A comprehensive evaluation of energy storage options for better sustainability

Due to ever increasing global energy demand and the limited nature of fossil fuel reserves, there has been tremendous research and development studies in the literature, focusing on alternative and clean energy resources and systems. Renewables are the promising choice when it comes to addressing some critical energy issues such as climate change and energy security. However, renewables have intermittent and discontinuous supplies; hence, they need to be stored in ways that are affordable, reliable, flexible, clean, safe, and efficient. As a result, energy storage is becoming a crucial step to build innovative energy systems for a sustainable future. Energy can be stored in many forms, from electrical to chemical (eg, hydrogen), or electrochemical, thermal, electromagnetic, etc. Each form consists of different technologies, some of which are already commercially mature while others are at early research and development stages. Each of these options can be tailored to meet different end users' needs at different scales. Therefore, this study aims to conduct a comprehensive review on the most recent status of energy storage options, along with the requirements of various end users, and characteristics of smart energy storage systems. The main objective is to summarize the performance evaluation statuses of mechanical, electrochemical, chemical, thermal, and electromagnetic energy storage technologies. The selected performance measures are capacity flexibility, energy arbitrage, system balancing, congestion management, environmental impact, and power quality. In the end, some key recommendations and future directions for energy storage systems are provided.

Doi: 10.1002/er.4102

Publication Date: 2018

Publication Name: International Journal of Energy Research

Research Interests:
Renewable Energy, Hydrogen, Energy Storage (in Engineering), Environmental Sustainability, Batteries, and 2 moreElectricity and Distributed generation & energy storage systems

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REVIEW PAPER

A comprehensive evaluation of energy storage options forbetter sustainability

Canan Acar

Faculty of Engineering and NaturalSciences, Bahcesehir University, Ç

anCaddesi No: 4

–

6 34353 Be

ikta

, Istanbul,Turkey

Correspondence

Canan Acar, Faculty of Engineering andNatural Sciences, Bahcesehir University,Ç

an Caddesi No: 4

–

6 34353 Be

ikta

,Istanbul, Turkey.Email: canan.acar@eng.bau.edu.tr

Summary

needs at different scales. Therefore, this study aims to conduct a comprehen-sive review on the most recent status of energy storage options, along withthe requirements of various end users, and characteristics of smart energy stor-age systems. The main objective is to summarize the performance evaluationstatuses of mechanical, electrochemical, chemical, thermal, and electromag-netic energy storage technologies. The selected performance measures arecapacity flexibility, energy arbitrage, system balancing, congestion manage-ment, environmental impact, and power quality. In the end, some key recom-mendations and future directions for energy storage systems are provided.

KEYWORDS

batteries, electricity, energy storage, hydrogen, renewables, sustainability

INTRODUCTION

Increasing world population and rise in standards of liv-ing have been the 2 reasons behind ever growing globalenergy demand. So far, this demand has heavily beenmet by burning fossil fuels. However, their limited andnonhomogeneous reserves, climate change concerns,and energy security concerns have shifted the attentiontowards alternative energy sources and systems, such asrenewables. Although they have tremendous advantagesin terms of energy security and environmental impact,renewables are not continuous supplies of energy,

NOMENCLATURE:

CAES, Compressed air energy storage; CTES,Cold thermal energy storage; SMES, Superconducting magnetic energy storage; UPS, Uninterrupted power supply

Received: 12 March 2018 Revised: 18 April 2018 Accepted: 18 April 2018DOI: 10.1002/er.4102

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therefore, they need to be stored in reliable, safe, effec-tive, and environmentally benign ways for a sustainablefuture.

In the literature, there are many studies focusing onsmart energy systems for a sustainable future, and it is widely accepted that these systems require a variety of energy storage options designed to meet different enduse requirements. In traditional electricity generationand distribution systems, the challenge is to precisely adjust the supply to meet the fluctuating demand. Theexcess energy is usually converted to different forms otherthan electricity such as potential, kinetic, and chemical.The aim of this approach is to bridge the gap betweensupply and demand when there is a mismatch betweenthem.

