIMER The information published in this report was carefully compiled and reviewed. The members of the PV – UPSCALE consortium do not make any claim or warranties as to the accuracy or completeness of its content and do not assume any liability arising there from.

Impact of PV systems in high capacity PV settlements iii

Executive Summary With fast growing penetration of PV and other distributed power generation capacity, the impact of PV on the grid and vice versa is under discussion. Main concerns are the maximum tolerable level and the quality of the supply voltage. These concerns as well as the acceptable penetration limits have been verified by measurements in PV developments in several countries. Several case studies of urban real estate developments with a high share of distributed PV generation were investigated and the situation in the respective low voltage grid segment is analysed. Issues investigated include:

• network design • maximum permissible capacity of PV • power quality related to standard EN 50 160 • voltage rise effects • harmonic current injection from PV • power flow across transformer

The sites analysed for this study are:

• Solarsiedlung “Am Schlierberg”, Freiburg, Germany • Holidaypark Bronsbergen, The Netherlands • Heerhugowaard, sun city “Mayersloot”, The Netherlands • “Soleil-Marguerite“, Lyon, France

Site details “Solarsiedlung Am Schlierberg” is a recently constructed real estate development in the city of Freiburg, Germany. It comprises about 440 kWp PV arrays on some 70 residences, as well as on a large office and business block. PV systems are connected to the grid through in total 160 inverters. PV systems are distributed fairly evenly along the feeders. Layout of the distribution system is standard; the area is supplied through a 400 kVA transformer. The holiday park “Bronsbergen”, is situated in Zutphen, Netherlands. It comprises a total of 210 cottages with PV panels mounted on the roof of 108 cottages. The total PV power installed is around 315 kWp. The nominal power of the transformer feeding all the cottages is 400 kVA. The ratio of nominal PV Power to transformer rated power is 80 %. The average PV power per house with PV is 2.9 kWp; including non-PV houses it is 1.5 kWp. The “Mayersloot” site is located at Langedijk, Heerhugowaard. In this area many houses employing PV systems have been built in recent years. The site comprises a total of 70 houses, 21 houses employing a PV generator. The PV houses are all connected to the ends of two feeders. This leads to the greatest possible rise in voltage level. Total PV capacity installed is 130 kWp. The ratio of nominal PV Power to transformer rated power is 33 %. The average PV power per house with PV is 6.2 kWp; including non-PV houses it is 1.9 kWp. The “Soleil-Marguerite” PV system is located on a building in a high density urban area with a mix of offices and dwellings. The PV system comprises about 13 kWp and 6 inverters. It is included in this report to emphasise the negligible impact of a comparatively small PV system on the voltage quality of the low voltage network.

Impact of PV systems in high capacity PV settlements iv

Following table summarizes key features of the real estates involved Site rated

transformer power [kVA]

rated PV power

[kWp]

PV power/ transformer

power [%]

PV power per apartment 1)

[kWp]

Solarsiedlung “Am Schlierberg”, Freiburg, Germany

400 440 110 6.3 / 3.2

Holidaypark Bronsbergen, The Netherlands 400 315 80 2.9 / 1.5 Heerhugowaard, sun city “Mayersloot”, The Netherlands

400 130 33 6.2 / 1.9

“Soleil-Marguerite“, Lyon, France unknown 13 - -

1) PV residences only / total number of apartments connected to transformer Results Measurement campaigns in four urban PV real estate areas and systems have demonstrated that PV generation is compatible with LV distribution networks even at high PV density. Distributed generation from PV systems with a high ratio of generation capacity to transformer rating, i.e. a ratio of 80 % and higher, in general does not deteriorate the quality of the grid. Power quality was found to be affected only with regard to increased voltage levels at the end of LV feeders. Generally, all power quality requirements as described by the European standard EN 50 160 were satisfied. Acceptable PV capacity The ratio of nominal PV capacity to rated transformer power for the systems monitored includes the values 33 %, 80 % and 110 %. For the whole area supplied by the transformer, including buildings without PV, the average installed PV capacity reaches values of 1.5 KWp, 1.9 kWp and 3.2 kWp per apartment. The maximum tolerable capacity of PV to a single LV feeder was found to be about 7 kWp per apartment. Obviously, evenly distributing PV systems over a feeder allows more capacity than concentrating PV systems at the end of a feeder. As a rule of thumb PV systems in a typical urban European LV grid segment should not cause any trouble, if power is limited to 70 % of the rated power of the feeding transformer. In some cases higher amounts of PV power are possible. The simultaneous production of PV power is the bottleneck for implementing higher amounts of PV power, since it does not follow the “after diversity maximum demand” (ADMD) rules for customer loads. In new networks, the grid design can be adapted for the PV systems that might be connected in future by properly sizing the transformer and cables. There is no theoretical technical limit, if the design can be “made on purpose”. By reducing the set voltage of the transformer from 235 V, a level often found in LV distribution networks, to the nominal level of 230 V, a higher PV capacity could easily be accommodated. Loading of equipment During the time of highest PV generation a power export to the MV grid was noticed. The peak exported power in any of the projects did not exceed 160 kW. This is less than half the transformers rated power.

Impact of PV systems in high capacity PV settlements v

Power quality In general, no detrimental effects on power quality was noticed. Flicker problems were not observed. However, in one case voltage harmonics were found to exceed permitted values. They were traced back to resonance effects between network harmonics, cable impedance and a high inverter input capacitance. Selecting inverters with a low input capacitance would avoid this effect. In another system current harmonics from inverters were found to exceed nationally permitted limits under high power. Possible improvements Power unbalance between the phases was found to be increased, if there was an uneven distribution of inverters over the three phases. This could be avoided by integral planning of inverter distribution. For new developments, setting the transformer ratio to a secondary voltage level between Vn and 98 %*Vn could avoid any practical capacity limit from voltage rise.

Impact of PV systems in high capacity PV settlements vi

The PV-Upscale project PV-UP-SCALE (PV in Urban Policies – Strategic and Comprehensive Approach for Long-term Expansion) is a European funded project under the Intelligent Energy for Europe programme related to the large-scale implementation of Photovoltaics (PV) in European cities. Its’ objective is to bring to the attention of the stakeholders in the urban planning process the economic drivers, bottlenecks like grid issues and the do’s and don’ts within the PV process. To reach the urban decision makers workshops have been organised and a quality handbook has been written using experience gained with PV Urban projects in the Netherlands, Germany, France, Spain and the United Kingdom. The project complements the activities that are being executed in the International Energy Agency – Photovoltaic Power Systems Programme (IEA PVPS) Implementing Agreement, in particular IEA PVPS Task 10. It takes information from Task 7 (building integrated PV), which ended in 2001 and Task 5 (grid issues), ended in 2003. The structure of the project is summarised in the following figure.

