Large-scale compressed hydrogen storage as part of renewable electricity storage systems

Storing energy in the form of hydrogen is a promising green alternative. Thus, there is a high interest to analyze the status quo of the different storage options. This paper focuses on the large-scale compressed hydrogen storage options with respect to three categories: storage vessels, geological storage, and other underground storage alternatives. In this study, we investigated a wide variety of compressed hydrogen storage technologies, discussing in fair detail their theory of operation, potential, and challenges. The analysis confirms that a techno-economic chain analysis is required to evaluate the viability of one storage option over another for a case by case. Some of the discussed technologies are immature; however, this does not rule out these technologies; rather, it portrays the research opportunities in the field and the foreseen potential of these technologies. Furthermore, we see that hydrogen would have a significant role in balancing intermittent renewable electricity production.     

Grid flexibility and storage required to achieve very high penetration of variable renewable electricity

We examine the changes to the electric power system required to incorporate high penetration of variable wind and solar electricity generation in a transmission constrained grid. Simulations were performed in the Texas, US (ERCOT) grid where different mixes of wind, solar photovoltaic and concentrating solar power meet up to 80% of the electric demand. The primary constraints on incorporation of these sources at large scale are the limited time coincidence of the resource with normal electricity demand, combined with the limited flexibility of thermal generators to reduce output. An additional constraint in the ERCOT system is the current inability to exchange power with neighboring grids.     

Education and training in renewable energy sources in Serbia and Montenegro

This paper reports the status of Education and Training in Renewable Energy Sources (RES) in Serbia and Montenegro (SAM) at the end of May 2003. It was found that universities in SAM do not give diplomas in RES. RES subjects primarily solar and wind energy are taught at graduate levels. RES units are taught as a part of some classical engineering disciplines at undergraduate level especially in solar and biomass energy. Teaching is mainly at encyclopedic level and staff is mainly trained in general fields. This education may be regarded as unsatisfactory and should be expanded and intensified in future.     

Can renewable energy sources sustain affluent society?

Figures commonly quoted on costs of generating energy from renewable sources can give the impression that it will be possible to switch to renewables as the foundation for the continuation of industrial societies with high material living standards. Although renewable energy must be the sole source in a sustainable society, major difficulties become evident when conversions, storage and supply for high latitudes are considered. It is concluded that renewable energy sources will not be able to sustain present rich world levels of energy use and that a sustainable world order must be based on acceptance of much lower per capita levels of energy use, much lower living standards and a zero growth economy.     

Optimum energy storage techniques for the improvement of renewable energy sources-based electricity generation economic efficiency

The high wind and solar potential along with the extremely high electricity production cost met in the majority of Greek Aegean islands comprising autonomous electrical networks, imply the urgency for new renewable energy sources (RES) investments. To by-pass the electrical grid stability constraints arising from an extensive RES utilization, the adaptation of an appropriate energy storage system (ESS) is essential. In the present analysis, the cost effect of introducing selected storage technologies in a large variety of autonomous electrical grids so as to ensure higher levels of RES penetration, in particular wind and solar, is examined in detail. A systematic parametrical analysis concerning the effect of the ESSs’ main parameters on the economic behavior of the entire installation is also included. According to the results obtained, a properly sized RES-based electricity generation station in collaboration with the appropriate energy storage equipment is a promising solution for the energy demand problems of numerous autonomous electrical networks existing worldwide, at the same time suggesting a clean energy generation alternative and contributing to the diminution of the important environmental problems resulting from the operation of thermal power stations.     

Overview of US patents for energy management of renewable energy systems with hydrogen

The problems of energy shortage, severe pollution, and global warming are becoming increasingly severe. Renewable energy systems with hydrogen have been widely used. In recent years, much literature has described the energy management of renewable energy systems with hydrogen in a comprehensive way. However, most of them are proposed and discussed from an academic point of view. There are likewise several different approaches and ideas in the patents that address the energy management of hydrogen renewable energy systems. Moreover, most patents are oriented toward industrial applications and still need to be reviewed and analyzed. To fill this gap, this paper reviews relevant US patents to find potential and industrial hydrogen applications and energy management strategies in renewable energy systems. The work presented in this paper will provide solutions and guidance in solving energy management problems in renewable energy systems.     

Global warming and renewable energy sources for sustainable development in Turkey

Turkey, with its young population and growing energy demand per person, its fast growing urbanization, and its economic development, has been one of the fast growing power markets of the world for the last two decades. It is expected that the demand for electric energy in Turkey will be 300 billion kWh by the year 2010 and 580 billion kWh by the year 2020. Turkey is heavily dependent on expensive imported energy resources that place a big burden on the economy and air pollution is becoming a great environmental concern in the country. In this regard, renewable energy resources appear to be the one of the most efficient and effective solutions for clean and sustainable energy development in Turkey. Turkey's geographical location has several advantages for extensive use of most of these renewable energy sources. This article presents a review of the potential and utilization of the renewable energy sources in Turkey.     

