Life cycle sustainability assessment of electricity options for the UK

The UK electricity mix will change significantly in the future. This provides an opportunity to consider the full life cycle sustainability of the options currently considered as most suitable for the UK: gas, nuclear, offshore wind and photovoltaics (PV). In an attempt to identify the most sustainable options and inform policy, this paper applies a sustainability assessment framework developed previously by the authors to compare these electricity options. To put discussion in context, coal is also considered as a significant contributor to the current electricity supply. Each option is assessed and compared in terms of its economic, environmental and social implications, using a range of sustainability indicators. The results show that no one technology is superior and that certain trade‐offs must be made. For example, nuclear and offshore wind power have the lowest life cycle environmental impacts, except for freshwater ecotoxicity for which gas is the best option; coal and gas are the cheapest options (£74 and 66/MWh, respectively, at 10% discount), but both have high global warming potential (1072 and 379 g CO₂ eq./kWh); PV has relatively low global warming potential (88 g CO₂ eq./kWh) but high cost (£302/MWh), as well as high ozone layer and resource depletion. Nuclear, wind and PV increase some aspects of energy security: in the case of nuclear, this is due to inherent fuel storage capabilities (energy density 290 million times that of natural gas), whereas wind and PV decrease fossil fuel import requirements by up to 0.2 toe/MWh. However, all three options require additional installed capacity for grid management. Nuclear also poses complex risk and intergenerational questions such as the creation of 10.16 m³/TWh of nuclear waste for long‐term geological storage. Copyright © 2012 John Wiley & Sons, Ltd.     

光伏发电系统高效逆变器的研制

太阳能作为一种取之不尽、用之不竭的环保能源 ,已成为人们的共识 ,在我国其研究被列入高科技领域。此类系统结构简单、成本低廉 ,特别是为边远贫困地区、解决医疗、电视差转等远离电源地方使用 ,带来方便     

Retail electricity tariff and mechanism design to incentivize distributed renewable generation

This paper examines the question of how to incentivize the adoption and use of renewable energy resources, with particular attention on distributed renewable energy (DRE). Prior experience suggests that price and quantity-based programs, such as feed-in tariffs, provide more efficient renewable adoption and use and lower program costs than programs that set quantity targets only. We also examine some cost-allocation issues raised by the use of DRE systems and fixed time-invariant retail pricing. This combination can result in customers with DRE systems paying a disproportionately small portion of system capacity costs. We suggest two retail-pricing schemes, real-time pricing and a two-part tariff with demand charges, to address these issues.     

Biofilm formation and electricity generation of a microbial fuel cell started up under different external resistances

To investigate the effects of external resistance on the biofilm formation and electricity generation of microbial fuel cells (MFCs), active biomass, the content of extracellular polymeric substances (EPS) and the morphology and structure of the biofilms developed at 10, 50, 250 and 1000 Ω are characterized. It is demonstrated that the structure of biofilm plays a crucial role in the maximum power density and sustainable current generation of MFCs. The results show that the maximum power density of the MFCs increases from 0.93 ± 0.02 W m⁻² to 2.61 ± 0.18 W m⁻² when the external resistance decreases from 1000 to 50 Ω. However, on further decreasing the external resistance to 10 Ω, the maximum power density decreased to 1.25 ± 0.01 W m⁻² because of a less active biomass and higher EPS content in the biofilm. Additionally, the 10 Ω MFC shows a highest maximum sustainable current of 8.49 ± 0.19 A m⁻². This result can be attributed to the existence of void spaces beneficial for proton and buffer transport within the anode biofilm, which maintains a suitable microenvironment for electrochemically active microorganisms.     

Potential of solar electricity generation in the European Union member states and candidate countries

During the years 2001–2005, a European solar radiation database was developed using a solar radiation model and climatic data integrated within the Photovoltaic Geographic Information System (PVGIS). The database, with a resolution of 1 km × 1 km, consists of monthly and yearly averages of global irradiation and related climatic parameters, representing the period 1981–1990. The database has been used to analyse regional and national differences of solar energy resource and to assess the photovoltaic (PV) potential in the 25 European Union member states and 5 candidate countries. The calculation of electricity generation potential by contemporary PV technology is a basic step in analysing scenarios for the future energy supply and for a rational implementation of legal and financial frameworks to support the developing industrial production of PV. Three aspects are explored within this paper: (1) the expected average annual electricity generation of a ‘standard’ 1 kW_p grid-connected PV system; (2) the theoretical potential of PV electricity generation; (3) determination of required installed capacity for each country to supply 1% of the national electricity consumption from PV. The analysis shows that PV can already provide a significant contribution to a mixed renewable energy portfolio in the present and future European Union.     