Structure of PV-UP-SCALE project

Impact of PV systems in high capacity PV settlements vii

PV-UP-SCALE consortium brings together complementary expertise from Educational, Research and Development, Engineering, Architecture and Utility sectors: Sectors Educational,

Research

ECN- Energy research Center of the Netherlands, Research Institute, The Netherlands (Project Coordinator)

Vienna University of Technology - EEG, Energy Economics Group, Austria

Fraunhofer Institute für Solare Energiesysteme, Research Institute, Germany

Universidad Politecnica de Madrid – Instituto de Energía Solar, Spain

Consultancy HORISUN- Consulting, The Netherlands

HESPUL- Consulting, France

Halcrow- Halcrow Group Ltd, Consulting, United Kingdom

Ecofys- Ecofys Energieberatung und Handelsgesellschaft GmbH, Consulting, Germany

Electricity Continuon- Netbeheer NV, Utility, The Netherlands

MVV- MVV Energie AG, Utility, Germany Of the project Work Packages, Work Package 4 (WP4) is the one dealing with technical issues of grid interconnection such as mutual impacts of PV systems and Distribution networks, interconnection guidelines, network risks, and required inputs to network planning. Fortunately, some thorough collaborative work on PV grid issues has been done under the framework of IEA PVPS-Task 5, R&D projects previously supported by the European Commission, and national and international Standardization bodies (IEC-TC82, CENELEC-SC82). WP4 draws upon on this work to contribute to identify remaining barriers and solutions for a successful dissemination of PV systems in electricity networks of urban areas. For more information, please visit the project web-site: www.pvupscale.org

Impact of PV systems in high capacity PV settlements viii

Table of Content Executive Summary .....................................................................................................iii The PV-Upscale project ...............................................................................................vi 1 Introduction.............................................................................................................1 2 Presentation of Sites ..............................................................................................2

2.1 Freiburg, Germany, “Solarsiedlung Am Schlierberg”.............................................. 2 2.1.1 Site description “Solarsiedlung Am Schlierberg“...................................................................2

2.1.1.1 Real estate development ..................................................................................................2 2.1.1.2 Electrical network ..............................................................................................................3 2.1.1.3 PV Systems.......................................................................................................................4

2.1.2 Measurements.......................................................................................................................4 2.1.3 Results ..................................................................................................................................5

2.1.3.1 Voltage distribution at transformer ....................................................................................5 2.1.3.2 Voltage quality at transformer (EN 50 160).......................................................................5 2.1.3.3 Real power flow at transformer .........................................................................................6 2.1.3.4 Voltage quality (EN 50 160) at end of feeder 1.................................................................8 2.1.3.5 Voltage rise from PV power at end of feeder ....................................................................8 2.1.3.6 Harmonic distortion, harmonics spectra – voltage, current............................................ 10 2.1.3.7 Voltage unbalance (at end of feeder)............................................................................. 12

2.1.4 Summary “Schlierberg” ...................................................................................................... 12 2.2 Holidaypark Bronsbergen......................................................................................... 13

2.2.1 Site description Holidaypark Bronsbergen......................................................................... 13 2.2.1.1 Real estate development ............................................................................................... 13 2.2.1.2 Electrical network ........................................................................................................... 15 2.2.1.3 PV systems .................................................................................................................... 15

2.2.2 Measurements.................................................................................................................... 15 2.2.3 Results ............................................................................................................................... 16

2.2.3.1 Voltage level at transformer ........................................................................................... 16 2.2.3.2 Voltage quality at transformer (EN 50 160).................................................................... 17 2.2.3.3 Power flow at transformer .............................................................................................. 17 2.2.3.4 Voltage quality at end of feeder ..................................................................................... 18 2.2.3.5 Voltage rise from PV power at end of the feeder ........................................................... 19 2.2.3.6 Harmonic distortion, harmonic spectra – voltage, current.............................................. 19 2.2.3.7 Voltage unbalance.......................................................................................................... 21 2.2.3.8 Inverter tripping .............................................................................................................. 21 2.2.3.9 Flicker............................................................................................................................. 21 2.2.3.10 Ripple control signals ................................................................................................. 21

2.2.4 Summary “Bronsbergen“.................................................................................................... 21 2.3 Heerhugowaard, sun city “Mayersloot” .................................................................. 22

2.3.1 Site description Heerhugowaard, sun city “Mayersloot”..................................................... 22 2.3.1.1 Real estate development ............................................................................................... 22 2.3.1.2 Electrical network ........................................................................................................... 23

Impact of PV systems in high capacity PV settlements ix

2.3.1.3 PV systems .................................................................................................................... 24 2.3.2 Measurements.................................................................................................................... 24 2.3.3 Results ............................................................................................................................... 24

2.3.3.1 Voltage level at transformer ........................................................................................... 24 2.3.3.2 Voltage quality (EN 50 160) at transformer.................................................................... 25 2.3.3.3 Voltage quality at end of feeder ..................................................................................... 26 2.3.3.4 Voltage rise from PV power at end of the feeder ........................................................... 26 2.3.3.5 Harmonic distortion, harmonic spectra – voltage, current.............................................. 27 2.3.3.6 Voltage unbalance.......................................................................................................... 28 2.3.3.7 Flicker............................................................................................................................. 28 2.3.3.8 Ripple control signals ..................................................................................................... 29

2.3.4 Summary “Mayersloot“....................................................................................................... 29 2.4 “Soleil-Marguerite“ photovoltaic system ................................................................ 30

2.4.1 Site description................................................................................................................... 30 2.4.1.1 Real estate development ............................................................................................... 30 2.4.1.2 Electrical network ........................................................................................................... 30 2.4.1.3 PV Systems.................................................................................................................... 30

2.4.2 Measurements.................................................................................................................... 31 2.4.3 Results ............................................................................................................................... 32

2.4.3.1 Voltage quality at end of feeder (EN 50 160)................................................................. 32 2.4.3.2 Voltage rise from PV power at end of feeder ................................................................. 33 2.4.3.3 Harmonic distortion, harmonics spectra – voltage, current............................................ 33 2.4.3.4 Voltage unbalance at end of feeder ............................................................................... 37 2.4.3.5 Flicker............................................................................................................................. 37 2.4.3.6 Ripple control signals ..................................................................................................... 39 2.4.3.7 Other issues ................................................................................................................... 39

2.4.4 Summary “Soleil-Marguerite“ ............................................................................................. 40 3 Conclusions ..........................................................................................................41 4 References ............................................................................................................42 5 Annex.....................................................................................................................43

5.1 EN 50 160 requirements for LV grid......................................................................... 43

Impact of PV systems in high capacity PV settlements 1

1 Introduction With fast growing penetration of PV and other distributed power generation capacity, the impact of PV on the grid and vice versa is under discussion. The main concerns are the maximum tolerable capacity and the quality of the supply voltage. An extensive theoretical study [1] had shown that in German urban areas the increase of voltage due to reverse power flow is the limiting factor for penetration of PV on the LV grid. This effect limits PV capacity in typical residential settlements to about 3.5 kWp per household. These concerns as well as the acceptable penetration limits have been checked by measurements in PV developments in several countries. In this report several case studies of real estate developments with a high population of distributed PV generation are described, and the situation in the respective low voltage grid segment is analysed. Issues investigated include:

• maximum permissible capacity of PV • power quality related to standard EN 50 160 • voltage rise effects • harmonic current injection from PV • power flow across transformer

The sites analysed for this study are:

• Solarsiedlung “Am Schlierberg”, Freiburg, Germany • Holidaypark Bronsbergen, The Netherlands • Heerhugowaard, sun city “Mayersloot”, The Netherlands • “Soleil-Marguerite“, Lyon, France

Following table summarizes key features of the real estates involved. Table I: key features of the real estates investigated Site rated

transformer power [kVA]

rated PV power

[kWp]

PV power/ transformer

power [%]

PV power per apartment 1)

[kWp]

Solarsiedlung “Am Schlierberg”, Freiburg, Germany 400 440 110 6.3 / 3.2 Holidaypark Bronsbergen, The Netherlands 400 315 80 2.9 / 1.5 Heerhugowaard, sun city “Mayersloot”, The Netherlands 400 130 33 6.2 / 1.9 “Soleil-Marguerite“, Lyon, France unknown 13 - -

2) PV residences only / total number of apartments connected to transformer


2 Presentation of Sites

2.1 Freiburg, Germany, “Solarsiedlung Am Schlierberg”

2.1.1 Site description “Solarsiedlung Am Schlierberg“ In the city of Freiburg a real estate development called “Solarsiedlung Am Schlierberg” was completed in 2006. It features a PV system on every single house [2]. About 440 kWp capacity was installed and distributed over some 60 PV systems comprising some 160 inverters. A measurement campaign was conducted after the PV installations had been commissioned. This campaign complemented earlier measurements, which were performed during the construction of the settlement when about 50 % of final PV and loads were installed [4]. In the following sections some information can be found on real estate development, electrical network and the used PV systems.

