Comparison of typical meteorological year and on-site measurements for solar PV site selection

The standard approach when simulating photovoltaic output is to employ Typical Meteorological Year (TMY) data sets. This paper uses statistical analyses to investigate several TMYs. The objectives are: (1) to ascertain which TMY generation method most accurately reproduces solar conditions in the UK; (2) to discover the minimum time resolution at which TMYs delver reliable results; and (3) to determine if there are any circumstances in which TMYs can replace long-term time series

Transient preconditioning in CIGS solar cells and modules

Transient preconditioning refers to a light induced performance change in CIGS which occurs and relaxes on a millisecond to seconds timescale. This effect appears to be distinct from the better known and more persistent preconditioning which typically takes several hours or days to relax. In this paper some properties of this phenomenon are explored including the variation of if the effect with voltage and temperature. The consequences for repeatable and accurate device measurement are explored. In particular the transient rise in photocurrent during measurements using a pulsed simulator can be successfully eradicated using voltage preconditioning when there is no gap between the preconditioning voltage being applied and the start of the illumination pulse

Electrical mismatch within single junction amorphous silicon and micromorph tandem thin film PV modules

Due to the electrical mismatch between the individual cells, the actual efficiency of a PV module is always lower than the sum of the cells under normal measurement conditions. The effect of this electrical mismatch is simulated for single junction amorphous silicon PV modules as well as micromorph thin film PV modules. This paper reports on the design of the realistic parameter distribution for the I-V simulation. It shows that due to the current mismatch in a double junction solar cell, these devices seem to be more significantly affected by similar variation in parameters, which would indicate that tighter production control is necessary but also that it will be more involved to measure these devices with sufficient accuracy. It is shown that device mismatch actually results in a lower fill factor, which is slightly different to what is seen for single cells

An LED-based photovoltaic measurement system with variable spectrum and flash speed

Outdoor environmental variability generates the need for indoor systems for PV module characterisation. To combine the advantages of the most commonly used simulators (steady-state and pulsed) and eliminate their disadvantages, an LED-based solar simulator prototype has been developed. The system can produce light at variable flash speeds and pulse shapes or can operate as a continuous light source for long-term measurements. The system achieves 1-Sun intensity at a closely matched, continuous spectrum. Full control of all light sources allows variable intensity and spectral distribution during measurements. A technical description and the results of initial qualification tests are given

Uncertainty in calibration and characterisation of pyranometers

This work quantifies the uncertainties of thermoelectric pyranometer measurements made with different calibration methods. Measurement campaigns supported both the evaluation of pyranometer calibrations and newly proposed approaches to characterise the pyranometers in indoor and outdoor conditions. Estimated uncertainties were then applied to a year-long irradiance dataset to evaluate the impact on the assessment of the annual solar irradiation. This study highlights the differences seen when calibrating pyranometers under different conditions and procedures. Such deeper insight of pyranometers response aims ultimately to assist the integration of short-term (pyranometers) and long-term (satellite-based) data to a more accurate evaluation of PV energy yield

Towards a fully LED-based solar simulator - spectral mismatch considerations

LED solar simulators have a high potential for high quality characterisation of solar cells. One of the main challenges is to achieve a close spectral match to the AM1.5 solar spectrum from 350nm to 1300nm. The main sources of measurement uncertainty are the spectral mismatch, the non-uniformity of light and the reference cell. The spectral mismatch can increase the measurement uncertainty significantly. In order to minimize a major uncertainty factor a close spectral match needs to be acquired. It will be shown that the usage of LEDs, which are narrow wavelength emitting light sources, can improve the measurement accuracy of the solar simulator by accurately matching the solar spectrum. The process of choosing the best combination of wavelengths and the LED population per wavelength is a complex, dual optimization problem. This paper evaluates the optimisation algorithms chosen and examines the influence of different fitness functions in acquiring a Class A+ spectral match

Performance measurements at varying irradiance spectrum, intensity and module temperature of amorphous silicon solar cells

This paper demonstrates photovoltaic (PV) device performance measurements for energy rating and energy yield calculation derived indoors with an LED-based solar simulator prototype under varying irradiance (G), temperature (T) and spectrum (E), opening the possibility for much faster and more accurate energy yield prediction than previously possible from measurements acquired either indoors or outdoors, with the additional inclusion of spectral influences. The main aspects of the LED-based solar simulator used are described briefly and the measurement method with its requirements is explained in detail. Also presented are the first performance measurements made with an amorphous silicon solar cell; measuring the spectral effects reported in outdoor measurements for the first time in the laboratory. Results show a good agreement with previously reported spectral effects from outdoor measurements and underline the importance to consider all three environmental vectors (irradiance, spectrum and device temperature) for energy yield focused measurements

An LED-based photovoltaic measurement system with variable spectrum and flash speed

Outdoor environmental variability leads to the need of artificial illumination systems for PV module characterisation. The two main solar simulator types in use for this purpose, steady state and flash simulators, each have advantages and disadvantages regarding practicality of use and breadth of applicability. To combine the advantages of both types and eliminate the disadvantages, an LED-based solar simulator has been developed, capable of producing light in variable flash speeds and pulse shapes or as a continuous light for long-term measurements. The system features full control of all light sources allowing variable intensity and spectral distribution during measurements. The paper gives a technical description of the measurement system. The results of the initial qualification tests and initial measurements are included

Advantages in using LEDS as the main light source in solar simulators for measuring PV device characteristics

Advances in photovoltaic technology resulted in increased complexity of device calibration, largely being affected by deviations of test spectrum from natural spectra. While the output spectrum of some solar simulators is adjustable, generally only light intensity and module temperature can be varied. This is due to the light sources used in current simulators. LEDs offer an additional degree of freedom, when using an appropriate combination of wavelengths. This paper presents the advantages of this lighting technology for solar simulation and backs these up through results of the prototype unit developed at the Centre for Renewable Energy Systems Technology. The ability to keep LEDs stable for a long time and dim them with minimal changes in the spectrum allows generation of a spectrum closely matched to AM1.5G standard test spectrum or indeed even realistic variations of the outdoor spectrum. LEDs can be controlled very fast within microseconds or operated continuously, combining a steady state and a flash solar simulator with additional functions such as variable flash frequencies and flash shape. Combined with the life expectancy exceeding 50.000h, LEDs are a strong candidate for solar simulator light sources introducing a significant improvement in calibration lifetime as well as significantly reduced running cost. The usage of LEDs can enhance today’s characteristic measurement functions and even opens possibilities to fully characterise solar cells indoors within a much shorter time than is possible today, over a range of conditions previously only available through outdoor characterisation

Towards an accurate and automated characterisation of multi-junction solar cells

A theoretical approach of automated characterisation of single as well as multi-junction solar cells has been developed. The method will be implemented in CREST’s measurement system. It delivers not only I-V characteristics at reference spectrum but also absolute spectral response of the test cell. Thus it opens the way for inline spectral response measurements. The method requires nothing more than a multisource solar simulator, some basic information about the test cell and a calibrated reference cell. Single- and multi-junction measurement procedures are briefly reviewed; the automatic measurement approach is explained and underlined with real and simulation results