Transforming the electricity generation of the Berlin–Brandenburg region,Germany

We present possible steps for Germany's capital region for a pathway towards high-level renewable energy contributions. To this end, we give an overview of the current energy policy and status of electricity generation and demand of two federal states: the capital city Berlin and the surrounding state of Brandenburg. In a second step we present alternative, feasible scenarios with focus on the years 2020 and 2030. All scenarios were numerically evaluated in hourly time steps using a cost optimisation approach. The required installed capacities in an 80% renewables scenario in the year 2020 consist of 8.8 GW wind energy, 4.8 GW photovoltaics, 0.4 GW_el bioenergy, 0.6 GW_el methanation and a gas storage capacity of 180 GWh_th. In order to meet a renewable electricity share of 100% in 2030, approximately 9.5 GW wind energy, 10.2 GW photovoltaics and 0.4 GW_el bioenergy will be needed, complemented by a methanation capacity of about 1.5 GW_el and gas storage of about 530 GWh_th. In 2030, an additional 11 GWh_el of battery storage capacity will be required. Approximately 3 GW of thermal gas power plants will be necessary to cover the residual load in both scenarios. Furthermore, we studied the transmission capacities of extra-high voltage transmission lines in a second simulation and found them to be sufficient for the energy distribution within the investigated region.     

The geothermal system of Ischia Island (southern Italy): Critical review and sustainability analysis of geothermal resource for electricity generation

In this paper we analyze the main available data related to the geothermal system of Ischia Island, starting from the first geothermal exploration in 1939. Our aim is to define a conceptual model of the geothermal reservoir, according to geological, geochemical, geophysical and stratigraphic data. In recent times, the interest on geothermal exploitation for electricity generation in Italy is rapidly increasing and the Ischia Island is one of the main targets for future geothermal exploitation. Nowadays, one of the main economic resources of the island is the tourism, mainly driven by the famous thermal springs; so, it is crucial to study the possible interaction between geothermal exploitation and thermal spring activities. To this aim, we also analyze the possible disturbance on temperature and pressure in the shallow geothermal reservoir, due to the heat withdrawal for electric production related to small power plant size (1–5 MWe). Such analysis has been performed by using numerical simulations based on a well known thermofluid-dynamical code (TOUGH2^®). Obtained results show that such geothermal exploitation generates a perturbation of temperature and pressure field which, however, is confined in a small volume around the well. At shallow level (0–100 m) the exploitation does not produce any appreciable disturbance, and can be made compatible with thermal spring exploitation. Moreover, such results are crucial both for the evaluation of volcanological processes in the island and for the general assessment of geothermal resource sustainability.     

Microalgae-microbial fuel cell (mMFC): an integrated process for electricity generation,wastewater treatment,CO2 sequestration and biomass production

The world today is facing a crisis of energy and environmental pollution. Conventional or photosynthetic microbial fuel cell (MFC) is an advanced “green” energy technology that utilizes living microorganisms to convert biochemical or light energy into electricity through metabolic reaction and photosynthesis, offering a potential solution for the above-mentioned crisis. Further incorporating microalgae into MFC, microalgae-microbial fuel cell (mMFC) integrates electricity generation, wastewater treatment, CO₂ sequestration and biomass production in a single, self-sustainable technology. This review first describes the fundamentals of MFC as well as its applications in treating domestic, municipal, agricultural and industrial wastewaters. Then, mMFC-based configurations and applications with its advantages compared with MFC are explained in particular, together with the parameters governing its performance. Lastly, the opportunities and challenges involved in the development of mMFCs are also explored.     

