The effectiveness of storage and relocation options in renewable energy systems

Across the world, energy planners and transmission system operators are faced with decisions on how to deal with challenges associated with high penetration levels of intermittent energy resources and combined heat and power (CHP). At the same time, distributed plant operators are eager to reduce uncertainties related to fuel and electricity price fluctuations. These interests meet-up for options in distributed supply that introduces the principle of storage and relocation, typically by integrating heat pumps (HP) or electric boilers (EBs) into the operational strategies of existing CHP plants. This paper introduces the principle of storage and relocation by energy system design, and proposes for the storage and relocation potential of a technology option to be found by comparing options by their storage and relocation coefficient R_c, defined as the statistical correlation between net electricity exchange between plant and grid, and the electricity demand minus intermittent renewable electricity production. Detailed operational analyses made for various CHP options within the West Danish energy system, point to the concepts of CHP-HP and CHP-HP cold storage for effectively increasing energy system flexibility. For CHP-HP cold storage, R_c increases from 0.518 to 0.547, while the plant's fuel efficiency increases from 92.0% to 97.2%. These findings are discussed within frameworks of renewable energy systems, suggesting principles for 1st, 2nd, and 3rd generation system designs.     

Life-cycle energy efficiency estimation of large-scale ammonia fuel energy storage system

本文讨论了氨作为燃料使用会具备与传统化石燃料显著不同的环境效益,并进一步探讨了氨作为储能介质的特点,包括储能密度和规模大、受地理条件约束小、便于运输存储等。本文还针对目前的合成氨路线从理论分析和工业实际两个方面对合成效率进行了估算和评价。针对目前国内核能、风能、太阳能等清洁能源电力的低谷或弃电问题,建议采用以制氨的方式存储或外运,以便于在电力不足时将其用于发电。建议并评估了几条基于制氨并发电的路线,并基于现有氨燃料的发电效率计算了各路线在全生命周期内的总储能效率（25%～40%）和以电换电的效率[2.5～4.0(度/10度）]。     

A review on hydrogen production and utilization: Challenges and opportunities

Environment-friendly, safe and reliable energy supplies are indispensable to society for sustainable development and high life quality where even though social, environmental, political and economic challenges may play a vital role in their provision. Our continuously growing energy demand is driven by extensive growth in economic development and population and places an ever-increasing burden on fossil fuel utilization that represent a substantial percentage of this increasing energy demand but also creates challenges associated with increased greenhouse gas (GHG) emissions and resource depletion. Such challenges make the global transition obligatory from conventional to renewable energy sources. Hydrogen is emerging as a new energy vector outside its typical role and receiving more recognition globally as a potential fuel pathway, as it offers advantages in use cases and unlike synthetic carbon-based fuels can be truly carbon neutral or even negative on a life cycle basis. This review paper provides critical analysis of the state-of-the-art in blue and green hydrogen production methods using conventional and renewable energy sources, utilization of hydrogen, storage, transportation, distribution and key challenges and opportunities in the commercial deployment of such systems. Some of the key promising renewable energy sources to produce hydrogen, such as solar and wind, are intermittent; hydrogen appears to be the best candidate to be employed for multiple purposes blending the roles of fuel energy carrier and energy storage modality. Furthermore, this study offers a comparative assessment of different non-renewable and renewable hydrogen production systems based on system design, cost, global warming potential (GWP), infrastructure and efficiency. Finally the key challenges and opportunities associated with hydrogen production, storage, transportation and distribution and commercial-scale deployment are addressed.     

Heat pumps and energy storage - The challenges of implementation

The wider implementation of variable renewable energy sources such as wind across the UK and Ireland will demand interconnection, energy storage and more dynamic energy systems to maintain a stable energy system that makes full use of one of our best renewable energy resources. However large scale energy storage e.g. pumped storage may be economically challenging. Therefore can thermal energy storage deployed domestically fulfil an element of such an energy storage role? Current electricity pricing is based on a ½ hourly timeframe which will be demonstrated to have some benefits for hot water heating from electrical water heaters in the first instance. However heat pumps linked to energy storage can displace fossil fuel heating systems and therefore the question is whether a renewable tariff based on “excess” wind for example is sufficient to operate heat pumps. An initial analysis of this scenario will be presented and its potential role in challenging aspects of fuel poverty.     

