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330 KiB

Open AccessArticle

by Blanca Antizar-Ladislao and Juan L. Turrion-Gomez

Energies 2010, 3(2), 194-205; https://doi.org/10.3390/en3020194 - 28 Jan 2010

Cited by 30 | Viewed by 11222

In the last five years or so, biofuels have been given notable consideration worldwide as an alternative to fossil fuels, due to their potential to reduce greenhouse gas emissions by partial replacement of oil as a transport fuel. The production of biofuels using [...] Read more.

In the last five years or so, biofuels have been given notable consideration worldwide as an alternative to fossil fuels, due to their potential to reduce greenhouse gas emissions by partial replacement of oil as a transport fuel. The production of biofuels using a sustainable approach, should consider local production of biofuels, obtained from local feedstocks and adapted to the socio-economical and environmental characteristics of the particular region where they are developed. Thus, decentralized energy from waste systems will exploit local biomass to optimize their production and consumption. Waste streams such as agricultural and wood residues, municipal solid waste, vegetable oils, and algae residues can all be integrated in energy from waste systems. An integral optimization of decentralized energy from waste systems should not be based on the optimization of each single process, but the overall optimization of the whole process. This is by obtaining optimal energy and environmental benefits, as well as collateral beneficial co-products such as soil fertilizers which will result in a higher food crop production and carbon dioxide fixation which will abate climate change. Full article

(This article belongs to the Special Issue Biofuels: Energy and Fuels, Chemical Engineering, Biotechnology and Environmental Sciences)

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807 KiB

Open AccessArticle

Online Parameter Estimation of the Ni-MH Batteries Based on Statistical Methods

by Chang-hao Piao, Wen-li Fu, Gai-hui Lei and Chong-du Cho

Energies 2010, 3(2), 206-215; https://doi.org/10.3390/en3020206 - 10 Feb 2010

Cited by 23 | Viewed by 9228

Abstract

Based on the application of the power batteries, this paper uses a statistical method to estimate the internal resistance and open-circuit voltage of Ni-MH battery. Battery status is monitored and simulated by battery pack test bench. Through using ideal battery model and fitting [...] Read more.

Based on the application of the power batteries, this paper uses a statistical method to estimate the internal resistance and open-circuit voltage of Ni-MH battery. Battery status is monitored and simulated by battery pack test bench. Through using ideal battery model and fitting the data of measured voltage and current, the battery internal resistance and open-circuit voltage are estimated. The average relative error between battery statistic internal resistance and pulse internal resistance is less than 15% in different state of charge. Relative error is influenced by dispersion and symmetry of charge or discharge current. Average of absolute error in open-circuit voltage is about 5% respectively. The results show that it is feasible and accurate to estimate the parameters of Ni-MH battery by using statistical method. Full article

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265 KiB

Open AccessArticle

Probabilistic Design of Wind Turbines

by John D. Sørensen and Henrik S. Toft

Energies 2010, 3(2), 241-257; https://doi.org/10.3390/en3020241 - 23 Feb 2010

Cited by 92 | Viewed by 12583

Abstract

Probabilistic design of wind turbines requires definition of the structural elements to be included in the probabilistic basis: e.g., blades, tower, foundation; identification of important failure modes; careful stochastic modeling of the uncertain parameters; recommendations for target reliability levels and recommendation for consideration [...] Read more.

Probabilistic design of wind turbines requires definition of the structural elements to be included in the probabilistic basis: e.g., blades, tower, foundation; identification of important failure modes; careful stochastic modeling of the uncertain parameters; recommendations for target reliability levels and recommendation for consideration of system aspects. The uncertainties are characterized as aleatoric (physical uncertainty) or epistemic (statistical, measurement and model uncertainties). Methods for uncertainty modeling consistent with methods for estimating the reliability are described. It is described how uncertainties in wind turbine design related to computational models, statistical data from test specimens, results from a few full-scale tests and from prototype wind turbines can be accounted for using the Maximum Likelihood Method and a Bayesian approach. Assessment of the optimal reliability level by cost-benefit optimization is illustrated by an offshore wind turbine example. Uncertainty modeling is illustrated by an example where physical, statistical and model uncertainties are estimated. Full article

(This article belongs to the Special Issue Wind Energy)

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898 KiB

Open AccessArticle

The WRF Model Forecast-Derived Low-Level Wind Shear Climatology over the United States Great Plains

by Brandon Storm and Sukanta Basu

Energies 2010, 3(2), 258-276; https://doi.org/10.3390/en3020258 - 23 Feb 2010

Cited by 56 | Viewed by 13497

Abstract

For wind resource assessment projects, it is common practice to use a power-law relationship (U(z) ~ z^α) and a fixed shear exponent (α = 1=7) to extrapolate the observed wind speed from a low measurement level to high turbine [...] Read more.

