Dynamic simulation of hydrogen-based zero energy buildings with hydrogen energy storage for various climate conditions

Solar energy systems are an effective way to meet the needs of zone heating, cooling, electricity, and domestic hot water. However, to reach sustainability, and energy storage unit should be considered for installation. In this study, two combined cooling, heating and power (CCHP) systems are simulated and studied using TRNSYS software; both using natural gas engine generators and photovoltaics as prime movers and a hydrogen fuel cell/electrolyzer storage unit, one with absorption chiller and another with compression chiller cooling. For the study, a residential building is modeled for three major populated climate zones of the United States of America, namely, Hot-humid, mixed-humid and cold using DesignBuilder and EnergyPlus software. The energy demand for its HVAC operation and domestic electricity is obtained and used for system simulation in TRNSYS software. Due to choosing actual equipment for the CCHP arrangement, precise economic and environmental models are designed to further evaluate the possibility of execution of the system. The results show that absorption chiller-equipped CCHP has better performance both environmentally and economically. In addition, the outcome shows that the suggested systems show less favorability to be utilized in hot humid climate zones.     

Primary energy and economic analysis of combined heating, cooling and power systems

In this paper, the primary energy consumption and the economic viability of a combined heating, cooling and power (CHCP) system are derived. The focus is on small-scale applications in the range below 100 kW_H/70 kW_C/58 kW_el. CHCP is discussed between the boundaries of combined heating and power (CHP) and combined cooling and power (CCP) using a lumped parameter model. The method used is independent of a specific load profile for a building; only the full-load hours for heating and cooling are needed to predict the economic viability. German data is used for the example. A sensitivity analysis reveals the parameters with the highest impact on the primary energy consumption and the energy costs. The primary energy factors, the energy prices and the electric efficiency of the CHP are the dominating parameters. Increasing electricity prices favour the introduction of CHP and CHCP systems whereas increasing gas prices inhibit it. The energy cost analysis is extended to an economic analysis taking maintenance and investment costs into account. One result of this paper is a simple diagram which shows how many annual operation hours are needed for heating and cooling with CHCP to be more economical than a reference system.     

CO2-emissions reduction potential and costs of a decentralized energy system for providing electricity,cooling and heating in an office-building in Tokyo

Decentralized energy systems are thought to have great potential for supplying electricity, cooling, and heating to buildings. A decentralized system combining a solid oxide fuel cell (SOFC) with an absorption chiller-heater (ACH) is proposed. The CO₂-emissions and costs of using different configurations of this SOFC-based system to provide an office building in Tokyo with electricity, cooling and heating are calculated by using an SOFC-model and an absorption-chiller model together with data for cooling and heating loads measured at an office building in downtown Tokyo. The results are compared with the CO₂-emissions and costs of a conventional system that obtains the base electricity requirements as well as electricity for an electric chiller–heater system from the central power grid. The fully decentralized SOFC-based energy system could result in a potential CO₂ reduction of over 30% at an estimated cost increase of about 70% compared to the conventional system.     

Evaluation of energy saving of CCHP systems using an active energy storage regulation method

节能性是评价冷热电联供系统的重要指标之一.阐述了分布式冷热电联供系统中主动储能调控方法的原理.基于用户侧负荷特性和燃气轮机变工况运行规律的分析,采用相对节能率作为评价联供系统节能性的指标,以夏季冷电并供时的饭店类型建筑典型负荷为案例,探讨主动储能调控在分布式冷热电联供系统中的节能效果及影响因素.结果表明,与常规分产系统相比,无主动储能的相对节能率为11.8%,主动储能调控的联供系统相对节能率为21.6%.相对节能率的大小受到电压缩制冷系统性能系数和用户负荷冷电比的影响,电压缩制冷系统性能系数越高则联供系统相对节能率越低,用户负荷冷电比越高,联供系统相对节能率越高.     

A comprehensive energy solution for households employing a micro combined cooling,heating and power generation system

In recent years, micro combined cooling, heating and power generation (mCCHP) systems have attracted much attention in the energy demand side sector. The input energy of a mCCHP system is natural gas, while the outputs include heating, cooling and electricity energy. The mCCHP system is deemed as a possible solution for households with multiple energy demands. Given this background, a mCCHP based comprehensive energy solution for households is proposed in this paper. First, the mathematical model of a home energy hub (HEH) is presented to describe the inputs, outputs, conversion and consumption process of multiple energies in households. Then, electrical loads and thermal demands are classified and modeled in detail, and the coordination and complementation between electricity and natural gas are studied. Afterwards, the concept of thermal comfort is introduced and a robust optimization model for HEH is developed considering electricity price uncertainties. Finally, a household using a mCCHP as the energy conversion device is studied. The simulation results show that the comprehensive energy solution proposed in this work can realize multiple kinds of energy supplies for households with the minimized total energy cost.     