Domestic integration of micro-renewable electricity generation in Ireland – The current status and economic reality

The utilisation of renewable energy resources for power generation is extremely important for Ireland due to the lack of indigenous fossil fuel resources. A micro-wind turbine is by far the most commonly used grid-connected micro-renewable electricity generation system for domestic applications in Ireland, followed by solar PV. Unfortunately, neither a single micro-wind turbine nor a single solar PV system can provide a continuous power supply due to variations in weather and climate conditions. The coupling of these two systems however can improve the power supply reliability by using the complementary characteristics of wind and solar energy. In this paper, a micro-renewable electricity-generation-system integration technique, tailored for applications in Ireland but generally applicable, is presented. Net present value is the parameter used to identify the optimal system. The optimal system can be a mono system, formed from a single micro-wind turbine or a single solar PV system, or a hybrid system formed from a combination of both. A renewable energy requirement is a constraint used in the integration to eliminate systems that cannot provide sufficient energy from renewable energy resources. The integration technique is applied to find the optimal system, under current Irish conditions, that can be formed from six sample micro-wind turbines and/or solar PV systems assembled from three sample solar PV modules. The analyses show that, with a 50% renewable energy requirement, the optimal system is a mono system containing a 2.4 kW micro-wind turbine; however, critically, the system is not economically viable. Four parameter studies assessing the effect of household electrical load, imported electricity price, exported electricity tariff and wind speed have also been conducted. From these studies it is seen that the most effective way to improve the financial performance of all systems is to offer a higher exported electricity tariff; installing a mono/hybrid system containing a micro-wind turbine in a location with a good wind resource can also have a significant effect.     

Using multi-criteria and thermodynamic analysis to optimize process parameters for mixed reforming of biogas

Syngas is a gas mixture that can be obtained from a variety of raw materials and used as source of hydrogen. Biogas is an interesting raw material from which to produce syngas via thermo-catalytic reforming because it is abundant, can be obtained from low-cost feedstock, and is potentially carbon-neutral. However, difficulties arise because biogas composition changes from source to source, the reforming process can be quite energy-intensive and there is associated catalyst deactivation through carbon deposition. Mixed reforming of biogas with steam and/or air shows benefits in terms of carbon deposition and energy requirements, but the reaction network is complicated and finding the optimal operating conditions is not trivial. Although several analytical techniques have been used in the literature to find the optimal process conditions, a direct comparison is difficult due to the different criteria and/or boundaries considered. This paper aims to develop a novel and comprehensive methodology for identifying the optimal thermodynamic operating conditions (temperature and feed ratios) for mixed reforming of biogas with air and steam, based on equilibrium data manipulated via two multi-criteria decision making (MCDM) techniques in series, namely the entropy and the TOPSIS methods. The optimal scenario is when biogas made of 50–60% CH₄ in CO₂ is reacted in the reforming reactor at CH₄/CO₂/O₂/H₂O = 1/1–0.67/0–0.1/3–2.4 and 790-735 °C, resulting in a product stream composed of 66–65% H₂, 0.8–1% CO and 33-28% CO₂ on a dry basis after the water-gas shift section. At these conditions the hydrogen yield and the conversion of methane in the biogas can be simultaneously maximized, while the yield of solid carbon and the net energy requirement of the overall process can be minimized. In conjunction with the numerical results, the main outcome of this paper is the development of a novel method based on MCDM techniques for the optimization of the operating conditions in a network of reactions.     

Optimization of fuel cell system operating conditions for fuel cell vehicles

Proton exchange membrane fuel cell (PEMFC) technology for use in fuel cell vehicles and other applications has been intensively developed in recent decades. Besides the fuel cell stack, air and fuel control and thermal and water management are major challenges in the development of the fuel cell for vehicle applications. The air supply system can have a major impact on overall system efficiency. In this paper a fuel cell system model for optimizing system operating conditions was developed which includes the transient dynamics of the air system with varying back pressure. Compared to the conventional fixed back pressure operation, the optimal operation discussed in this paper can achieve higher system efficiency over the full load range. Finally, the model is applied as part of a dynamic forward-looking vehicle model of a load-following direct hydrogen fuel cell vehicle to explore the energy economy optimization potential of fuel cell vehicles.     