For wind resource assessment projects, it is common practice to use a power-law relationship (U(z) ~ z^α) and a fixed shear exponent (α = 1=7) to extrapolate the observed wind speed from a low measurement level to high turbine hub-heights. However, recent studies using tall-tower observations have found that the annual average shear exponents at several locations over the United States Great Plains (USGP) are significantly higher than 1=7. These findings highlight the critical need for detailed spatio-temporal characterizations of wind shear climatology over the USGP, where numerous large wind farms will be constructed in the foreseeable future. In this paper, a new generation numerical weather prediction model—the Weather Research and Forecasting (WRF) model, a fast and relatively inexpensive alternative to time-consuming and costly tall-tower projects, is utilized to determine whether it can reliably estimate the shear exponent and the magnitude of the directional shear at any arbitrary location over the USGP. Our results indicate that the WRF model qualitatively captures several low-level wind shear characteristics. However, there is definitely room for physics parameterization improvements for the WRF model to reliably represent the lower part of the atmospheric boundary layer. Full article

(This article belongs to the Special Issue Wind Energy)

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Review

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230 KiB

Open AccessReview

Recent Advances in Direct Coal Liquefaction

by Hengfu Shui, Zhenyi Cai and Chunbao Xu

Energies 2010, 3(2), 155-170; https://doi.org/10.3390/en3020155 - 27 Jan 2010

Cited by 132 | Viewed by 13718

Abstract

The growing demand for petroleum, accompanied by the declining petroleum reserves and the concerns over energy security, has intensified the interest in direct coal liquefaction (DCL), particularly in countries such as China which is rich in coal resources, but short of petroleum. In [...] Read more.

The growing demand for petroleum, accompanied by the declining petroleum reserves and the concerns over energy security, has intensified the interest in direct coal liquefaction (DCL), particularly in countries such as China which is rich in coal resources, but short of petroleum. In addition to a general introduction on the mechanisms and processes of DCL, this paper overviews some recent advances in DCL technology with respect to the influencing factors for DCL reactions (temperature, solvent, pressure, atmospheres, etc.), the effects of coal pre-treatments for DCL (swelling, thermal treatment, hydrothermal treatment, etc.), as well as recent development in multi-staged DCL processes, DCL catalysts and co-liquefaction of coal with biomass. Full article

(This article belongs to the Special Issue Coal Gasification and Liquefaction)

2318 KiB

Open AccessReview

Spectrally-Selective Photonic Structures for PV Applications

by Marius Peters, Jan Christoph Goldschmidt, Philipp Löper, Bernhard Groß, Johannes Üpping, Frank Dimroth, Ralf B. Wehrspohn and Benedikt Bläsi

Energies 2010, 3(2), 171-193; https://doi.org/10.3390/en3020171 - 27 Jan 2010

Cited by 65 | Viewed by 14288

Abstract

We review several examples of how spectrally-selective photonic structures may be used to improve solar cell systems. Firstly, we introduce different spectrally-selective structures that are based on interference effects. Examples shown include Rugate filter, edge filter and 3D photonic crystals such as artificial [...] Read more.

We review several examples of how spectrally-selective photonic structures may be used to improve solar cell systems. Firstly, we introduce different spectrally-selective structures that are based on interference effects. Examples shown include Rugate filter, edge filter and 3D photonic crystals such as artificial opals. In the second part, we discuss several examples of photovoltaic (PV) concepts that utilize spectral selectivity such as fluorescence collectors, upconversion systems, spectrum splitting concepts and the intermediate reflector concept. The potential of spectrally selective filters in the context of solar cells is discussed. Full article

(This article belongs to the Special Issue Solar Cells)

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1147 KiB

Open AccessReview

Gasification Processes Old and New: A Basic Review of the Major Technologies

by Ronald W. Breault

Energies 2010, 3(2), 216-240; https://doi.org/10.3390/en3020216 - 23 Feb 2010

Cited by 176 | Viewed by 25077

Abstract

This paper has been put together to provide a single source document that not only reviews the historical development of gasification but also compares the process to combustion. It also provides a short discussion on integrated gasification and combined cycle processes. The major [...] Read more.

This paper has been put together to provide a single source document that not only reviews the historical development of gasification but also compares the process to combustion. It also provides a short discussion on integrated gasification and combined cycle processes. The major focus of the paper is to describe the twelve major gasifiers being marketed today. Some of these are already fully developed while others are in various stages of development. The hydrodynamics and kinetics of each are reviewed along with the most likely gas composition from each of the technologies when using a variety of fuels under different conditions from air blown to oxygen blown and atmospheric pressure to several atmospheres. Full article

(This article belongs to the Special Issue Coal Gasification and Liquefaction)

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Energies, Volume 3, Issue 2 (February 2010) – 7 articles , Pages 155-276

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