DISTRIBUTION IMPACT STUDY (DIS) GUIDELINE Guideline for Studying the Impact of Rooftop PV-Systems on Distribution Networks in the Philippines

Transcription

1 DISTRIBUTION IMPACT STUDY (DIS) GUIDELINE Guideline fr Studying the Impact f Rftp PV-Systems n Distributin Netwrks in the Philippines

2 Imprint Authrs Meller & Peller Engineering (M.P.E.) GmbH December 2013 (Versin 1) Publisher Deutsche Gesellschaft für Internatinale Zusammenarbeit (GIZ) GmbH On behalf f the German Federal Ministry f Ecnmic Affairs and Energy (BMWi) Cntact Deutsche Gesellschaft für Internatinale Zusammenarbeit (GIZ) GmbH Köthener Str. 2, Berlin, Germany Fax: +49 (0) pep-sutheastasia@giz.de Web: Web: This guideline is part f the Prject Develpment Prgramme (PDP) Suth-East Asia. PDP Suth-East Asia is implemented by the Deutsche Gesellschaft für Internatinale Zusammenarbeit (GIZ) GmbH n behalf f the German Federal Ministry f Ecnmic Affairs and Energy (BMWi) under the renewables Made in Germany initiative. Mre infrmatin abut PDP and abut renewable energy markets in Suth-East Asia can be fund n the website This publicatin, including all its infrmatin, is prtected by cpyright. GIZ cannt be liable fr any material r immaterial damages caused directly r indirectly by the use r disuse f parts. Any use that is nt expressly permitted under cpyright legislatin requires the prir cnsent f GIZ. All cntents were created with the utmst care and in gd faith. GIZ assumes n respnsibility fr the accuracy, timeliness, cmpleteness r quality f the infrmatin prvided.

3 Cntent 1 Backgrund Purpse f this Dcument Applicatin Prcess 1 2 PV-Inverters Technlgy Requirements f the Technical Intercnnectin Rules accrding t the Net-Metering Standard Technical Characteristics f PV-Inverters 5 3 Distributin Impact Studies (DIS) Technical Scpe Technical Scpe accrding t the Distributin Cde Impact n Thermal Cmpnent Ratings and Vltage Variatins n LV-feeders General Study Methdlgy Example Impact n Thermal Cmpnent Ratings and Vltage Variatins n LV-feeders Crdinatin f Prtectin System Harmnic Perfrmance Flicker 12 References 13 i

4 List f Figures Figure 1: Wrkflw f Applicatin Prcess (taken frm [4]) 2 Figure 2: DC-Surce with Inverter 3 Figure 3: Lad Prfile, PV-prfile (1kWp), Residual Lad Prfile 6 Figure 4: Lad Prfile, PV-prfile (4kWp), Residual Lad Prfile 7 Figure 5: Lad Prfile, PV-prfile (6kWp), Residual Lad Prfile 7 Figure 6: Example f a LV-feeder with PV generatin 8 Figure 7: Residual Feeder Lad fr different PV-injectin scenaris 8 Figure 8: Vltage at the end f the LV-feeder fr different PV-injectin scenaris 9 Figure 9: Example f a LV-feeder with PV generatin 11 Measurement W Watt Wp Watt peak Wh Watt hur kw Kilwatt kwp Kilwatt peak kwh Kilwatt hur MW Megawatt MWp Megawatt peak MWh Megawatt hur GW Gigawatt GWp Gigawatt peak GWh Gigawatt hur ii

5 List f Acrnyms DAS DIS DSOAR DU IGBT IGCT LV MV PV QE TDD THD VDE Distributin Assets Study Distributin Impact Study Distributin Service and Open Access Rules f the Philippines Distributin Utility Insulated-gate biplar transistr Integrated gate-cmmutated thyristr Lw Vltage Medium Vltage Phtvltaics Qualified End Unser Ttal Demand Distrtin, THD f current Ttal Harmnic Distrtin German Assciatin fr Electrical, Electrnic and Infrmatin Technlgies iii

