Energies2014, 7(9), 5717-5739; doi:10.3390/en7095717 - published 1 September 2014 Show/Hide Abstract
Abstract: Thermodynamics studies the transformations of energy occurring in open systems. Living systems, with particular reference to cells, are complex systems in which energy transformations occur. Thermo-electro-chemical processes and transports occur across their border, the cells membranes. These processes take place with important differences between healthy and diseased states. In particular, different thermal and biochemical behaviours can be highlighted between these two states and they can be related to the energy transformations inside the living systems, in particular the metabolic behaviour. Moreover, living systems waste heat. This heat is the consequence of the internal irreversibility. Irreversibility is effectively studied by using the Gouy-Stodola theorem. Consequently, this approach can be introduced in the analysis of the states of living systems, in order to obtain a unifying approach to study them. Indeed, this approach allows us to consider living systems as black boxes and analyze only the inflows and outflows and their changes in relation to the modification of the environment, so information on the systems can be obtained by analyzing their behaviour in relation to the modification of external perturbations. This paper presents a review of the recent results obtained in the thermodynamics analysis of cell systems.
Energies2014, 7(9), 5701-5716; doi:10.3390/en7095701 - published 1 September 2014 Show/Hide Abstract
Abstract: Small-scale digesters, similar to popular Chinese designs, have the potential to address the energy needs of smaller dairy farmers in temperate U.S. climates. To assess this potential, a 1.14 m3 (300 gallon) modified fixed-dome digester was installed and operated, at variable temperatures (5.3 to 27.9 °C) typical of the Midwestern United States, from March 2010 to March 2011 (363 days). Temperature, gas production, and other variables were recorded. The system was fed with dilute dairy manure with 6% volatile solids (VS) and an organic loading rate (OLR) ranging from 0.83 to 2.43 kg volatile solids (VS)/m3/day. The system was loaded with no interruption and exhibited no signs of inhibition from July 2010 to mid-November 2010 (129 days). During this period the digester temperature was over 20 °C with an average daily biogas production of 842 ± 69 L/day, a methane yield of 0.168 m3/kg VS added, and a Volatile Solids reduction of 36%. After the temperature dropped below 20 °C, the digester showed signs of inhibition and soured. These findings suggest that an ambient temperature, modified fixed dome digester could operate without temperature inhibition for approximately six months (169 days) a year in a temperate climate when digester temperatures exceed 20 °C. However, during colder months the digester temperature must maintained above 20 °C for viable gas production year round.
Energies2014, 7(9), 5675-5700; doi:10.3390/en7095675 - published 28 August 2014 Show/Hide Abstract
Abstract: In this work, a novel acausal and reconfigurable battery pack model is presented. The model structure adopted for the battery cell is based on an equivalent circuit representation. The circuit elements are modified to take account of both hysteresis and diffusion limitation. The latter is known to be a nonlinear function of large operating currents or long operating times. It is shown that the integration of a current dependent time constant within the cell model better emulates the solid diffusional dynamics of lithium intercalation into the active material under large electrical loads. The advantages of an acausal modeling approach, when scaling-up individual cell models into a complete battery system are also presented. Particular consideration is given to emulating the impact of cell to cell variations on pack performance. Using statistical analysis of battery tests, cell model parameter variations are characterized and quantified. The cell and scaled-up pack model are parameterized for a number of commercially available cell formats, energy capacities and chemistries. The new models are validated using transient, real-world, electrical data measured from an electric vehicle (EV) operating within an urban environment.
Energies2014, 7(9), 5647-5674; doi:10.3390/en7095647 - published 28 August 2014 Show/Hide Abstract
Abstract: Intermediate temperature-solid oxide fuel cell (IT-SOFC) Ni-(ZrO2)x(Y2O3)1−x (Ni-YSZ) anodes formed by two layers, with different thicknesses and morphologies, offer the possibility of obtaining adequate electrochemical performance coupled to satisfactory mechanical properties. We investigate bi-layered Ni-YSZ anodes from a modeling point of view. The model includes reaction kinetics (Butler-Volmer equation), mass transport (Dusty-Gas model), and charge transport (Ohm’s law), and allows to gain an insight into the distribution of the electrochemical reaction within the electrode. Additionally, the model allows to evaluate a reciprocal overall electrode resistance 1/Rp ≈ 6 S·cm−2 for a bi-layer electrode formed by a 10 µm thick active layer (AL) composed of 0.25 µm radius Ni and YSZ particles (34% vol. Ni), coupled to a 700 µm thick support layer (SL) formed by 0.5 µm radius Ni and YSZ particles (50% vol. Ni), and operated at a temperature of 1023 K. Simulation results compare satisfactorily to literature experimental data. The model allows to investigate, in detail, the effect of morphological and geometric parameters on the various sources of losses, which is the first step for an optimized electrode design.
Energies2014, 7(9), 5624-5646; doi:10.3390/en7095624 - published 27 August 2014 Show/Hide Abstract
Abstract: This paper provides a model-free approach based on the Multi-Resolution Simultaneous Perturbation Stochastic Approximation (MR-SPSA) for maximizing power production of wind farms. The main advantage is that the method based on MR-SPSA can achieve fast controller tuning without any plant model by exploiting the information of the wind farm configuration such as turbines location and wind direction. In order to simulate the performance of the model-free scheme, a wind farm model with dynamic characterization of wake interaction between turbines is used and then the proposed method is applied to the Horns Rev wind farm. Simulation results illustrate that the method based on MR-SPSA achieves the maximum total power production with faster convergence compared with other existing model-free methods.
Energies2014, 7(9), 5601-5623; doi:10.3390/en7095601 - published 27 August 2014 Show/Hide Abstract
Abstract: Policymakers are seeking a transformation of the energy system driven by concerns about climate change, energy security and affordability. At the same time, emerging developments in underpinning science and engineering are opening up new possibilities across the whole technology spectrum covering renewables and other supply side technologies, energy demand and energy infrastructure. This paper reviews both the “policy pull” for energy innovation activities and the “science and technology push”. It explores the expectations of a variety of organisations in both the public and private sector regarding these pressures and possibilities by assessing various scenarios and outlook exercises that have been published since 2013. It reveals a wide range of beliefs about the future development of the energy system. The paper then moves on to analyse private sector expenditure on energy research and development (R&D) and public sector budgets for energy R&D and demonstration (RD&D). This analysis demonstrates significant divergences in patterns of innovation between the private and public sectors and leads to the hypothesis that the private sector is, broadly, taking measures to reinforce the existing energy paradigm while the public sector is focusing on new energy technologies that support wider policy objectives. This pattern is consistent with past technological transitions, with innovation efforts that would transform the energy system being counteracted by countervailing efforts that reinforce the existing fossil fuel-based paradigm.