2.1.1.1 Real estate development “Solarsiedlung Am Schlierberg” is located in the southern outskirts of the city of Freiburg. It was built “from scratch” on the area of a former garrison. To the east and the north there are older residential areas situated. To the South, newly constructed apartment blocks fed by the same transformer as the PV development are located. The whole development was privately funded. It was initiated and inspired by the architect Rolf Disch. Details of the history and architecture of this real estate project are discussed in PV UPSCALE´s work package 3, case studies [3].

Figure 1: Aerial view of “Solarsiedlung Am Schlierberg” (photo: Solarsiedlung Freiburg GmbH)

The development features highly energy efficient buildings with an annual heating demand below 20 kWh/m² (passive house standard). Easterly rows were built in the years 2000 to 2004, western rows and the business block “Sonnenschiff” from 2004 to 2006. The last PV systems were connected to the grid in the fall of 2006. Since the time when the first measurements had been conducted, some 20 apartments,


4700 m² office/shopping area, some 200 kWp PV arrays and some 70 apartments outside the solar development have been added, but all supplied through the same transformer,. Ratio of nominal PV Power to transformer rated power is 110 %. The average power per apartment in the settlement without “Sonnenschiff” is 6.3 kWp, including all non-PV apartments it is 3.2 KWp.

2.1.1.2 Electrical network The electrical network had been designed as it would have been without any PV system. A transformer with a nominal power of Sn = 400 kVA feeds several feeders of 150 mm² Al cables. Short circuit power at the transformer – a measure for the network impedance - is 11 MVA. Along the roads distribution cabinets are located, where all flats are individually connected by 35 mm² Al cables to the main feeders. PV capacity of main feeders is listed in table II, the layout of the electrical network is shown in figure 2. Table II: PV capacity (module ratings) per feeder in kWp and year of completion

feeder 1 2 3+4 total

Pnom [kWp] 176 153 112 441

completion 2005 2002 2006

47 kWp

41 kWp

40 kWp

25 kWp

39 kWp

26 kWp

22 kWp

27 kWp

29 kWp

33 kWp

40 kWp

18 kWp

18 kWp

18 kWp

18 kWp

Feeder 2

Feeder 1

Feeder 3+4

47 kWp

41 kWp

40 kWp

25 kWp

39 kWp

47 kWp

41 kWp

40 kWp

25 kWp

39 kWp

26 kWp

22 kWp

27 kWp

29 kWp

33 kWp

26 kWp

22 kWp

27 kWp

29 kWp

33 kWp

40 kWp

18 kWp

18 kWp

18 kWp

18 kWp

40 kWp

18 kWp

18 kWp

18 kWp

18 kWp

Feeder 2

Feeder 1

Feeder 3+4

MP 1

MP 3

MP 2

MP 4

47 kWp

41 kWp

40 kWp

25 kWp

39 kWp

26 kWp

22 kWp

27 kWp

29 kWp

33 kWp

40 kWp

18 kWp

18 kWp

18 kWp

18 kWp

Feeder 2

Feeder 1

Feeder 3+4

47 kWp

41 kWp

40 kWp

25 kWp

39 kWp

47 kWp

41 kWp

40 kWp

25 kWp

39 kWp

26 kWp

22 kWp

27 kWp

29 kWp

33 kWp

26 kWp

22 kWp

27 kWp

29 kWp

33 kWp

40 kWp

18 kWp

18 kWp

18 kWp

18 kWp

40 kWp

18 kWp

18 kWp

18 kWp

18 kWp

Feeder 2

Feeder 1

Feeder 3+4

MP 1

MP 3

MP 2

MP 4

47 kWp

41 kWp

40 kWp

25 kWp

39 kWp

26 kWp

22 kWp

27 kWp

29 kWp

33 kWp

40 kWp

18 kWp

18 kWp

18 kWp

18 kWp

Feeder 2

Feeder 1

Feeder 3+4

47 kWp

41 kWp

40 kWp

25 kWp

39 kWp

47 kWp

41 kWp

40 kWp

25 kWp

39 kWp

26 kWp

22 kWp

27 kWp

29 kWp

33 kWp

26 kWp

22 kWp

27 kWp

29 kWp

33 kWp

40 kWp

18 kWp

18 kWp

18 kWp

18 kWp

40 kWp

18 kWp

18 kWp

18 kWp

18 kWp

Feeder 2

Feeder 1

Feeder 3+4

MP 1

MP 3

MP 2

MP 4

Figure 2: Structure of the LV network and size of PV arrays. Row houses are connected through four feeders. To the south more apartment blocks are wired to the same transformer and add to the transformer load. Locations marked by “MP X” refer to measurement points and are explained in section 2.1.2.


The basic guideline for connecting distributed generators to the grid was issued by the German association of Electricity Companies VDEW [5]. This guideline allows a voltage rise of 2 % of nominal voltage, i.e. 4.6 V, from local generators. For the transformer at “Solarsiedlung Schlierberg”, considering its short circuit power of 11 MVA, this corresponds to about 220 kVA inverter power. The cable used (NAYY 4x150) can carry a current of 275 A according to manufacturers data sheet1 [12]. Potential maximum current from PV is about 230 A in feeder 1. Thus, an overloading of cables due to PV power is not possible.

2.1.1.3 PV Systems In total the installations comprise about 440 kWp of PV modules and some 160 inverters. In the residential area – excluding the business block “Sonnenschiff” - a capacity of 6 kWp per apartment is installed. PV systems are constructed using 1-phase systems as a building block. Depending on the available roof area, i.e. width of an apartment, a single house system comprises 2 to 4 one-phase systems. Earlier systems employ inverters of type SMA SB 2000 and SB 2500. Later systems in the westerly rows and “Sonnenschiff” mainly employ SMA SB 5000 as well as some SB 3300 and SWR 3100. All inverters use the German “ENS” (grid impedance measurement method) for islanding detection. The PV system and the loads are connected in parallel at the distribution cabinet of each apartment. The main cabling is thus loaded with the balance of residential generation and consumption.

2.1.2 Measurements The PV installations had been completed in September 2006 and thus for 2007 regular operation of the whole development could be expected. Recent measurements were taken in the summer of 2006 and summer 2007, with measurements on MP4 dating from 2002/2003. To represent the worst-case in terms of voltage rise, measurement periods include a part of the holiday season when many families are assumed to be on vacation. All measurement campaigns include at least one week of data. Measurements were taken at four network nodes (see fig. 2): • at the end of feeder 1 (MP1) • at the end of feeder 2 (MP2) • at transformer LV terminals (MP3) • at transformer connection of feeder 2 (MP4) 10 min average values were recorded according to EN 50 160. The issues investigated were: • power quality related to standard EN 50 160 • voltage level at the remotest network nodes • power flow across transformer • harmonic current injection by inverters

1 buried underground, ground temperature 20 °C.


2.1.3 Results First, analysis of the transformer operation is given, since the transformer gives the reference voltage for the remainder of the electrical system. Then results of “end of feeder 1” are presented, where PV capacity had been added most recently. “Feeder 1” represents the effect of some 60 inverters on one feeder. “End of feeder 2” shows nearly identical effects as “end of feeder 1” and is therefore not presented as well.

2.1.3.1 Voltage distribution at transformer The voltage distribution at the transformer covering the period June and July, 2008, is shown in Figure 3. It shows a nearly Gaussian distribution around 235 V. This is 5 V above the nominal grid voltage. Typically, utilities adjust transformer voltage slightly above nominal voltage to ensure a sufficient voltage level at the end of the feeder in the presence of voltage drops along the feeder.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

226

228

230

232

234

236

238

240

242

244

246

248

250

252

Voltage [V]

prob

abili

ty

L1L2L3

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

226

228

230

232

234

236

238

240

242

244

246

248

250

252

Voltage [V]

prob

abili

ty

L1L2L3

Figure 3: Distribution of voltage at transformer secondary side for June + July of 2008. Mean

voltage is 235.5 V.