Transient simulation and techno-economic assessment of a near-zero energy building using a hydrogen storage system and different backup fuels

Proposing a cost-effective off-grid Hybrid Renewable Energy System (HRES) with hydrogen energy storage with a minimum CO2 emission is the main objective of the current study. The electricity demand of an office building is considered to be supplied by Photovoltaic Panels and wind turbines. The office building, modeled in Energy Plus and Open studio, has annual electricity consumption of 500 MWh electricity. 48.9% of the required electricity can be generated via renewable resources. Considering a system without energy storage, the remaining amount of electricity is generated from diesel generators. Hence, for reducing CO2 emission and fuel costs, a hydrogen energy storage system (ESS) is integrated into the system. Hydrogen ESS is responsible for supplying 38.6% of the demand electricity, which means that it can increase the energy supplying ability of the system from 48.9% to 87.5%. In addition to analyzing the application of the hydrogen storage system, the effect of four different kinds of fuel is considered as well. effects of Natural gas, Diesel, Propane, and LPG on the system's application are investigated in this study. Results indicate that natural gas emits less amount of CO2 compared to other fuels and also has a fuel cost of 3054 $/year, while hydrogen ESS is available. For the renewable system without ESS, the fuel cost rises to 10,266 $/year. However, liquid gas, Propane, and LPG have better performance in terms of CO2 emission and fuel cost, respectively.     

A multi-model method to assess the value of power-to-gas using excess renewable

Power-to-Gas (P2G) is a process that produces a gas from electricity, which is most commonly hydrogen via electrolysis. While some studies have considered hydrogen as a power-to-power storage vector, it could also be used as a fuel across the energy system, for example for transport or heat generation. Here, two energy models are used to explore the potential contribution of P2G as a cost-effective source of hydrogen, particularly for future energy systems with high variable renewable energy (VRE) in which there are occasional periods when electricity supply exceeds demand. A detailed electricity system model is iterated with a multi-vector energy system model using a soft-linking approach. This iterative approach addresses shortcomings in each model to better understand the optimal capacity of P2G and the potential economic capture rate of excess VRE. The modelling method is applied to Great Britain in 2050 as a case study. A substantial proportion of excess VRE in 2050 can be captured by P2G, and it is economically competitive compared with alternative sources. Moreover, the effectiveness and economic viability of P2G for reducing excess renewable is robust at even very high levels of renewable penetration.     

How to achieve a 100% RES electricity supply for Portugal?

Portugal is a country with an energy system highly dependent on oil and gas imports. Imports of oil and gas accounted for 85% of the country’s requirements in 2005 and 86% in 2006. Meanwhile, the share of renewable energy sources (RES) in the total primary energy consumption was only 14% in 2006. When focusing only on electricity production, the situation is somewhat better. The share of RES in gross electricity production varies between 20% and 35% and is dependent on the hydropower production in wet and dry years. This paper presents, on a national scale, Portugal’s energy system planning and technical solutions for achieving 100% RES electricity production. Planning was based on hourly energy balance and use of H₂RES software. The H₂RES model provides the ability to integrate various types of storages into energy systems in order to increase penetration of the intermittent renewable energy sources or to achieve a 100% renewable island, region or country. The paper also represents a stepping-stone for studies offering wider possibilities in matching and satisfying electricity supply in Portugal with potential renewable energy sources. Special attention has been given to intermittent sources such as wind, solar and ocean waves that can be coupled to appropriate energy storage systems charged with surplus amounts of produced electricity. The storage systems also decrease installed power requirements for generating units. Consequently, these storages will assist in avoiding unnecessary rejection of renewable potential and reaching a sufficient security of energy supply.     

