BS EN 50530:2010+A1:2013 BSI Standards Publication Overall efficiency of grid connected photovoltaic inverters BRITISH STANDARD BS EN 50530:2010+A1:2013 National foreword This British Standard is the UK implementation of EN 50530:2010+A1:2013 It supersedes BS EN 50530:2010, which is withdrawn The start and finish of text introduced or altered by amendment is indicated in the text by tags Tags indicating changes to CENELEC text carry the number of the CENELEC amendment For example, text altered by CENELEC amendment A1 is indicated by !" The UK participation in its preparation was entrusted to Technical Committee GEL/82, Photovoltaic Energy Systems A list of organizations represented on this committee can be obtained on request to its secretary This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application © The British Standards Institution 2013 Published by BSI Standards Limited 2013 ISBN 978 580 80513 ICS 27.160 Compliance with a British Standard cannot confer immunity from legal obligations This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 May 2010 Amendments/corrigenda issued since publication Date Text affected 30 June 2013 Implementation of CENELEC amendment A1:2013 EN 50530:2010+A1 EUROPEAN STANDARD NORME EUROPÉENNE March 2013 EUROPÄISCHE NORM ICS 27.160 English version Overall efficiency of grid connected photovoltaic inverters Efficacité globale des onduleurs photovoltaïques raccordés au réseau Gesamtwirkungsgrad von PhotovoltaikWechselrichtern This European Standard was approved by CENELEC on 2010-04-01 CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung Management Centre: Avenue Marnix 17, B - 1000 Brussels © 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members Ref No EN 50530:2010 E BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) –2– Foreword This European Standard was prepared by the Technical Committee CENELEC TC 82, Solar photovoltaic energy systems It was submitted to the Unique Acceptance Procedure and approved by CENELEC on 2010-04-01 Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CEN and CENELEC shall not be held responsible for identifying any or all such patent rights The following dates were fixed: – – latest date by which the EN has to be implemented at national level by publication of an identical national standard or by endorsement latest date by which the national standards conflicting with the EN have to be withdrawn (dop) 2011-04-01 (dow) 2013-04-01 Foreword to amendment A1 This document (EN 50530:2010/A1:2013) has been prepared by CLC/TC 82 "Solar photovoltaic energy systems" The following dates are fixed: • latest date by which this document has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 2013-12-24 • latest date by which the national standards conflicting with this document have to be withdrawn (dow) 2015-12-24 Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights –3– BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) Contents Scope .5 Normative references .5 Terms and definitions 3.1 Inverter input (PV generator) 3.2 Inverter output (grid) .6 3.3 Measured quantities .6 3.4 Calculated quantities 3.5 Other definitions .8 MPPT efficiency 4.1 General description 4.2 Test set-up 4.3 !Conversion and static MPPT efficiency" .9 4.4 Dynamic MPPT efficiency 11 Calculation of the overall efficiency 13 Annex A (normative) Requirements on the measuring apparatus 14 A.1 PV generator simulator 14 A.2 AC power supply 15 Annex B (normative) Test conditions for dynamic MPPT efficiency .16 B.1 Test profiles 16 B.2 !Test sequence with ramps 10 % - 50 % GSTC" 17 B.3 !Test sequence with ramps 30 % - 100 % GSTC" 18 B.4 Start-up and shut-down test with slow ramps .18 B.5 Total test duration 19 Annex C (normative) Models of current/voltage characteristic of PV generator 20 C.1 !PV generator model for MPPT performance tests" 20 C.2 Alternative PV generator model for MPPT performance tests 25 Annex D (informative) Inverter efficiency 27 D.1 General / Introduction 27 D.2 Conversion efficiency 27 Bibliography 35 BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) –4– Figures Figure – Exemplary test set-up for