Energies

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3044 KiB

Open AccessArticle

Wind Integration into Energy Systems with a High Share of Nuclear Power—What Are the Compromises?

by Behnam Zakeri, Samuli Rinne and Sanna Syri

Energies 2015, 8(4), 2493-2527; https://doi.org/10.3390/en8042493 - 31 Mar 2015

Cited by 28 | Viewed by 8536

Towards low-carbon energy systems, there are countries with ongoing plans for expanding their nuclear power capacity, and simultaneously advancing the role of variable renewable energy sources (RES), namely wind and solar energy. This crossroads of capital-intensive, baseload power production and uncontrollable, intermittent RES [...] Read more.

Towards low-carbon energy systems, there are countries with ongoing plans for expanding their nuclear power capacity, and simultaneously advancing the role of variable renewable energy sources (RES), namely wind and solar energy. This crossroads of capital-intensive, baseload power production and uncontrollable, intermittent RES may entail new challenges in the optimal and economic operation of power systems. This study examines this case by hourly analysis of a national-level energy system with the EnergyPLAN modeling tool, coupled with wind integration simulations (including uncertainty) implemented using MATLAB. We evaluate the maximum feasible wind integration under different scenarios for nuclear power plants, energy demand, and the flexibility of energy infrastructure for a real case study (Finland). We propose wind-nuclear compromise charts to envision the impact of any mix of these two technologies on four parameters: total costs, power exchange, carbon emissions, and renewable energy integration. The results suggest that nuclear power constrains the room for maximum uptake of wind energy by a descending parabolic relationship. If nuclear power production exceeds 50% of the total power demand, wind will be unlikely to penetrate in shares over 15% of the respective demand. Moreover, we investigate the role of four flexibility options: demand side management, electrical energy storage, smart electric heating, and large-scale heat pumps (backed with thermal energy storage). Heat pumps (which are in connection with combined heat and power (CHP) and district heating systems) offer the highest efficiency in balancing excess power from variable RES. However, power-to-heat options offer a limited capability for absorbing excess power, as oversupply arises mainly in the periods with relatively low demand for heat. This calls for longer-term energy storage and/or other flexibility options to achieve the planned targets in wind-nuclear scenarios. Full article

(This article belongs to the Special Issue Selected Papers from ECOS 2014 — the 27st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems)

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1101 KiB

Open AccessArticle

Modelling of a Solid Oxide Fuel Cell CHP System Coupled with a Hot Water Storage Tank for a Single Household

by Vincenzo Liso, Yingru Zhao, Wenyuan Yang and Mads Pagh Nielsen

Energies 2015, 8(3), 2211-2229; https://doi.org/10.3390/en8032211 - 20 Mar 2015

Cited by 15 | Viewed by 8090

Abstract

In this paper a solid oxide fuel cell (SOFC) system for cogeneration of heat and power integrated with a stratified heat storage tank is studied. The use of a storage tank with thermal stratification allows one to increase the annual operating hours of [...] Read more.

In this paper a solid oxide fuel cell (SOFC) system for cogeneration of heat and power integrated with a stratified heat storage tank is studied. The use of a storage tank with thermal stratification allows one to increase the annual operating hours of CHP: heat can be produced when the request is low (for instance during the night), taking advantage of thermal stratification to increases the heat recovery performance. A model of the SOFC system is presented to estimate the energy required to meet the average electric energy demand of the residence. Two fuels are considered, namely syngas produced by gasification and natural gas. The tank model considers the temperature gradients over the tank height. The results of the numerical simulation are used to size the SOFC system and storage heat tank to provide energy for a small household using two different fuels. In particular it was shown that in the case of syngas, due to larger system heat output, a larger tank volume was required in order to accumulate unused heat over the night. The detailed description of the tank model will be useful to energy system modelers when sizing hot water tanks. Problem formulation is reported also using a Matlab script. Full article

(This article belongs to the Special Issue Selected Papers from ECOS 2014 — the 27st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems)

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989 KiB

Open AccessArticle

Thermodynamic Rarity and the Loss of Mineral Wealth

by Antonio Valero and Alicia Valero

Energies 2015, 8(2), 821-836; https://doi.org/10.3390/en8020821 - 26 Jan 2015

Cited by 23 | Viewed by 6870

Abstract

The second law of thermodynamics and, specifically, exergy analysis have been traditionally used for the assessment and optimization of energy systems. Nevertheless, as shown in this paper, exergy could also constitute a powerful tool for the evaluation of mineral commodities. That said, new [...] Read more.