2.1.3.2 Voltage quality at transformer (EN 50 160) Voltage quality at the customers´ premises is described by the European standard EN 50 160 [6]. This standard defines several quality criteria and corresponding limits. It requires that 95 % of data points, taken as 10 min averages, do not exceed the respective limit. 5 % of data may exceed the limit. Due to the transition of the nominal voltage level from 220 V to a common 230 V (in mainland Europe) the upper limit for voltage was set to 106 % until the end of 2007. In 2008 the upper limit is 110 %. The main provisions of EN 50 160 are listed in Appendix 1. For this evaluation the conservative voltage limit of 106 %, corresponding to 243.8 V, had been


used. Relevant voltage limits are shown in table III for comparison. Table III: Voltage tolerance level of EN 50 160 for 95 % of data.

year till 2007 2008

relative voltage [%] 106 110

absolute voltage [V] 243.8 253 Figure 4 gives an overview on the EN 50 160 criteria and results over four weeks of measurement in summer 2007.

Figure 4: Voltage quality at transformer secondary side according to EN 50 160. For each parameter the analysis for each phase is given. Red bars indicate critical 95 % percentage of data points. Blue bars account for remaining 5 % of data points. Limits as indicated by the horizontal red line are not violated by 95 % of data points. Some few data points indicate harmonics and flicker levels above the threshold.

2.1.3.3 Real power flow at transformer To show the reverse power flow, the week of highest power export was selected (ffigure 5). The highest power delivery to the MV grid observed was 150 kW. This is far below the rated transformer power of 400 kVA. During construction of the whole development, the network operator had considered the ratio of generation and loading on the transformer and added loads proportionally to the progress of PV generation.


-350-300-250-200-150-100

-500

50100150200

day

P [k

W]

delivery

consumption

Figure 5: Load over transformer during week of highest power delivery (2006-07-23 – 2006-07-30).

Positive values indicate reverse power flow. Peak delivery at a level of some 150 kW occurred on a Sunday.

For 2003 we had noted some 15 kW power unbalance between phases L1 and L3 during power export. In 2006 the unbalance was found to be about 30 kW as can be seen in fig. 6. Phase 1 delivers most power. This corresponds to a slightly higher voltage of L1 as can be seen in figure 6. It is assumed that inverters are not distributed evenly on the three phases, but concentrated on phase L1.

-100

-80

-60

-40

-20

0

20

40

60

80

day

P [k

W]

P [kW] L1P [kW] L2P [kW] L3

Figure 6: Real power load over transformer per phase during the first two days of the week 2006-

07-23 – 2006-07-30. Positive values indicate power export. Load unbalance increases during daytime.


2.1.3.4 Voltage quality (EN 50 160) at end of feeder 1 Figure 7 gives an overview of the EN 50 160 criteria and results of measurements at the end of feeder 1 in summer 2006. There is no violation of the standard, however some 0.5 % of voltage data points for L2 and harmonic data points for L1 exceeded the voltage limit. “Events” indicate a large number of very short voltage excursions with 10 ms - 100 ms duration. In the standard, there is no limit given for these short time events.

Figure 7: Overview diagram for EN 50 160. Red bars indicate critical 95 % percentage of data points. Limits as indicated by the horizontal red line are not violated. Some few data points indicate voltage levels above the threshold.

2.1.3.5 Voltage rise from PV power at end of feeder Evaluation according to EN 50 160 indicated some voltage swells. This effect is more clearly visible in figures 8 and 9. Fig. 8 depicts the voltage distribution at MP1 (data recorded during last week of July, 2007). Figure 9 displays the correlation of PV generation and voltage rise for this network node. It can be seen to be a linear relation.


0

0.05

0.10

0.15

0.20

0.2522

5

227

229

231

233

235

237

239

241

243

245

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251

253

Voltage [V]

prob

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ty

L1L2L3

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0.05

0.10

0.15

0.20

0.2522

5

227

229

231

233

235

237

239

241

243

245

247

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253

Voltage [V]

prob

abili

ty

L1L2L3

Figure 8: Distribution of voltage at MP1. Deviations from a Gaussian shape are due to PV

generation.

230

232

234

236

238

240

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246

2500- 2000- 1500- 1000- 500- 0

power [W]

volta

ge [V

]

Urms L1 Urms L2 Urms L3

2007 tolerance level of EN 50 160

Figure 9: Voltage at MP1 increases as function of delivered inverter power. It should be noted that

the observed voltage rise is due to the superposition of the voltage rise effects of all PV systems on that feeder, not only from the power of the last system.


2.1.3.6 Harmonic distortion, harmonics spectra – voltage, current To assess harmonics generation from inverters the Total Harmonic Distortion of the voltage (THD_U) at MP1 was observed. Figure 10 shows the result: THD_U level falls well below the standard’s limit of 8 %. It shows no dependency on PV power. In fact, THD_U is higher when no PV power is available, i.e. in the evening and at night. This suggests that distortion is mainly caused by conventional appliances.

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Figure 10: Harmonic distortion (THD) voltage at MP1 as function of delivered inverter power.

According to the “VDEW connection requirements” [5], individual inverters for PV systems have to meet the standard EN 61000-3-2 with regard to their harmonic current generation. Figure 11 depicts the lower harmonics part of the current spectrum in feeder 2 at MP 4 measured during May/June 2003 as an example. The harmonic currents represent the net balance of the total current of some 60 operational inverters and the connected domestic loads from 25 homes. All harmonic current levels stay well below the permissible limits (figure 12).


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Figure 11: Graph of selected harmonic currents in phase 2 at MP 4 over a sunny day. The first

graph depicts irradiance.

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Figure 12: Low order harmonic currents measured at MP 4 in May/June 2003, typically the time

period with the highest irradiation in the year.


2.1.3.7 Voltage unbalance (at end of feeder) In this section the aspect of voltage unbalance is analysed in more detail. Figure 8 – voltage distribution - has shown some unbalance between the phases. Figure 7 has already shown that the EN 50 160 standard is not violated. Figure 13 shows the time sequence of the “unbalance index”, the ratio of inverse sequence/normal sequence, again for the last week in July, 2008. Unbalance typically stays below 1 %, which is well below the permitted limit of 2 %.

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11,21,41,61,8

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volta

ge im

bala

nce

[%]

Figure 13: Time series diagram of voltage unbalance at MP 1. Time is one week in arbitrary units.

EN 50 160 permits up to 2 % unbalance. This value was never reached during the monitoring period.

2.1.4 Summary “Schlierberg” “Solarsiedlung Am Schlierberg” is a recently constructed real estate development comprising about 440 kWp PV arrays on some 70 residences as well as on a large office and building block. PV systems are connected in parallel to the premises´ loads. They are distributed roughly evenly along the feeders. The area is supplied through a 400 kVA transformer, so the ratio of PV capacity to transformer power is 110 %. A measurement campaign in the development showed that power quality is only slightly affected by the PV systems. All power quality requirements as described by the European standard EN 50 160 were satisfied. At the network nodes, which are furthest away from the transformer station, increased voltage levels had been measured. However, measured voltage levels fall very well into the tolerance bands. For the whole area supplied by the transformer, which includes buildings without PV, an average PV power of about 4 kWp per apartment is installed. The maximum tolerable capacity of PV on a single LV feeder was found to be about 7 kWp per apartment. By reducing the slightly higher set voltage of the transformer to the nominal level, an even higher PV capacity could be accommodated. During the time of highest PV generation a power export to the MV grid was noticed. The peak delivered power was found to be 170 kW. Also, unbalance between phases was found at increased levels during PV generation, probably due to an uneven distribution of inverters over the three phases. This should be avoided by integrated planning of inverter distribution.


2.2 Holidaypark Bronsbergen The holiday park `Bronsbergen`, is situated in Zutphen, Netherlands. PV panels are mounted on the roof of 108 cottages out of a total of 210 cottages, see figure 14. Most of these cottages are used for holidays only; therefore the load is small compared to regular domestic residences.

Figure 14: Holiday park, roofs with solar panels. The total solar power installed is around 315 kW

peak.

