Spectral Solar Radiation Data Base Documentation, Vol. I

Table of Contents

1.0 Introduction


The need for spectral solar radiation data has been expressed in several forums [1-4]. The basic need is for data that can be used with solar collector spectral responsivity data to scientifically and quantitatively determine how the collector responds to natural variations in the spectral content of solar radiation, and thereby determine how its performance is affected. In the photovoltaic (PV) community, for example, there is no consensus on the magnitude of spectral effects because there are no standard procedures for evaluating outdoor spectral sensitivity of PV devices, the sensitivity is device dependent, and the quality and uncertainty of the spectral solar radiation data used in the analyses are unknown or undocumented [5]. In many cases, only one standard or reference spectrum is used to report the performance of a PV device, and the uncertainty associated with natural spectral variations is unknown.

To study the spectral sensitivity of a solar collector, its spectral response, quantum efficiency, or spectral absorption/transmission curve is multiplied by incident spectral solar radiation for a range of realistic outdoor conditions, and the results are integrated over the entire spectrum and the desired time period. All measurement uncertainty (in the spectral data and spectral response) must be evaluated to determine the statistical significance of any variations in the solar collector's performance that are attributed to spectral variations. To make this determination, spectral solar radiation data, with documented measurement uncertainty, are required.

In 1984, EPRI and SERI met to define a research project that would address the need for measured, outdoor spectral solar radiation data for a range of climate conditions. A formal project was initiated in 1985 in which EPRI provided funds to SERI to perform three tasks: (1) modify, calibrate, and deliver to EPRI two computer-controlled LI-COR, Inc. model LI-1800 spectroradiometers; (2) train EPRI- designated operators to use software that acquires spectral solar radiation and concurrent broadband solar radiation and meteorological data; and (3) develop data collection guidelines [6]. EPRI also initiated cooperative agreements with FSEC and PG&E to collect these data at their sites in Cape Canaveral, Fla., and San Ramon, Calif., respectively. In 1986, EPRI extended the agreement with SERI to use remaining project funds to assist with the start-up of measurements at FSEC and PG&E.

Spectral solar radiation and supporting data were collected at FSEC and PG&E and sent to SERI for quality-control processing and archiving [7]. SERI coordinated the data collection, periodically calibrated the spectroradiometers, added data to the data base, and documented and formatted the data base under the Department of Energy (DOE)/SERI Resource Assessment Program.

Data that are included in the data base were collected at FSEC from October 1986 to April 1988, and at PG&E from April 1987 to April 1988. FSEC operated one EPRI and one SERI spectroradiometer almost daily at Cape Canaveral (see Figure 2-1), which contributed nearly 2800 spectra to the data base. PG&E operated one EPRI spectroradiometer at San Ramon, Calif., (see Figure 2-2), as resources permitted, contributing nearly 300 spectra to the data base. SERI collected about 200 spectra in the Denver/Golden, Colo. (see Figure 2-3), area from November 1987 to February 1988 as part of a research project to study urban spectral solar radiation, and added these data to the data base [7].

3.0 Approach

Table of Contents

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