Energy Storage Technology For Performance Enhancement of Power Systems

Published On: Jan 28, 2016


Today’s energy world is at a turning point. Resources are depleting, pollution is increasing and the climate is changing. As we are about to run out of fossil fuels in the next few decades, it is important to find substitutes that will guarantee our future energy supply on a sustainable basis. The global energy demand is huge and is set to grow by approximately 37% until 2040 (as per World Energy Outlook 2014). This global energy need, at the same time, has to be cleaner than the energy produced from the traditional generation technologies like coal, natural gas, etc. With this backdrop, the electrical grid and the power systems are experiencing rise of some disruptive innovations and possibly tomorrow’s power grid would see flow of power from both directions and an island of power systems comprising of Distributed Generation (micro grids, mini grid), Renewable Energy, etc.

While the extensive use of such energy sources can minimize threat of global warming and climate change, however the power output of these sources are not as reliable and as easy to manage the energy demand than the traditional power sources. One of the effective ways to overcome this challenge (reliable power delivery) is to store the power produced by these systems and subsequently use it in a controlled manner. The role of enabling technologies such as energy storage is becoming more important as the world moves towards deeper penetrations of innovative power systems. In order for these new sources of energy to become reliable as primary sources of energy, energy storage is a crucial factor.

The blog identifies the energy storage technologies available today, their market segments and its applications, key drivers, types of storage technologies, etc. that would be an enabler in overcoming the challenges of modern grids and distributed generation through available alternative energy sources.

ENERGY STORAGE MARKET SEGMENTS ACROSS THE VALUE CHAIN AND KEY DRIVERS

Energy storage technologies can operate across different technical and commercial functions of the electricity market segments, including generation, transmission, distribution, end-use or direct off-grid use. Key applications across each segments are illustrated below:

Brief description of each application is mentioned below:

  • Spinning Reserve: Depending on the application, the system can respond within milliseconds or minutes and supply power to maintain network continuity while the back-up generator is started and brought on line. This enables generators to work at optimum power output.
  • Ancillary Services: provide additional services used to maintain key technical characteristics of the system, including standards for frequency, voltage, reactive power control, network loading, etc.
  • Wholesale Arbitrage: provide the ability to match generation to wholesale market demand. Also, it can provide additional capacity in certain circumstances reducing the need for fossil fuel peaking power stations.
  • Power Quality and Reliability: Network operators have system reliability and quality standards which must be maintained. Energy storage can be used to maintain or improve system performance thus avoiding penalties from regulators.
  • Backup Security: The use of energy storage as a source of back-up power, providing UPS services, is an important application of energy storage.
  • Demand Management Incentive: Utilizing alternative technologies like energy storage, instead of upgrading existing networks by fossil fuels yields in incentives, tax benefits, etc.
  • Time of Use (TOU) Arbitrage: The ability for consumers to use energy storage to avoid high electricity tariffs by shifting load or shaving peak demand to a cheaper TOU charges.
  • Fuel Savings: The use of energy storage in the off-grid sectors, enable avoidance of costly fuel operating costs.

In each of these market segments, energy storage technologies can simultaneously fulfil multiple roles varying from load shifting, to spinning reserve, wholesale arbitrage and power quality.

Some of the prominent drivers for storage technologies are:

  • Increasing renewable energy targets: Large increases in the uptake of both utility-scale and distributed generation is growing to such an extent that energy storage is becoming increasingly important to smooth intermittent generation output and help manage the mismatch between supply and demand.
  • Increasing network costs: Energy storage has the ability to improve the efficiency of network operation by improving asset utilization through reducing peak demand.
  • Increasing need for reliable backup power: Backup power requirements in many sectors, such as telecom and data centers, are becoming more stringent. New energy storage devices, with their improved performance, are becoming the proven solutions in these niche markets.

TYPES OF ENERGY STORAGE TECHNOLOGIES

Energy storage technologies can be divided into three types,

  1. Mature technologies, including pumped hydro, compressed air (CAES)
  2. Conventional battery energy storage
  3. Emerging technologies, including flywheels, super capacitors and others.

Let us first understand in brief the description of key technologies, followed by qualitative comparison of those technologies.

  • Pumped Hydro Storage (PHS): makes use of two vertically separated water reservoirs. It uses low cost electricity to pump water from the lower to the higher elevated reservoir using either a pump and turbine or a reversible pump turbine. During periods of high demand, it acts like a conventional hydro power plant, releasing water to drive turbines and thereby generating electricity.
  • Compressed Air Energy Storage (CAES): systems use off-peak electricity to compress air, storing it in underground caverns or storage tanks. This air is later released to a combustor in a natural gas turbine to generate electricity during peak periods.
  • Battery Energy Storage (BES): is a mature technology that converts electrical energy into chemical energy for storage and then later discharge. Lead Acid batteries are the most common and widely used type of battery. Sodium sulphur batteries, nickel‐cadmium, and lithium‐ion batteries are newer technologies that offer high efficiency values and higher energy densities than lead acid batteries (though at a significantly higher cost).
  • Flywheel Storage (FS): involves using an electric motor to spin a flywheel at high velocity. The flywheel spins in a vacuum housing on magnetic bearings to reduce friction and maintain rotational velocity (and thus energy) of the flywheel. When electricity is demanded (discharge), the motor acts as a generator, converting the rotational energy into electricity.
  • Super-capacitors (SC): store energy in large electrostatic fields between two conductive plates, which are separated by a small distance. Electricity can be quickly stored and released using this technology in order to produce short bursts of power.