MPPT efficiency measurements Figure B.1 – !Test sequence for fluctuations between small and medium irradiance" 16 Figure B.2 – !Test sequence for fluctuations between medium and high irradiance" 16 Figure B.3 – Test sequence for the start-up and shut-down test of grid connected inverters 19 Figure C.1 – Irradiation-dependent U-I- and U-P characteristic of a c-Si PV generator 23 Figure C.2 – Irradiation-dependent U-I- and U-P characteristic of a thin-film PV generator 24 Tables Table – !Test specifications for the on version and static MPPT efficiency " 10 Table A.1 – General requirements on the simulated I/V characteristic of the PV generator 14 )" 17 Table B.1 – ! Dynamic MPPT-Test 10 % ⇒ 50 % GSTC (valid for the evaluation of ηMPPTdyn Table B.2 – !Dynamic MPPT-Test 30 % ⇒ 100 % GSTC (valid for the evaluation of η MPPTdyn)" 18 Table B.3 18 Table C.1 – Technology-dependent parameters 20 Table C.2 – Technology-dependent parameters 22 Table C.3 – MPP-values obtained with the cSi PV model 22 Table C.4 – MPP-values obtained with the TF-PV mode 25 –5– BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) Scope This European Standard provides a procedure for the measurement of the efficiency of the maximum power point tracking (MPPT) of inverters, which are used in grid-connected photovoltaic systems In that case the inverter energizes a low voltage grid with rated AC voltage and rated frequency Both the static and dynamic MPPT efficiency is considered Based on the static MPPT efficiency and conversion efficiency the overall inverter efficiency is calculated The dynamic MPPT efficiency is indicated separately Normative references The following referenced documents are indispensable for the application of this document For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies !Text deleted" EN 50160, Voltage characteristics of electricity supplied by public distribution networks EN 50524, Data sheet and name plate for photovoltaic inverters CLC/TS 61836, Solar photovoltaic energy systems - Terms, definitions and symbols (IEC/TS 61836:2007) Terms and definitions For the purposes of this document, the following terms and definitions apply 3.1 Inverter input (PV generator) 3.1.1 maximum input voltage (UDCmax) allowed maximum voltage at the inverter input NOTE Exceeding of UDCmax may destroy the equipment under test 3.1.2 minimum input voltage (UDCmin) minimum input voltage for the inverter to energize the utility grid, independent of mode of operation 3.1.3 rated input voltage (UDC,r) input voltage specified by the manufacturer, to which other data sheet information refers NOTE If this value is not specified by the manufacturer, Vdc,r = (Vmppmax + Vmppmin)/2 shall be used 3.1.4 maximum MPP voltage (UMPPmax) maximum voltage at which the inverter can convert its rated power under MPPT conditions NOTE If the specified value of the manufacturer for UMPPmax is higher than 0,8 × UDCmax, the measurement must be performed with UMPPmax = 0,8 × UDCmax BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) –6– 3.1.5 minimum MPP voltage (UMPPmin) minimum voltage at which the inverter can convert its rated power under MPPT conditions NOTE The actual minimum MPP voltage may depend on the grid voltage level 3.1.6 rated input power (PDC,r) rated input power of the inverter, which can be converted under continuous operating conditions ! NOTE If this value is not specified by the manufacturer, it can be defined as P DC,r = PAC,r / η conv,r, in which η conv,r is the conversion efficiency at rated DC voltage If the rated conversion efficiency is not specified, it shall be measured." 