Design and optimum energy management of a hybrid renewable energy system based on efficient various hydrogen production

Utilizing renewable energy resources is one of the convenient ways to reduce greenhouse gas emissions. However, the intermittent nature of these resources has led to stochastic characteristics in the generation and load balancing of the microgrid systems. To handle these issues, an energy management optimization for microgrids operation should be done to urge the minimization of total system costs, emissions, and fuel consumption. An optimization program for decreasing the operational cost of a hybrid microgrid consisting of photovoltaic array, wind unit, electrolyzer, hydrogen storage system, reformer, and fuel cell is presented. Two different methods of producing hydrogen are considered in this study to ensure the effectiveness of the developed methodology. In the microgrid system with high penetration of renewable energy resources, using storage technologies to compensate for the intermittency of these resources is necessary. To evaluate the functioning of the microgrid system, a mathematical model for each source is developed to coordinate the system operation involving energy conversion between hydrogen and electricity. Particle Swarm Optimization Algorithm is utilized to determine the optimum size and operational energy management within the system. It is evident from the results that there is about a 10% reduction in the amount of CH₄ consumption in reformer when the electrolyzer was employed in the system. It is observed that the CH₄ reduction in summer and fall is higher than other seasons (10.6% and 11.5%, respectively). The reason is that the highest RES production occurs in these seasons during a year. It is also worth mentioning that the electrolyzer technology would play a significant role in decreasing the CH₄ consumption in the microgrid system.     

The value of flexible fuel mixing in hydrogen-fueled gas turbines – A techno-economic study

In electricity systems mainly supplied with variable renewable electricity (VRE), the variable generation must be balanced. Hydrogen as an energy carrier, combined with storage, has the ability to shift electricity generation in time and thereby support the electricity system. The aim of this work is to analyze the competitiveness of hydrogen-fueled gas turbines, including both open and combined cycles, with flexible fuel mixing of hydrogen and biomethane in zero-carbon emissions electricity systems. The work applies a techno-economic optimization model to future European electricity systems with high shares of VRE.The results show that the most competitive gas turbine option is a combined cycle configuration that is capable of handling up to 100% hydrogen, fed with various mixtures of hydrogen and biomethane. The results also indicate that the endogenously calculated hydrogen cost rarely exceeds 5 €/kg_H2 when used in gas turbines, and that a hydrogen cost of 3–4 €/kg_H2 is, for most of the scenarios investigated, competitive. Furthermore, the results show that hydrogen gas turbines are more competitive in wind-based energy systems, as compared to solar-based systems, in that the fluctuations of the electricity generation in the former are fewer, more irregular and of longer duration. Thus, it is the characteristics of an energy system, and not necessarily the cost of hydrogen, that determine the competitiveness of hydrogen gas turbines.     

Hydrogen as an energy carrier in stand-alone applications based on PV and PV–micro-hydro systems

The paper compares two different models of a hypothetical stand-alone energy system based only on renewable sources (solar irradiance and micro-hydro power) integrated with a system for the production of hydrogen (electrolyzer, compressed gas storage and proton exchange membrane fuel cell or PEMFC). The models of both systems have been designed to supply the electricity needs of a residential user in a remote area (a valley of the Alps in Italy) during a complete year of operation, without integration of traditional fossil fuel energy devices. A simulation model has been developed to analyze the energy performance of these systems. The technical feasibility and the behavior of the systems will be evaluated through the analysis of some data (e.g. the production and consumption of electricity along the year by the different components; the heat management; the production, storage and utilization of hydrogen).     

Improving the technical, environmental and social performance of wind energy systems using biomass-based energy storage

A completely renewable baseload electricity generation system is proposed by combining wind energy, compressed air energy storage, and biomass gasification. This system can eliminate problems associated with wind intermittency and provide a source of electrical energy functionally equivalent to a large fossil or nuclear power plant. Compressed air energy storage (CAES) can be economically deployed in the Midwestern US, an area with significant low-cost wind resources. CAES systems require a combustible fuel, typically natural gas, which results in fuel price risk and greenhouse gas emissions. Replacing natural gas with synfuel derived from biomass gasification eliminates the use of fossil fuels, virtually eliminating net CO₂ emissions from the system. In addition, by deriving energy completely from farm sources, this type of system may reduce some opposition to long distance transmission lines in rural areas, which may be an obstacle to large-scale wind deployment.     