Multiple effects of energy storage units on combined cooling,heating and power (CCHP) systems

Albeit numerous studies discussing manifold issues of combined cooling, heating and power (CCHP) systems, there is still lack of theoretical studies indicating to what extent the energy mismatch and the deviating working conditions affect the CCHP performance, absence of reports systematically summarizing the multiple effects of energy saving units (ESUs), and deficiency of research quantifying the benefits from ESUs to energy savings. The shortage of such studies will confuse some CCHP designers when a CCHP system is designed. Therefore, in this research, theoretical discussions have been undertaken about the energy mismatch issue between CCHP systems and their users as well as the multiple effects of ESUs on CCHP systems. An improved calculational method of energy storage rate (ESR) has been adopted to evaluate the energy savings performance of CCHP systems. Two general heat‐to‐electricity ratios (R_user for CCHP users and R_CCHP for CCHP systems) have been used to quantify the energy mismatch between CCHP systems and their users. In the regime of ‘priority of providing cooling’, the ESR reaches its maximum when R_user is equal to R_CCHP. Otherwise, the ESR tends to decrease rapidly, especially when the electrical demand must be supplemented from the grid. Furthermore, when the CCHP system produces more electricity than required, the payment mode of extra electricity from the CCHP system will significantly affect the ESR. Therefore, it is imperative to reach an international consensus regarding the dispose of extra CCHP products. The theoretical analyses also corroborate the advantages of incorporating an ESU into a CCHP system. The ESU enables the CCHP system components to operate at their optimal working conditions. Meanwhile, the power generation unit and the absorption refrigerator capacities can then be reduced. Moreover, the ESU also promotes the productivity of electricity and ensures an undiminished ESR regardless of what extra electricity payment mode is adopted. Copyright © 2016 John Wiley & Sons, Ltd.     

Potential of power-to-heat from excess wind energy on the city level

ABSTRACT

This study discusses the potential of power-to-heat (P2H) as an effective option to reduce greenhouse gas emissions in the heating sector and energy curtailment. P2H promotes the integration of electricity from renewable energy sources into the power grid by utilizing otherwise unused electricity (excess energy) for space heating. To estimate the contribution of this effect from a techno-economic perspective, a linear problem is defined by minimizing the overall heating costs and solved by an open source model generator. Four different scenarios are modeled on a city level, using real heat demand data from a case study regarding the municipality of Greifswald, a region with dominant wind-energy. Results indicate that district heating networks are an important technology for coupling power and heat to meet CO₂ reduction targets. In addition, further integration of renewable energy is promoted to reduce overall emissions and achieve Germany’s climate protection goals by 2050.     

Geothermal energy utilization in Turkey

This paper investigates the status of geothermal development in Turkey as of the end of 1999. Turkey is one of the countries with significant potential in geothermal energy. Resource assessments have been made many times by the Mineral Research and Exploration Directorate (MTA) of Turkey. The main uses of geothermal energy are mostly moderate‐ and low‐temperature applications such as space heating and domestic hot water supply, greenhouse heating, swimming and balneology, industrial processes, heat pumps and electricity generation. The data accumulated since 1962 show that the estimated geothermal power and direct use potential are about 4500 MW_e and 31 500 MW_t, respectively. The direct use capacity in thermal applications is in total 640 MW_t representing only 2 per cent of its total potential. Since 1990, space heating and greenhouse developments have exhibited a significant progress. The total area of greenhouses heated by geothermal energy reached up to about 31 ha with a heating capacity of 69.61 MW_t. A geothermal power plant with a capacity of 20.4 MW_e and a CO₂ factory with a capacity of 40000 ton yr^?1 have been operated in the Denizli‐Kizildere field since 1984 and 1986, respectively. Ground source heat pumps have been used in residential buildings for heating and cooling for approximately 2 years. Present applications have shown that geothermal energy in Turkey is clean and much cheaper compared to the other energy sources like fossil fuels and therefore is a promising alternative. As the projects are recognized by the public, the progress will continue. Copyright © 2001 John Wiley & Sons, Ltd.     

