The Role of Energy Storage with Renewable Electricity Generation

Abstract

Renewable energy resource like solar and wind have huge potential to reduce the dependence on fossil fuel, but due to their intermittent nature of output according to variation of season, reliability of grid affected therefore energy storage system become an important part of the of renewable electricity generation system. Pumped hydro energy storage, compressed air energy storage, flywheels, capacitors, and super conducting magnetic storage technologies have been developed, but many of these are limited in their capacity, characteristics and site dependence. Currently battery energy storage system is not much adopted within grid, but with development their density, versatility and efficiency it is observed that BESS- (battery Energy Storage system) will be adopted in large quantity.

1. Introduction

Energy demand for single consumer to power station is varying throughout the whole day, and there is variability and uncertainty in the power quality, also there is imbalance of energy demand and supply which is completed using fossil fuels. These create environment pollution and global warming effects, that’s why our main focus is diverted towards renewable energy resources; on the other hand these are variable and intermittent nature of energy generation so for their flexibility, stability and reliability energy storage technologies are put into practice. By transmitting the stored energy temporal as well as geographic gaps between demand and supply can be filled, also the areas having poor energy infrastructure or not electrified can be energized with the reliable source of energy storage (ES) [1]. Also, as there is no direct connection between consumer and electricity generation sources, Whole power generated at power station doesn’t reach to the consumers, and large amount of energy is being lost in the form of losses, in this way current gird system become inefficient. System can be made more efficient by using battery energy storage system in gird, by running plants near to their full capacity, and also by using maximum amount of power generated at power stations [2]. In power distribution system battery energy storage system is provided in two ways, either storage is provided at distribution substation or at distribution feeder also SCADA (supervisory control and data acquisition) equipment, control schemes, and economics of scale can easily access using centralized storage technologies [3]. Power quality is maintained easily with the installation of comparatively sized batteries in the installation of large solar PV plants, battery energy storage control system is done either automatically or using solar couple system [4]. Majority of energy storage within grid is present in the form of pumped hydro storage plants about 125 GW, it makes about 3% of global power capacity [5]. Pumped hydro energy storage, compressed air energy storage, flywheels, capacitors, and super conducting magnetic storage technologies have been developed, but many of these are limited in their capacity, characteristics and site dependence. Currently battery energy storage system is not much adopted within grid, but with development their density, versatility and efficiency it is observed that BESS will be adopted in large quantity [6].

2. Literature review

Although fossil fuel complete our desire of electricity but on the other hand these are destructing the planet, so now day’s renewable energy resources including hydroelectric, geothermal, solar thermal, biofuels, biomass, wave, tidal, and wind are being used to generate electrical power. More importantly, wind and solar are more developed due to their environment friendly characteristics [7]. There is uncertainty in the output of solar and wind or it can be said that their output is not constant, and depend on season whether it is sunny days or cloudy and also the location for proper required wind speed. This uncertainty in output of these renewable energy resources result in the requirement of energy storage devices for the reliability and improvement in economy of power system [8]. Major problem associated for renewable energy resources is the inconsistent power output, that can easily be reduced and solved using battery energy storage technology, along with that it result in decarburization of energy mix and mitigation of CO₂ emission, and global warming effects. BESS can easily be adopted in off grid as well as in on grid system, also at any location in the power system from generation to consumer. Batteries installed at solar photovoltaic PV and wind power plant allow owners to store the energy when energy prices are low or there is inexpensive and uneconomic to supply to grid, and can be released to use during high prices time. Batteries installed with PV system and wind generator at household level increase self-produced and self-consumption electricity, a household PV system with battery system result in increment of self-consumed energy about 30% without storage to 60–70%, along with that efficiency is increased and also additional power requirement from grid is decreased [9].

Now a day most of the storage in every country is the pumped hydro storage with the capacity of 200 MW, about 25 MW of electrical power is generated using pumped hydro storage plant, out of that 22 MW is being generated in United States. These plants are basically used during peak demand time, also providing water for the nuclear and steam power plant to enhance their performance efficiency and frequency control and regulation [10]. Another bulk storage technique in which air is compressed at the time of low demand with low energy prices, and during peak hour power can be generated at low cost with respect to stand alone gas turbines [11]. Because of new technology in concentrated solar thermal power system and photovoltaic system, demand of energy storage system is increasing in offshore platforms, and telecommunication installations (which are remote area power supply system), mobile applications, emergency backup, gird connected renewable power plants, and stressed electricity supply system [12].