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7 DISTRIBUTION IMPACT OF ROOFTOP-PV 1 Backgrund 1.1 Purpse f this Dcument On 27 May 2013, the Energy Regulatry Cmmissin adpted ERC Reslutin 09, Series f 2013 apprving the Rules Enabling the Net-Metering Prgram fr Renewable Energy. This reslutin was published n 10 July 2013 in newspapers f general circulatin in the cuntry and tk effect 15 days thereafter. Thus, the Net-Metering Rules tk effect in the Philippines n July 24, Net-metering allws custmers f Distributin Utilities (DUs) t install an n-site Renewable Energy (RE) facility nt exceeding 100 kilwatts (kw) in capacity s they can generate electricity fr their wn use. Any electricity generated that is nt cnsumed by the custmer is autmatically exprted t the DU s distributin system. The DU then gives a pes credit fr the excess electricity received equivalent t the DU s blended generatin cst, excluding ther generatin adjustments, and deducts the credits earned t the custmer s electric bill. As part f the technical evaluatin the DU has the ptin t perfrm a Distributin Impact Study (DIS) t assess the ability f the Distributin system t safely and reliably accmmdate a prpsed intercnnectin f a generatin surce and if any upgrades may be required. This dcument will: Define a guideline fr the typical scpe f DIS fr Renewable Generatrs that will be cnnected under a Net-Metering Agreement. Define criteria allwing a decisin whether DIS will be required r nt. The guidelines presented in this dcument are mainly based n internatinal practice fr the cnnectin f renewable generatin t LV netwrks and prpse simplified methds fr reducing time and effrt needed fr determining the impact f renewable generatrs n LV netwrks. 1.2 Applicatin Prcess The Applicatin Prcess fr Renewable Generatrs that shall be cnnected t LV-netwrks f the Philippines is defined in the Net-Metering-Rules [1] and further explained in [4]. It cvers the whle prcess, starting frm a written request fr receiving infrmatin and data required fr the submissin f an applicatin and ends with the signature f a cnnectin agreement (see Figure 1). This applicatin prcess further defines that the Distributin Utility (DU) shall decide whether the executin f a Distributin Impact Study (DIS) and/r a Distributin Assets Study (DAS) shall be required in accrdance with the Distributin Service and Open Access Rules f the Philippines (DSOAR) [2]. The DSOAR [2] further specify the purpse f DIS and DAS: A DIS shall identify whether any distributin cnstraints, re-dispatch ptins, additinal dedicated Cnnectin Assets, r Distributin System upgrades shall be required t prvide the requested service. Based n the results f a DIS, a DAS shall be executed with the purpse f identifying in detail additinally required distributin assets and crrespnding csts. Accrding t DSOAR [2], a DIS is always executed by the Distributin Utility (DU), whereas a DA can either be executed by the applicant itself r the DU. The Net-Metering rules [1] d nt explicitly mentin the pssibility that a DAS can be executed by a Net-Metering applicant. The csts f a DIS and a DAS always have t be cvered by the applicant. 1

8 The Philippine Distributin Cde [3] specifies the scpe f DIS as fllws: The Distributr shall cnduct Distributin Impact Studies t evaluate the impact f the prpsed cnnectin r mdificatin t an existing cnnectin n the Distributin System. The evaluatin shall include the fllwing: Impact f shrt-circuit infeed n the distributin equipment Crdinatin f Prtectin System Impact f User Develpment n Pwer Quality The Distributr may disapprve an applicatin fr cnnectin r a mdificatin t an existing cnnectin t the Distributin System if it is determined thrugh the Distributin System Impact Studies that the prpsed cnnectin r mdificatin will result in the degradatin f the Distributin System. Figure 1: Wrkflw f Applicatin Prcess (taken frm [4]) When cmparing the definitin f DIS in the DSOAR [2] and the Distributin Cde [3] a slight difference with regard t the purpse f DIS can be nticed:

9 DISTRIBUTION IMPACT OF ROOFTOP-PV Accrding t DSOAR, a DIS has t be carried ut fr identifying required netwrk upgrades, which in turn will avid any degradatin f the perfrmance f the distributin system, whereas Accrding t the Distributin Cde, the result f DIS will be used fr decide whether a cnnectin will be permitted r nt. Because the Net-Metering Rules [1] explicitly refer t DSOAR [2] in sectin 5.5 f [1], it can be assumed that the result f DIS will be used fr defining required distributin netwrk upgrades (thrugh DAS) and nt fr rejecting an applicatin withut having analyzed ptential netwrk upgrades. 2 PV-Inverters 2.1 Technlgy Figure 2: DC-Surce with Inverter Phtvltaic (PV) mdules prduce a DC-vltage and a DC-current that is cnverted int AC by an inverter. The cnnectin t the LV feeder is either single phase r three-phase, depending n the size f PV-inverter. Mdern PV inverters are f the vltage surce type using self-cmmutated technlgies built by IGBTs r IGCTs. Because f the high switching frequency f mdern inverters, which is in a range f up t 20 khz, the level f harmnic current injectins is usually very lw. Fr mst system studies, a PV inverter can be mdelled by a cntrlled current surce having a defined active and reactive current respnse. Because the utput f PV-inverters is fully cntrllable, relevant aspects such as reactive pwer cntrl capability r its respnse t vltage r frequency disturbances fllws the requirements f applicable cnnectin cnditins (r intercnnectin rules, grid cde, etc.). 2.2 Requirements f the Technical Intercnnectin Rules accrding t the Net-Metering Standard The relevant technical characteristics, as specified by relevant intercnnectin rules [1] can be summarized as fllws: Cntinuus peratin in a vltage range f +/-10% and a frequency range f 58,2Hz < f < 61,8Hz Pwer Factr: Accrding t [1] there is n pwer factr cntrl requirement. The nly requirement with regard t pwer factr is that it must be abve csphi=0,85 lagging during all times. Hence, fr distributin impact studies, it can be assumed that PV-inverters will perate at unity pwer factr. During Vltage Disturbance, a PV inverter must remain cnnected fr vltage dips dwn t a retained vltage f zer fr 150ms. Fr retained vltages between 30% f nminal vltage and 90% f nminal vltage a linear interplatin between 600ms and 3 s applies. There is n requirement with regard t the actual behavir f PV-inverters during a vltage dips specified 3

10 in [1]. Hwever, it is recmmended t require frm PV-inverters either: t set their current (active and reactive current) t a value equal t zer r at least nt t increase their current abve the pre-fault value. If PV-inverters behave during vltage dips accrding t such a requirement, their impact n shrt circuit levels and feeder-prtectin selectivity can be neglected. Because PV-inverters have very fast current cntrl capability, they are able t cmply with such requirements. Pwer Quality: DC-currents: Accrding t the Net-Metering Rules [1], DC-currents must nt exceed 0,5% f the full lad rated current f the inverter. Such requirement must be verified by type tests f PVinverters. It is nt further relevant t Distributin Impact Studies. Flicker Severity: With regard t Flicker, the Net-Metering Rules [1] refer t sectin f the Distributin Cde [3] and must nt exceed a shrt-term flicker severity limit f Pst=1 and Pst=0,8 at the cnnectin pint f any user in the system. This requirement relates t vltage flicker at the cnnectin pint f any User (generatin r lad) in a distributin netwrk and is hence a result f: Backgrund Flicker at the MV-statin feeding the LV-feeder f interest. All flicker surces (lads and generatrs) in the LV-feeder f interest. Harmnics: With regard t harmnic distrtin, the Net-Metering Rules [1] make reference t sectin f the Distributin Cde [3]. Accrding t this, there are tw harmnics requirements t cmply with: THD f vltage n greater than 5% at the cnnectin pint f any user in the system. TDD (Ttal Demand Distrtin, THD f current) f any User System shall be n greater than 5% during nrmal peratin. Because harmnic vltage is a result f: Backgrund harmnics at the MV-statin feeder the LV-feeder f interest. Harmnic current injectins f all Users (lad and generatin) in the LV-feeder f interest. Harmnic vltage distrtin must be studied cnsidering a cmplete feeder. The secnd criterin hwever (TDD f current n greater than 5% f rated full lad current) is a device-specific prperty and must be verified using type tests f PV-inverters. Vltage Unbalance: The Net-Metering Rules [1] dn t address vltage unbalance explicitly but because f the general reference t the Distributin Cde, it can be assumed that sectin f the Distributin Cde [3] als applies t Net-Metering Devices. This sectin states that vltage unbalance, which is defined by the maximum deviatin f the three phase vltages frm the average f the three phase vltages rated t the average f the three phase vltages shall nt exceed 2.5%. This requirement is imprtant fr the definitin up t which size single phase inverters will be permitted.

