Solar Simulation Problems and Solutions

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May 9, 1988 - continuous arc lamp solar simulators use the high pressure xenon-arc lamp because it operates as an intense point source. The bright point.
SOLAR SIMULATION K. Emery,

Solar

- PROBLEMS AND SOLUTIONS D. Myers

Energy Research Institute 1617 Cole Blvd. Golden, CO USA 80401

ABSTRACT Solar

simulators

are

an

integral

part

of

any

This paper laboratory involved in photovoltaics (PV). quantifies the effects of bulb aging, reflections oii the simulator optics and fixturing, spectral irradiance, and variations in temporal and spatial characteristics of solar simulators on PV device performance. As the distance between the integrating optics or bulb decreases the spatial nonuniformity parallel and A shon focal perpendicular to the test plane increases. length increases the possibility for an artificial The study quantifies increase in the measured current. the effect on the spectral irradiance and the spectral mismatch error for different bulb types. different bulbs of the same type, bulb age, bulb voltage, and distance from the bulb to the test plane. INTRODUCTION

A large number of different light sources, including natural sunlight, can be used in PV ~periorma”ce me*s”reme”ts. their suitability can be categorized according to their relative cost, illumination area. spatial uniformity, temporal stability, and spectral irradiance. The cost factor includes the purchase price and maintenance. The ideal solar simulator should have the in and following features; a spatial nonuniformity several centimeters above the test plane of less than + 1%. a variation in total irradiance with time of less than +I%, and be filtered for a given references spectrum to have a spectral mismatch error of less than f 1%. These requirements are essential in obtaining an accuracy of Although better than f2% in efficiency measurements. several commercially available solar simulators meet these stringent criteria, the cost can be $100,000 or more. Numerous ASTM class A solar simulators [II are available that are less expensive and are adequate for efficiency measuements accurate to i 5%. CONTINUOUS ARC LAMP SIMULATORS Commercial

continuous

arc

lamp

and S. Rummel

SOLAR solar

simulators

use the high pressure xenon-arc lamp because it The bright point operates as an intense point source. source with integrating optics achieves excellent However, if the spatial uniformity OYC, a large area. PV application is for light soaking or for quality control in a manufacturing environment a compact some metal arc lamp 01 low pressure xenon lamp housed in a custom enclosure may be more appropriate.

Manufacturers have built such systems for cell and module testing for less than $1000. Tbe long bulb life (>20000 hours) make them ideal for applications where an ASTM class C [I] solar simulator is acceptable. The irradiance several characteristics for SpeCtd commercial solar simulators have been compared by Manufacturers have been several groups [2-41 improving the filtering of these simulators 10 better match the direct normal (51, global [6] or AM0 l71 reference spectrum. The specrral irradiance of the continuous xenonarc lamps shift from the “blue” 10 the “red” as the bulb ages l3]. Figure 1 quantifies this shift in spectrum with bulb age ior two separate bulbs in terms of the change in the spectral mismatch error, M [g] for a variety of test cell - reference cell combinations (Fig. 2). The spectral irradiance of the Spectralab X-25 solar simulator used in this study with a new 2.5kW bulb operating at a current of 95A, is compared with the spectral irradiance after 1457 hours of operation in Fig. 3. Figure 1 shows that most of the spectral shift occurs in the first 200 hours of operation. A closely matched test cell and reference cell show a minimal change in spectral mismatch with bulb age, while a poor match is most sensitive 10 the shift in spectral irradiance with The scatter in the M reflects the precision bulb age. error of spectral irradiance mea~mement~ using stateof-the-art spectroradiometers [9] (LICOR LI-1800 for 300-1100 urn and the Optronics 746D for the IlOOThe integrated irradiance 2500nm wavelength region). over the 800.1100nm region for the Optronics spectroradiometer was normalized 10 agree the LICOR uniformity spatial spectroradiometer to eliminate differences between the two spectrorerelated diameter’s measurements. Many simulator related artifacts can be eliminated by using a reference cell that has the same Ii the relative spectral response as the test device. reference device and test cell do no, have the same geometry, then the it is possible that the measured current of the test device may be ,oo large. Enhancements in the measured current of up to 20% have been observed by the author and reported [lo-131. These enhancements could be attributed to reflections off the reference cell package (high reflectivity package), simulator optics (distance to the test plane