The second law of thermodynamics and, specifically, exergy analysis have been traditionally used for the assessment and optimization of energy systems. Nevertheless, as shown in this paper, exergy could also constitute a powerful tool for the evaluation of mineral commodities. That said, new or re-defined exergy-based concepts need to be developed. This paper presents Thanatia as a baseline for evaluating the exergy of any mineral in the crust and opens the door to discuss the “thermodynamic rarity” concept as a basis for exergy analyses for mineral systems. Thermodynamic rarity is understood as the amount of exergy needed to obtain a given mineral from a completely degraded state, denoted as Thanatia. The rarer the mineral, the greater the associated exergy costs. It quantifies value, as it relates to concentration, chemical composition and cohesion, key aspects that determine whether a mine is exploitable. The theory further allows one to quantify the gradual loss of mineral capital on Earth as a consequence of “rarefaction processes” that occur at a mineral’s end-of-life, when a commodity is wasted, and at its beginning-of-life, where mining ore grades decline after extraction. Full article

(This article belongs to the Special Issue Selected Papers from ECOS 2014 — the 27st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems)

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663 KiB

Open AccessArticle

Stochastic Multicriteria Acceptability Analysis for Evaluation of Combined Heat and Power Units

by Haichao Wang, Wenling Jiao, Risto Lahdelma, Chuanzhi Zhu and Pinghua Zou

Energies 2015, 8(1), 59-78; https://doi.org/10.3390/en8010059 - 24 Dec 2014

Cited by 28 | Viewed by 5971

Abstract

Combined heat and power (CHP) is a promising technology that can contribute to energy efficiency and environmental protection. More CHP-based energy systems are planned for the future. This makes the evaluation and selection of CHP systems very important. In this paper, 16 CHP [...] Read more.

Combined heat and power (CHP) is a promising technology that can contribute to energy efficiency and environmental protection. More CHP-based energy systems are planned for the future. This makes the evaluation and selection of CHP systems very important. In this paper, 16 CHP units representing different technologies are taken into account for multicriteria evaluation with respect to the end users’ requirements. These CHP technologies cover a wide range of power outputs and fuel types. They are evaluated from the energy, economy and environment (3E) points of view, specifically including the criteria of efficiency, investment cost, electricity cost, heat cost, CO₂ production and footprint. Uncertainties and imprecision are common both in criteria measurements and weights, therefore the stochastic multicriteria acceptability analysis (SMAA) model is used in aiding this decision making problem. These uncertainties are treated better using a probability distribution function and Monte Carlo simulation in the model. Moreover, the idea of “feasible weight space (FWS)” which represents the union of all preference information from decision makers (DMs) is proposed. A complementary judgment matrix (CJM) is introduced to determine the FWS. It can be found that the idea of FWS plus CJM is well compatible with SMAA and thus make the evaluation reliable. Full article

(This article belongs to the Special Issue Selected Papers from ECOS 2014 — the 27st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems)

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1288 KiB

Open AccessArticle

Multi-Objective Combinatorial Optimization of Trigeneration Plants Based on Metaheuristics

by Mirko M. Stojiljković, Mladen M. Stojiljković and Bratislav D. Blagojević

Energies 2014, 7(12), 8554-8581; https://doi.org/10.3390/en7128554 - 22 Dec 2014

Cited by 23 | Viewed by 5618

Abstract

In this paper, a methodology for multi-objective optimization of trigeneration plants is presented. It is primarily applicable to the systems for buildings’ energy supply characterized by high load variations on daily, weekly and annual bases, as well as the components applicable for flexible [...] Read more.