11 DISTRIBUTION IMPACT OF ROOFTOP-PV 2.3 Technical Characteristics f PV-Inverters Technical characteristics f PV inverters are very flexible and mainly fllw crrespnding specificatins. The main characteristics f PV-inverters are: Can perate at a defined pwer factr (by default: csphi=1) Lw harmnics cntents because f high switching frequencies Lw impact n flicker Lw DC-current injectins Input data fr PV-inverters can be btained fr type-tested r even certified inverters, e.g. inverters certified accrding t the German VDE-standard [4] r accrding t IEC61727 [6]. In sme cases, pwer quality characteristics f PV-inverters are tested accrding t IEC , which has been develped fr wind turbine generatrs but whse pwer quality test prcedures are als applicable t PV-inverters. Such type tests r measurements shuld cntain the fllwing type f infrmatin relating t PV-inverters: Table f wrst-case harmnic current injectins (per frequency) Flicker step-change factr kf (in functin f active pwer utput and netwrk impedance angle) Flicker vltage-factr ku (in functin f active pwer utput and netwrk impedance angle) Cntinuus flicker cefficient c (in functin f active pwer utput and netwrk impedance angle) Level f DC-current injectins These data can directly be used fr carrying ut crrespnding Distributin Impact Studies (DIS). 3 Distributin Impact Studies (DIS) Technical Scpe 3.1 Technical Scpe accrding t the Distributin Cde The Distributin Cde [3] defines the fllwing technical scpe f Distributin Impact Studies (DIS): Impact f shrt-circuit infeed n the distributin equipment Crdinatin f Prtectin System Impact f User Develpment n Pwer Quality Hwever, fr identifying required feeder reinfrcements, this list f technical studies shuld be extended as fllws: Studies relating t thermal cmpnent ratings Studies relating t vltage variatins (especially Lng Duratin Vltage Variatins accrding t the definitins f the Distributin Cde). These lad flw studies f the relevant area f a distributin grid will identify the need fr netwrk reinfrcements such as reinfrced lines r cables, additinal lines/cables r a replacement f a distributin transfrmer and shuld be carried ut prir t pwer quality studies fr ensuring that the impact f cmpnent upgrades will be cvered by all subsequent impact studies. 5

12 3.2 Impact n Thermal Cmpnent Ratings and Vltage Variatins n LV-feeders General Study Methdlgy Studies relating t thermal cmpnent ratings and vltage variatins are mainly relevant if there are times during which a PV system prduces cnsiderably mre pwer than the crrespnding lad absrbs. As lng as PVprductin is belw the maximum demand f the crrespnding lad, the PV prductin will nly reduce line/cable ladings and vltage drps but nt increase it. Only in cases, in which the prductin f a PV-system starts exceeding the assciated lad, a vltage rise r increased thermal lading f lines r cables can be bserved. Accrding t the Distributin Cde [3] vltage in distributin grids (MV and LV) may vary between +/-10% f the rated vltage. With regard t vltage variatin studies in a LV-feeder with distributed generatin this means that distributin system impact studies must cnsider the fllwing tw wrst case scenaris: Case 1: Min. vltage at MV-bus bar, max. lad and n generatin. Case 2: Max. vltage at MV-bus bar, min. lad (during day-time) and max. generatin. With regard t Case 2 (min. lad) it has t be cnsidered that min. lad ften ccurs during night-time, when there is n PV generatin. Hence, it is imprtant t cnsider a min. lad during day time cnditin. In case f residential lads, this min. lad during day-time usually ccurs n wrking-days, when peple are ut fr wrk. In case f cmmercial lads, this situatin typically ccurs n week-ends. With regard t max./min. vltages at the feeding MV-bar, the typical vltage limits f peratin shuld be applied (e.g. +/- 5%). These limits are usually chsen in a way that there is sufficient rm fr additinal vltage drps (r vltage rises) n the LV-feeder. Fr studying the impact f PV installatins n thermal cmpnent ratings and vltage variatins, the fllwing steps shuld be executed: Define the relevant wrst case peratin scenaris Execute a lad flw study fr the tw wrst case peratin scenaris Evaluate maximum thermal lading and max. vltage rise n the feeder. Decide whether grid reinfrcements r a direct transfrmer cnnectin will be required Example Figure 3: Lad Prfile, PV-prfile (1kWp), Residual Lad Prfile

