Uncertainty estimates for global solar irradiance measurements used to evaluate PV device performance (original) (raw)
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Organic Photovoltaics V, 2004
Evaluating the performance of photovoltaic (PV) devices in the laboratory and in the field requires accurate knowledge of the optical radiation stimulating the devices. We briefly describe the radiometric instrumentation used for characterizing broadband and spectral irradiance for PV applications. Spectral radiometric measurement systems are used to characterize solar simulators (continuous and pulsed, or flash sources) and natural sunlight. Broadband radiometers (pyranometers and pyrheliometers) are used to assess solar resources for renewable applications and develop and validate broadband solar radiation models for estimating system performance. We describe the sources and magnitudes of uncertainty associated with calibrations and measurements using these instruments. The basic calibration and measurement uncertainty associated with this instrumentation are based on the guidelines described in the International Standards Organization (ISO) and Bureau Internationale des Poids et Mesures (BIPM) Guide to Uncertainty in Measurement. The additional contributions to uncertainty arising from the uncertainty in characterization functions and correction schemes are discussed and illustrated. Finally, empirical comparisons of several solar radiometer instrumentation sets illustrate that the best measurement accuracy for broadband radiation is on the order of 3%, and spectrally dependent uncertainty for spectroradiometer systems range from 4% in the visible to 8% to 10% in the ultraviolet and infrared.
Comparison of pyranometers vs. PV reference cells for evaluation of PV array performance
2012 38th IEEE Photovoltaic Specialists Conference, 2012
As the photovoltaics (PV) industry has grown, the need for accurately monitoring the solar resource of PV power plants has increased. Historically, the PV industry has relied on thermopile pyranometers for irradiance measurements, and a large body of historical irradiance data taken with pyranometers exists. However, interest in PV reference devices is increasing. In this paper, we discuss why PV reference devices are better suited for PV applications, and estimate the typical uncertainties in irradiance measurements made with both pyranometers and PV reference devices. We assert that the quantity of interest in monitoring a PV power plant is the equivalent irradiance under the IEC 60904-3 reference solar spectrum that would produce the same electrical response in the PV array as the incident solar radiation. For PV-plant monitoring applications, we find the uncertainties in irradiance measurements of this type to be on the order of ±5% for thermopile pyranometers and ±2.4% for PV reference devices.
Uncertainty calculation of indoor and outdoor performance measurements for PV modules
19th International Congress of Metrology (CIM2019), 2019
Since uncertainties are often overlooked, this analysis highlights why considering uncertainties on PV power or efficiency values is crucial in order to compare published values for different PV technologies. Following the International Energy Agency Report on “Uncertainties in PV System Yield predictions and Assessments” and European FP7 Sophia project, the state of the art of outdoor and indoor uncertainty calculations on PV modules performances is reviewed. Calculation tools are compared and discussed in order to identify the most relevant one. Indoor measurements are based on instantaneous measurements with a dedicated set up: a solar simulator, called “flash-test”. The simulated conditions are close to the standard tests conditions with a stable irradiance, AMG1.5 spectrum and at 25 °C ± 1 °C, which are more stable than outdoor tests. Outdoor measurements are taken performed on variable time periods. Variations over months are commonly observed within ± 5 % that is why averagin...
Measuring Solar Irradiance for Photovoltaics
IntechOpen eBooks, 2022
In recent years, solar energy technology has emerged as one of the leading renewable energy technologies currently available. Solar energy is enabled by the solar irradiance reaching the earth. Here we describe the characteristics of solar irradiance as well as the sources of variation. The different components of the solar irradiance and the instruments for measurement of these components are presented. In photovoltaics, the measurement of solar irradiance components is essential for research, quality control, feasibility studies, investment decisions, plant monitoring of the performance ratio, site comparison, and as input for shortterm irradiance forecasting. Some more details are also provided related to physics of measuring instruments, their calibration, and associated uncertainty.
Second international spectroradiometer intercomparison: results and impact on PV device calibration
Progress in Photovoltaics: Research and Applications, 2014
This paper describes the results of an intercomparison of spectroradiometers for measuring global normal incidence and direct normal incidence spectral irradiance in the visible and in the near infrared, together with an assessment of the impact these results may have on the calibration of the short circuit current (I sc) of triple-junction photovoltaic devices and on the relevant spectral mismatch calculation. The intercomparison was conducted by six European scientific laboratories and a Japanese industrial partner. Seven spectroradiometer systems, for a total of 13 different instruments/channels using two different technologies and made by four different manufacturers were involved. This group of systems represents a good cross section of the instrumentation for solar spectrum measurements available to date. The instruments were calibrated by each partner prior to the intercomparison following their usual procedure and traceability route in order to verify the entire measurement and traceability chain. The difference in measured spectral irradiance showed to have an impact on the calibration of a set of Iso-Type cells varying from ±2% to ±14% for middle and bottom cell, respectively.
Uncertainties on the outdoor characterization of PV modules and the calibration of reference modules
Solar Energy, 2017
This paper presents the IES-UPM experience in the outdoor characterization of PV modules. On days with clear sky conditions, a rather simple device consisting of a thermally-insulated wooden box allows the STC characteristics and the thermal coefficients of PV modules to be measured with low expanded uncertainty (±1.87% in power (k=2)). Particular attention has been paid to the calibration of the reference cell used for measuring the irradiance and making our measurements traceable to the International System of Units (S.I.). Furthermore, the uncertainty on the irradiance and module temperature measured by the reference PV modules calibrated with the help of this box has also been analyzed in relation to the angle of incidence of the direct irradiance. We think this experience is particularly interesting for local measurements in many countries currently incorporating PV plants in their electric grid, but lacking in specialized PV laboratories equipped with expensive solar simulators.
Uncertainty in Photovoltaic performance parameters – dependence on location and material
Solar Energy Materials and Solar Cells, 2009
The return from investments in PV systems in the main PV markets depends mostly on the electrical energy exported to the grid (kWh). Efficient system operation is generally assured by assessment of performance indicators, such as performance ratios (PR) that are calculated from monitored system performance data. Low site-specific PRs indicate operational problems that might result in a loss of profit or even a warranty case if a PR was previously guaranteed and this paper establishes the boundaries in which sub-optimal performance can be identified. This is achieved by calculating the uncertainties of the required measurements. It is shown that the uncertainty of performance indicators and thus the boundary at which sub-optimal performance can be identified varies with the operating environment and instrumentation set-ups. This study has investigated those boundaries for three measurement systems, three locations and two module types. It is shown that the uncertainties in the annual PR can be as high as 4.5% for Northern Europe, 50% higher than for a Southern European site. It is also shown that the determination of low system performance based on power measurements is extremely difficult and riddled with significant uncertainties, while the evaluation based on energy is much more robust.
Progress in Photovoltaics Research and Applications
This paper describes the preliminary results of an intercomparison of spectroradiometers for global (GNI) and direct normal incidence (DNI) irradiance in the visible (VIS) and near infrared (NIR) spectral regions together with an assessment of the impact these results may have on the calibration of triple-junction photovoltaic devices and on the relevant spectral mismatch calculation. The intercomparison was conducted by six European scientific laboratories and a Japanese industrial partner. Seven institutions and seven spectroradiometer systems, representing different technologies and manufacturers were involved, representing a good cross section of the todays' available instrumentation for solar spectrum measurements.