Controllable and affordable utility-scale electricity from intermittent wind resources and compressed air energy storage (CAES)

World wind energy resources are substantial, and in many areas, such as the US and northern Europe, could in theory supply all of the electricity demand. However, the remote or challenging location (i.e. offshore) and especially the intermittent character of the wind resources present formidable barriers to utilization on the scale required by a modern industrial economy. All of these technical challenges can be overcome. Long distance transmission is well understood, while offshore wind technology is being developed rapidly. Intermittent wind power can be transformed to a controllable power source with hybrid wind/compressed air energy storage (CAES) systems. The cost of electricity from such hybrid systems (including transmission) is affordable, and comparable to what users in some modern industrial economies already pay for electricity. This approach to intermittent energy integration has many advantages compared to the current strategy of forcing utilities to cope with supply uncertainty and transmission costs. Above all, it places intermittent wind on an equal technical footing with every other generation technology, including nuclear power, its most important long-term competitor.     

Rural electrification of a remote island by renewable energy sources

India has a large number of remote small villages and islands that lack in the electricity, and probability of connecting them with the high voltage gridlines in the near future is very poor due to financial and technical constraints. The main electrical load in these villages is domestic. In this paper a study has been presented for sustainable development of renewable energy sources to fulfill the energy demands of a remote island having a cluster of five villages. The total potential of electricity from these resources is estimated to be equivalent to 3530 kWh/day whereas demand is only 2310 kWh/day with an installed capacity of 450 kW, which is sufficient to replace the existing power generation system dominated by diesel operated system.     

Operational performance of energy storage as function of electricity prices for on-grid hybrid renewable energy system by optimized fuzzy logic controller

Realization of benefits from on-grid distributed generation based on renewable energy sources requires employment of energy storage to overcome the intermittency in power generation by such sources, while accounting for time-varying electricity prices. The objective of this study is to examine the effects of time-varying electricity prices on the performance of energy storage components for an on-grid hybrid renewable energy system (HRES) utilizing an optimized fuzzy logic controller (FLC). To achieve the objective, FLC membership functions are optimized for minimizing the operational cost of the HRES based on weekly and daily prediction of data for grid electricity price, electrical load, and environmental parameters, including wind speed, solar irradiation, and ambient temperature, using shuffled frog leap algorithm. FLC three inputs include (a) grid electricity price, (b) net power flow as the difference between energy produced and energy consumed, and (c) state of charge (SOC) of battery stack. It is confirmed that accounting for grid electricity price has considerable effects on the performance of energy storage components for operation of on-grid HRES, as the weekly and daily optimized FLCs result in less working hours for fuel cell and electrolyzer and less fluctuations in SOC of battery stack.     

Latent heat storage for solar energy systems: Transient simulation of refrigerant storage

This paper presents a brief review of the available latent heat storage systems for solar energy utilization. A new concept of latent heat storage of solar energy via the refrigerant-absorbent mass storage in absorption cycle heat pump systems used for solar space heating/cooling has been proposed and assessed thermodynamically. A computer modelling and numerical simulation study shows that the concept of refrigerant storage is fundamentally sound, technically feasible and yields the following advantages over other storage methods: (i) the storage capacity per unit volume is high as the latent heat of vaporization of the refrigerant is high; (ii) the heat loss from the storage to the surroundings is minimum as the storage temperature is near the ambient; (iii) prolonged energy storage is possible with no degradation in system performance and hence suitable for combined solar heating and airconditioning. The effects of operating parameters on the energy storage concentration and storage efficiency have been studied in detail.     

Efficiency and effectiveness of promotion systems for electricity generation from renewable energy sources - Lessons from EU countries

Currently, a wide range of strategies is implemented in different countries to increase the share of electricity from renewable energy sources (RES-E). A still controversial discussion is whether quantity-driven (like Tradable Green Certificates (TGCs) based on quotas) or price-driven (like feed-in-tariffs (FIT)) instruments lead to preferable solutions for society. The core objective of this paper is to compare the perspectives of quota-based certificate trading systems for an efficient and effective increase of RES-E with FIT. The major results of this analysis are: (i) The success stories of growth in RES-E in EU member states in recent years has been triggered by FIT implemented in a technology-specific manner at modest costs for European citizens; (ii) At present, TGC systems in most countries applied show a low effectiveness with respect to RES-E deployment of less mature technologies such as solar PV (with improving tendencies in e.g. the UK or Italy with respect to certain technologies); (iii) Compared to short term trading in TGC markets the intrinsic stability of FIT systems appears to be a key element for success; (iv) Hence, currently a well-designed (dynamic) FIT system provides a certain deployment of RES-E in the shortest time and at lowest costs for society.     

