Uncertainty of PV Module Energy Rating in accordance with IEC 61853
Werner Herrmann, TÜV Rheinland Solar GmbH
Introduction
The energy rating of PV modules is related to its energy yield performance in a specific climate. In contrast to the nominal output power, which is only related to the performance at a single operating point (Standard test Conditions, STC), the energy rating considers the interaction of the PV module characteristics with the climatic conditions at the operating site. With neglect of shading and soiling, the following PV module parameters affect the amount of produced energy: (a) temperature behaviour, (b) low irradiance behaviour, (c) spectral responsivity and (d) angular responsivity.
To be able to compare the energy yield performance of PV modules, the IEC 61853 standard series (Table 1) defines a specific metric, which describes the energy yield performance of PV modules by a single parameter, the Climate Specific Energy Rating (CSER).
| Title | |
|---|---|
| IEC 61853-1: 2011 | Photovoltaic (PV) module performance testing and energy rating - Part 1: Irradiance and temperature performance measurements and power rating |
| IEC 61853-2: 2016 | Photovoltaic (PV) module performance testing and energy rating - Part 2: Spectral responsivity, incidence angle and module operating temperature measurements |
| IEC 61853-3: 2018 | Photovoltaic (PV) module performance testing and energy rating - Part 3: Energy rating of PV modules |
| IEC 61853-4: 2018 | Photovoltaic (PV) module performance testing and energy rating - Part 4: Standard reference climatic profiles |
Table 1: IEC 61853 standard series
FIGURE 1
Figure 1: Methodology of IEC 61853 series for climate specific energy rating
As shown in Figure 1, the calculation of the Climate Specific Energy Rating (CSER) of PV modules requires the input of various PV module performance parameters (blue boxes) and tabulated reference data (grey boxes) that are documented in IEC 61853-4 (climate data) and IEC 60904-3 (AM1.5 spectral irradiance distribution). The yellow boxes represent data processing steps.
The CSER value is calculated according to the following equation
FORMEL 1[math]\displaystyle{ CSER= \frac {E_{MOD,Year}/H_{Year}} {P_{MAX,STC}/G_{REF,STC}} }[/math]
EMOD,Year is the calculated PV module annual energy yield (IEC 61853-3), HYear is the annual in-plane solar radiation of the selected reference climate (IEC 61853-4), PMAX,STC is the PV module nominal output power at STC and GREF,STC is the STC reference irradiance, which is set to 1000 W/m². The CSER parameter can be interpreted as the DC performance ratio of the PV module. CSER=1 means that the annual average operational efficiency corresponds to the STC efficiency of the PV module. In practice, CSER values differ from 1 and the deviation from 1 indicates annual yield losses or gains. Table 1 gives an overview of all input quantities for CSER calculation with remarks on uncertainty aspects.