13 DISTRIBUTION IMPACT OF ROOFTOP-PV Figure 4: Lad Prfile, PV-prfile (4kWp), Residual Lad Prfile Figure 5: Lad Prfile, PV-prfile (6kWp), Residual Lad Prfile Fr illustrating the relatinship between lad and PV generatin, Figure 3, Figure 4 and Figure 5 shw lad prfile, generatin prfile and residual lad prfile f a residential lad and a PV installatin with 1kWp, 4kWp and 6kWp respectively. These figures shw that: During mst times, residual lad is cnsiderably reduced cmpared t the actual lad The peak f residual lad remains almst unchanged cmpared t peak lad The wrst case exprt situatin ccurs during mid-day, when PV generatin is high and the lad has a lcal minimum. Fr illustrating the impact f PV-generatin n feeder lad and vltage prfile, the example f a simplified LVfeeder accrding Figure 6 is used. The lad prfiles f this example crrespnd t the lad prfile depicted in Figure 3, Figure 4 and Figure 5. The peak lad f the feeder is equal t Smax=kVA at a pwer factr f csphi=0,95. The fllwing fur scenaris with regard t PV-injectin are studied: Case 1: N PV generatin Case 2: Lw PV generatin, PVmax=11kWp 7

14 Case 3: High PV generatin, PVmax=44kWp Case 4: Very high PV generatin, PVmax=88kWp The results accrding t Figure 7 (residual feeder lad) and Figure 8 (vltage prfile) shw the fllwing: The wrst case exprt scenari ccurs during mid-day, cnfirming the wrst case assumptin stated in sectin Only if PV generatin exceeds the feeder lad, leading t a reverse pwer flw n the feeder, there will be a vltage rise acrss the feeder. In this case, maximum vltage rise ccurs during maximum PV generatin and minimum day-time lad. Maximum vltage drp acrss the feeder is almst nt influenced by PV generatin (assuming that peak lad ccurs in the evening). This example cnfirms the general methdlgy described in sectin Figure 6: Example f a LV-feeder with PV generatin Figure 7: Residual Feeder Lad fr different PV-injectin scenaris

15 DISTRIBUTION IMPACT OF ROOFTOP-PV Figure 8: Vltage at the end f the LV-feeder fr different PV-injectin scenaris 3.3 Impact n Thermal Cmpnent Ratings and Vltage Variatins n LV-feeders Accrding t the published versin f the Net-Metering rules [1], PV inverters must remain cnnected fr at least 150ms in the case f a slid fault n an LV-feeder. With regard t the respnse f a PV-inverter t such a vltage dip, n detailed specificatin is given in [1]. It is therefre recmmended t require frm PV-inverters ne f the fllwing types f behavir during grid faults: Zer current mde : Reductin f current (active and reactive current) t zer if vltage drps belw the cntinuus limit f peratin (90%). Pre-fault current : If vltage drps belw the cntinuus limit f peratin (belw 90%), it is nt permitted that the current exceeds its pre-fault value. In bth cases, there will be n cnsiderable shrt circuit infeed f PV-inverters and hence n cnsiderable impact n Distributin Equipment and nt shrt circuit studies will be required as part f DIS fr PV-cnnectins t LVfeeders. Hwever, in the case that n such requirement will be put in place, it has t be assumed that PV-inverters will deliver up t their maximum current capability during a vltage dip. This maximum (shrt-term) current capability must be btained frm the data sheet f each cnverter type. In the absence f any reliable infrmatin relating t this aspect it can be assumed that the maximum shrt-term current f a PV-inverter des nt exceed a value f I max=1,3 I rated It must further be cnsidered that this shrt circuit feed-back is a result f a current limit f a cntrller and hence nt a functin f any impedance between PV-inverter and fault lcatin. 9