Analysis of cooling,heating, and power systems based on site energy consumption

Feasibility of cooling, heating, and power systems frequently is based on economic considerations such as energy prices. However, a most adequate feasibility of CHP systems must be based on energy consumption followed by economic considerations. CHP systems designs must yield economical savings, but more importantly must yield real energy savings based on the best energy performance. For CHP systems, energy savings is related to primary energy and not to site energy. This paper presents a mathematical analysis demonstrating that CHP systems increase the site energy consumption (SEC). Increasing the SEC could yield misleading results in the economic feasibility of CHP systems. Three different operation modes are evaluated: (a) cooling, heating, and power; (b) heating and power; and (c) cooling and power, to represent the operation of the system throughout the year. Results show that CHP systems increase site energy consumption; therefore primary energy consumption (PEC) should be used instead of SEC when designing CHP systems.     

Design and analysis of an integrated concentrated solar and wind energy system with storage

This study analyzes a renewable energy‐driven innovative multigeneration system, in which wind and solar energy sources are utilized in an efficient way to generate several useful commodities such as hydrogen, oxygen, desalted water, space cooling, and space heating along with electricity. A 1‐km² heliostat field is considered to concentrate the solar light onto a spectrum splitter, where the light spectrum is separated into two portions as reflected and transmitted to be used as the energy source in the concentrated solar power (CSP) and concentrated photovoltaics (CPV) receivers, respectively. As such, CSP and CPV systems are integrated. Wind energy is proposed for generating electricity (146 MW) or thermal energy (138 MW) to compensate the energy need of the multigeneration system when there is insufficient solar energy. In addition, multiple commodities, 46 MW of electricity, 12 m³/h of desalted water, and 69 MW of cooling, are generated using the Rankine cycle and the rejected heat from its condenser. Further, the heat generated on CPV cells is recovered for efficient photovoltaic conversion and utilized in the space heating (34 MW) and proton exchange membrane (PEM) electrolyzer (239 kg/h) for hydrogen production. The energy and exergy efficiencies of the overall system are calculated as 61.3% and 47.8%, respectively. The exergy destruction rates of the main components are presented to identify the potential improvements of the system. Finally, parametric studies are performed to analyze the effect of changing parameters on the exergy destruction rates, production rates, and efficiencies.     

Parametric analysis of a solar energy based multigeneration plant with SOFC for hydrogen generation

Renewable energy-based hydrogen production plants can offer potential solutions to both ensuring sustainability in energy generation systems and designing environmentally friendly systems. In this combined work, a novel solar energy supported plant is proposed that can generate hydrogen, electricity, heating, cooling and hot water. With the suggested integrated plant, the potential of solar energy usage is increased for energy generation systems. The modeled integrated system generally consists of the solar power cycle, solid oxide fuel cell plant, gas turbine process, supercritical power plant, organic Rankine cycle, cooling cycle, hydrogen production and liquefaction plant, and hot water production sub-system. To conduct a comprehensive thermodynamic performance analysis of the suggested plant, the combined plant is modeled according to thermodynamic equilibrium equations. A performance assessment is also conducted to evaluate the impact of several plant indicators on performance characteristics of integrated system and its sub-parts. Hydrogen production rate in the suggested plant according to the performance analysis performed is realized as 0.0642 kg/s. While maximum exergy destruction rate is seen in the solar power plant with 8279 kW, the cooling plant has the lowest exergy destruction rate as 1098 kW. Also, the highest power generation is obtained from gas turbine cycle with 7053 kW. In addition, energetic and exergetic efficiencies of solar power based combined cycle are found as 56.48% and 54.06%, respectively.     

Operational optimisation of a complex trigeneration system connected to a district heating and cooling network

The combined production of electricity, heat and cold by polygeneration systems ensures maximum utilization of resources by reducing emissions and energy losses during distribution. Polygeneration systems are highly integrated systems characterized by the simultaneously production of different services (electricity, heating, cooling) by means of several technologies using fossil and renewable fuels that operates together to obtain a higher efficiency than that of an equivalent conventional system. The high number of distribution technologies available to produce electricity, heating and cooling and the different levels of integration make it difficult to select of the optimal configuration. Moreover, the high variability in the energy demand renders difficult the selection of the optimal operational strategy. Optimization methodologies are usually applied for the selection of the optimal configuration and operation of energy supply systems. This paper presents a scenario analysis using optimization models to perform an economic, energetic and environmental assessment of a new polygeneration system in Cerdanyola del Vallès (Spain) in the framework of the Polycity project of the European Concerto Program. This polygeneration system comprise high-efficiency natural gas cogeneration engines with thermal cooling facilities and it will provide electricity, heating and cooling for a new area in growth known as Alba park including a Synchrotron Light Facility and a Science and Technological park through a district heating and cooling network of four tubes. The results of the scenario analysis show that the polygeneration plant is an efficient way to reduce the primary energy consumption and CO₂ emissions (up to 24%).     