In this paper, a methodology for multi-objective optimization of trigeneration plants is presented. It is primarily applicable to the systems for buildings’ energy supply characterized by high load variations on daily, weekly and annual bases, as well as the components applicable for flexible operation. The idea is that this approach should enable high accuracy and flexibility in mathematical modeling, while remaining efficient enough. The optimization problem is structurally decomposed into two new problems. The main problem of synthesis and design optimization is combinatorial and solved with different metaheuristic methods. For each examined combination of the synthesis and design variables, when calculating the values of the objective functions, the inner, mixed integer linear programming operation optimization problem is solved with the branch-and-cut method. The applicability of the exploited metaheuristic methods is demonstrated. This approach is compared with the alternative, superstructure-based approach. The potential for combining them is also examined. The methodology is applied for multi-objective optimization of a trigeneration plant that could be used for the energy supply of a real residential settlement in Niš, Serbia. Here, two objectives are considered: annual total costs and primary energy consumption. Results are obtained in the form of a Pareto chart using the epsilon-constraint method. Full article

(This article belongs to the Special Issue Selected Papers from ECOS 2014 — the 27st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems)

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1746 KiB

Open AccessArticle

Comparative Analysis of Power Plant Options for Enhanced Geothermal Systems (EGS)

by Mengying Li and Noam Lior

Energies 2014, 7(12), 8427-8445; https://doi.org/10.3390/en7128427 - 17 Dec 2014

Cited by 26 | Viewed by 8679

Abstract

Enhanced geothermal systems (EGS) extract heat from underground hot dry rock (HDR) by first fracturing the HDR and then circulating a geofluid (typically water) into it and bringing the heated geofluid to a power plant to generate electricity. This study focuses on analysis, [...] Read more.

Enhanced geothermal systems (EGS) extract heat from underground hot dry rock (HDR) by first fracturing the HDR and then circulating a geofluid (typically water) into it and bringing the heated geofluid to a power plant to generate electricity. This study focuses on analysis, examination, and comparison of leading geothermal power plant configurations with a geofluid temperature from 200 to 800 °C, and also analyzes the embodied energy of EGS surface power plants. The power generation analysis is focused on flash type cycles for using subcritical geofluid (<374 °C) and expansion type cycles for using supercritical geofluid (>374 °C). Key findings of this study include: (i) double-flash plants have 24.3%–29.0% higher geofluid effectiveness than single-flash ones, and 3%–10% lower specific embodied energy; (ii) the expansion type plants have geofluid effectiveness > 750 kJ/kg, significantly higher than flash type plants (geofluid effectiveness < 300 kJ/kg) and the specific embodied energy is lower; (iii) to increase the turbine outlet vapor fraction from 0.75 to 0.90, we include superheating by geofluid but that reduces the geofluid effectiveness by 28.3%; (iv) for geofluid temperatures above 650 °C, double-expansion plants have a 2% higher geofluid effectiveness and 5%–8% lower specific embodied energy than single-expansion ones. Full article

(This article belongs to the Special Issue Selected Papers from ECOS 2014 — the 27st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems)

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724 KiB

Open AccessArticle

A Polygeneration System Based on Multi-Input Chemical Looping Combustion

by Xiaosong Zhang, Sheng Li and Hongguang Jin

Energies 2014, 7(11), 7166-7177; https://doi.org/10.3390/en7117166 - 06 Nov 2014

Cited by 12 | Viewed by 6282

Abstract

This paper proposes a polygeneration system based on a multi-input chemical looping combustion system, which generates methanol and electricity, through the use of natural gas and coal. In this system, the chemical looping hydrogen (CLH) production system and the coal-based methanol production system [...] Read more.

This paper proposes a polygeneration system based on a multi-input chemical looping combustion system, which generates methanol and electricity, through the use of natural gas and coal. In this system, the chemical looping hydrogen (CLH) production system and the coal-based methanol production system are integrated. A high quality fuel, natural gas, is used to improve the conversion ratio of coal. The Gibbs energy of the two kinds of fuels is fully used. Benefitting from the chemical looping process, 27% CO₂ can be captured without energy penalty. With the same outputs of methanol and electricity, the energy savings ratio of the new system is about 12%. Based on the exergy analyses, it is disclosed that the integration of synthetic utilization of natural gas and coal plays a significant role in reducing the exergy destruction of the new system. The promising results obtained in this paper may lead to a clean coal technology that will utilize natural gas and coal more efficiently and economically. Full article

(This article belongs to the Special Issue Selected Papers from ECOS 2014 — the 27st International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems)

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