2.2.1 Site description Holidaypark Bronsbergen The total solar power installed is around 315 kW peak. The nominal power of the transformer, feeding all the cottages is 400 kVA. In the following sections information can be found on real estate development, electrical network and the PV systems used. The ratio of nominal PV Power to transformer rated power is 80 %. The average power per house with PV is 2.9 kWp; including non-PV houses it is 1.5 KWp.

2.2.1.1 Real estate development The holiday park was built eight years ago in 2000. The roofs of the 108 cottages with PV systems are owned by the utility Nuon. Ownership will be transferred to the owner of the building after ten years of use. Energy from the PV systems is measured separately from the load of the cottages themselves.


Figure 15: Example of cottage with PV panels on the roof

An overview of the holiday park is given in figure 16 which is a picture from “google earth”.

Figure 16: Overview of the holiday park “Bronsbergen”


2.2.1.2 Electrical network Figure 17 shows the total concept of the low voltage grid on the holiday park. Four outgoing feeders are used for connecting all the cottages to the public grid, mainly using 150 mm² Al low-voltage cable. The nominal power of the transformer is 400 kVA. The average transformer secondary voltage is set to 230 V, lower than normal due to the PV systems connected.

Figure 17: Concept of the low voltage grid `Bronsbergen`

2.2.1.3 PV systems The PV systems in each cottage are connected to the grid with (in most cases) two inverters with a nominal power of 2.5 kVA, each. The inverters of each cottage are both connected to one phase and the PV systems are equally distributed over the phases. The systems are connected through a separate energy meter, to measure the PV production into the grid independent from the load of the cottage itself. The type of inverters is Mastervolt Sunmaster 2500.

2.2.2 Measurements A monitoring program was started in June 2005 for monitoring all power quality aspects in the low voltage grid. In the four outgoing feeders and at the low voltage side of the transformer power quality (PQ) measurement devices were placed as shown in figure 18. During this period the active and reactive power across the feeding transformer was measured. The measured data also gives the information about all power quality phenomena at the low-voltage side of the transformer. To complete the picture of actual power quality levels in the grid, measurements were taken in some cottages over several weeks. Due to the fact that most of these cottages are used for holidays the load is small compared with normal domestic houses.


Figure 18: PQ-measurement devices installed in the substation

2.2.3 Results In the next sections the results of all measurements are given. In each section the most important findings are described.

2.2.3.1 Voltage level at transformer Figure 19 shows the voltage level at the low voltage side of the transformer. The voltage variations are limited to approximately 8 V. The voltage variations are due to variations in the loads, generated PV power and voltage variations in the MV-grid. There are no unexpected voltage variations.

Figure 19: Voltage variation at the low voltage side of transformer


2.2.3.2 Voltage quality at transformer (EN 50 160) Voltage quality at the transformer is in general within the limits of EN 50 160. However, in cases of high production of PV power there is a harmonic oscillation problem. Due to a resonance effect the harmonic voltage of the 11th or 15th harmonic order is above the standards´ limit. An example of the measured voltage quality is shown in figure 20.

Figure 20: Voltage quality at the low voltage side of transformer

In this figure harmonic distortion is shown as the second group of bars from the left, above the label “voltage harmonics”. In this example the average falls within the limits, but due to the resonance the acceptable limit has been exceeded several times. Further details are given in section 2.2.3.6.

2.2.3.3 Power flow at transformer Figure 21 shows the power flow across the transformer. When the active power is negative, then the active power is flowing back into the MV grid. If the reactive power is negative, then the reactive power is capacitive, due to the capacitors in the PV inverters which are switched on in the morning and switched off in the evening. The difference between sunny and cloudy days shows very clearly.


Figure 21: Power flow across the transformer (in kW, kVA)

2.2.3.4 Voltage quality at end of feeder Voltage quality at the end of the feeder is in general within the limits of EN 50 160. Again in several cases a harmonic distortion exceeding these limits was measured. An example of a measurement is shown in figure 22. Mostly there is an increased level of the 11th and 15th harmonic voltage as is described in section 2.2.3.6.

Figure 22: Voltage quality at the end of a feeder. Voltage harmonics exceed the level set by

EN 50 160 in several cases.


2.2.3.5 Voltage rise from PV power at end of the feeder The voltage rise at the end of the feeder is within the acceptable limit. Figure 23 shows this voltage level together with the PV current generated in one of the cottages. The cottage is not located at the end of the feeder, but the measured voltage variations can be used to calculate the voltage at the end of the feeder.

Figure 23: Voltage (upper signal) and generated PV current in one of the cottages. Current is

shown indicatively only to show correlation of voltage with current pattern

The voltage varies between 233 V and 216 V. The voltage drop from peak load in the evenings is shown as high as the voltage rise from peak PV power.

2.2.3.6 Harmonic distortion, harmonic spectra – voltage, current As mentioned before there is a resonance phenomenon, which leads to an increase in the 11th and 15th harmonic voltage. The 11th harmonic voltage is increased mainly in phase 1 of the system and the 15th harmonic voltage is increased in phase 3. Measured harmonic voltages in the cottage are shown in figure 24. Figure 25 shows the current of the PV system at the same cottage. The PV systems are connected to phase 1 in this cottage.


Figure 24: Harmonic voltages, blue: h11, red: h15

Figure 25: Current of the PV system for the same time period. The strong correlation of PV

generation and increased harmonic voltages is clear.

This harmonic distortion occurs due to the resonances which occur due to the capacitance of the inverters and the inductance of the grid. The harmonic background distortion, the harmonic currents and the harmonic behaviour of the inverters also play an important role. A deeper analysis of this problem can be found in [8] and [7].


2.2.3.7 Voltage unbalance If the PV systems are equally distributed over the phases of the system, then there will be no unbalance. In general there is no reason for voltage unbalances due to the use of PV systems. In this particular case there were some current unbalances due to the unequal distribution of the PV systems. Nevertheless the voltage unbalance was limited.

2.2.3.8 Inverter tripping Inverter tripping was not measured as such, but will occur when there is a significant voltage dip. The protection devices in the inverter are sensitive to voltage dips, because they have to fulfil the requirements on anti-islanding. It is recommended that there should be a change in these requirements to delay the disconnection time which gives the inverters additional time to stay connected to the grid, if a voltage dip occurs. Inverter tripping, though it was not measured here, had been observed in other projects due to harmonic distortion.

2.2.3.9 Flicker An increase in the flicker level was observed in the moments when there was an increased level of harmonic distortion. In general, during times with regular levels of harmonic distortion, there is no increase in the flicker level. Also in other places, where many PV systems are connected to the grid, there was no significant increase in the flicker level. In general, it can be concluded that the impact on flicker is low or does not exist at all.

2.2.3.10 Ripple control signals In this project no interference with ripple control signals was detected. In general, also with other PV projects, problems with ripple control signals did not occur.

2.2.4 Summary “Bronsbergen“ The holiday park `Bronsbergen` comprises a total of 210 cottages. On the roof of 108 cottages, PV with a total nominal power 315 kWp is mounted. Most of these cottages are used as holiday homes; therefore the loads are small compared to regular residences. The nominal power of the transformer, feeding all the cottages is 400 kVA. The ratio of total PV power to transformer power is about 80 %; average PV capacity per apartment is 1.5 kWp. Voltage quality at the transformer is in general within the limits of EN 50 160. However, in cases of high production of PV some voltage harmonics were found. Due to a resonance effect the harmonic voltage of the 11th or 15th harmonic order exceeded the standards´ limit This phenomenon could be traced to high input capacities of the employed inverters. Increased voltage levels were not noticed; generally the quiescent voltage of the transformer was below 230 V. The area exported power on sunny days, a peak of 150 kW was noted repeatedly.


2.3 Heerhugowaard, sun city “Mayersloot” Mayersloot comprises a mix of domestic houses with and without PV systems. A photograph of the site is given in figure 26.