16 Unfrtunately, n internatinally accepted standard fr shrt circuit calculatin (IEC60909 r ANSI C37) is able t cnsider this type f current surce behavir. Therefre, the fllwing prcedure is recmmend; Step 1: Calculate the shrt circuit current accrding t IEC60909 r ANSI C37 ignring shrt circuit infeed frm PV-inverters (cnsidering grid-infeed nly) Step 2: Add the sum f the maximum pssible shrt circuit infeed f all PV-inverters in the analyzed LVfeeder t the grid-infeed fr btaining the resulting shrt-circuit current at each nde in the LV-feeder. Verify the shrt circuit rating f all cmpnents. In ther wrds, the maximum expected increase f shrt circuit current in a LV feeder can be estimated by the ttal maximum shrt-term current f all PV-inverters in the feeder. 3.4 Crdinatin f Prtectin System In the case that a generatr perates either in Zer Pwer r Pre-fault Current Mde, the impact f a PVinverter n prtectin selectivity can be neglected because there is n cnsiderable shrt-circuit cntributin f a PV-inverter. In the case that n such additinal requirement exists, the impact f back-feed frm all PV inverters cnnected t a LV-feeder has t be evaluated and settings f prtectin relays, LV-circuit breakers and trip levels f fuses have t be re-assessed. Because f the cmplexity f this task it is generally recmmended t require Zer Pwer Mdel behavir during grid faults. 3.5 Harmnic Perfrmance Accrding t the Net-Metering Rules [1] there are tw requirements with regard t harmnics: Harmnic Current distrtin must nt exceed a TDD f 5% (THD f current) Harmnic Vltage distrtin must nt exceed a THD f 5% at the cnnectin pint f any User. The assessment f the current distrtin criterin desn t require any system impact study because this is a devicespecific value. The assessment f harmnic vltage distrtin hwever requires studies, if it shall be evaluated prir t a cnnectin (and nt nly based n measurements, after cmmissining f the PV system). It is therefre recmmended t carry ut harmnic vltage distrtin studies in rder t assess whether the allcated harmnic currents will result in a limitatin f PV installatins r nt. The methdlgy f such a study culd be based n the fllwing steps: Define harmnic planning levels at the feeding MV nde (harmnic backgrund level L MV(h)) Define the maximum glbal harmnic vltage cntributin f lads in the LV feeder (G lad(h)) Define a reasnable maximum PV allcatin scenari in the LV feeder (ttal installed PV-capacity per LVnde) Calculate fr each nde the relevant upstream impedance (netwrk impedance at each nde Z up(h)) and the ttal harmnic current injectin (I PV(h)) resulting frm all dwnstream PV installatins by applying summatin law 2 accrding t IEC Calculate the glbal harmnic vltage cntributin f all dwnstream PV inverters fr each nde.