In the literature, there is an increasing amount of studies on energy storage systems. For instance, Sugimotoand Mochizuki

have provided detailed information oninorganic nanomaterials and their utilization as energy storage systems. Zakeri and Syri

have conducted lifecycle cost analysis of electrical energy storage systems.Luo et al

have overviewed the most recent status andfuture research directions of electrical energy storage sys-tems and their potential applications in power systems

operation. Sternberg and Bardow

have performed envi-ronmental assessment of energy storage systems with anaim of finding the

“

most green

”

energy storage alterna-tive. Balali et al

have reviewed the environmental, eco-nomic, and material developments of several energy storage systems for the wide deployment of solar and wind energy.Energy storage systems can be classified based on various criteria. One classification method is based onthe type of stored energy: such as mechanical, electro-chemical, chemical, thermal, and electromagnetic. Inmechanical energy storage systems, energy is usually stored in potential or kinetic energy form. Rodriguezet al

have investigated heat generation from mechanicalenergy storage metal

‐

organic frameworks and how toeliminate the potential problems related to theoverheating of the storage medium. Hameer andNiekerk

have reviewed mechanical energy storagesystems for large

‐

scale electrical energy storage.Steinmann

has provided an overview of thermo

‐

mechanical concepts for bulk energy storage. Amiranteet al

have overviewed recent developments in energy storage with a focus on mechanical, electrochemical,and hydrogen technologies.Electrochemical energy storage is one of the mosthighly studied methods in the literature due to growingattention on batteries. Kundu et al

have focused onthe emerging chemistry of sodium ion batteries for elec-trochemical energy storage. Lin et al

have studiednitrogen

‐

doped mesoporous carbon of extraordinary capacitance for electrochemical energy storage with anaim to develop highly efficient batteries. Augustynet al

have investigated pseudocapacitive oxide materialsfor high

‐

rate electrochemical energy storage. Xia et al

have examined metal

‐

organic frameworks and theirderived nanostructures for sustainable electrochemicalenergy storage and conversion. Mao et al

have reviewedgraphene

‐

based materials for flexible electrochemicalenergy storage.Chemical energy storage systems contain a broadrange of materials and methods. In general, chemicalenergy storage medium is referred as a

“

fuel.

”

Hydrogen,ammonia, and methane are some of the most commonchemical energy storage materials. In the literature, thereis growing attention on hydrogen, especially with evolv-ing technologies related to fuel cells and novel hydrogenproduction methods. Hydrogen has a broad range of applications from stationary to mobile and transporta-tion. As a matter of fact, hydrogen has been consideredfor aviation applications and be the key to sustainableaviation.

Hydrogen can be produced from a variety of energy and material sources in a sustainable manner. Inthe literature, there are various studies on efficient solarhydrogen generation

and hydrogen production from wastewaters.

Together with hydrogen, ammonia is seenas an efficient storage medium for renewable energy resources.

Despite its carbon content, methane alsohas a potential to be a part of sustainable chemical energy storage systems.

Thermal energy storage systems can be grouped into 2based on latent or sensible heat storage. Pielichowska andPielichowski

have reviewed phase

‐

change materials forthermal energy storage. Ji et al

have enhanced thermalconductivity of phase

‐

change materials with ultrathin

‐

graphite foams for efficient thermal energy storage.Zhang et al

have provided an overview of the recentdevelopments and practical aspects of thermal energy storage systems. Sharma et al

have investigated devel-opments in organic phase

‐

change materials and theirapplications in sustainable thermal energy storage sys-tems. Joseph et al

have conducted characterizationand real

‐

time testing of phase

‐

change materials for solarthermal energy storage.Compared with some conventional energy storagesystems such as mechanical energy storage, electromag-netic energy storage is relatively new, but there is increas-ing attention in the literature on these systems. Zhao andZhang

have studied electromagnetic energy storage andpower dissipation in nanostructures. Vulusala et al

havereviewed application of superconducting magnetic energy storage (SMES) in electrical power and energy systems.Saadatnia et al

have conducted modeling and

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performance analysis of duck

‐

shaped triboelectric andelectromagnetic generators for water wave energy harvesting.In the literature, there are several studies reviewingenergy storage technologies for specific applications (suchas for power networks) or scales (such as grid