Figure 26: view on Mayersloot

2.3.1 Site description Heerhugowaard, sun city “Mayersloot” The site is in Langedijk, Heerhugowaard, where the “city of the sun” is located. In recent years, many houses and buildings were built employing PV systems. The site comprises a total of 70 houses on two feeders of the transformer. 21 houses employ a PV generator. The ratio of nominal PV Power to transformer rated power is 33 %. The average power per house with PV is 6.2 kWp; including non-PV houses it is 1.9 KWp.

2.3.1.1 Real estate development A lot of PV projects are located in this residential area. Some houses on this site have PV systems and some do not. The houses were built around the year 2000 and to date no problems with the PV systems were reported. An overview of the houses connected to the network, and the houses which were installed with PV systems, is shown in figure 27.


Figure 27: Layout of the electrical network. Houses with PV, cable routing and cable sizes are

given.

2.3.1.2 Electrical network The grid had been designed, knowing that many PV systems would be connected. In general, this has led to a reinforced grid design, where less reduction of cross section area of the cables is applied than normal2. The layout of the electrical network is shown in figure 28. The transformer size is 400 kVA. There are four outgoing feeders. On two of the feeders, there are houses with PV systems connected, together with houses without PV. The houses with PV systems are concentrated at the end of the respective feeder. The total length of the cables and the type of cables are given in fig. 28. The length and cross-section of the cables provide a low impedance path for connection of all houses. For this reason problems with voltage level or other power quality phenomena are not expected.

2 Usually cable cross section is reduced towards feeder end to 95 mm² or 50 mm² as shown for the non PV houses

in figure 28.


Figure 28: Overview of the electrical network

2.3.1.3 PV systems The PV systems range in size from around 5 to 8.5 kWp per house, when a PV system is installed. The houses with PV are connected at the end of the two feeders, which gives the greatest rise in voltage level. The total PV capacity installed is 130 kWp. Installed inverters are Mastervolt Sunmaster 2500.

2.3.2 Measurements Power quality was measured in one house at the end of the feeder and in the substation during a summer week. Also the grid was simulated in “Power Factory”, a software tool for network calculations by the company “digsilent”. No differences between simulation and measurements were found and, therefore, no further measurements were taken. The results of the measurements are described in the coming paragraphs.

2.3.3 Results In the next sections the results of all measurements are given. In each section the most important conclusions are described.

2.3.3.1 Voltage level at transformer Over a short time the voltage level at the low voltage side of the transformer was measured. The results are shown in figure 29


Figure 29: Voltage level at low voltage side of the transformer; upper curve, blue: voltage, red:

current

The voltage level stays between 235 V and 242 V and is within acceptable limits. Due to the relatively high short circuit power at the transformer station the voltage variations are limited.

2.3.3.2 Voltage quality (EN 50 160) at transformer The voltage quality at the low voltage side of the transformer is within all limits. There is no significant change compared with the average voltage quality. So, the PV systems have not influenced power quality either positively or negatively.


2.3.3.3 Voltage quality at end of feeder Voltage quality at the end of the feeder is within acceptable levels as is shown in figure 30.

Figure 30: Voltage quality measured in a house at the end of the feeder

For events (voltage dips) there are no clear limits given by the standard, but the events which occurred did not have any relation with the PV systems installed. Again, due to the relatively stiff grid the influence on the voltage quality is minimal.

2.3.3.4 Voltage rise from PV power at end of the feeder During PV generation the voltage at the end of the feeder is higher than the voltage at the beginning of the feeder due to the reverse power flow. The relation between the generated PV power and the voltage level can be clearly seen in figure 31.


Figure 31: Voltage level at the end of the feeder; upper curve, blue: voltage, lower curve red:

current

The current in this figure is the current of one of the two PV inverters installed in this house. The maximum permissible voltage according to EN 50 160 is 253 V and the minimum permissible voltage 207 V. With its range form 227 V to 245 V the recorded voltage falls well between these limits.

2.3.3.5 Harmonic distortion, harmonic spectra – voltage, current Figure 32 shows the relation between the harmonic voltage distortion (THD-V) and the current of one inverter installed in the house at the end of the feeder. Also for this power quality phenomenon there is no significant relation between the generated PV power and the harmonic voltage distortion. From this and also from other PV projects it can be concluded that harmonic problems only occur when there is a resonance problem. This can occur when a lot of inverters are installed with a high input capacitance.


Figure 32: Voltage distortion and PV current; upper curve, blue: THD_V, L1, lower curve red:

current L1

2.3.3.6 Voltage unbalance If the PV systems are equally distributed over the phases of the system, then there will be no unbalance. In general there is no reason for voltage unbalances due to the use of PV systems. In this case there was no unbalance measured.

2.3.3.7 Flicker Figure 33 shows the flicker parameters Pst and Plt over the same time period as the measured PV current in figure 32. The peak flicker levels occur when no significant PV output current is observed. From this figure and from experience from other PV projects it can be concluded that there is no significant relation between PV power generation and flicker.


Figure 33: Measured flicker parameters Pst and Plt; blue: Pst, L1, red: Plt, L1t

2.3.3.8 Ripple control signals In this project no interference with ripple control signals is detected. In general, also with other PV projects, problems with ripple control signals did not occur.

2.3.4 Summary “Mayersloot“ “Mayersloot” is a site with domestic customers, some with and some without PV systems, all built in the year 2000. Total PV capacity installed is 130 kWp. The PV houses are all connected to the ends of two feeders, which gives the greatest rise in voltage level. Peak power of the PV systems installed is around 5 to 8.5 kWp per house, when a PV system is installed. Referred to the two feeders, to which PV is connected, the average nominal PV power is 1.9 kWp per house. During the seven years of operation no problems with the PV systems were reported. Transformer voltage level was generally rather high, between 235 V and 242 V and was within acceptable limits. Voltage quality at the end of the feeder was also within acceptable levels.


2.4 “Soleil-Marguerite“ photovoltaic system

2.4.1 Site description

2.4.1.1 Real estate development The site is located next to the Technical University of Lyon in France. In 2000 Hespul, a French non-profit organisation for the promotion of renewable energies, moved into an office building owned by a co-operative and ethical financial services bank, La Nef. Hespul then launched the idea of installing a PV system on the roof of this building. In order to invest in the PV system, Hespul and La Nef created an association dedicated to the promotion, installation and management of renewable energy systems called Soleil-Marguerite [9]. This association was a contractor of the European Commission funded UNIVERSOL Project which supported the installation of PV systems on buildings in Spain, United-Kingdom, The Netherlands and France comprising a total power of 827 kWp [10].

Figure 34: bird’s eye view of the Soleil-marguerite PV system installed on the roof of an office

building in Lyon-Villeurbanne, France

Although the Soleil-Marguerite photovoltaic system is not part of a PV real estate development, it is included in this report since a technical study was undertaken by EDF R&D project in order to assess the impact of this photovoltaic system on the voltage quality of the low voltage network [11].

2.4.1.2 Electrical network Detailed characteristics of the electrical network are not known, but the building on which the PV system is installed, is located in a high density urban area with a mix of offices and dwellings. Therefore, the local electrical network can be considered as a stiff grid.

2.4.1.3 PV Systems For Hespul, this project was the opportunity to become owner of its own PV system in order to go on promoting PV by organising technical visits and training sessions and allowing hands-on experience. For that reason, Hespul decided to have at least one sub-system from each main


French PV system supplier. Therefore this PV system is composed of 3 subsystems (table IV): Table IV: technical data of PV system Power

[kWp] module type Inverter type/ number system supplier

Sub-system 1 6.1 BP-Solar 585 BP Solar CGI 2400 / 3 BP-Solar Sub-system 2 2.1 Total-Energy

TE1700 SMA SWR 1700E / 1 Tenesol

Sub-system 3 4.6 Isofoton I-110 SMA SB 2100 TL / 2 Sunwatt - Isofoton total 13 6

Figures 35 and 36 give an impression of the installation.