This study shows the renewable energy generation and energy storage analysis in the Finland, It is committed that by year 2050 greenhouse effects will be reduced to 80–97% as compared to year 1990 [13]. Finland is dominating on run of river hydropower with limited capacity of 5.5Twh approximately, during months of December–April in winter season water is stored in reservoir and in summer season, that stored water is used to generate electrical power [14]. It is examined that energy storage technologies can play an important role for getting proper benefit of solar resources, along with that gas storage, thermal energy storage, stationary batteries and power to gird technologies are also discussed [15]. Solar photovoltaic and wind are variable sources of power generation; about 70% of total energy generation is being generated using these technologies, about 51% of renewable energy generation is stored and 47% is directly utilized [16]. This study is about United states, inspite of knowing the benefits of energy storage technologies, only 2.5% of total electric power of United States is being stored (out of that most part is hydro pumped storage system), which is about 10% of Europe and 15% of Japan energy storage [17]. About 99% of worldwide storage capacity of 127000 MW is pumped storage, at second compressed air storage with capacity of 440 MW. Electrochemical energy storage has lot of system friendly characteristics i.e. high round trip efficiency, no any pollution, flexible energy and power characteristics, long life and low maintenance. Because of compact size of batteries, these are suitable for distributed locations, also can reduce variation in output voltage of solar PV and wing power plants [18]. From this study it is estimated to increase the renewable generation around 60–80% by the year 2030, which is currently about 20% of total generation of the country; at same time, high cost of battery and un availability of suitable location will result in the limited installment for compressed air energy storage and pumped hydro storage technologies [19].

3. Summary of empirical literature regarding impacts of energy storage technologies

Ref. no	Year	Storage technologies	Summary and conclusion
05	2016	Pumped hydro energy storage	Electricity can be generated at lower price using pumped hydro energy storage system, also solar and wind power plant installation can result in cost free surplus energy.
02	2016	Battery Energy Storage System	Installation of variable renewable energy resources and battery energy storage can play an important role for 100% renewable energy based Finland.
[7]	2015	Pumped hydro energy storage	The wastage of energy either solar or wind can be minimized using pumped hydro energy storage system
[19]	2015	Battery Energy Storage	The efficiency, lifetime cycle, discharge time and weight of battery energy storage technology are considered as superior to all other storage technologies. Lithium ion batteries are only used in small electronic devices, but not for large amount of storage because of their high cost and limited performance characteristics.
[20]	2015	Thermal, pumped hydro and battery Energy Storage	Thermal energy storage, batteries, sodium Sulphur, lithium ion, pumped hydro storage and compressed air energy storage are suitable technologies for large scale storage of the order of 10–100 s of MW h.
[21]	2015	Hybrid energy storage system of batteries and capacitors	Hybrid electrical energy storage system of batteries and super capacitors result in increment in battery life and reduction in their cost.
[22]	2015	Compressed air energy storage, flywheel, batteries, super capacitors, hydropower and hydrogen energy storage	The variation in electrical power price as well as in their price can be avoided with the installation of electrical energy storage devices, also enhancing decentralized generation technology.
[23]	2014	Electrical Energy Storage	Small capacity energy storage devices can be encouraged at negative electricity prices.
[24]	2014	Remotely located renewable energy storage	In poorly interconnected island grid system or remotely located renewable energy based system, electrical energy storage are behave as an added value energy resource.
[25]	2014	Battery Energy Storage	Wind and Solar energy generation result in dispatch ability and reliability problems in decentralized generation, which are mitigated with the help of EES systems; redox battery is concluded as most promising technology.
[26]	2014	Hybrid Electrical Energy Storage	Different techniques are analyzed for enhancing the performance of hybrid electrical energy storage system with keeping low cost, along with their merits and de merits.
[27]	2014	Battery and Electrical Energy Storage	The installation of renewable generation in distribution system result in changing in design and operation of power system, hence battery energy storage as well as other EES system are used to support the existing power system as well as developing power system infrastructure.
[28]	2014	Electrical Energy Storage	It is concluded from the study that electrical energy storage system integrated voltage control system are more accurate, and valuable as compare to conventional voltage control schemes.
[29]	2014	Electrical Energy Storage	As EES has some issues, their policy and barriers, their solution in North America are being discussed.
[30]	2013	Battery Energy storage	It is concluded that for gird integrated storage, it is important to enhance the life cycle in order to improve the scalability of battery technologies.
[31]	2013	Battery energy Storage	Zn-air batteries and NANiCl batteries are promising technologies for buildings, due to their high energy density and power capability, and high life cycle.
[32]	2013	Super capacitors storage	Long life cycle, high charge and discharge efficiency, and high power density characteristics of electrochemical super capacitors technologies are the key features to use these technologies into aerospace, automobiles, and portable electronics.
[33]	2013	Hybrid Electrical Energy storage	Optimal hybrid electrical energy storage system result in about 60% more return on investment as compare to lead acid battery system.
[34]	2013	Hybrid Electrical Energy Storage	Residential user connected to gird connected hybrid electrical energy storage system, can get benefit of lowering the electricity price by storing energy during low price hours and releasing that energy during high price time.
[35]	2012	Battery Energy Storage	Emission control of power plants can be efficiently done with the help of battery energy storage system.
[36]	2012	Fuel cell	It is concluded that a more optimal cell with efficiency of more than 90% can be developed with same densities.
[37]	2011	Hybrid Electrical Energy Storage	It is concluded that proposed Hybrid energy Storage System HEES system result in improvement of capacity utilization, and in cycle efficiency up to 108% and 127% for dc power demand profile and high current pulsed power profile respectively.
[38]	2011	Electrical Energy Storage	Proposed method can reduce the fuel consumption and power capacity installation of peak load units up to 50%.
[39]	2011	Super capacitor Storage	From super capacitor to battery and battery to super capacitor charge migration result in improvement I efficiency about 51.3%.
[40]	2010	Fuel Cell	By connecting energy buffer to the grid, active power can be provided as well as power flow can be smoothed.
[8]	2010	Electrical Energy Storage	Variable generation energy sources require more flexible operation and generation reserves, which are completed by energy storage system.
[41]	2008	Flywheel and Pumped hydro Energy Storage	It is concluded that development in flywheels and pumped hydro power also should play an important role in such a niche marketplace