3.1.7 maximum input current (IDC,max) maximum input current of the inverter under continuous operating conditions NOTE At inverters with several independent inputs, this value may depend on the chosen input configuration 3.2 Inverter output (grid) 3.2.1 rated grid voltage (UAC,r) utility grid voltage to which other data sheet information refers 3.2.2 rated power (PAC,r) active power the inverter can deliver in continuous operation 3.3 Measured quantities 3.3.1 PV simulator MPP-Power (PMPP, PVS) MPP power provided by the PV simulator 3.3.2 input power (PDC) measured input power of the device under test 3.3.3 PV simulator MPP voltage (UMPP, PVS) MPP voltage provided by the PV simulator 3.3.4 input voltage (UDC) measured input voltage of the device under test 3.3.5 PV simulator MPP current (IMPP, PVS) MPP current provided by the PV simulator 3.3.6 input current (IDC) measured input current of the device under test 3.3.7 output power (PAC) measured AC output power of the device under test –7– BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) 3.3.8 output voltage (UAC) measured AC voltage 3.3.9 output current (IAC) measured AC output current of the device under test 3.4 Calculated quantities 3.4.1 MPPT efficiency, energetic (ηMPPT) ratio of the energy drawn by the device under test within a defined measuring period TM to the energy provided theoretically by the PV simulator in the maximum power point (MPP): TM ∫p DC (t ) ⋅ dt ηMPPT = TM (1) ∫p MPP (t ) ⋅ dt where pDC(t) instantaneous value of the power drawn by the device under test; pMPP(t) instantaneous value of the MPP power provided theoretically by the PV simulator 3.4.2 conversion efficiency, energetic (ηconv) ratio of the energy delivered by the device under test at the AC terminal within a defined measuring period TM to the energy accepted by the device under test at the DC terminal: TM ηconv = ∫p AC TM (t ) ⋅ dt (2) ∫p DC (t ) ⋅ dt where pAC(t) instantaneous value of the delivered power at the AC terminal of the device under test; pDC(t) instantaneous value of the accepted power at the DC terminal of the device under test 3.4.3 overall (total) efficiency, energetic (ηt) ratio of the energy delivered by the device under test at the AC terminals within a defined measuring period TM to the energy provided theoretically by the PV simulator: TM ∫p AC (t ) ⋅ dt ηt = TM ∫p MPP respectively η t = ηconv ⋅ ηMPPT (t ) ⋅ dt (3) BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) –8– 3.5 Other definitions 3.5.1 photovoltaic array simulator current source emulating the static and dynamic behaviour of a PV array, in particular the current-voltage characteristic (cf IEC/TS 61836) The requirements are outlined in Clause A.1 MPPT and conversion efficiencies 4.1 General description ! The MPPT efficiency describes the accuracy of an inverter to set its operating conditions to match the maximum power point on the characteristic curve of a PV generator The MPPT efficiency is divided into the static and dynamic conditions As with inverters with poor MPPT performance, the resulting DC input voltage is different from MPP voltage and conversion efficiency depends on DC input voltage, measurements of static MPPT efficiency and static power conversion efficiency according to 4.3 shall be performed simultaneously (detailed explanation in the informative Annex F) " Both the static as well as the dynamic MPPT efficiencies are determined from the sampled instantaneous values of voltage and current at the input of the inverter It indicates which amount of the theoretically usable PV generator power is actually used by the inverter a) Static MPPT efficiency The static MPPT efficiency is determined by means of measurement as follows: ηMPPTstat = PMPP , PVS ⋅ TM ∑U DC ,i ⋅ I DC ,i ⋅ ∆T (4) i where UDC,i sampled value of the inverter’s input voltage; IDC,i sampled value of the inverter’s input current; TM overall measuring period; ∆T period between two subsequent sample values The static MPPT efficiency describes the accuracy of an inverter to regulate on the maximum power point on a given static characteristic curve of a PV generator NOTE UDC,i and IDC,i must be sampled at the same time b) Dynamic MPPT efficiency Variations of the irradiation intensity and the resulting transition of the inverter to the new operation point are not considered with the static MPPT efficiency For the evaluation of this transient characteristic the dynamic MPPT efficiency is specified The dynamic MPPT efficiency is defined as: ηMPPTdyn = ∑P MPP , PVS , j j ⋅ ∆T j ∑U i DC ,i ⋅ I DC ,i ⋅ ∆Ti (5) BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) – 24 – Figure C.2 – Irradiation-dependent