Figure 35: The PV generator is mounted on a flat roof

Figure 36: inverters are mounted outdoor at a protected, northern wall

2.4.2 Measurements As part of the project UNIVERSOL [10], EDF R&D carried out a study in order to assess the


impact of a photovoltaic system on the voltage quality of the low voltage network [11]. EDF R&D undertook two types of measurements on this PV system:

• During three weeks (from 07/09/2004 to 28/09/2004): Measurements were taken at the connection point to the distribution network, of currents, voltages, powers, harmonics and flicker during regular operation in order to produce a quality check-up of the installation (10 min average values)

• During one day (28/09/2004) : Measurements were taken at the connection point to the distribution network, of transients in order to assess the impact of the PV system on the distribution network during specific events such as the connection or the disconnection to the distribution network (20 ms sampling rate)

In particular, this study focused on specific voltage quality characteristics such as: • slow variations of voltage

• quick variations of voltage

• harmonics in the range 0 – 9 kHz.

2.4.3 Results The overall result of this study was that, except the consumption of reactive power and slightly increased level of H6 and H8 harmonic currents, the impact of this PV system on the low voltage distribution grid is low:

• Power : the photovoltaic system consumes reactive power during the generation period, which was not expected and not in accordance with the national legal framework

• Frequency : very low variations, the values stay in the regulation range

• Slow variations of the voltage : very low, the values stay in the regulation range

• Flicker : very low, the values stay in the regulation range

• Voltage unbalance : very low, the values stay in the regulation range

• Voltage spikes: no voltage spikes during operations

• current harmonics (0 to 9 kHz) : the levels stay low, except the harmonic currents H6 and H8 which exceed 0.5 % when the installation supplied a power higher than a certain threshold (about 4 kW)

• Inter-harmonic voltage at the frequency 175 Hz: low value, it had no influence on the plants using the 175 Hz remote-control system.

2.4.3.1 Voltage quality at end of feeder (EN 50 160) Under regular operating conditions, load changes cause variations of the average supply voltage on a time scale of a few tens of seconds. The EN 50 160 standard requires that the range of variation of magnitude of the supply voltage should fall

• either between Vn +10 % and Vn -15 % or

• into Vn ± 10 % for 95 % of a week.

This study found that, during a week of measurements, the voltage supply stayed between


229.9V (Vn -0.04 %) and 241.89 V (Vn +5.17%), this means between the values defined by the EN 50 160. Other aspects of the EN 50 160 standard are described below.

2.4.3.2 Voltage rise from PV power at end of feeder Although not situated at the end of a feeder, the voltage of the distribution grid was analysed in relation to the power delivered by the PV system (see figure 37). The study concluded that the grid voltage seemed to be independent of the power, mainly due to the fact that the nominal power of the PV system is low compared to the load in this urban area.

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2.4.3.3 Harmonic distortion, harmonics spectra – voltage, current Harmonic Voltages in the 0-2500 Hz range and harmonic currents in the 0-2000 Hz range were measured during the long term monitoring campaign. The study concluded that harmonic voltage levels are low and always below limits set by the EN 50 160 and the IEC 61000-2-12 standards (see figure 38). Concerning harmonic currents, levels are also low, except for H6 and H8 harmonic currents that are above the 0.5 % level (see figures 39, 40). These limits refer to a legal text, an arrêté, that defined the harmonic emissions for producers connected to the MV grid [13]. The values are given in % by harmonic order.


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Figure 39: harmonic currents in the 0 to 2000 Hz range and comparison to permissible limits. H6

and H8 harmonic currents are higher than limits stated in national regulation [13].


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The harmonic distortion of voltage and current is characterised by a parameter called “Total Harmonic Distortion” (THD). Concerning harmonics voltages, THDmax measured was 5.4 %. This is below the maximum value of 8 % set by EN 50 160 (see figure 41).


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Figure 41: Total Harmonic Distortion (THD) of voltage and current for a week. Daily peak THD

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Higher harmonic voltages and currents up to 9 kHz were measured only during one day and are well below the standard’s [13] limits (see figure 42 and 43).

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Figure 43: harmonic currents in the 2 to 9 kHz range and comparison to permitted limits.

2.4.3.4 Voltage unbalance at end of feeder The unbalance Vu of the supply voltage is defined by the negative sequence component Vi expressed in percent of the positive sequence component Vd. Compliance with EN 50 160 is verified when 95 % of the sequence of valid 10 minutes of Vi values are within the 0 to 2 % range of the positive sequence component. The study concluded that the PV system did not generate voltage unbalance as the maximum negative sequence component was 0.77 % of the positive sequence component.

2.4.3.5 Flicker Flicker is the effect produced by lamps on the visual human perception in case of voltage fluctuations. The severity of the disturbance caused by this effect disturbance is described by two parameters: the short term severity Pst and the long term severity Plt. First, no relation between Pst values observed, and PV production was found during the week of measurements. Maximum Pst values were measured at night and not during the PV generation period or during connection or disconnection of the PV system to the grid (see figure 44). Also, as the maximum Plt value recorded was 0.7, this is well below the level of 1 for 95 % of the measured values as required in EN 50 160. The study concluded that the PV system was not the cause of Flicker (see figure 45).


0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

Day

Pst [

%]

0

1

2

3

4

5

6

7

8

9

10

Pow

er [k

VA]

Pst

Power

Figure 44: short term severity Pst and power

00,10,20,30,40,50,60,70,80,9

1

Day

Plt [

%]


Figure 45: long term severity Plt during week of measurement


2.4.3.6 Ripple control signals In France, the frequency of the ripple control signal used by utilities to change the price of electricity for different periods of the day is 175 Hz. In order to guarantee the proper operation of ripple control devices the 175 Hz voltage harmonic must stay below 0.6 %. The study concluded that the PV system does not impact the ripple control signal as the maximum 175 Hz voltage harmonic level measured was 0.31 %.

2.4.3.7 Other issues • Reactive Power: as can be seen on figure 46 the photovoltaic system consumes reactive

power during the generation period, which was not expected and not in accordance with the national legal framework. The reason why this system consumes reactive power is not known at the time of writing.

• Frequency: the EN 50 160 standard indicates that the ranges of frequency variations for interconnected supply systems are: 50 Hz ± 0.5 % for 99.5 % of values and 47 - 52 Hz for 100 % of values. The study found that the variation of frequency was very low as the measured frequency stayed between 49.94 Hz and 50.06 Hz.

• Effects of connection and disconnection to the distribution network: measurements of transients at fast sampling rate were undertaken during one day in order to assess the impact of the PV system on the distribution network during specific events such as the connection or the disconnection to the distribution network. This study concluded that, during such event, the voltage stayed within the range set by the EN 50 160 standard (see figures 46 and 47).

-1500-1000-500

0500

1000150020002500

0 4 8 13 17 21 25 30 34 38 42 46 51 55 59

Time [s]

P [W

] and

Q [V

ar]

231,50

231,75

232,00

232,25

232,50

232,75

233,00

Volta

ge [V

]

Figure 46: Voltage (green), reactive power (bottom curve - blue) and real power (centre curve -

magenta) during the connection of the PV system to the grid


-1500-1000-500

0500

10001500200025003000

0 4 8 13 17 21 25 30 34 38 42 46 51 55 59

Time [s]

P [W

] and

Q [V

ar]

229,00

229,50

230,00

230,50

231,00

231,50

232,00

232,50

Volta

ge [V

]

Figure 47: Voltage (green), real power (upper curve – magenta) and reactive power (bottom curve

– blue) during forced disconnection of the PV system from the grid

2.4.4 Summary “Soleil-Marguerite“ The Soleil-Marguerite photovoltaic system is located in a high density urban area with a mix of offices and dwellings. Therefore, the local electrical network can be considered as a stiff grid. The PV system comprises about 13 kWp and 6 inverters. It is included in this report to show the negligible impact of a comparatively small PV system on the voltage quality of the low voltage network. Detailed characteristics of the electrical network are not known, but the building on which the PV system is installed, is located in a high density urban area with a mix of offices and dwellings. Therefore, the local electrical network can be considered as a stiff grid. The overall results of the “Soleil-Marguerite“ study was that the impact of this PV system on the low voltage distribution grid was low. However, consumption of reactive power was higher than expected and required by national guidelines and at high generation power the level of H6 and H8 harmonic currents from inverters was found to exceed the limits set in a national standard [13].