Reducing cycling costs in coal fired power plants through power to hydrogen

The increase of renewable share in the energy generation mix makes necessary to increase the flexibility of the electricity market. Thus, fossil fuel thermal power plants have to adapt their electricity production to compensate these fluctuations. Operation at partial load means a significant loss of efficiency and important reduction of incomes from electricity sales in the fossil power plant. Among the energy storage technologies proposed to overcome these problems, Power to Gas (PtG) allows for the massive storage of surplus electricity in form of hydrogen or synthetic natural gas. In this work, the integration of a Power to Gas system (50 MWe) with fossil fuel thermal power plants (500 MWe) is proposed to reduce the minimum complaint load and avoid shutdowns. This concept allows a continuous operation of power plants during periods with low demand, avoiding the penalty cost of shutdown. The operation of the hybrid system has been modelled to calculate efficiencies, hydrogen and electricity production as a function of the load of the fossil fuel power plant. Results show that the utilisation of PtG diminishes the specific cost of producing electricity between a 20% and 50%, depending on the framework considered (hot, warm and cold start-up). The main contribution is the reduction of the shutdown penalties rather than the incomes from the sale of the hydrogen. At the light of the obtained results, the hybrid system may be implemented to increase the cost-effectiveness of existing fossil fuel power plants while adapting the energy mix to high shares of variable renewable electricity sources.     

Grid-connected renewables,storage and the UK electricity market

This article is mainly a counterpoint to an article by Swift-Hook in the journal of Renewable Energy titled “Grid-connected intermittent renewables are the last to be stored”. It also describes the four main distinct UK markets where electrical energy and services are traded, in order to provide a context for the discussion of renewable energy and energy storage in the UK electricity system. In Swift-Hook’s article it was argued that “grid-connected intermittent renewables like wind energy will never be stored unless nothing else is available” and that “storage is counter-productive for fuel saving”. We, however, find evidence that “grid-connected intermittent renewables” have been, and will continue to be stored when it suits the “UK market” to do so. Furthermore, Swift-Hook’s article neglects the potential wider benefits that storage offers to UK energy policy’s goals, in terms of reduced emissions (when used in conjunction with renewables) and enhanced security of supply.     

Analysis of the problem of optimal placement and capacity of the hydrogen energy storage system in the power system

Nowadays the trend of increasing the generation units based on renewable energy sources in the electric power system can be observed. Obviously, this is due to the intensifying level of consumer load and demand for electricity. However, renewable generation is characterized by intermittent energy production, which can cause and potential imbalance between generation and demand, especially during off-peak periods. Therefore, in order to ensure a reliable power supply to consumers, it is necessary to use a maneuverable reserve of capacity, such as energy storage systems, in conjunction with the renewable energy source unit. Over the past 10 years, the energy storage market has grown by almost 50%: the installed capacity of energy storage system in the world is about 5 GW. Analysis of the literature on the subject determines the need to study the impact of these devices on the parameters of electric power systems and one of the primary tasks is to determine the optimal location and capacity of energy storage system in the power system. This paper presents the result of solving the task of determining the optimal parameters of a hydrogen energy storage system using the particle swarm optimization method for example a test scheme radial distribution system – 33 bus IEEE. The choice of the type of energy storage is based on such advantages of a hydrogen energy storage system as environmental friendliness, high energy capacity and the ability to store electricity for a long period of time. In addition, compared to lithium-ion batteries, hydrogen energy storage systems have a long life time of about 25 years, during this period of time there is no degradation and significant deterioration of its properties. All these advantages of hydrogen as an energy carrier allow to take into account not only the criterion of total value of active power losses and its maximum reduction respectively, but the possibility and economic efficiency of partial use of the stored hydrogen for other needs when determining the optimal scenario of their operation in the process of discharge.     

Hydrogen storage for off-grid power supply

The use of intermittent renewable energy sources for power supply to off-grid electricity consumers depends on energy storage technology to guarantee continuous supply. Potential applications of storage-guaranteed systems range from small installations for remote telecoms, water-pumping and single dwellings, to farms and whole communities for whom grid connection is too expensive or otherwise infeasible, to industrial, military and humanitarian uses. In this paper we explore some of the technical issues surrounding the use of hydrogen storage, in conjunction with a PEM electrolyser and PEM fuel cell, to guarantee electricity supply when the energy source is intermittent, most typically solar photovoltaic. We advocate metal-hydride storage and compare its energy density to that of Li-ion battery storage, concluding that a significantly smaller package is possible with metal-hydride storage. A simple approach to match the output of a photovoltaic array to an electrolyser is presented. The properties required for the metal-hydride storage material to interface the electrolyser to the fuel cell are discussed in detail. It is concluded that relatively conventional Mischmetal-based AB₅ alloys are suitable for this application.     