‐

scale), aspecific type of energy (such as wind), or only for thermalor electrical energy storage. In this study, it is aimed tocomparatively assess performances of a wide variety of energy storage systems (including chemical and thermalenergy storage to electrical energy storage systems) by taking 11 different criteria into account. The ultimategoal of this study is to provide a comprehensive resourcefor researchers, industry, and policy makers on potentialimprovement potentials of each energy storage method.The main motivation behind this study is the need toprovide a comprehensive review and investigation onenergy storage systems, which could potentially guideresearchers, policy makers, different industries, andenergy market customers. In the literature, there is a lackof studies focusing on a complete technical, environmen-tal, energetic, and economic evaluation of energy storagesystems. Therefore, in this study, the primary goal is toconduct a performance investigation of some key energy storage technologies, which are mechanical, electrochem-ical, chemical, thermal, and electromagnetic energy stor-age technologies. Specific energy, energy density, specificpower, power density, efficiency, lifespan, self

‐

dischargerate, energy capital cost, power capital cost, and environ-mental impact are the performance measures to evaluatethe current status of the energy storage systems. In theend, several recommendations and future directions areprovided for the quality and end use enhancement of energy storage technologies.

ENERGY STORAGE AND ITSBENEFITS

There are many different energy storage systems in theliterature, including mechanical, chemical, electrochemi-cal, thermal, and electromagnetic energy storage. Each of these systems are capable of meeting different end users

energy demands, which make them have different char-acteristics. Figure 1 shows the general expectations fromenergy storage systems.In Figure 1, high storage capacities mean high volu-metric (eg, kWh/L) and gravimetric (eg, kWh/kg) densi-ties. Cost of an energy storage system includes capital,fuel, and operations and maintenance costs, therefore,all of these items should be as low as possible in a desir-able energy storage system. Adaptability indicates effec-tive operation under situations where input and outputdemand rates are varying. High efficiency also meanslow heat generation and/or heat loss in energy storagesystems. And finally, better environmental performancerequires less (or zero) negative impact on the environ-ment (ie, benign to land, water, and air).In reality, energy storage systems have diverse charac-teristics, and there are additional expectations from eachone of them, depending on different end user require-ments. However, they all are employed together to pro- vide reliable, affordable, safe, efficient, and clean energy when the supply and demand do not meet each other.Many of the characteristics of energy storage systemsare similar to traditional energy generation systems. Onthe other hand, they have some additional attributes, which make energy systems more complex. The mostnoticeable example to this is that energy storage systemsare considered to be a part of both production (system)and end use (service) part of overall energy systems.Therefore, they might be treated as generators and systemload at the same time.Unlike energy production systems (except hydro-power plants), energy generation from the storage systemis for a limited period. This means that in energy storagesystems, the highest (peak) generation can be sustainedfor a defined period depending on the amount of energy formerly stored in the systems. In addition, most of theenergy storage systems have cycling limits on top of thelimited power generation capacities. However, despitetheir challenges, energy storage systems have the signifi-cant advantage of meeting energy demands when thereis no or limited supply. Along with this major benefit,their additional environmental, economic, and technicalbenefits make them necessary and fundamental in energy systems. Figure 2 shows the criteria to evaluate whendesigning (or choosing) an appropriate energy storagesystem.Figure 2 shows some very important criteria to con-sider when designing (or choosing) an appropriate energy storage system. For instance, if a system has high charg-ing and discharging power ratings but a low storagecapacity (eg, can be an energy supply for couple of hours),it might be a good choice for quick and short emergency

FIGURE 1

General expectations from energy storage systems[Colour figure can be viewed at wileyonlinelibrary.com]

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situations, power banks, etc, but not for seasonal energy storage. Another example is that a system with low capi-tal cost and high operating cost would be a better fit forshort

‐

term energy storage (eg, peak demand and emer-gency situations) needs. On the other hand, a system withhigh capital and low operating costs is better suited forlong

