Energy rating of PV modules: comparison of methods and approach

The real electrical parameters rarely correspond to the nominal electrical parameters supplied by the manufacturers. Moreover initial degradation occurs in almost all types of modules during the first period of exposure. Project planners and installers are increasingly asked to provide production and behaviour estimates for the systems they install. Therefore a direct performance comparison of PV modules is needed. The ISAAC-TISO centre carried out systematic outdoor testing, under real operating conditions, and indoor tests on the most important modules currently on the market. In March 2006 a new 15 month test cycle (no.10) started. Fourteen different module types were chosen, trying to include the greater part of available technologies: 8 mc-Si, 2 sc-Si, 1 HIT, 2 a-Si and 1 CdTe. All the modules were purchased anonymously. I-V measurements @STC are periodically performed. In test cycle 10 the power at the purchase of a c-Si module is on average 1.5% lower with respect to Pn but ranging from 0.2% and-3.8%. Stabilized power after 15 months is on average 3.6% lower with respect to Pn and ranging from-0.7% and-8.2%. All types of modules are in the warranty limits. Differences (average of 2 modules) in annual energy production [kWh/kWp], of 14 different module types compared to the best module, with nominal power Pn as reference, reach 10%. The thin-film modules have a slightly higher energy yield with respect to c-Si modules but evaluation of these technologies is complicated by the fact that their STC power changes in time (degradation and recovery effects).

It is very important for manufacturers, designers and end users to know in advance whether a PV module behaves in operating conditions better than another one. ENEA has developed a customized measurement system made of electronic loads and an High speed data acquisition system able to acquire automatically IV curves at different temperature and irradiation levels. Before being submitted to the outdoor measurements, the photovoltaic modules have been characterized in ENEA laboratory in order to evaluate the nominal powers. Performance Ratio (PR) has been evaluated during outdoor measurements for crystalline-Si and CIGS PV modules so has been possible to make comparative evaluations among the modules technologies.

2019

The paper presents results from an inter laboratory comparison (ILC) of crystalline silicon PV module performance measurements from three different institutions within South Africa. The analysis quantifies the differences in power, current, and voltage measurements and compares power to the stated uncertainties for the measurements. The paper also explains the basics of PV module performance measurements, the link to PV module nameplate ratings, and describes the sources of uncertainty in the measurements. The results of the 2019 ILC I-V measurements among three South African institutions show differences of +/-2.0% or less for maximum power measurements of crystalline PV modules, relative to the CSIR results. These differences are within the stated uncertainty for the measurements but greater than the +/-0.5% differences among international reference labs reported in a 2017.

Solar Energy, 2013

A proposal for generating standard climatic data sets for use in energy rating of photovoltaic (PV) modules is presented which will give a good comparability between different technologies. The current proposal of standard data sets consisting of "typical days" do not give realistic estimates of PV performance and thus is not sufficient as a rating standard. A dataset striking the balance between being significant for any location but does not consisting of too much data is required. A method to generate such a dataset is presented, meeting all the requirements of an international standard while being sufficiently accurate to differentiate between different devices of different manufacturers. It is suggested to work with annual data-sets for specific climatic zones, and compare devices based on their module performance ratio. Using geographical information systems and proven modeling approaches, it is demonstrated that seven such annual data sets give sufficient detail and relevance to allow a comparison of different PV device technologies in all European operating environments. The method to use GIS datasets to identify suitable sites and then use more accurate, specific measurement data based on long-term averages for chosen sites. It is shown that the year-to-year variation is minimal, thus making these datasets suitable for comparing typical energy yields of different devices, i.e. carry out an energy rating. The study is currently limited to European data and climatic zones, which is sufficient to derive the methodology for generating and classifying the data. An international standard will, however, need a wider coverage. The extension to other data-sets and climatic zones is proposed and will have to be carried out by the appropriate standards bodies if this is to become an internationally accepted standard.

2015

Performance of a PV installation depends critically on the modules behaviour. That is the reason why a good estimation of energy production of a PV installation relies not only on the goodness of the module power characterization at standard test conditions, but also on the goodness of the characterisation of the module behaviour related to the variation of irradiance and temperature. So, it is closer to the reality running a simulation exercise of energy production with the actual values measured outdoors than with the values obtained from datasheets. This paper presents a device specifically implemented to measure outdoors the power of modules at standard test conditions, as well as their efficiency variation with irradiance and their temperature coefficients. Results of measurements with this device are also reported.

