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| Titel |
Power spectral density and scaling exponent of high frequency global solar radiation sequences |
| VerfasserIn |
Rudy Calif, François G. Schmitt, Yongxiang Huang |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083226
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| Zusammenfassung |
| The part of the solar power production from photovlotaïcs systems is constantly increasing in
the electric grids. Solar energy converter devices such as photovoltaic cells are very sensitive
to instantaneous solar radiation fluctuations. Thus rapid variation of solar radiation due to
changes in the local meteorological condition can induce large amplitude fluctuations of the
produced electrical power and reduce the overall efficiency of the system. When
large amount of photovoltaic electricity is send into a weak or small electricity
network such as island network, the electric grid security can be in jeopardy due to
these power fluctuations. The integration of this energy in the electrical network
remains a major challenge, due to the high variability of solar radiation in time and
space. To palliate these difficulties, it is essential to identify the characteristic of
these fluctuations in order to anticipate the eventuality of power shortage or power
surge.
The objective of this study is to present an approach based on Empirical Mode
Decomposition (EMD) and Hilbert-Huang Transform (HHT) to highlight the scaling
properties of global solar irradiance data G(t).
The scale of invariance is detected on this dataset using the Empirical Mode
Decomposition in association with arbitrary-order Hilbert spectral analysis, a generalization
of (HHT) or Hilbert Spectral Analysis (HSA). The first step is the EMD, consists in
decomposing the normalized global solar radiation data G′(t) into several Intrinsic Mode
Functions (IMF) Ci(t) without giving an a priori basis. Consequently, the normalized
original solar radiation sequence G′(t) can be written as a sum of Ci(t) with a
residual rn. From all IMF modes, a joint PDF P(f,A) of locally and instantaneous
frequency f and amplitude A, is estimated. To characterize the scaling behavior in
amplitude-frequency space, an arbitrary-order Hilbert marginal spectrum is defined
to:
-«
- q
Iq(f) = 0 P (f,A)A dA
(1)
with q -¥ 0 In case of scale invariance: Iq(f) ~ f-Ψ(q) , Ψ(q) is the scaling exponent. This
allows to characterize the scaling behavior of a process: fractal or multifractal with
intermittent properties. For q = 2, the Hilbert spectrum is defined. In this work, The data are
collected at the University site of Guadeloupe, an island in the West Indies, located at 16°15
N latitude 60°30 W longitude. Our measurements sampled at 1 Hz were performed during
one year period. The analyzed data present a power spectral density E(f) displaying a power
law of the form E(f) ~ f-β with 1.6 -¤ β -¤ 2.2 for frequencies f -¤ 0.1 Hz, corresponding
to time scales T -¥ 10 s. Furthermore, global solar radiation data possesses multifractal
properties. For comparison, other multifractal analysis techniques such as structure
functions, MDFA, wavelet leaders are also used. This preliminary work set the
basis for further investigation dedicated to simulate and forecast a sequence of solar
energy fluctuation under different meteorological conditions, in the multifractal
framework. |
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