Title: Direct normal irradiance related definitions and applications: The circumsolar issue

Abstract

The direct irradiance received on a plane normal to the sun, called direct normal irradiance (DNI), is of particular relevance to concentrated solar technologies, including concentrating solar thermal plants and concentrated photovoltaic systems. Following various standards from the International Organization for Standardization (ISO), the DNI definition is related to the irradiance from a small solid angle of the sky, centered on the position of the sun. Half-angle apertures of pyrheliometers measuring DNI have varied over time, up to ≈10°. The current recommendation of the World Meteorological Organization (WMO) for this half-angle is 2.5°. Solar concentrating collectors have an angular acceptance function that can be significantly narrower, especially for technologies with high concentration ratios. The disagreement between the various interpretations of DNI, from the theoretical definition used in atmospheric physics and radiative transfer modeling to practical definitions corresponding to specific measurements or conversion technologies is significant, especially in the presence of cirrus clouds or large concentration of aerosols. Under such sky conditions, the circumsolar radiation—i.e. the diffuse radiation coming from the vicinity of the sun—contributes significantly to the DNI ground measurement, although some concentrating collectors cannot utilize the bulk of it. These issues have been identified in the EU-funded projects MACC-IImore » (Monitoring Atmospheric Composition and Climate-Interim Implementation) and SFERA (Solar Facilities for the European Research Area), and have been discussed within a panel of international experts in the framework of the Solar Heating and Cooling (SHC) program of the International Energy Agency’s (IEA’s) Task 46 “Solar Resource Assessment and Forecasting”. In accordance with these discussions, the terms of reference related to DNI are specified here. The important role of circumsolar radiation is evidenced, and its potential contribution is evaluated for typical atmospheric conditions. Thus, thorough analysis of performance of concentrating solar systems, it is recommended that, in addition to the conventional DNI related to 2.5° half-angle of today’s pyrheliometers, solar resource data sets also report the sunshape, the circumsolar contribution or the circumsolar ratio (CSR).« less

Authors:

Blanc, P. ^[1]; Espinar, B. ^[1]; Geuder, N. ^[2]; Gueymard, C. ^[3]; Meyer, R. ^[4]; Pitz-Paal, R. ^[5]; Reinhardt, B. ^[6]; Renne, D. ^[7]; Segupta, M. ^[7]; Wald, L. ^[1]; Wilbert, S. ^[8]

---

+ Show Author Affiliations

1. PSL Univ., Sophia Antipolis Cedex (France)
2. Stuttgart Univ. of Applied Sciences, Stuttgart (Germany)
3. Solar Consulting Services, Colebrook, NH (United States)
4. Suntrace GmbH, Hamburg (Germany)
5. DLR, Cologne (Germany)
6. DLR, Oberpfaffenhofen (Germany); Ludwig-Maximilians-Univ., Munich (Germany)
7. National Renewable Energy Lab. (NREL), Golden, CO (United States)
8. DLR, Tabernas (Spain)

Publication Date:

Tue Oct 21 00:00:00 EDT 2014

Research Org.:

National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1242470

Report Number(s):

NREL/JA-5D00-63177
Journal ID: ISSN 0038-092X

Grant/Contract Number:  

AC36-08GO28308

Resource Type:

Accepted Manuscript

Journal Name:

Solar Energy

Additional Journal Information:

Journal Volume: 110; Journal Issue: C; Related Information: Solar Energy; Journal ID: ISSN 0038-092X

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

14 SOLAR ENERGY; 47 OTHER INSTRUMENTATION; direct normal irradiance; circumsolar irradiance; circumsolar ratio; pyrheliometer; concentrating solar technologies