Overview of energy storage systems for storing electricity from renewable energy sources in Saudi Arabia

Renewable power (photovoltaic, solar thermal or wind) is inherently intermittent and fluctuating. If renewable power has to become a major source of base-load dispatchable power, electricity storage systems of multi-MW capacity and multi-hours duration are indispensable. An overview of the advanced energy storage systems to store electrical energy generated by renewable energy sources is presented along with climatic conditions and supply demand situation of power in Saudi Arabia. Based on the review, battery features needed for the storage of electricity generated from renewable energy sources are: low cost, high efficiency, long cycle life, mature technology, withstand high ambient temperatures, large power and energy capacities and environmentally benign. Although there are various commercially available electrical energy storage systems (EESS), no single storage system meets all the requirements for an ideal EESS. Each EESS has a suitable application range.     

Investment decisions in imperfect power markets with hydrogen storage and large share of intermittent electricity

This paper analyzes the impact of hydrogen as energy storage on production and investment decisions in an electricity market when individual participants behave strategically. We develop a game-theoretic model on investment and generation game à la Cournot under the open-loop information structure. This framework is implemented as a mixed complementarity problem and applied to the German case assuming the phase-out of the German nuclear power plants, rising renewable energy supply and increasing energy demand for electric vehicles. The numerical results of our analysis indicate that utilization of energy storage has a positive effect on energy systems with large amount of intermittent electricity and inelastic demand. We find that additional hydrogen storage capacities improve system reliability, increase overall welfare and decrease GHG emissions. Adding demand for hydrogen as a fuel for FCEVs allows for a synergetic use of the technology and changes the investment incentives for energy storage. Although the power-to-gas technology has a price-smoothing effect the overall generation capacity is higher with energy storage providing additional supply security in markets with a large amount of intermittent energy production.     

Optimization of diesel engine performances for a hybrid wind–diesel system with compressed air energy storage

Electricity supply in remote areas around the world is mostly guaranteed by diesel generators. This relatively inefficient and expensive method is responsible for 1.2 million tons of greenhouse gas (GHG) emission in Canada annually. Some low- and high-penetration wind-diesel hybrid systems (WDS) have been experimented in order to reduce the diesel consumption. We explore the re-engineering of current diesel power plants with the introduction of high-penetration wind systems together with compressed air energy storage (CAES). This is a viable alternative to major the overall percentage of renewable energy and reduce the cost of electricity. In this paper, we present the operative principle of this hybrid system, its economic benefits and advantages and we finally propose a numerical model of each of its components. Moreover, we are demonstrating the energy efficiency of the system, particularly in terms of the increase of the engine performance and the reduction of its fuel consumption illustrated and supported by a village in northern Quebec.     

The economics of power generation and energy storage via Solid Oxide Cell and ammonia

Green hydrogen finds its vital role in bridging the intermittent supplied renewable energy and fossil fuel infrastructure in a broad energy transition context. The bottleneck still lies in hydrogen's low volumetric energy density, prohibiting long-distance, large-scale, and cost-effective transportation. As a promising hydrogen carrier, ammonia possesses mature production, storage, transportation, and distribution supply chains. These advantages of ammonia enabled the possibility of transforming the renewable hydrogen at a minimum initial cost. This paper investigates the technological and economic feasibility of green ammonia utilization in the Solid Oxide Cells for power generation and energy storage. The result shows that the cost of Ammonia induced energy (183.75 US$/MWh) is significantly higher than that of natural gas power plants (81.77 US$/MWh). The main contributor is the fuel cost. In the optimum case, with fuel costs substantially dropping, the conceptual plant can be highly feasible, and the generated energy (97.40 USS$/MWh) is comparable to the conventional power plant.