17 DISTRIBUTION IMPACT OF ROOFTOP-PV Calculate harmnic vltage distrtins and THD at the first nde in the LV feeder (nde 1 in Figure 9) using the fllwing parameters: Harmnic planning level f upstream grid L MV(h) Maximum glbal harmnic vltage cntributin f LV-lads: G lad(h) Calculate glbal harmnic vltage cntributin f all dwnstream PV inverters: G PV(h) Calculate harmnic vltage U 1(h) Calculate THD at nde 1 Calculate harmnic vltage distrtin and THD at all ther ndes in the feeder recursively With regard t harmnic planning levels and glbal harmnic vltage cntributin f LV-lads, Table 1 f IEC culd be referred and scaled apprpriately. Figure 9: Example f a LV-feeder with PV generatin The frmulas required fr calculating the abve listed parameters fr each nde are the fllwing: Calculatin f ttal harmnic current injectin resulting frm all dwnstream PV installatins: I n dwn ( h) I ( h) 1 i i1 Calculatin f glbal harmnic vltage cntributin f dwnstream PV inverters: G h) Z ( h) I ( ) PV 1( 1 dwn1 h Calculatin f harmnic vltage: U 1( h) L ( h) Glad2 ( h) GPV 1( h ) Calculatin f THD at nde 1: THD n U ( h) 1 h 2 1 U n 11

18 Recursive calculatin f harmnic vltage distrtins at ther ndes in the feeder: G h) G ( h) Z ( h I PV 2 ( PV 1 12 ) dwn2 with: I n dwn ( h) I ( h) 2 i i2 and U 2( h) L ( h) Glad2 ( h) GPV 2( h ) The summatins are based n a superpsitin f harmnic vltages accrding t summatin law II/IEC [8]. The cefficient is defined as fllws: h<5 =1 5<=h<=10 =1,4 h>10 =2 Fr harmnic current injectins f PV-inverters, harmnic currents accrding t IEC61727, which are in-line with a TDD f 5% can be assumed. The lad cntributins G ladi can be allcated r calculated analgusly t the PV-cntributins n basis f harmnic lad-current injectins. Much easier than an applicatin f the abve frmulas (e.g. using EXCEL spreadsheets) wuld be the use f a pwer system analysis sftware that supprts harmnic analysis accrding t IEC , summatin law 2, directly. 3.6 Flicker As stated in sectin 3.2, the impact f PV-inverters n flicker is generally lw because a PV-inverter des nt represent a cnsiderable flicker surce, as lng as the cntrller f the PV-inverter is prperly tuned. Therefre, it shuld be sufficient t carry ut type tests f PV-inverters r nly use inverters that are certified accrding t IEC61727 [6] System-wide studies fr calculating flicker levels at all ndes will then nt be required.

19 DISTRIBUTION IMPACT OF ROOFTOP-PV References [1] Republic f the Philippines Energy Regulatry Cmmissin: A Reslutin Adpting the Rules Enabling the Net-Metering Prgram fr Renewable Energy, Reslutin N. 09, Series f 2013 [2] Republic f the Philippines Energy Regulatry Cmmissin: Distributin Services and Open Access Rules (DSOAR), ERC Case N RM, [3] Republic f the Philippines Energy Regulatry Cmmissin: Philippine Distributin Cde, December 2001 [4] Deutsche Gesellschaft für Internatinale Zusammenarbeit (GIZ) GmbH n behalf f the German Federal Ministry f Ecnmic Affairs and Energy: Manual fr Intercnnectin Reprt fr supprting the intercnnectin f Rftp-PV-Systems in the Philippines, [5] VDE-AR-N 4105 : : Pwer generatin systems cnnected t the lw vltage distributin netwrk Technical minimum requirements fr the cnnectin t and parallel peratin with lw vltage distributin netwrks, VDE, 2011 [6] IEC61727: Phtvltaic (PV)-systems - Characteristics f the utility interface, Secnd Editin, 2004 [7] IEC : Wind turbines Part 21: Measurement and assessment f pwer quality characteristics f grid cnnected wind turbines, Editin 2.0, [8] IEC : Electrmagnetic cmpatibility (EMC) Part 3-6: Limits Assessment f emissin limits fr the cnnectin f distrting installatins t MV, HV and EHV pwer systems Further infrmatin: Deutsche Gesellschaft für Internatinale Zusammenarbeit (GIZ) GmbH n behalf f the German Federal Ministry f Ecnmic Affairs and Energy: Net-Metering Reference Guide, 13

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