energies Review Overview of Compressed Air Energy Storage and Technology Development Jidai Wang 1,*, Kunpeng Lu 1, Lan Ma 1, Jihong Wang 2,3 ID , Mark Dooner 2, Shihong Miao 3, Jian Li 3 and Dan Wang 3,* 1 College of Mechanical and Electronic Engineering, Shandong University of Science and Technology, Qingdao 266590, China; [email protected] (K.L.); [email protected] (L.M.) 2 School of Engineering, University of Warwick, West Midlands, Coventry CV47AL, UK; [email protected] or [email protected] (J.W.); [email protected] (M.D.) 3 State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China; [email protected] (S.M.); [email protected] (J.L.) * Correspondence: [email protected] (J.W.); [email protected] (D.W.); Tel.: +86-158-5420-2209 (J.W.); +86-130-0619-0033 (D.W.) Received: 18 May 2017; Accepted: 7 July 2017; Published: 13 July 2017 Abstract: With the increase of power generation from renewable energy sources and due to their intermittent nature, the power grid is facing the great challenge in maintaining the power network stability and reliability. To address the challenge, one of the options is to detach the power generation from consumption via energy storage. The intention of this paper is to give an overview of the current technology developments in compressed air energy storage (CAES) and the future direction of the technology development in this area. Compared with other energy storage technologies, CAES is proven to be a clean and sustainable type of energy storage with the unique features of high capacity and long-duration of the storage. Its scale and cost are similar to pumped hydroelectric storage (PHS), thus CAES has attracted much attention in recent years while further development for PHS is restricted by the availability of suitable geological locations. The paper presents the state-of-the-art of current CAES technology development, analyses the major technological barriers/weaknesses and proposes suggestions for future technology development. This paper should provide a useful reference for CAES technology research and development strategy. Keywords: compressed air energy storage (CAES); renewable energy; energy storage 1. Introduction How to maintain economic growth and at the same time reduce the usage of fossil fuel for environmental protection is a global challenge. Various efforts are being made, mainly in two aspects: to reduce the energy consumption by improving energy efficiency and to explore clean and sustainable renewable energy sources [1,2]. Wind, solar and other alternative energy sources are being explored and rapidly developed. Wind power is considered as one of the renewable energy sources with a great development potential in the 21st century. However, the high-level penetration of wind power generation in the grid causes serious problems of power grid stability and reliability due to the intermittence and volatility of wind power. Suitable solutions are urgently needed and energy storage has been recognized as one of the most promising technologies for addressing the problems [3,4]. Energy storage, especially PHS, has a long history of being used for grid dispatching and peak shaving. Coal and gas reserves were historically considered as the major storage forms for flexible dispatch of energy. As technology developed, various feasible energy storage technological solutions have emerged on the market. At the ENERGY STORAGE CHINA 2016 conference, the China Energy Energies 2017, 10, 991; doi:10.3390/en10070991 www.mdpi.com/journal/energies Energies 2017, 10, 991 2 of 22 Energies 2017, 10, 991 2 of 22 Storage Alliance reported that China had 118 energy storage projects in operation (employing Li-ion, Storage Alliance reported that China had 118 energy storage projects in operation (employing Li-ion, lead-acid and flow batteries, and excluding PHS, CAES and thermal energy storage). This represents lead-acid and flow batteries, and excluding PHS, CAES and thermal energy storage). This represents 105.5 MW of installed capacity with a 110% (2010–2015) annual growth rate, meaning a predicated 105.5 MW of installed capacity with a 110% (2010–2015) annual growth rate, meaning a predicated capacity of up to 24.2 GW (excluding PHS) and 40 GW (including PHS) by 2020 [5]. capacity of up to 24.2 GW (excluding PHS) and 40 GW (including PHS) by 2020 [5]. Energy storage can be organized into several categories based on the nature of its operation and Energy storage can be organized into several categories based on the nature of its operation storage medium used: primary fuel (such as coal, oil storage, etc.), intermediate fuel (such as gas, and storage medium used: primary fuel (such as coal, oil storage, etc.), intermediate fuel (such as hydrogen, etc.), electrical energy storage and other forms [1]. The recent status of electrical