Using AHP and binary integer programming to optimize the initial distribution of hydrogen infrastructures in Andalusia

The use of vehicles powered by hydrogen from renewable sources can be a viable alternative for Andalusia, given its accessibility to renewable energies and the problems of energy dependence and pollution resulting from the current energy model. However, the introduction of this type of technology requires an initial infrastructure that solves the classical chicken and egg problem. Given that hydrogen fueling infrastructure will require significant initial capital investment, it is reasonable to assume that a possible strategy of introduction could be the establishment of a station network that is sparse to avoid redundancy and therefore minimize costs. In this paper, we utilize Analytic Hierarchy Process to rank, on the basis of several supply, demand and environmental criteria, the more than 750 municipalities of Andalusia according to their suitability for the establishment of hydrogen fueling stations. Subsequently, we incorporate these results into an optimization problem to achieve optimal planning of the number and location of hydrogen fueling stations to provide coverage for the region.     

Turkish aggregate electricity demand: An outlook to 2020

This paper investigates the relationship between Turkish aggregate electricity consumption, GDP and electricity prices in order to forecast future Turkish aggregate electricity demand. To achieve this, an aggregate electricity demand function for Turkey is estimated by applying the structural time series technique to annual data over the period 1960 to 2008. The results suggest that GDP, electricity prices and a UEDT (Underlying Energy Demand Trend) are all important drivers of Turkish electricity demand. The estimated income and price elasticities are found to be 0.17 and −0.11 respectively with the estimated UEDT found to be generally upward sloping (electricity using) but at a generally decreasing rate. Based on the estimated equation, and different forecast assumptions, it is predicted that Turkish aggregate electricity demand will be somewhere between 259 TWh and 368 TWh in 2020.     

From waste to electricity through integrated plasma gasification/fuel cell (IPGFC) system

The waste management is become a very crucial issue in many countries, due to the ever- increasing amount of waste material, both domiciliary and industrial, generated.The main strategies for the waste management are the increase of material recovery (MR), which can reduce the landfill disposal, the improvement of energy recovery (ER) from waste and the minimization of the environmental impact.These two last objectives can be achieved by introducing a novel technology for waste treatment based on a plasma torch gasification system integrated with a high efficiency energy conversion system, such as combined cycle power plant or high-temperature fuel cells.This work aims to evaluate the performance of an Integrated Plasma Gasification/Fuel Cell system (IPGFC) in order to establish its energy suitability and environmental feature.The performance analysis of this system has been carried out by using a numerical model properly defined and implemented in Aspen Plus™ code environment. The model is based on the combination of a thermochemical model of the plasma gasification unit, previously developed by the authors (the so-called EquiPlasmaJet model), and an electrochemical model for the SOFC fuel cell stack simulation.The EPJ model has been employed to predict the syngas composition and the energy balance of an RDF (Refuse Derived Fuel) plasma arc gasifier (that uses air as plasma gas), whereas the SOFC electrochemical model, that is a system-level model, has allowed to forecast the stack performance in terms of electrical power and efficiency.Results point out that the IPGFC system is able to produce a net power of 4.2 MW per kg of RDF with an electric efficiency of about 33%. This efficiency is high in comparison with those reached by conventional technologies based on RDF incineration (20%).     

Optimization of molten carbonate fuel cell (MCFC) and homogeneous charge compression ignition (HCCI) engine hybrid system for distributed power generation

In a previous study, a new hybrid system of molten carbonate fuel cell (MCFC) and homogeneous charge compression ignition (HCCI) engine was developed, where the HCCI engine replaces the catalytic burner and produces additional power by using the left-over heating values from the fuel cell stack. In the present study, to reduce the additional cost and footprint of the engine system in a hybrid configuration, the possibility of engine downsizing is investigated by using two strategies, i.e. the use of a turbocharger and the use of high geometric compression ratio for the engine design, both of which are to increase the density of the intake charge and thus the volumetric efficiency of the engine. Combining these two strategies, we suggest a new engine design with ∼60% of displacement volume of the original engine. In addition, operating strategies are developed to run the new hybrid system under part load conditions. It is successfully demonstrated that the system can operate down to 65% of the power level of the design point, while the system efficiency remains almost unchanged near 63%.     