3.1 Applications of energy storage technologies

Applications of energy storage technologies are categorized as follow based on their discharging length.

3.2 Storage technologies for power quality applications

Transient stability and frequency regulation are the part of power quality applications, which require less than a second it means rapid response, but their time may goes up to 10 minutes. Following technologies are used in these applications:

3.3 Flywheel

It stores energy in the form of rotating mass, because of high efficiency and rapid response these are suitable for frequency regulation [8]. This technology is many advantages like high efficiency, quick response, he life of service, low operation and maintenance cost, stable system, clean technology, but the energy density is low, easy to be self-discharge which is only suitable for short time applications.

3.4 Capacitors

Super capacitor and superconducting magnetic energy storage are two main carrier of electromagnetic energy storage. This technology has high power density, low maintenance and operational cost, quick response, long life span, and their charging and discharging rate is critical. These are used in transient voltage stability application due to their fastest response among all energy storage devices and energy is stored in the form of electric charges. But, these are redistricted to use in long time duration application due to their low energy capacity; with the advancement and research work their use and density can be increased in grid [8].

3.5 Superconducting Magnetic Energy Storage (SMES)

The coil of superconducting material store energy in the form of magnetic field, are fast responding energy storage devices, but are restricted to use in short duration discharge time and their total energy capacity [8].

4. Storage technologies for bridging power

When there is error in unit commitment and contingency reserves, these applications provide load forecast, contingency reserves and additional reserves, and require rapid response and discharge time. Lead acid, Nickel metal hydride, lithium ion and Nickel cadmium batteries can provide frequency regulation, on the other hand can limit battery life [8].

4.1 Storage technologies for energy management

These applications require continuous discharge rating for several hours; following technologies are used in the technologies.

4.2 Thermal energy storage

In this storage system energy is not stored and directly used, so some times this can be ignored as electricity storage technology, but can be equivalent to electricity storage in some applications. In solar thermal generator, solar power is store in molten salt or another medium is used to generate electricity [8].

4.3 Pumped hydro energy based storage

In this method of energy storage, potential energy of water is being stored by pumping water from lower reservoir to the higher level at low price or during off peak time and same stored water is used in the peak hours by operating turbine to generate electrical power. To transfer water from lower reservoir to higher reservoir wind and solar based pumped storage hydroelectric storage system are shown in Figures 1 and 2. Electricity can be generated at low price using this technique, but it requires appropriate geography and availability of sufficient amount of water. Currently this storage system is working as large scale energy storage, along with improving the daily capacity factor of power plants. According to Electric power Research Institute about 99% of the bulk energy storage around the world (127GW) is done using pumped hydro energy storage system [42]. Large PHES system has capacity of more than 10 MW, small PHES system has capacity from KW to 10 MW, and micro PHES system has capacity of 100KW and the Plants having capacity less than 5KW are known as Pico pumped hydro energy storage system. As installation of renewable energy is increasing, PHES is becoming an important part of energy generation system due to their efficiency in range of 70% to 80. In different geographically areas wind base pumped hydro energy storage systems are considered as most economical and technical competitive [43, 44].