The energy transition towards hydrogen utilization for green life and sustainable human development in Patagonia

Energy transitions towards cleaner and transparent systems in Patagonia are examined, considering energy data for hydrogen utilization to store variable renewable energy. The interrelated sectors – power, heating, cooling and transport – demand large amounts of energy and power. Wind transformation and distributed energy management can achieve synergies towards a new energy paradigm. Fossil fuels should be replaced by a system capable of storing massive amounts of electricity and fuels. Full energy services are not affordable employing only rechargeable batteries or air and water pumping. We analyze wind resources, electricity grids, and hydrogen developments carried out in Argentina, and the perspective of large wind-hydrogen facilities for export. We verify the current demand of natural gas and electricity, and propose the start of distributed production, management and utilization of hydrogen in Patagonia and to supply the most populated areas reaching Buenos Aires. Hydrogen sea transportation from South Patagonia to Rio de la Plata could be feasible. “The whole process would help the training of qualified human resources and also encourage the establishment of companies dedicated to renewable and hydrogen technology activities.”     

Development and modelling of a novel electricity-hydrogen energy system based on reversible solid oxide cells and power to gas technology

Compared to the conventional thermal units and electrolytic devices, reversible fuel cells have very high efficiencies on both fuel cell mode of generating electricity and electrolysis mode of producing hydrogen or CH_x. However, previous studies about fuel cells and its benefits of power to gas are not fully investigated in the electricity-gas energy system. Moreover, state-of-art studies indicate that hydrogen could be directly injected to the existing natural gas (NG) pipeline within an amount of 5%–20%, which are considered to make a slight influence on the natural gas technologies. This work proposes a novel electricity-hydrogen energy system based on reversible solid oxide cells (RSOCs) to demonstrate the future vision of multi-energy systems on integrating multiple energy carriers such as electricity, pure hydrogen, synthetic natural gas (SNG) and mixed gas of H₂-natural gas. The P2G processes of RSOC are sub-divided modelled by power to H₂ (P2H) and power to SNG (P2SNG). The co-electrolysis/generation processes and time-dependent start-up costs are considered within a unit commitment model of RSOC. The proposed electricity-hydrogen energy system optimization model is formulated as mixed-integer linear programming (MILP), where the H₂-blended mixed gas flow is linearized by an incremental linearize relaxation technic. The aim of the optimization is to reduce the energy cost and enhance the system's ability to integrate sufficient renewables through NG networks. Besides quantified the benefits of renewable level and H₂ injection limit on the P2G process, the numerical results show that RSOC combined with H₂/SNG injection results in productive economic and environmental benefits through the energy system.     

Spanish energy roadmap to 2020: Socioeconomic implications of renewable targets

The European Union has established challenging targets for the share of renewable energies to be achieved by 2020; for Spain, 20% of the final energy consumption must be from renewable sources at such time. The aim of this paper is the analysis of the consequences for the electricity sector (in terms of excess cost of electricity, investment requirements, land occupation, CO₂ emissions and overcapacity of conventional power) of several possibilities to comply with the desired targets. Scenarios are created from different hypotheses for energy demand, biofuel share in final energy in transport, contribution of renewables for heating and cooling, renewable electricity generation (generation mix, deployment rate, learning curves, land availability) and conventional power generation (lifetime of current installations, committed deployment, fossil fuel costs and CO₂ emissions cost). A key input in the estimations presented is the technical potential and the cost of electricity from renewable sources, which have been estimated in previous, detailed studies by the present authors using a methodology based on a GIS (Geographical Information System) and high resolution meteorological data. Depending on the scenario, the attainment of the targets will lead to an increase in the cost of electricity from 19% to 37% with respect to 2007.     