A multivariate framework to study spatio‐temporal dependency of electricity load and wind power

With massive wind power integration, the spatial distribution of electricity load centers and wind power plants make it plausible to study the inter‐spatial dependence and temporal correlation for the effective working of the power system. In this paper, a novel multivariate framework is developed to study the spatio‐temporal dependency using vine copula. Hourly resolution of load and wind power data obtained from a US regional transmission operator spanning 3 years and spatially distributed in 19 load and two wind power zones are considered in this study. Data collection, in terms of dimension, tends to increase in future, and to tackle this high‐dimensional data, a reproducible sampling algorithm using vine copula is developed. The sampling algorithm employs k ‐means clustering along with singular value decomposition technique to ease the computational burden. Selection of appropriate clustering technique and copula family is realized by the goodness of clustering and goodness of fit tests. The paper concludes with a discussion on the importance of spatio‐temporal modeling of load and wind power and the advantage of the proposed multivariate sampling algorithm using vine copula.     

A deterministic approach in the optimization of a nuclear power system from fuel resource point of view

A CANDU-CANDU(Th/Pu)-LMFBR(PuO₂) nuclear power system is considered, on a 65 year time horizon. The system is characterized by a number of independent variables and integral parameters that depend on them. In performing the optimization of the system we outline first of all the following components of the independent variable vector:(1) DT₁—the delay time in reprocessing Pu from CANDUs, (2) DT₂—the delay time in reprocessing Pu partially consumed in the CANDU (Th/Pu)s, (3) b₃—the fuel burn-up in CANDU (Th/Pu)s, (4) q—the control parameter of the total power growth. The components of the independent variable vector, also called decision variables, are subjected to some direct restrictions. In this paper it is admitted that, from the multitude of integral parameters of the system, the annual electric energy has the greatest importance in the case of a non-econometric approach. This is the objective function of the system optimization problem and depends on the independent variable vector or decision vector. In addition, from the fuel resource point of view, the Unat and Pu cumulative consumptions have a special importance. These are called restriction functions because one looks for the decision vector subject to some direct restrictions (on components) so that, some restrictions on the consumption functions being satisfied, a maximum of the annual electric energy produced in the system at the end of the considered interval is obtained. In this way, the problem has a clear structure of an optimization model of non-linear programming type and it can be treated in specific way for a given field of the above restriction function values. As a result, a set of optimal solutions for development of a CANDU-CANDU(Th/Pu)-LMFBR(PuO₂) system, of interest from a nuclear energy policy point of view, is obtained.     

A new analytical approach to evaluate and optimize the performance of an irreversible solid oxide fuel cell-gas turbine hybrid system

Based on the current models of the solid oxide fuel cell and gas turbine, a generic model of a solid oxide fuel cell-gas turbine hybrid system is established, in which the multiple irreversibilities existing in real hybrid systems are taken into account. Expressions for the efficiencies and power outputs of both the subsystems and the hybrid system are analytically derived. The general performance characteristics of the hybrid system are revealed and the optimum criteria of the main performance parameters are determined. The effects of some key irreversibilities existing in the fuel cell and gas turbine on the performance of the hybrid systems are discussed in detail. The results obtained may be directly used to discuss some special cases of the hybrid system.     

Cost/benefit analysis of transmission grid expansion to enable further integration of renewable electricity generation in Austria

This paper elaborates on the costs and benefits of expanding the Austrian transmission system and the implementation of innovative grid-impacting technologies (e.g. flexible AC transmission systems (FACTS), dynamic line rating (DLR)) to support further integration of renewable energy sources for electricity generation (RES-E). Therefore, a fundamental market model has been developed - respecting DC load flows - and applied for analysing different future scenarios, notably for the time horizon 2020, 2030 and 2050. Up to 2020 and 2030, special focus is put on the finalisation of the so-called “380 kV-level transmission ring” in Austria to enable enhanced RES-E integration. The results confirm that transmission power line expansion in the states of Salzburg and Carinthia is important to connect imports from Germany with pumped hydro storage capacities, on the one hand, and the wind farms in the east with the pumped hydro storages in the western part of Austria, on the other hand. For 2050, the results indicate that the implementation of FACTS and DLR can reduce RES-E curtailment significantly.