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Principle of Decomposition of the Radiation Components |
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- Glossary
- Starting from daily GHI (Global Horizontal Irradiation) => case of HC1
- Starting from 15 min GHI => case of HC3
- Essential references
- Equations
NB: The ESRA conventions for the azimuth angles is 0° when looking toward equator.
Glossary
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Starting from daily GHI (Global Horizontal Irradiation) => case of HC1
Starting point: the daily Global Irradiation data over the horizontal plane (GHI_d). Case of HC1. |
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DHI_d: The equation 6 of Erbs, Klein and Duffie (1982) is used to assess the diffuse fraction from the daily global irradiation values over the horizontal plane (GHI_d), or more precisely from the Clearness Index Kt (GHI/E0)
ESRA (2000): eq. 3.4.5a and 3.4.5b p 118 and p 119
BHI_d: The direct component is assessed by removing the diffuse from the global irradiance: BHI_d = GHI_d - DHI_d
GHI_min: Collares-Peirera and Rabl (1979). A large number of application fields required an intra-day time step for the irradiation values. But as it is often the case with archived data, the irradiation values are limited to monthly or daily values.
Collares-Peirera and Rabl offered to the community of solar radiation an important contribution since they propose an estimation model to derive the hourly (or less) irradiation values from the daily ones. The idea is to start from the daily profil that fits the daily irradiation value in case of clear sky conditions. The profil has sinus shape. The principle is to modulate this clear-sky intra-day to fit the given daily irradiation value. Please note that there is no consideration of the historical weather of each day.
Application fields: Computation of the HC1monthDNI (soda webservice for free), computation of the HC1 data with a time step inferior to the day (on request only), computation of the HC1 data over the inclined surface (on request only), used by PVsyst when monthly irradiation values are inputs of the software...
ESRA (2000): eq. 3.5.24a, eq. 3.5.24b, eq. 3.5.24c and eq. 3.5.25 p129
DHI_min: the algorithm of Liu and Jordan (1960), described in the ESRA (2000), permits to assess the hourly (or on smaller time intervals) diffuse fraction from the global irradiance.
ESRA 2000: eq 3.5.25 and eq 3.5.26 p129
DTI_min: The algorithm of Muneer (1990) is exploited to extract the proportion of diffuse radiation collected by any inclined surface. At the origin, this model has been defined on a hourly basis. Nevertheless, it can be extended to an interval of time lower than the hour since it works on a adimension parameter, the Kc (GHI/clearsky).
ESRA (2000): eq. 3.6.5a to eq. 3.6.7b, pp:142-143
BTI_min: The direct (Beam) component computation over the inclined surface is based on pure geometry, directly obtained from the BHI:
RTI_min: The reflected component is a fonction of the GHI_min, the albedo and of the tilt of the plane (similar to the proportion of sky seen by the tilted surface): RTI_min = GHI_min*albedo*(1-cos(tilt/2))
Then, temporal aggregation is performed if requested by the user and the components are summed up to formed the Global fraction.
Starting from 15 min GHI => case of HC3
Starting point: the 15 min Global Horizontal Irradiation data (GHI_15min). Case of HC3. |
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DHI_15min: The model used to compute DHI_15min depends on the version of HelioClim3 you consider.
HC3v2 uses the equation 1 of Erbs, Klein and Duffie (eq 1, 1982).
HC3v3: the reference is Arias 2009.
BHI_min: idem previous section.
Then the different components needs to be computed over the tilted surface or the normal surface. The model to compute the diffuse part of the radiation over an inclined surface is the one of Muneer (1990).
BTI_min: idem previous section.
RTI_min: idem previous section.
Then, temporal aggregation is performed if requested by the user and the components are summed up to formed the Global fraction.
Essential references
Ruiz-Arias, J.A. 2009. Modelization of the Terrain's morphology Influence on the Solar Radiation Field at the Earth's surface. Doctoral Thesis (PhD) eq. 4.34, University of Jaé, April 2009, 202 p.
Erbs D.G., S.A. Klein and J.A. Duffie, 1982. "Estimation of the Diffuse Radiation Fraction for Hourly, Daily and Monthly-average Global Radiation", Solar Energy, Vol. 28, N°4, pp. 293-302.
Erbs D.G., "Methods For Estimating the Diffuse Fraction of Hourly, Daily, and Monthly-Average Global Solar Radiation", Masters Thesis, University of Wisconsin-Madison, 1980.
NB: Please note that even is Erbs, Klein and Duffie (1982) is the generally the reference found to assess DHI from GHI, Erbs already gave several elements on the decompositions two years earlier in his PhD thesis (Erbs 1980).
ESRA (2000): European Solar Radiation Atlas, 2000. Fourth edition, includ. CD-ROM. Edited by J. Greif, K. Scharmer. Scientific advisors: R. Dogniaux, J. K. Page. Authors : L. Wald, M. Albuisson, G. Czeplak, B. Bourges, R. Aguiar, H. Lund, A. Joukoff, U. Terzenbach, H. G. Beyer, E. P. Borisenko. Published for the Commission of the European Communities by Presses de l'Ecole, Ecole des Mines de Paris, France, France.
Muneer T., 1990. "Solar radiation model for Europe." Building Serv. Eng. Res. Techno., Vol. 11, pp. 153-163.
Equations
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Erbs, Klein and Duffie 1982, eq 6. function: split_Gdd_Ddt_hp, in the library split.h dans mon code statkraft: calc_DGdt, in the library split.h wss: solar angle at sunset |
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Liu and Jordan 1960 |
Muneer (1990) |
Last update: 4/20/12 1:50 PM