energy storage gas, hydrogen, etc.), electrical energy storage and other forms [1]. The recent status of electrical technologies is presented in the Table 1 [6–10], and the cost of different energy storage technologies is energy storage technologies is presented in the Table1[ 6–10], and the cost of different energy storage shown in Figure 1 [6–11], including the capital energy cost pitted against capital power cost. technologies is shown in Figure1[ 6–11], including the capital energy cost pitted against capital power cost. Table 1. Technical characteristics of electrical energy technologies [6–10]. EnergyTable 1. TechnicalPower characteristicsSuitable of electrical energy technologies [6–10]. Lifetime Discharge Cycling Technology Density Rating Storage Maturity (years) Time Times (cycles) Energy(Wh/L) Power(MW) SuitableDuration Cycling Lifetime Discharge Technology Density Rating Storage Times Maturity PHS 0.5–2 30–5000 H-Mon (years)40–60 1Time–24 H+ 10,000–30,000 Mature Flywheel (Wh/L)20–80 (MW)0.1–20 DurationSec-Min 15–20 Sec-15 Min (cycles)20,000 Early Com CAESPHS 0.5–22–6 30–5000≥300 H-MonH-Mon 40–6020–40 1–241–24 H+H+ 10,000–30,0008000–12,000 MatureEarly Com Flywheel 20–80 0.1–20 Sec-Min 15–20 Sec-15 Min 20,000 Early Com Capacitor 2–6 0–0.05 Sec-H 1–10 Millis-1 H 50,000+ Com CAES 2–6 ≥300 H-Mon 20–40 1–24 H+ 8000–12,000 Early Com SMESCapacitor 0.2 2–6–6 0–0.050.1–10 Millis Sec-H-H 1–1020–30 Millis-1≥30 Min H 50,000+10,000+ Demo/Early Com Com TESSMES 80 0.2–6–500 0.1 0.1–10–300 Min Millis-H-Days 20–305–30 ≥130–24 Min H+ 10,000+- Demo/EarlyDemo/Early Com Com Solar TESfuel 500 80–500–10,000 0.1–3000–10 Min-DaysH-Mon 5–30- 1–241–24 H+H+ - Demo/EarlyDeveloping Com HydrogenSolar fuel 500–10,000 0–10 H-Mon - 1–24 H+ Developing Hydrogen 500–3000 0–50 H-mon 5–20 Sec-24 H+ 1000+ Developing/Demo fuel cell 500–3000 0–50 H-mon 5–20 Sec-24 H+ 1000+ Developing/Demo fuel cell Li-Li-ionion 150–500150–500 0–1000–100 Min-DaysMin-Days 5–155–15 Min-HMin-H 1000–10,0001000–10,000 DemoDemo LeadLead-acid-acid 50–9050–90 0–400–40 Min-DaysMin-Days 5–155–15 Sec-HSec-H 500–10,000500–10,000 MatureMature Abbreviations:Abbreviations: SMES, SMES, Superconducting Superconducting magnetic magnetic energy storage; storage; TES, TES, Thermal Thermal energy energy storage. storage. InIn more more detail detail,, a a meticulous meticulous comparative comparative life life cycle cycle cost cost (LCC) (LCC) analysis analysis of of electricity electricity storage storage systemssystems was was provided provided by by Zakeri Zakeri and and Syri Syri,, and and the the LCC LCC of of a a CAES CAES plant plant is is highly highly dependent dependent on on fuel fuel costs,costs, emissions emissions costs, costs, and and charging charging electricity electricity prices prices [11] [11].. Comparing Comparing the the investment investment cost, cost, capacity, capacity, lifelifetime,time, energy energy density density and and storage storage duration duration,, PHS PHS and and CAES CAES are are suitable suitable for for use use in in large large-scale-scale commercialcommercial applications applications where where they they are more economic [6 [6–12]].. 10000 SMES ) h W k Flywheel / $ ( t s 1000 o Li-ion C Capacitor y Super g r e Capacitor n CAES E l a t Lead i p 100 a acid PHS C TES Fuel Cells 0 0 1000 10000 Capital Power Cost ($/kW) FigureFigure 1. 1. CapitalCapital energy energy cost cost vs. vs. capital capital power power cost cost [6 [6––10].10]. PHSPHS,, as shown inin FigureFigure2 ,2, is is one one of of the the most most widely-used widely-used energy energy storage storage technologies, technologies, which which has hasdemonstrated demonstrated its merits its merits in terms in ofterms technological of technolog maturity,ical maturity, high cycle high efficiency, cycle efficiency, large rated large power, rated long power,service lifelong and service low operatinglife and cost,low operating but the location cost, but choices the arelocation highly choices restricted, are constructionhighly restrict cyclesed, constructionare long, maintenance cycles are costslong,are maintenance high and it costs impacts are high the local and environment,it impacts the so local the environment further utilization, so the of furtherPHS is limitedutilization [13 –of15 ].PHS In additionis limited to [13 PHS,–15 CAES]. In addition is another to feasiblePHS, CAES way tois realizeanother large-scale feasible way power to realize large-scale power storage. Since 1949 when Stal Laval proposed to store compressed air using Energies 2017, 10, 991 3 of 22 EnergiesEnergies 20172017,, 1010,, 991991 33 ofof 2222 undergroundstorage.underground Since cavern 1949cavern whenss,, thethe Stal researchresearch Laval proposedinin CAESCAES hashas to store beenbeen compressed progressingprogressing air [16][16] using.