3 Conclusions Measurement campaigns in four urban PV real estate areas and systems have demonstrated that PV generation is compatible with LV distribution networks even at high PV density. This report confirms that distributed generation from PV systems with a high ratio of generation capacity to rated transformer power, a ratio of 80 % and higher, in general does not deteriorate the quality of the grid. Power quality was found to be affected only with regard to increased voltage levels at the end of LV feeders. Generally, all power quality requirements as described by the European standard EN 50 160 were satisfied. Acceptable PV capacity The ratio of nominal PV capacity to rated transformer power for the systems monitored includes the values 33 %, 80 % and 110 %. For the whole area supplied by the transformer, including buildings without PV, the average installed PV capacity reaches values of 1.5 KWp, 1.9 kWp and 3.2 kWp per apartment. The maximum tolerable capacity of PV to a single LV feeder was found to be about 7 kWp per apartment. Obviously, evenly distributing PV systems over a feeder allows more capacity than concentrating PV systems at the end of a feeder. As a rule of thumb PV capacity in an LV grid segment should not cause any problems, if power is limited to 70 % of the rated power of the feeding transformer. In some cases even higher amounts of PV power were possible. The implementation of PV systems in existing networks is limited to this 70 % because most grids are designed assuming a relatively low load for each customer (ADMD of 1 - 1.5 kVA). This can be assumed because of the low simultaneous use of all loads connected to the network. PV power, however, is generated simultaneously by all systems. The simultaneous production of PV power is the bottleneck for implementing higher amounts of PV-power. In new networks, the grid design can be adapted for the PV systems that may be connected to it in future by properly sizing transformer and cables. There is no theoretical technical limit, if the network design can be “made for purpose”. By reducing the set voltage of the transformer from 235 V to the nominal level of 230 V, an even higher PV capacity could be accommodated. Loading of equipment During the time of highest PV generation a power export to the MV grid was noticed. The peak exported power in any of the projects did not exceed 160 kW, less than half the transformers rated power. Power quality In general, no detrimental effect on power quality was noticed. Flicker problems were not noticed. However, in one case voltage harmonics were found to exceed permitted values. This was traced back to resonance effects between network harmonics, cable impedance and a high inverter input capacitance. Selecting inverters with a low input capacitance would avoid this effect. In another system current harmonics from inverters were found to exceed limits set by a national French standard under high power levels. Possible improvements Power unbalance between the phases was found to be increased, if there was an uneven distribution of inverters over the three phases. This should be avoided by integrated planning of inverter distribution. For new developments setting the transformer ratio to a secondary voltage level between Vn and 98 %*Vn could avoid any practical capacity limit from voltage rise.


4 References

[1] J. Scheffler; Bestimmung der maximal zulässigen Netzanschlussleistung photovoltaischer Energiewandlunganlagen in Wohnsiedlungsgebieten (Determination of the maximum permissible power capacity of PV systems in residential areas), Dissertation, Technical University Chemnitz, 2002

[2] http://www.solarsiedlung.de/

[3] http://www.pvupscale.org/IMG/pdf/Schlierberg.pdf

[4] H. Laukamp, M. Thoma, T. Meyer, Th. Erge; Impact of a large capacity of distributed PV production on the low voltage grid, Proc. 19. European PVSEC, Paris 2004

[5] VDEW; Eigenerzeugungsanlagen am Niederspannungsnetz – Richtlinie für Anschluss und Parallelbetrieb von Eigenerzeugungsanlagen am Niederspannungsnetz (private electricity generation systems at the low voltage grid – Guideline for connecting and operating of distributed generation systems on the low voltage grid, issued 2001), 4. Ausgabe 2001

[6] EN 50 160: 1995; Voltage characteristics of electricity supplied by public distribution systems

[7] J.F.G. Cobben, Power Quality, Implication on the point of connection, Doctoral dissertation, University of Technology Eindhoven, 2007.

[8] J. F. G. Cobben, Kling, W. L., Heskes, P. J., & Oldenkamp, H. (2005, June). Predict the level of harmonic distortion due to dispersed generation. CIRED,Turin, Italy.

[9] www.soleilmarguerite.org

[10] www.universol-france.org

[11] C. Duvauchelle, G. Duvallet, C. Moré, T. C. Thaï, Quality impact of the photovoltaic generator "Association Soleil Marguerite" on the public distribution network, report HR-42/04/046/A, EDF R&D / EFESE – MIRE, 2004

[12] Strombelastbarkeit für NYY, NAYY, NYCY, NYCWY, NACWY Kabel http://www.helukabel.de/pdf/german/technik/T29__STROMBELASTBARKEIT_FUER_NYY_%20NAYY_NYCY_%20NYCWY_%20NACWY.pdf, 2008-06-19

[13] Arrêté technique du 21 juillet 1997 relatif aux conditions techniques de raccordement au réseau public des installations de production autonome d'énergie électrique de moins de 1 MW, legal document, France, Paris, 1997

Acknowledgements To home owners for access to apartments and buildings To the European Union for financial support in the frame of the CEC supported projects PV-UPSCALE (EIE/05/171 and UNIVERSOL (NNE5/2001/293)


5 Annex

5.1 EN 50 160 requirements for LV grid The following table gives the currently valid (year 2008) requirements of EN 50 160. General requirements (except for frequency) are:

• at least one week of measurement • 10 min average rms values • 95 % of data shall fall within limits

• Parameter EN 50 160 requirements

Power frequency mean value of fundamental measured over 10 s:

±1% (49.5 - 50.5 Hz) for 99.5% of week

-6%/+4% (47- 52 Hz) for 100% of week

Magnitude of the supply voltage

±10 % for 95 % of week,

Supply voltage variations ±10 % for 95 % of week,

Voltage level variations ±10 % for 95 % of week,

Rapid voltage changes

Flicker

level changes ≤ 5 % normal, >10 % infrequently

Plt ≤ 1 for 95 % of week

Supply voltage dips Majority: duration <1s, depth < 60 %.

Locally limited dips caused by load switching: 10 – 50 %

Short interruptions of supply voltage

duration < = 3 minutes: few tens - few hundreds/year Duration 70 % of them < 1 s

Long interruption of supply voltage

duration > 3 minutes: <10 - 50/year

Temporary, power frequency overvoltages

<1.5 kV rms

Transient overvoltages generally < 6 kV, occasionally higher; rise time: ms - μs.

Supply voltage unbalance ≤ 2 % ≤ 3 % in some locations

Harmonic voltage individual harmonics: see table below THD ≤ 8 % (including all harmonics up to the order 40)

Interharmonic voltage under consideration

Mains signalling voltage according to frequency dependent curve


Table 1: Values of individual harmonic voltages at the supply terminals for orders up to

25 given in percent of the fundamental voltage U1

Odd harmonics Even harmonics

Not multiples of 3 Multiples of 3

Order h Relative voltage (Un) Order h Relative

voltage (Un) Order h Relative voltage (Un)

5 6.0 % 3 5.0 % 2 2.0 %

7 5.0 % 9 1.5 % 4 1.0 %

11 3.5 % 15 0.5 % 6 24 0.5 %

13 3.0 % 21 0.5 %

17 2.0 %

19 1.5 %

23 1.5 %

25 1.5 % NOTE No values are given for harmonics of order higher than 25, as they are usually small, but largely

unpredictable due to resonance effects.

WP4 – Deliverable 4.3 IMPACT OF PHOTOVOLTAIC … · IMPACT OF PHOTOVOLTAIC GENERATION ON POWER...

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