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

Initial solar cell characterisation test and comparison with a LED-based solar simulator with variable flash speed and spectrum

A continues-wavelength LED-based solar simulator has been developed to optimise the measurement of solar cells. It achieves more then one Sun intensity over an area of 200x200mm2. Use of LEDs as the main light source enabled advanced functions like variable flash speed and shape and variable spectrum. The simulator hardware is described briefly and simulator classification results are given. Initial measurements with error analysis of a mono crystalline silicon solar cell are presented, proofing that a LED-based solar simulator has potential to outperform today’s state of the art solar simulators

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

Uncertainty considerations of indoor PV module calibration based on Monte Carlo simulations

Uncertainties in the calibration of PV devices affect the power rating of modules and thus their value. The expanded measurement uncertainty in Pmax of modules at state-of-art indoor calibration facilities is between 1.6- 3.85% based on conventional Si technologies. The uncertainties of TF technologies are agreed to be higher. The contributions from different uncertainty sources are combined according to the GUM Uncertainty Framework. The Framework has the limitation of considering only the mean and standard deviation of symmetric distributions. This paper advocates the use of the Monte Carlo (MC) method for calculating the overall uncertainty of module calibration that is specific to the device-under-test and the measuring setup. Since the MC method retains all the information from the input quantities, more comprehensive probability density functions can be assigned to the main contributors. Recognised systematic effects can be accounted for by assigning asymmetric distributions to given contributions eliminating the need for correction. The use of the MC method for the total uncertainty calculation allows for a more detailed estimation of the input influences and their understanding and minimisation. In the simulated case study this led to reduction in uncertainty from ±2.5% in Isc to [+1.93%:-1.97%] for a 95% coverage interval

LEDs based characterisation of photovoltaic devices

This work discusses the advantages and disadvantages of using LEDs in a solar simulator. Details of a prototype simulator developed in CREST are given and ongoing developments of the system are discussed. Possible applications unique to simulators using LEDs are outlined, which show its potential to outperform conventional systems and reduce measurement uncertainties while at the same time offering an extensive variety of device performance investigation avenues

Temperature coefficient measurements of PV modules and uncertainty analysis

Temperature coefficient (TC) measurements of PV devices are required for energy yield estimations. However, a large deviation in measurement results is still being reported. This paper outlines the measurement setup at CREST, the sources of uncertainty and their estimation and methods for propagating them to the final uncertainty of the TC. While for very small uncertainties Ordinary Least Squares (OLS) linear regression may be appropriate for realistic uncertainties a Weighted Total Least Squares (WTLS) is recommended

Effect of I-V translations of irradiance-temperature on the energy yield prediction of PV module and spectral changes over irradiance and temperature

Energy rating is gaining importance in the photovoltaic (PV) community as it, unless power rating at standard conditions, allows an accurate estimation of the performance of PV modules in different climatic conditions. The device characterisation currently requires the measurement of a performance matrix using irradiance and temperature where values between measurements might be interpolated. Spectral changes are included by correcting using a quantum efficiency measurement. I-V translations of PV modules give better idea about the measurements of the PV modules as a function of irradiance and temperature. Two methods of I-V translations are applied in this study. Bilinear interpolation between the consecutive points of three selective data sets of irradiance and temperature in the power matrix reduces the prediction error below 2.5% compared to over 6% with linear interpolation between two extreme data set points in the power matrix