U-I- and U-P characteristic of a thin-film PV generator – 25 – BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) Table C.4 – MPP-values obtained with the TF-PV mode ! C.2 G W/m UMPP V PMPP W 50 88,8 44,4 100 93,9 93,9 200 98,2 196,6 300 100,2 300,7 500 101,5 507,9 750 101,3 759,8 000 100 000,3 Alternative PV generator model for MPPT performance tests” Other models of the PV generator characteristics like the 1-diode model or the 2-diode can be used as well The characteristics should preferably fulfil the technology dependent parameters according to Table C.1 If the model cannot fulfil the requirements of Table C.1 the achieved Technology dependent parameters have to be stated and the used model should be stated together with its parameters Example: cSi-PV generator with 1-diode model I PV + I PV RS U PVmU U + I PV RS T = I ph − I e − − PV RP where I ph =I ph ,STC ⋅ G and G STC I = C0 Tmod e UT = − Eg kT and kTmod e0 IPV module current in A; I0 diode saturation current in A; Iph photo current (source current) in A; UPV module voltage in V; UT temperature voltage in V; Eg bandgap in eV; RS serial resistance in Ω; " (C.15) BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) ! RP – 26 – parallel resistance in Ω; T ambient temperature in K; Tmod module temperature in K; G irradiance in W/m ; c constant for the linear temperature model in K; C0 coefficient of diode saturation current in A/K ; m diode factor; e0 elementary charge in C; k Boltzmann constant in J/K For the application of the 1-diode model for the crystalline technology, the following parameters can be applied: – C0 = 101,668 A/K ; – m = 1,113; – Rs = 47,731 mΩ; – Rp = 11,173 Ω; – the photo current at GSTC amounts to Iph = A; – the band gap amounts to 1,1 eV With these parameters, a standard PV cell is obtained that fulfils the requirements of Table C.1 By parallel or serial interconnections of the standard cell, PV generators of arbitrary size can be configured " BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) – 27 – Annex D (normative) Efficiency weighting factors D.1 European efficiency For the calculation of a weighted European MPPT and conversion efficiency the following formula and factors are to be applied: ηMPPTstat , EUR = a EU_1 ⋅ηMPP _1 + a EU_2 ⋅ηMPP _ + a EU_3 ⋅ηMPP _3 + a EU_4 ⋅ηMPP _ (D.1) +a EU_5 ⋅ηMPP _ + a EU_6 ⋅ηMPP _ aEU_i weighting factor ηMPP_i static MPPT efficiency at partial MPP power MPP_i Table D.1 – Weighting factors and partial MPP power levels for the calculation of the European efficiency Weighting Factor aEU_1 aEU_2 aEU_3 aEU_4 aEU_5 aEU_6 0.03 0.06 0.13 0.1 0.48 0.2 Partial MPP power PMPP,PVS/PDC, r MPP_1 MPP_2 MPP_3 MPP_4 MPP_5 MPP_6 0.05 0.1 0.2 0.3 0.5 D.2 CEC efficiency For the calculation of a weighted CEC MPPT and conversion efficiency the following formula and factors are to be applied: ηMPPTstat ,CEC = a CEC_1 ⋅ηMPP _1 + a CEC_2 ⋅ηMPP _ + a CEC_3 ⋅ηMPP _3 + a CEC_4 ⋅ηMPP _ (D.2) +a CEC_5 ⋅ηMPP _ + a CEC_6 ⋅ηMPP _ aCEC_i weighting factor ηMPP_i static MPPT efficiency at partial MPP power MPP_i Table D.2 – Weighting factors and partial MPP power levels for the calculation of the CEC efficiency (California Energy Commission) Weighting Factor aCEC_1 aCEC_2 aCEC_3 aCEC_4 aCEC_5 aCEC_6 0.04 0.05 0.12 0.21 0.53 0.05 Partial MPP power PMPP,PVS/PDC, r MPP_1 MPP_2 MPP_3 MPP_4 MPP_5 MPP_6 0.1 0.2 0.3 0.5 0.75 BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) – 28 – Annex E (normative) Specification of the static MPPT and conversion efficiency in terms of normalised rated AC power NOTE The procedure in this Annex is exemplified for the case of conversion efficiency measurements It can be applied to MPPT efficiency measurements in the same way As a result from the static MPPT and conversion efficiency measurement the following data are available - Output power of the inverter PAC - Input power of the inverter PDC - by PAC and PDC calculated efficiency η A normalisation of PDC and PAC to the rated dc power PDC,r leads to the values in Table E.1 The values in brackets are for exemplary clarification only Table E.1 – Measured quantities at the conversion efficiency