Figure 1.

Wind power based pumped hydro energy storage system [7].

Figure 2.

Solar PV based pumped hydro energy storage system [7].

As solar energy is available to us during day time about 6–8 hours in a day, hence to get the proper and maximum benefit of this solar energy solar based pumped hydro energy storage system PHES system is made; using that method the required energy is transmitted through the grid system and remaining excessive energy is used to store the water in upper reservoir from lower reservoir during off peak period, and by releasing that water during peak hours electrical power can be cost effectively generated. It has large capacity, long service and low unit cost, but due to geographical conditions impact this technology is somehow redistricted.

4.4 Compressed Air Energy Storage (CAES)

Air is compressed and energy is stored in an airtight underground storage cavern, at the time of energy requirement that compressed air is taken from vessel, heated and expanded in high pressure gas turbine, where that air is mixed with fuel and combustion takes place and exhaust is expanded through low pressure turbine to environment through chimney. CAES has compression ratio of 0.6–0.8 and heat rate of 4000–4300 BTU/kWh [8]. This technology has huge capacity, as well as operation time, and service lifetime, along with that it can supply combine heat, cold and electrical power. But, due to their low capacity and complexity, and location dependent this technology is also redistricted.

5. Heat storage

Latent heat and sensible heat storage are two basic types or technologies used in heat storage. In sensible heat storage, water (heat storage medium) is heated to increase the temperature; latent heat storage uses the regenerative material achieving phase change heat storage, which is implemented on the solar thermal power generation. During rainy season, electricity can be produced using photo thermal system; in this way output is able to adjust according to requirement. Thermal storage system have efficiency about 95%–97%, cost is low as compare to that of large scale battery storage about (1/30th).

6. Chemical energy storage

Hydrogen or any other synthetic gas is used as electrolyte and synthetized into methane gas with carbon di oxide, this technology is known as secondary energy carrier. This storage system is cleaner and can be storage system of above 100GWh energy, but their efficiency is low about 40%–50%, security is low and also cost is high. Many countries are using hydrogen storage system, in which fuel cell is basic manner to utilize hydrogen. Currently the main aim for its application is to improve its cost, efficiency and lifespan, leading to a prospect of better renewable energy utilization and large-scale hydrogen as the fundamental energy system.

6.1 Battery energy storage

High temperature batteries and liquid electrolyte flow batteries are two general types of batteries used in energy management system. In year 2009 sodium sulphur batteries were consider as most mature high temperature batteries; liquid electrolyte flow battery has this advantage that their energy and power component can be sized independently [8].

6.2 Types of batteries

Lead acid, Lithium ion, Nickel metal hydride, Nickel cadmium, sodium sulphur, Sodium Nickel chloride, redox flow and zinc air batteries are mostly used in energy storage system. Each type of battery has their own characteristic like storage capacity, life time cycle, cost and charging/discharging cycles. Sodium sulphur batteries response very quickly and their life cycle is about 15 years, but are expensive [45]. For small amount of storage applications, Lithium ion and nickel cadmium are attractive, but for higher amount of energy storage applications these batteries are expensive. According to IRENA 2015b, storage technology is chosen on the base of their parameters [46].

6.3 Lead acid batteries

This type of battery has low cost, and deep cycle, and are used in industrial applications as well as in on grid application since hundred years. But, due to their lower specific energy and power, lower cycle life and longer charging time, their capacity in large capacity renewable energy is less as compare to sulphur and Lithium ion batteries. These batteries are well suited for frequency regulation applications because of their low upfront cost, and with the advancement in research it is aimed to increase life cycle, charge acceptance, cost reduction, discharge performance. To improve the power active materials having low internal resistance and life cycle is improved using enhancing the design [9].

6.4 Lithium based batteries

Recently, lithium ion batteries are used in residential and commercial usage and in electric and hybrid vehicles, worldwide grid connected battery capacity is currently about 200 MW and is increasing very fast. Because of their high energy efficiency, compactness, maintenance free design, long life and versatility, these batteries are justified but for their precise management and charge control purpose electronic devices are used which make the system to be complex. With the research there will be improvement in their life cycle, energy density, cost reduction and charging/discharging characteristics and market value will be increased [9].