‐

term energy needs such as seasonal storage. There-fore, it can be said that the criteria listed in Figure 2 isused for determining what kind of a task an energy stor-age system would be the most appropriate choice.In addition to the criteria presented in Figure 2, thereare some other important elements, for instance,response speed, black start capability, flexible capacity,congestion management, and power quality. When anenergy storage system is being selected and/or designedfor a specific need, these additional criteria are alsoimportant to take into account. For instance, duringemergencies (eg, earthquakes and disease outbreaks),emergency response and congestion management couldbecome more important than the flexible capacity.Figure 3 shows critical distinctive aspects to take intoaccount when selecting an appropriate energy storagetechnology.The critical aspects shown in Figure 3 are also impor-tant when selecting an energy storage technology for atraditional power plant. For instance, energy storage sys-tems with rapid response times and short dischargeperiods could be useful in applications related to powersystem stability.Energy arbitrage is one of the tremendous advantagesof energy storage systems compared with using energy generation systems alone. Energy storage systems can beused to store electrical (or thermal) energy when the mar-ket prices are low, and this stored energy can be usedand/or sold when the prices are higher (eg, pumpedhydro storage). Cold thermal storage, for instance, takesadvantage of low electricity prices at night to store the

“

cold,

”

which automatically reduces the system load (ie,compressor and cooler) during peak times. Anotheradvantage of using storage systems along with energy generation technologies is the nature of renewable energy supplies. With energy storage systems, the mismatchbetween fluctuating renewable supplies and demandcan be eliminated, which provides stability to both gener-ation and load.Benefits of energy storage systems are shown inFigure 4. It should be noted that most of the energy stor-age systems are not capable of providing all these benefitstogether. For instance, flywheels and supercapacitors areresponding very fast to changes in supply and demand.However, currently, they are not as affordable as other

FIGURE 2

Criteria to evaluate the performance of an energy storage system [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 3

Critical distinctive aspects to take into account whenselecting an appropriate energy storage technology [Colour figurecan be viewed at wileyonlinelibrary.com]

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storage options in terms of energy arbitrage. These sys-tems are also not capable of meeting the multihour peakenergy requirements.One of the challenges of energy systems is the fluctu-ations on the demand side. End users require reliableenergy supply at all times, including the peak demand, which forces energy suppliers to find additional energy resources. In some cases, peak demand happens very rarely such as couple of hours per year, and it is very costly to meet this demand via additional power genera-tion capacity. In such cases, energy storage offers theadvantage of flexible capacity and meet the peak demand without being an extra load on the generation side.Energy storage systems do not only have the advantageof meeting the peak demand. Its flexible capacity allowsthe generation side work on a steady (optimum perfor-mance) state while the storage system bridges the gapbetween supply and demand instantaneously. Flexiblecapacity is also key to renewable energy systems sincerenewable supplies are not continuous (eg, wind andsunny/cloudy days), and the peak demand and supply times generally do not happen at the same time (eg, peakdemand occurs in the evening when there is no sun).Therefore, efficient, reliable, affordable, safe, and cleantechnologies are needed to store renewable energy sources.Energy storage systems have additional advantages onthe end users

side. For instance, with energy storage sys-tems, the end users are less affected by the peak demandcharges, and they have access to high quality backuppower at all times, which are significant economic advan-tages from customers

perspective. In addition, withenergy storage systems, the peak demand pressure andtransmission and distribution losses are minimized andmight be eliminated. Therefore, flexible capacity can beconsidered as a main advantage of energy systems andthis benefit could accelerate the development and deploy-ment of novel energy storage systems in the entire energy supply

‐

demand chain.Currently, energy arbitrage benefits of storage systemsis mostly accomplished via pumped storage. In pumpedstorage, bulk quantities of energy is shifted from low tohigh price hours and vice versa. Together with flexiblecapacity, energy arbitrage have been seen as the key eco-nomic advantages of energy storage systems.Reliable operation of the entire energy supply chain(including 3S: source

‐

system

‐

service) requires effectivesystem balancing. System balancing can be accomplished via a variety of ancillary services to ensure:

•

Effective energy transmission from source to service(load)

•

Reliable and safe operation

•

Uninterrupted service to end users (customers)

•

Balanced supply and demand

•

Adequate contingency (or emergency) reserves

•

Stability of the entire network

•

Black start capability Stability of the entire energy supply

‐

demand chain isessential, and it means the ability to quickly restoresteady (optimum) operation after a disruption (such asan outage) without damaging the system any further.Energy storage systems could provide reliable supply insuch times when the conventional energy generation sys-tems are slow to respond to system disturbances. This isespecially critical in isolated locations where the central,large, and traditional facilities might not effectively respond to disturbances and bring back to stable opera-tion quickly. Therefore, energy storage systems are essen-tial to ensure stability of the entire energy supply anddemand networks. Another critical requirement for sys-tem stability is black start capability, which is importantduring recovery from any disturbances or disruptions.Black start capability means that an energy generator(or supply) can start its operation without any stationary power requirements. Currently, most of the energy gener-ators need stationary power to start up. However, energy storage systems could ensure the black start capability ina reliable and effective manner.Most of the power plants are placed far away fromhigh population, heavy demand points. As a result, high

