ライブラリー Annual Energy Outlook 2000

A review on compressed air energy storage: Basic principles, past milestones and recent developments

More effective energy production requires a greater penetration of storage technologies. This paper takes a looks at and compares the landscape of energy storage devices. Solutions across four categories of storage, namely: mechanical, chemical, electromagnetic and thermal storage are compared on the basis of energy/power density, specific energy/power, efficiency, lifespan, cycle life, self-discharge rates, capital energy/power costs, scale, application, technical maturity as well as environmental impact. It’s noted that virtually every storage technology is seeing improvements. This paper provides an overview of some of the problems with existing storage systems and identifies some key technologies that hold promise.

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A Numerical and Graphical Review of Energy Storage Technologies

Wind energy research: State-of-the-art and future research directions

Grid scale electrical energy storage is considered facilitative for the increased deployment of renewable energy. Recent progress in the development of large scale thermal energy storage systems operated at medium and high temperatures has sparked the interest in the application of this technology as a storage sink for electricity. Life expectancies in the range of 20–30 years, low capacity-specific costs, a low environmental impact and flexibility regarding sites make thermo-mechanical energy storage a promising option for future bulk storage of electricity. A large number of concepts have been developed, which vary in storage efficiency, complexity and maturity. This paper provides an overview of the basic concepts for thermo-mechanical energy storage and describes various implementations and their characteristics. The utilization of waste heat, the combined delivery of heat and power during discharge and the integration of storage modules into power plants are described as additional options for some of these thermo-mechanical concepts.

Thermo-mechanical concepts for bulk energy storage

Liquid piston compression efficiency with droplet heat transfer

Downwind force angles are small for current turbines systems (1–5 MW) such that they may be readily accommodated by conventional upwind configurations. However, analysis indicates that extreme-scale systems (10–20 MW) will have larger angles that may benefit from downwind-aligned configurations. To examine potential rotor mass reduction, the pre-alignment concept was investigated a two-bladed configuration by keeping the structural and aerodynamic characteristics of each blade fixed (to avoids a complete blade re-design). Simulations for a 13.2 MW rated rotor at steady-state conditions show that this concept-level two-bladed design may yield 25% rotor mass savings while also reducing average blade stress over all wind speeds. These results employed a pre-alignment on the basis of a wind speed of 1.25 times the rated wind speed. The downwind pre-aligned concept may also reduce damage equivalent loads on the blades by 60% for steady rated wind conditions. Even higher mass and damage equivalent load savings (relative to conventional upwind designs) may be possible for larger systems (15–20 MW) for which load-alignment angles become even larger. However, much more work is needed to determine whether this concept can be translated into a practical design that must meet a wide myriad of other criteria. Copyright © 2017 John Wiley & Sons, Ltd.

Downwind pre-aligned rotors for extreme-scale wind turbines

Wind turbine output energy varies over time with local wind speed and is typically inconsistent with grid power demand. Without energy storage, the resulting difference between rated (peak) power and average power output leads to over-sizing of electrical generator and transmission lines. This conventional arrangement can be avoided if wind turbines can be coupled with energy storage to eliminate the output variations and instead produce their average power on a continuous basis. This would allow a smaller, lower-cost, constant-speed generator and a reduced capacity transmission system sized only for average power output. To accomplish this goal, this study discusses a concept for a storage system for a 5 MW off-shore wind turbine, which integrates a spray-based compressed air energy storage with a 35 MPa accumulator. The compressor employs a liquid piston for air sealing and employs water spray to augment heat transfer for high-efficiency. The overall compression is proposed in three stages with pressure ratios of 10:1, 7:1, and 5:1, all operated at 1 Hz to maintain moderate liquid surface acceleration. Based on a simple and fundamental description of the system, compression efficiency was found to be strongly dependent on droplet surface area, which can be achieved through either high mass loading or small drop sizes. The simulations also show that direct injection spray can increase overall three-stage compression efficiency to as high as 89%, substantially better than the 27% associated with a conventional adiabatic compression at the same pressure ratio. In addition, this study introduces a key performance parameter, termed the Levelization Factor, which can be used to quantify the impact of storage on wind energy systems. However, experiments and simulations based on 3-D geometries with design details are needed to determine the potential of this concept.

Chao Qin

Papers

Liquid piston compression efficiency with droplet heat transfer

Downwind pre-aligned rotors for extreme-scale wind turbines

Spray-cooling concept for wind-based compressed air energy storage

Hydraulic-electric hybrid wind turbines: Tower mass saving and energy storage capacity

Pre-aligned downwind rotor for a 13.2 MW wind turbine