6.5 Nickel based batteries

This type of battery is specially used in those applications having long cycle or fast charging conditions and extreme climate. Nickel based batteries work correctly in low temperature (less than −40 degree centigrade) environment; also it has long cycle and design life as well as good cycling pattern. Hence in can be said that these batteries are competitive technology choice for the areas where renewable energies are stored and cyclically, and it is considered as world’s most power full battery. In future with the advancement, their life cycle, and temperature ranges can be increased; alkaline batteries cannot be replace by any other type if battery because of their operational safety, reliability, performance and durability to face adverse environment [9].

6.6 Sodium based batteries

Long life cycle, high efficiency, fast response, and high energy density characteristics, make these type of batteries to be suitable for on grid applications; but it require high temperature and extra insulation and active heating. Sodium nickel chlorides are used at small level in on grid and off grid applications, but with the research advancement their recharge power and life cycle can be enhanced and that will result in reduction of their cost [9].

7. Challenges and future orientations of EES/the future for energy storage and renewable integration

As we are moving towards renewable energy for our electricity generation, and also with the development in battery energy storage technology and their life and cost, it is important to say that battery will be an important part of power system in near future. Battery storage system makes the grid to be more flexible and modernize, just like improvement of cycling performance of conventional thermal units at lower prices, coordination of hydro with solar and wind power plants, advancement in control system and communication [47]. With the development in battery energy storage system, their cost and performance characteristics are being improved, that make an important role in their market value. By storing energy using battery storage technology near to the loads transmission and distribution losses reduced, hence system efficiency is increased; stacked services and multiple value streams and services (which are easily monetize able in deregulated markets) are illustrated in Figure 3. The energy storage technology has promising application prospect in renewable energy generation grid integration, distributed generation, micro grid, transmission and distribution, smart grid and ancillary services. However, the large scale application of energy storage technology still faces challenges both in the technical and economic aspects. For the development in energy storage system, some new break throughs are required in capacity, long-lifespan, low-cost, high-security for electrochemical energy storage, high efficiency. Along with that simulation and operation optimization on storage technology should be focused in order to support theoretical as well as well practical knowledge for projects demonstration for promoting the commercialization and industrial system. At the same time it is necessary to establish a complete and rigorous professional cohesion, reasonable classification, transparency, openness and energy storage standards, which will provide strong support for research and development, production and application of energy storage, and promote the development of energy storage technology and related industries. Currently, lack of policies to support the technology, and high cost and other issues are main challenges for energy storage system in industrial applications. Two aspects should be considered in the future: on the one hand, it is necessary to propose energy storage system solutions with the participations from electricity users, electrical enterprises, researcher, economical organizations and social originations, and on the other hand, the suitable industry market mechanism and the subsidy policy should be promoted. Researchers should be promoted and encouraged for applications of energy storage in order to provide development model and achieve commercial operation of energy storage.

Figure 3.

Multiple value streams of battery energy storage [International Renewable energy agency 2016, Electric power research institute, & US department of Energy] [47].

8. Conclusion

With the generation of electricity using renewable energy resources, the dependence on fossil fuels can be reduced; but these are variable and intermittent nature of energy generation so for their flexibility, stability and reliability energy storage technologies are put into practice. Major problem associated for renewable energy resources is the inconsistent power output, that can easily be reduced and solved using battery energy storage technology, along with that it result in decarburization of energy mix and mitigation of CO₂ emission, and global warming effects. Long life cycle, high charge and discharge efficiency, and high power density characteristics of electrochemical super capacitors technologies are the key features to use these technologies into aerospace, automobiles, and portable electronics. From super capacitor to battery and battery to super capacitor charge migration result in improvement I efficiency about 51.3%. As solar energy is available to us during day time about 6–8 hours in a day, hence to get the proper and maximum benefit of this solar energy solar based pumped hydro energy storage system PHES system is made BESS can easily be adopted in off grid as well as in on grid system, also at any location in the power system from generation to consumer. With the development in battery energy storage system, their cost and performance characteristics are being improved, that make an important role in their market value. By storing energy using battery storage technology near to the loads transmission and distribution losses reduced, hence system efficiency is increased.

Acknowledgments

The author is thanking the Mehran University of Engineering and Technology Jamshoro for providing the necessary facilities for doing this research.