test PDC/PDC,r pDC_1 = PAC/PDC,r pAC_1 =(0.9740) Efficiency η η1 = (0.9740) pDC_0.75 = 0.75 pAC_0.75 = (0.7370) η0.75 = (0.9827) pDC_0.5 = 0.5 pAC_0.5 = (0.4940) η0.5 = (0.9880) pDC_0.3 = 0.3 pAC_0.3 = (0.2960) η0.5 = (0.9867) pDC_0.25 = 0.25 pAC_0.25 = (0.2460) η0.25 = (0.9840) pDC_0.2 = 0.2 pAC_0.2 = (0.1950) η0.2 = (0.9750) pDC_0.1 = 0.1 pAC_0.1 = (0.0930) η0.1 = (0.9300) pDC_0.05 = 0.05 pAC_0.05 = (0.0420) η0.05 = (0.8400) Based on these results an approximation for the specification of the efficiency in term of normalised rated AC power is given in the following steps Re-normalisation of output power PAC to the rated output power PAC,r It is assumed that the output power of the inverter is equal to its rated output power PAC,r, when the inverter is operated at the rated input power PDC,r on the DC side In this case the quotient of PAC,r and PDC,r is the rated efficiency ηr, which is used to calculate the normalised output power pAC p′AC = P PAC P P 1 = AC ⋅ DC , r = AC ⋅ = p AC ⋅ PAC , r PDC ,r PAC ,r PDC , r ηr ηr (E.1) BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) – 29 – Representation of the conversion efficiency in terms of normalised rated output power According to (E.1) the efficiency can be represented in terms of normalised rated output power However, the power values p′AC differ from the nodes as defined in section 4.5.1 as shown in Table E.2 Table E.2 – Conversion efficiency in term of rated AC power p′AC = PAC/PAC,r η p′AC_1 = 1,000000 η1 = 0,9740 p′AC_0.75 = (0,756674) η0.75 =0,9827 p′AC_0.5 = (0,507187) η0.5 =0,9880 p′AC_0.3 = (0,303901) η0.3 =0,9867 p′AC_0.25 = (0,252567) η0.25 =0,9840 p′AC_0.2 = (0,200205) η0.2 =0,9750 p′AC_0.1 = (0,095483) η0.1 =0,9300 p′AC_0.05 = (0,043121) η0.05 =0,8400 If the values of p′AC as calculated by this procedure are within a range of ±5% of the normative nodes in section 4.5.1 a sufficient accuracy is assumed and a further interpolation is not required The limits are outlined in Table E.3 Table E.3 – Allowed limits for the nodes of the normalised AC power Minimum value of normalised AC power p′AC Normative value of normalised AC power p′AC Maximum value of normalised AC power p′AC 0.95 1.05 0.7125 0.75 0.7875 0.475 0.5 0.525 0.285 0.3 0.315 0.2375 0.25 0.2625 0.19 0.2 0.21 0.095 0.1 0.105 0.0475 0.05 0.0525 Interpolation on normative nodes If the calculated values of p′AC are not within the limits of Table E.3, an interpolation on the normative values need to be performed The interpolation is done by means of the average slope in the measured efficiency values The new efficiency values are then calculated by means of a linear equation Thus, the efficiency values η′′i exactly at the normative nodes p″AC are seeked for as shown in Table E.4 Table E.4 – Seeked values by means of interpolation AC power node Efficiency p′′AC _1 = η1′′ p′′AC _ 0.75 = 0.75 η′′0.75 BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) Calculation of – 30 – p′′AC _ 0.5 = 0.5 η′′0.5 p′′AC _ 0.3 = 0.3 η′′0.3 p′′AC _ 0.25 = 0.25 η′′0.25 p′′AC _ 0.2 = 0.2 η′′0.2 p′′AC _ 0.1 = 0.1 η′′0.1 p′′AC _ 0.05 = 0.05 η′′0.05 η1′′ : It is assumed that at rated DC power on the input side the inverter delivers rated AC power at the output Therefore η1′′ is always η1′′ = η1 Calculation of η′′0.75 : The average slope in the point m0.75 = ( p AC _ 0.75 , η0.75 ) is ∆η ∆p AC η1 − η0.75 η0.75 − η0.5 = 0.5 ⋅ + p AC _1 − p AC _ 0.75 p AC _ 0.75 − p AC _ 0.5 0.974 − 0.9827 0.9827 − 0.9880 = 0.5 ⋅ + − 0.7567 0.7567 − 0.5072 = −0.0285 The linear equation with slope m0.75 through the point ( p AC _ 0.75 , η0.75 ) is η′′ = η0.75 + m0.75 ⋅ ( p′′AC + p AC _ 0.75 ) , where η′′ is the new efficiency at the power node p″AC If p′′AC is set to p′′AC = p′′AC _ 0.75 = 0.75 , the new interpolated efficiency value is found: η′′0.75 = η0.75 + m0.75 ⋅ ( 0.75 − p AC _ 0.75 ) = 0.9827 − 0.0285 ⋅ ( 0.75 − 0.7567 ) = 0.9829 Calculation of η′′0.5 : According to the explanations above the interpolated efficiency value η′′0.75 is found by BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) – 31 – η0.75 − η0.5 η0.5 − η0.3 η′′0.5 = η0.5 + m0.5 ⋅ ( 0.5 − p AC _ 0.5 ) with m0.5 = 0.5 ⋅ + p AC _ 0.75 − p AC _ 0.5 p AC _ 0.5 − p AC _ 0.3 Calculation of η′′0.3 : η0.5 − η0.3 η0.3 − η0.25 η′′0.3 = η0.3 + m0.3 ⋅ ( 0.3 − p AC _ 0.3 ) with m0.3 = 0.5 ⋅ + p AC _ 0.5 − p AC _ 0.3 p AC _ 0.3 − p AC _ 0.25 Calculation of η′′0.25 : η0.3 − η0.25 η0.25 − η0.2 η′′0.25 = η0.25 + m0.25 ⋅ ( 0.25 − p AC _ 0.25 ) with m0.25 = 0.5 ⋅ + p AC _ 0.3 − p AC _ 0.25 p AC _ 0.25 − p AC _ 0.2 Calculation of η′′0.2 : η0.25 − η0.2 η′′0.2 = η0.2 + m0.2 ⋅ ( 0.2 − p AC _ 0.2 ) with m0.2 = 0.5 ⋅ p AC _ 0.25 − p AC _ 0.2 Calculation of η0.2 − η0.1 + p AC _ 0.2 − p AC _ 0.1 η′′0.1 : η0.2 − η0.1 η0.1 − η0.05 η′′0.1 = η0.1 + m0.1 ⋅ ( 0.1 − p AC _ 0.1 ) with m0.1 = 0.5 ⋅ + p AC _ 0.2 − p AC _ 0.1 p AC _ 0.1 − p AC _ 0.05 Calculation of η′′0.05 : η0.1 − η0.05 η′′0.05 = η0.05 + m0.05 ⋅ ( 0.05 − p AC _ 0.05 ) with m0.05 = p AC _ 0.1 − p AC _ 0.05 Result Based on the measured values in Table E.3 the interpolated conversion efficiency values in terms of rated AC power are shown in Table E.5 Table E.4 – Interpolated conversion efficiencies η1′′ η′′0.75 η′′0.5 η′′0.3 η′′0.25 η′′0.2 η′′0.1 η′′0.05 0,97400 0,98286 0,98805 0,98655 0,98371 0,97494 0,93485 0,85182 BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) – 32 – Annex F (informative) Inverter efficiency F.1 General / Introduction For PV modules there is a tendency to improve specifications in a way that not only power specifications at STC (and at lower irradiance levels) are indicated, but also energy yields measured during a certain time period under real weather conditions This will make possible an improvement for the calculation of the DC-energy yield of a PV array But if energy losses caused by poor MPP-tracking of the inverter are not considered, another essential uncertainty for accurate determination of the energy yield of gridconnected PV plants remains The introduction of overall or total efficiency ηt as described in this standard will resolve this problem The scope of the standard is to define a quantity (overall efficiency ηt) which includes both conversion efficiency and MPP-tracking properties and gives a more accurate description of the overall behaviour of grid-connected PV inverters than conversion efficiency ηconv alone A grid-connected inverter consists of two main parts, the MPP-tracker, which has to draw always the maximum available power PMPP from the array (varying according to irradiance G and module temperature T), and the DC-AC converter, which has to convert the available DC power PDC to AC power PAC as efficiently as possible The most important thing is to ensure a good static performance of the inverter Therefore one part of this standard concentrates on static performance As changing weather situations depend on the location, in addition some tests for dynamic performance are defined, which mainly show the sensitivity of an inverter against varying irradiance conditions F.2 Conversion efficiency Definition: DC-AC conversion efficiency ηconv = PAC PDC (F.1) DC-AC conversion efficiency ηconv of an inverter depends both on the DC power and on the DC voltage used [ηconv = f(PDC, UDC)] Thus for a correct indication of ηconv the DC-input voltage at which the conversion efficiency was determined should be given according to EN 50524 F.3 MPP-tracking efficiency With increasing conversion efficiencies the MPP-tracking efficiency becomes more and more important and must be determined by suitable measurements Until now, measurements of actual MPPTperformance of a PV inverter are quite difficult and require sophisticated measuring equipment Quite often it is assumed by manufacturers, plant designers and simulation programs, that a grid connected PV inverter always operates at the MPP However, this is not always the case; therefore such an approach is not sincere – 33 – BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) MPP-tracking efficiency can be defined as follows: TM ∫p DC (t ) ⋅ dt ηMPPT = TM ∫p (F.2) MPP (t ) ⋅ dt The I-U-curve and the maximum available power PMPP at the maximum power point (MPP) of a PV array depends on actual in-plane irradiance and module temperature Depending on actual in-plane irradiance and