Literature Review : Electrical Energy Storage for Scotland

This report examines the role and value of energy storage in the context of electricity systems that are expected to absorb increasing quantities of time variable electricity generation from renewable sources in the years ahead. Particular attention is given to Scotland with its vast renewable energy potential and limited interconnection to the parts of the UK with the major electricity loads. Energy storage technologies cover a wide range of levels of development from mature technologies like pumped hydro with over 50 years of operational experience, to technologies still under development such as flow batteries and hydrogen storage systems, and all of these are reviewed. All scales of possible application are considered here from whole power system support, through community power provision, down to individual households

Ubiquitous energy storage

This paper presents a vision of a future power system with "ubiquitous energy storage", where storage would be utilized at all levels of the electricity system. The growing requirement for storage is reviewed, driven by the expansion of distributed generation. The capabilities and existing applications of various storage technologies are presented, providing a useful review of the state of the art. Energy storage will have to be integrated with the power system and there are various ways in which this may be achieved. Some of these options are discussed, as are commercial and regulatory issues. In two case studies, the costs and benefits of some storage options are assessed. It is concluded that electrical storage is not cost effective but that thermal storage offers attractive opportunities

Energy storage apparatus

A high efficiency, flywheel type energy storage device which comprises an electronically commutated d.c. motor/generator unit having a massive flywheel rotor magnetically suspended around a ring shaped stator is presented. During periods of low energy demand, the storage devices were operated as a motor, and the flywheel motor was brought up to operating speed. Energy was drawn from the device functioning as a generator as the flywheel rotor rotated during high energy demand periods

Feasibility study of energy storage by concentrating/desalinating water : concentrated water energy storage

The paper is to report the work on a preliminary feasibility study of energy storage by concentrating/desalinating water. First, a novel concentrated water energy storage (CWES) is proposed which aims to use off-peak electricity to build the osmotic potential between water bodies with different concentrations, namely brine and freshwater. During peak time, the osmotic potential energy is released to generate electricity. Two scenarios of CWES are specified including a CWES system using reverse osmosis (RO) and pressure retarded osmosis (PRO), and a CWES system co-storing/generating energy and freshwater using “osmotic-equivalent” wastewater. A comprehensive case study is carried out with focusing on the configuration of CWES using RO and PRO. It is found that the limiting cycle efficiency of the CWES using RO and PRO is inversely proportional to the RO water recovery and independent of the initial salinity. Therefore, to balance the energy density and cycle efficiency of CWES, it is recommended to operate a system at lower RO water recovery with higher concentration of the initial solution. Detailed energy analysis of detrimental effects in mass transfer, e.g. concentration polarization and salt leakage, and energy losses of pressurisation and expansion of pressurised water, are studied. Finally, a preliminary cost analysis of CWES is given

Small-scale energy storage in a distributed future

With increasing interest in the co-location of energy supply and demand through distributed generation will there be any need for large-scale energy-storage schemes in the future provision of energy? Indeed, if the future of energy supply is small-scale why should this not also apply to energy storage? This paper will examine the current drive towards localised heat and power production and available options for storage of energy at the point of demand. The economics, practicality and impact of localised storage will be analysed along with the potential for energy efficiency measures and load management to reduce energy storage requirements at the small scale

A review of solar collectors and thermal energy storage in solar thermal applications

Thermal applications are drawing increasing attention in the solar energy research field, due to their high performance in energy storage density and energy conversion efficiency. In these applications, solar collectors and thermal energy storage systems are the two core components. This paper focuses on the latest developments and advances in solar thermal applications, providing a review of solar collectors and thermal energy storage systems. Various types of solar collectors are reviewed and discussed, including both non-concentrating collectors (low temperature applications) and concentrating collectors (high temperature applications). These are studied in terms of optical optimisation, heat loss reduction, heat recuperation enhancement and different sun-tracking mechanisms. Various types of thermal energy storage systems are also reviewed and discussed, including sensible heat storage, latent heat storage, chemical storage and cascaded storage. They are studied in terms of design criteria, material selection and different heat transfer enhancement technologies. Last but not least, existing and future solar power stations are overviewed.Peer reviewe

Thermal energy storage

The general scope of study on thermal energy storage development includes: (1) survey and review possible concepts for storing thermal energy; (2) evaluate the potentials of the surveyed concepts for practical applications in the low and high temperature ranges for thermal control and storage, with particular emphasis on the low temperature range, and designate the most promising concepts; and (3) determine the nature of further studies required to expeditiously convert the most promising concept(s) to practical applications. Cryogenic temperature control by means of energy storage materials was also included

Thermodynamic analysis of a novel fossil-fuel–free energy storage system with a trans-critical carbon dioxide cycle and heat pump

This paper presents and analyzes a novel fossil-fuel–free trans-critical energy storage system that uses CO2 as the working fluid in a closed loop shuttled between two saline aquifers or caverns at different depths: one a low-pressure reservoir and the other a high-pressure reservoir. Thermal energy storage and a heat pump are adopted to eliminate the need for external natural gas for heating the CO2 entering the energy recovery turbines. We carefully analyze the energy storage and recovery processes to reveal the actual efficiency of the system. We also highlight thermodynamic and sensitivity analyses of the performance of this fossil-fuel–free trans-critical energy storage system based on a steady-state mathematical method. It is found that the fossil-fuel–free trans-critical CO2 energy storage system has good comprehensive thermodynamic performance. The exergy efficiency, round-trip efficiency, and energy storage efficiency are 67.89%, 66%, and 58.41%, and the energy generated of per unit storage volume is 2.12 kW·h/m3, and the main contribution to exergy destruction is the turbine reheater, from which we can quantify how performance can be improved. Moreover, with a higher energy storage and recovery pressure and lower pressure in the low-pressure reservoir, this novel system shows promising performance

The SERI solar energy storage program

In support of the DOE thermal and chemical energy storage program, the solar energy storage program (SERI) provides research on advanced technologies, systems analyses, and assessments of thermal energy storage for solar applications in support of the Thermal and Chemical Energy Storage Program of the DOE Division of Energy Storage Systems. Currently, research is in progress on direct contact latent heat storage and thermochemical energy storage and transport. Systems analyses are being performed of thermal energy storage for solar thermal applications, and surveys and assessments are being prepared of thermal energy storage in solar applications. A ranking methodology for comparing thermal storage systems (performance and cost) is presented. Research in latent heat storage and thermochemical storage and transport is reported

Combined solar collector and energy storage system

A combined solar energy collector, fluid chiller and energy storage system is disclosed. A movable interior insulated panel in a storage tank is positionable flush against the storage tank wall to insulate the tank for energy storage. The movable interior insulated panel is alternately positionable to form a solar collector or fluid chiller through which the fluid flows by natural circulation