FIGURE 4

Important benefits of energy storage systems [Colourfigure can be viewed at wileyonlinelibrary.com]

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voltage transmission lines are required to bring power toconsumers in cities, industrial areas, rural villages, etc.And when the demand sides require increased supply,these transmission lines could suffer from congestion.One way of reducing congestion is to locate generationsites near heavy consumption sites, which lowers thepressure on transmission lines and has economic bene-fits. However, several problems associated with conven-tional power plants such as land requirement, noise,and emissions make it challenging to move these plantsnear end use points. Therefore, energy storage systemsare seen as key to solve congestion problems due to thedistance (and transmission issues) between energy sourceand use points. When used together with renewableenergy resources, storage systems could have additionalbenefits of recovering excess renewable supply when thedemand is low and this stored energy can later bereleased when the demand is high and supply is low.The relationship between energy storage systems andtheir environmental impact is usually considered to becomplex in the literature. For example, none of theenergy storage systems is 100% efficient, and they gener-ally increase overall energy demand, which, as a result,enhances the negative environmental impact of energy generation systems. In the literature, there are some stud-ies indicating that energy storage systems increase green-house gas emissions because they are additional loadsduring nonpeak times, making traditional fossil fuelpowered plants operate at higher capacities. However,this problem can easily be eliminated with the inclusionof renewable sources in the energy market. As a matterof fact, energy storage systems accelerate the introductionand expansion of renewable energy generation in themarket, which can be seen as a significant advantage interms of being environmentally benign.Power quality is an indicator of reliability, safety,and efficiency of energy generation system components. Weak power quality could potentially increase mainte-nance costs, trigger system malfunctions, and upsurgeenergy consumption of system components such asmotors. One potential reason of inadequate power qual-ity is variable generator outputs. Energy storage systemscould solve low power quality related issues andenhance system reliability, which is especially importantfor some customers, such as industrial and commercialusers.

ENERGY STORAGE SYSTEMS

In this section, mechanical, electrochemical, thermal, andelectromagnetic energy storage systems are briefly reviewed along with their technological and economicstatus. Energy storage systems, in general, are capable of holding energy in one form for later use. The expectationfrom energy storage is the ability to keep the storedenergy content in between charging and dischargingperiod with minimal loss. In this study, the selected sys-tems first convert electrical energy in a different formduring charging for effective storage. The selected sys-tems are classified based on the type of stored energy, ascan be seen from Figure 5.In addition to the energy storage systems shown inFigure 5, most of the end use applications can act asenergy storage technologies. An example to this is adjust-ment of energy consumption time and peak demand.Additional examples are reduction of daytime coolingdemand by precooling, utility control of electric waterheaters, adjusting the time of municipal water use(eg, for irrigation systems), etc. Even though these activi-ties can be classified as energy storage methods, they areactually demand management activities, and thereforethey are not evaluated in this study.Selecting the most appropriate energy storage optiondepends on the available resources, site location, end userdemands, power requirements, etc. Table 1 categorizesenergy storage systems based on their power ratings andpotential applications.In the next subsections, environmental, technical,cost, and energetic performance results of mechanical,electrochemical, chemical, thermal, and electromagneticstorage systems are discussed. The performance resultsare taken from recent literature and ranked based onthe following equations:

•

Criteria that are aimed to be maximized (eg, specificenergy, energy density, specific power, power density,efficiency, and lifespan):

Rank

result

max ×10

(1)

•

Criteria that are aimed to be minimized (eg, self

‐

discharge rate, energy capital cost, power capitalcost, and environmental impact):

Rank

max

−

result

max ×10

(2)Here,

result

indicates the performance result of anindividual method (eg, specific energy storage capacity of pumped hydro), and

max

is the highest value in thatcategory (eg, highest specific energy capacity). Thereported units of each category can be listed as specificenergy (Wh/kg), energy density (Wh/L), specific power(W/kg), power density (W/L), efficiency (%), lifespan

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Report