Parameters

PHS

CAES

BES

FS

SC

Technology

Proven

Proven

Proven

Promising

Proven

Storage Mechanism

Mechanical

Mechanical

Electrochemical

Mechanical

Electrical

Typical Range

Up to 2.1 GW

25 – 350 MW

100 W – 20 MW

On kW scale

1 kW – 250 kW

Environmental/Emission concerns

No emission

No emission

Very Low

No emission

No emission

Expected Life (Years)

40-60

20-25

5 – 15

30

30

Self-Discharge rate

Very Low

Very Low

Very Low

Very High

Very High

Electrical Efficiency

75-80%

>60%

88-90%

90-95%

>95%

Key Applications

Spinning reserve, Wholesale arbitrage

Wholesale arbitrage (Peak shaving), Spinning reserve

Spinning reserve, Power quality

Voltage regulation

Emergency power sources, power quality

Key Advantages

High bridging time, Infinite number of cycles

Large power and Energy density

High energy density, High bridging time

High efficiency, Steep accessibility

Maintenance free,
High power and energy density

Key Disadvantage-s

Ecological problem (at-least 2 reservoirs needed)

Large space required

Low power density, hazardous to environment

Small power range

Less storage capacity, low bridging time

Table 2. Qualitative Comparison of Key Energy Storage Technologies

From Table 2, it is clear that a variety of energy storage technologies exists with each one possessing different attributes and intended for different applications. The choice of the ideal storage technology to be used depends on a number of factors. The key ones, among others, are the amount of energy to be stored, the time for which this stored energy is required to be retained or to be released, spacing and environmental constraints, cost, and the exact location of the network on which the storage is required.

CASE STUDY – LEAD ACID BATTERY STORAGE SOLUTION FOR MEETING UTILITY’S PEAK LOAD

Problem Statement: The utility Kodiak Electric Association (KEA) in Alaska has a peak load of 27 MW and base load of around 11 MW. It’s existing power capacity consisted of 23 MW hydropower and 33 MW diesel generation, in addition to 4.5 MW of installed wind power capacity. The utility was further in phase of adding additional 4.5 MW of wind capacity into the system, however the existing power assets would not be able to provide sufficient frequency response to help compensate for the additional capacity to come on stream.

Solution Adopted: KEA selected battery storage solution (instead of adding diesel generation) to provide frequency response on stream as spinning reserve. The battery system by Xtreme Power delivered a 3 MW advanced lead – acid battery solution to the utility. The lead – acid battery system was considered because the system remains at a high state of charge and can discharge quickly for very short periods. The system monitors grid conditions 100 times per second and can instantly deliver 3 MW of power within 50 milliseconds, if grid frequency falls significantly. The system responds to an average of 285 of these events throughout each day and enables much fuller use of the wind resource. The total cost for turnkey storage system was approx. INR 20 Cr. ($ 1 million/MW) (excluding costs incurred by the utility, including a step-up transformer and MV switchgear).

Benefits & Conclusion: In the first six months of implementation, KEA integrated another ~4.4 MW of wind power into grid, displacing diesel generation that would have higher generation costs and increasing environmental concerns too. The utility’s decision to use storage system was based on a desire to increase its renewable wind source integration, improve sustainability and reduce operating costs.
(For details, visit link: ALASKA, U.S., ISLAND/OFF-GRID FREQUENCY RESPONSE)

CONCLUSION

We thus note that there are daunting challenges to harness sustainable power supply through alternative energy sources for the future. Such energy sources contribute varied quantum of energy in intermittent forms. There is a clear need and capability of Energy storage which can be deployed throughout electricity systems to help facilitate increased penetrations of intermittent renewable generation, while producing numerous other operational benefits in parallel, such as load shifting, grid stability and power quality.

REFERENCES

  1. World Energy Outlook 2014 – International Energy Agency
  2. Electrical Power Quality & Utilization Magazine Volume 4, Issue 1 – Kuldeep Sahay & Bharti Dwivedi, Institute of Engineering & Technology Lucknow, Uttar Pradesh Technical University, Departement of Electrical Engineering, March 2009
  3. Performance Enhancement of Voltage Compensators with Battery – Supercapacitor Combination – International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181, Vol. 4 Issue 07, July-2015
  4. Electricity Energy Storage Technology Options – A White Paper Primer on Applications, Costs, and Benefits, December 2010
  5. Energy Storage Technologies & Their Role in Renewable Integration – Andreas Oberhofer , Research Associate, Global Energy Network Institute (GENI), July 2012
  6. 2020 Strategic Analysis of Energy Storage in California – Public Interest Energy Research (PIER) Program, FINAL PROJECT REPORT, November 2011
  7. Evaluating Energy Storage Options: A Case Study At Los Angeles Harbor College – Bren School of Environmental Science & Management Group Project
  8. Energy Storage Study – AECOM Australia Pty Ltd, 13 July 2015
  9. Overview of current and future energy storage technologies for electric power applications – Ioannis Hadjipaschalis, Andreas Poullikkas *, Venizelos Efthimiou Electricity Authority of Cyprus, 2009
  10. Energy storage opportunities and challenges – A west coast perspective white paper, April 4, 2014
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