The paper deals with an extensive PV modules monitoring activity carried out at the outdoor station ESTER of the University of Rome Tor Vergata. The purpose of the work was to evaluate and compare the performances of PV silicon modules of polycrystalline and amorphous technologies during a medium term outdoor exposure at optimized tilt angle, facing south. Two PV modules, one polycrystalline by Kyocera and one double junction amorphous by EPV Solar have been exposed since May 2009. A complete characterization of the weather conditions at the site during the test has been performed and the most relevant parameters for the performance comparison of the two technologies have been derived. In order to compare different technologies and power productions, the energy Yield (Y) and Performance Ratio (PR) for the two modules have been evaluated on a monthly and yearly basis. The typical seasonal trend of PR has been observed for the polycrystalline module, essentially due to the temperature influence on the module performances. For the EPV module, instead, a degradation trend has been observed for the first months of operation. Subsequently a significant recovery in the PR and energy production has been registered.

This work covers extensive outdoor testing of a pc-Si module from Photowatt (PW1400-24V). All tests were performed at PSI's Solar Test Facility. The location of PSI represents a typical site in the Swiss Midland. The module was fixed on a sun tracker and tested under clear sky conditions as well as under a cloudy sky. During testing, the global-normal irradiance varied between 105 and 1084 W/m 2 , the cell temperature between 18 and 71°C, and the relative air mass between 1.3 and 7.9. About 900 current/voltage characteristics were automatically acquired, leading to the efficiency as a function of irradiance, cell temperature and air mass. The data were used to develop a new efficiency model to calculate the efficiency under all relevant operating conditions. The model contains six parameters. They were determined by applying non-linear fitting techniques. Applying mathematical transformations reported on earlier, the measurements and the efficiency model can be compared and validated in two-dimensional representations. The module shows an acceptable efficiency behavior over the irradiance range. The STC efficiency (referred to the active cell area) was found to be 13.0 %, corresponding to an STC module output power of 147.4 W (according to manufacturer: 160 W). An efficiency maximum of 13.3 % was found at 628 W/m 2 . The efficiency linearly decreases with temperature. Its temperature coefficient was found to be -0.0468 percentage points/°C. Regarding the impact of air mass, the efficiency exhibits a maximum value of 13.2 % at an air mass of 5.72. The module shows very good red light sensitivity in the late afternoon. Using measured meteorological data from a sunny site in the South of Jordan, the electricity production for the Photowatt module was calculated. The yearly output of South-oriented, 30°-inclined modules was found to be 303 kWh/(m 2 cell area). For sun-tracked modules, the annual output amounts to 416 kWh/(m 2 cell area).

his paper presents the effects of irradiance and temperature on the performances of PV module technologies. Since the efficiency of photovoltaic cells vary with the operating condition, there is need to access the rate of these variations for the different photovoltaic solar cells technologies. Simulations of parameters of the PV modules to evaluate their performances under changing environmental conditions are carried out using MATLAB. The results show that, thin film solar cell technologies; amorphous silicon (a-Si) and copper indium gallium disillined (CIGS), response to variation in both irradiance and temperature more rapidly. However, CIGS’s efficiency, uniquely, decreases with increase in temperature. This fact is in agreement with the experimental results reported.

Progress in Photovoltaics: Research and Applications, 2006

The performance of a photovoltaic module at Standard Test Conditions (STC) is valuable for comparing the peak performance of different module types. It does not, however, give enough information to accurately predict how much energy a module will deliver when subjected to real operating conditions. There are several proposals for an energy rating for PV modules which attempt to account for the varying operating conditions that one encounters in the field. In this paper, we present an approach with the emphasis on simplicity and practicality that incorporates existing standard measurements to determine the energy output as a function of global in-plane irradiance and ambient temperature. The method is applied to crystalline Si modules and tested with outdoor measurements, and a good accuracy of prediction of energy production is observed. Finally, a proposal is made for a simple Energy Rating labeling of PV modules.

Journal of Solar Energy Engineering, 2006

Computer simulation tools used to predict the energy production of photovoltaic systems are needed in order to make informed economic decisions. These tools require input parameters that characterize module performance under various operational and environmental conditions. Depending upon the complexity of the simulation model, the required input parameters can vary from the limited information found on labels affixed to photovoltaic modules to an extensive set of parameters. The required input parameters are normally obtained indoors using a solar simulator or flash tester, or measured outdoors under natural sunlight. This paper compares measured performance parameters for three photovoltaic modules tested outdoors at the National Institute of Standards and Technology (NIST) and Sandia National Laboratories (SNL). Two of the three modules were custom fabricated using monocrystalline and silicon film cells. The third, a commercially available module, utilized triple-junction amorpho...