module temperature, a PV array operates on a certain I-U-curve and a correlated PV-curve At a certain point (maximum power point, MPP), the available power from the array reaches its maximum value PMPP at the related MPP voltage UMPP For optimum performance, a grid-connected inverter is equipped with a MPP-tracker that tries to keep the operating point of the inverter always at the MPP despite irradiance- and/or module temperature-changes that also influence PMPP and UMPP (MPPTracking, MPPT) Depending on the MPP-tracking algorithm used by the inverter, at certain power and voltage levels more or less significant deviations from the MPP may occur In this case, the average value of PDC is lower than PMPP, which can reduce energy yield of the whole PV plant up to a few %: PDC = ηMPPT⋅PMPP (ηMPPT < 1) (F.3) In the general case with ηMPPT < 100 %, the operating voltage UDC of the inverter deviates from the MPPvoltage UMPP This fact must be considered, if starting from PDC the resulting AC output power PAC has to be calculated with the conversion efficiency ηconv which depends on UDC, i.e ηconv = f(PDC, UDC) F.4 Overall efficiency η t If ηconv and ηMPPT are known, the overall efficiency ηt = ηconv⋅ηMPPT can be calculated The resulting DC power PDC calculated with Equation (D.3) is then converted to AC power PAC by means of conversion efficiency ηconv according to Equation (D.1) Therefore: PAC = ηconv ⋅PDC = ηconv ⋅ηMPPT⋅PMPP = ηt⋅PMPP (F.4) The overall efficiency ηt can also be considered as η t = η conv ⋅ η MPPT = PAC PMPP (F.5) There is a principal systematic error if only the conversion efficiency ηconv at UMPP is used for the calculations according to Equation (D.5) If only the value for PDC < PMPP is known, which was calculated with ηMPPT, it is completely undetermined, if the inverter operates at UDC1 < UMPP or UDC2 > UMPP Therefore for a correct calculation of PAC from PDC by means of conversion efficiency ηconv, for an inverter operating at UDC1 the conversion efficiency ηconv (PDC, UDC1) and for an inverter operating at UDC2 the conversion efficiency ηconv (PDC, UDC2) must be used! BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) – 34 – F.5 Consequences For high precision measurements of ηMPPT and ηt high-precision PV array simulators with high stability are required As in the general case UDC is not defined by a mere indication of a value for ηMPPT, it must be ensured that the product of ηMPPT and ηconv respects the correct input voltage level UDC, when the overall efficiency is calculated The values of ηMPPT and ηconv must be measured at the same voltage UDC Therefore the measurement of the conversion efficiency and the static MPP tracking should be performed simultaneously – 35 – BS EN 50530:2010+A1:2013 EN 50530:2010+A1:2013 (E) Bibliography [1] Bletterie et al.: „Redefinition of the European efficiency – Finding the compromise between simplicity and accuracy“, EUPVSEC, Valencia 2008 [2] H Häberlin, L Borgna, M Kämpfer und U Zwahlen: "Total Efficiency ηtot – A new Quantity for better Characterisation of Grid-Connected PV Inverters" 20th EU PV Conf., Barcelona, Spain, June 2005 [3] Volker Quaschning, “Simulation der Abschattungsverluste bei solarelektrischen Systemen”, Dissertation Technische Universität Berlin, 1996 [4] G Valentin: „Benutzerhandbuch PV*SOL Version 2.5“, Berlin, 2005 ® This page deliberately left blank This page deliberately left blank NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW British Standards Institution (BSI) BSI is the national body responsible for preparing British Standards and other standards-related publications, information and services BSI is incorporated by Royal Charter British Standards and other standardization products are published by BSI Standards Limited About us Revisions We bring together business, industry, government, consumers, innovators and others to shape their combined experience and expertise into standards -based solutions Our British Standards and other publications are updated by amendment or revision The knowledge embodied in our standards has been 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