Large-scale integration of wind power into different energy systems

The paper presents the ability of different energy systems and regulation strategies to integrate wind power. The ability is expressed by the following three factors: the degree of electricity excess production caused by fluctuations in wind and Combined Heat and Power (CHP) heat demands, the ability to utilise wind power to reduce CO₂ emission in the system, and the ability to benefit from exchange of electricity on the market. Energy systems and regulation strategies are analysed in the range of a wind power input from 0 to 100% of the electricity demand. Based on the Danish energy system, in which 50% of the electricity demand is produced in CHP, a number of future energy systems with CO₂ reduction potentials are analysed, i.e. systems with more CHP, systems using electricity for transportation (battery or hydrogen vehicles) and systems with fuel-cell technologies. For the present and such potential future energy systems different regulation strategies have been analysed, i.e. the inclusion of small CHP plants into the regulation task of electricity balancing and ancillary grid stability services and investments in electric heating, heat pumps and heat storage capacity. The results of the analyses make it possible to compare short-term and long-term potentials of different strategies of large-scale integration of wind power.     

An evaluation of domestic solar energy potential in Taiwan incorporating land use analysis

Solar energy is widely regarded as a major renewable energy source, which in future energy systems will be able to contribute to the security of energy supply and the reduction of CO₂ emissions. This study combined an evaluation of solar energy resources in Taiwan with land use analysis, which allows the potentials and restrictions of solar energy exploitation resulting from local land use conditions to be considered. The findings unveiled in this study indicate that photovoltaic electricity generation and solar water heating have the potential of producing 36.1 and 10.2 TWh of electricity and thermal energy annually in Taiwan, accounting for 16.3% and 127.5% of the total domestic consumption of electricity and energy for household water heating in 2009, respectively. However, the exploited solar photovoltaic power generation in 2009 accounted for only 0.02% of total potential in Taiwan, while the exploited solar water heating accounted for 11.6% of total potential. Market price and investment incentive are the dominant factors that affect market acceptance of solar energy installation in Taiwan. The administrative barriers to the purchase and transmission of electricity generated from renewable energy sources have to be removed before the potential contribution of solar energy can be realized.     

燃气轮机冷热电联产系统技术与经济性分析

分析了现有商业燃气轮机用于热电联产系统和冷热电联产系统时的性能。与常规分产系统相比,两系统在热力学性能上均有较大优势,绝大多数节能率超过20％。功率较小的燃气轮机单位造价偏高,用于冷热电联产系统时经济性较差;随着功率的增加经济性不断改善,冷热电联产系统的经济性受到很多因素的影响,其中运行时间和电价的影响最明显,其次为燃料价格的影响,热价和冷价的影响相对最小;这些因素在燃气轮机功率较小时影响较大,随功率的增加影响逐渐减小。     

Life cycle energy and environmental analysis of a microgrid power pavilion

Microgrids—generating systems incorporating multiple distributed generator sets linked together to provide local electricity and heat—are one possible alterative to the existing centralized energy system. Potential advantages of microgrids include flexibility in fuel supply options, the ability to limit emissions of greenhouse gases, and energy efficiency improvements through combined heat and power (CHP) applications. As a case study in microgrid performance, this analysis uses a life cycle assessment approach to evaluate the energy and emissions performance of the NextEnergy microgrid Power Pavilion in Detroit, Michigan and a reference conventional system. The microgrid includes generator sets fueled by solar energy, hydrogen, and natural gas. Hydrogen fuel is sourced from both a natural gas steam reforming operation and as a by‐product of a chlorine production operation. The chlorine plant receives electricity exclusively from a hydropower generating station. Results indicate that the use of this microgrid offers a total energy reduction potential of up to 38%, while reductions in non‐renewable energy use could reach 51%. Similarly, emissions of CO₂, a key global warming gas, can be reduced by as much as 60% relative to conventional heat and power systems. Hydrogen fuels are shown to provide a net energy and emissions benefit relative to natural gas only when sourced primarily from the chlorine plant. Copyright © 2006 John Wiley & Sons, Ltd.     

The potential contribution of geothermal energy to electricity supply in Saudi Arabia

With increase in demand for electricity at 7.5% per year, the major concern of Saudi Arabia is the amount of CO₂ being emitted. The country has the potential of generating 200×10⁶ kWh from hydrothermal sources and 120×10⁶ terawatt hour from Enhanced Geothermal System (EGS) sources. In addition to electricity generation and desalination, the country has substantial source for direct application such as space cooling and heating, a sector that consumes 80% of the electricity generated from fossil fuels. Geothermal energy can offset easily 17 million kWh of electricity that is being used for desalination. At least a part of 181,000 Gg of CO₂ emitted by conventional space cooling units can also be mitigated through ground-source heat pump technology immediately. Future development of EGS sources together with the wet geothermal systems will make the country stronger in terms of oil reserves saved and increase in exports.