An energy management approach for renewable energy integration with power generation and water desalination

The share of the renewable energy sources (RES) in the global electricity market is substantially increasing as a result of the commitment of many countries to increase the contribution of the RES to their energy mix. However, the integration of RES in the electricity grid increases the complexity of the grid management due to the variability and the intermittent nature of these energy sources. Energy storage solutions such as batteries offer either short-term storage that is not sufficient or longer period storage that is significantly expensive. This paper introduces an energy management approach which can be applied in the case of power and desalinated water generation. The approach is based on mathematical optimization model which accounts for random variations in demands and energy supply. The approach allows using desalination plants as a deferrable load to mitigate for the variability of the renewable energy supply and water and/or electricity demands. A mathematical linear programming model is developed to show the applicability of this idea and its effectiveness in reducing the impact of the uncertainty in the environment. The model is solved for the real world case of Saudi Arabia. The optimal solution accounts for random variations in the renewable energy supply and water and/or electricity demands while minimizing the total costs for generating water and power.     

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.     

Sustainable application of renewable sources in water pumping systems: Optimized energy system configuration

Eighteen years ago, in Portugal, the expenses in a water supply system associated with energy consumption were quite low. However, with the successive crises of energy fuel and the increase of the energy tariff as well as the water demand, the energy consumption is becoming a larger and a more important part of the total budget of water supply pumping systems. Also, new governmental policies, essentially in developed countries, are trying to implement renewable energies. For these reasons, a case-study in Portugal of a water pumping system was analysed to operate connected to solar and wind energy sources.     

Successful renewable energy development in a competitive electricity market: A Texas case study

The development of renewable energy in markets with competition at wholesale and retail levels poses challenges not present in areas served by vertically-integrated utilities. The intermittent nature of some renewable energy resources impact reliability, operations, and market prices, in turn affecting all market participants. Meeting renewable energy goals may require coordination among many market players.     

Reviewing optimisation criteria for energy systems analyses of renewable energy integration

The utilisation of fluctuating renewable energy sources is increasing world-wide; however, so is the concern about how to integrate these resources into the energy systems. The design of optimal energy resource mixes in climate change mitigation actions is a challenge faced in many places. This optimisation may be implemented according to economic objectives or with a focus on techno-operational aims and within these two main groupings, several different criteria may potentially be applied to the design process.In this article, a series of optimisation criteria are reviewed and subsequently applied to an energy system model of Western Denmark in an analysis of how to use heat pumps for the integration of wind power.The analyses demonstrate that the fact whether the system in question is modelled as operated in island mode or not has a large impact on the definition of the optimal wind power level. If energy savings and CO₂ emission reductions beyond the system boundary are not included in the analysis, then it is either not feasible to expand wind power to a high degree or it is conversely more feasible to install relocation technologies that can utilise any excess production. The analyses also demonstrate that different optimisation criteria render different optimal designs.     

Mapping the potential for decentralized energy generation based on renewable energy sources in the Republic of Croatia

There are regions in the Republic of Croatia (underdeveloped, devastated by war, depopulated, as well as islands and mountainous areas) which are still disconnected from the electricity network or where the current network capacity is insufficient. In addition, these regions have good renewable energy potential. Since the decentralized energy generation (DEG) covers a broad range of technologies, including many renewable energy technologies (RET) that provide small-scale power at sites close to the users, this concept could be of interest for these locations. This paper identifies the areas in Croatia where such systems could be applied. Consideration is given to geographical locations as well as possible applications. Wind, hydro, solar photovoltaic, geothermal, and biomass conversion systems were analyzed from a technological and economic point of view. Since the renewable energy sources (RES) data for Croatia are rather scarce, the intention was to give a survey of the present situation and an estimate of future potential for DEG based on RES. The energy potential (given as capacity and energy capability) and production costs were calculated on a regional basis and per type of RET. Finally, the RES cost–supply curves for 2006 and 2010 are given.     

An econometric analysis of residential expenditures on energy conservation and renewable energy sources

Economic theory suggests that residential expenditures on energy conservation and renewable energy sources will be determined by the ability of households to purchase conservation inputs, their incentive to invest in conserving energy, the energy efficiency of existing homes and miscellaneous factors such as climate and age of the home-owner. Empirical analyses of energy-related expenditures reported on individual income tax returns confirm the importance of household income, energy price increases and climate conditions in determining energy conservation investments. Income tax credits are also found to have stimulated residential spending on conservation and renewable energy.     

Optimized battery-management system to improve storage lifetime in renewable energy systems

Lead-acid batteries are the main technology used in renewable energy systems (RESs) and autonomous power-supply systems due to their maturity and low cost, factors that will remain valid for the next few years. It is often stated, however, that batteries in RES applications exhibit shorter lifetimes than those expected by manufacturers’ data or those experienced in real traditional applications. Overall, in relation to all other components in RESs, the battery lifetime is quite short and has an intensive impact on the costs of the total system.