Abstract
Abstract. The ever-increasing energy demand has led to overexploitation of fossil fuels deposits, while renewables offer a viable alternative. Since renewable energy resources derive from phenomena related to either atmospheric or geophysical processes, unpredictability is inherent to renewable energy systems. An innovative and simple stochastic tool, the climacogram, was chosen to explore the degree of unpredictability. By applying the climacogram across the related timeseries and spatial-series it was feasible to identify the degree of unpredictability in each process through the Hurst parameter, an index that quantifies the level of uncertainty. All examined processes display a Hurst parameter larger than 0.5, indicating increased uncertainty on the long term. This implies that only through stochastic analysis may renewable energy resources be reliably manageable and cost efficient. In this context, a pilot application of a hybrid renewable energy system in the Greek island of Astypalaia is discussed, for which we show how the uncertainty (in terms of variability) of the input hydrometeorological processes alters the uncertainty of the output energy values.
Highlights
Nowadays fossil fuels cover 80 % of the energy demand globally
There are various methods to estimate the Hurst parameter, based on the climacogram, the power spectrum, the autocovariance, etc. (Dimitriadis and Koutsoyiannis, 2015); the climacogram is defined as the log-log plot of variance of the averaged process versus averaging time scale, whereas the power spectrum of a random process describes the distribution of its variance over the frequency
The Hurst parameter varies across different time scales, which is supported by recent research results (Dimitriadis, 2017) and it is estimated greater than 0.5 for all examined processes
Summary
Nowadays fossil fuels cover 80 % of the energy demand globally. The irregular variability of the related geophysical processes introduces a remarkable degree of uncertainty to the renewable energy resources systems and, the predictability of related energy production is often limited. The more complex the process (in terms of stochastic behavior, Koutsoyiannis, 2017) the larger the introduced uncertainty, even for the conventional energy sources. It is expected that the energy produced by fossil fuels is not varying significantly in time, suggesting that it should follow a deterministic behaviour (and fully predictable in all scales and time horizons) due to fixed deposits, its production, at least in the long term, is uncertain, due to monetary, currency (e.g. petro-currency) and geopolitical reasons (Karakatsanis et al, 2017). The great challenge with renewables is the lack of predictability at all temporal scales, affecting both the design and operation of the associated systems
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