INEEL November 2017

Panel 5: Mechanical Energy Storage Systems (Flywheels)

November 14th, Cuernavaca, Morelos, México

INEEL November 2017

5. MECHANICAL ENERGY STORAGE SYSTEMS (ESS)

5.1. Flywheels

5.1.1. State of the Art and Technology

A flywheel stores mechanical energy by means of the principle of the rotating mass. It is a mechanical storage device that emulates the storage of electrical energy converting it into kinetic rotating energy; and can convert that kinetic energy, again, to electrical energy when required.

The input energy to the flywheel energy storage system (FESS) is usually extracted from an electrical source from the grid or from any other source of electric power. The flywheel is then accelerated, storing mechanical energy and when it reaches a constant rotating speed, requires less energy to maintain it energized; When the flywheel delivers the accumulated energy it is discharged, becoming slower. The rotating wheel is driven by an electric machine (electric motor-generator) that performs the exchange of electrical energy to kinetic energy and vice versa. The flywheel and the electric machine have a common axis of rotation, so the control of the electric machine allows controlling the flywheel.

The flywheels energy storage systems are constituted by: a rotating rotor, an electric machine (motor-generator), four bearings (two axial thrust and two radial), a power electronics interface and a container or housing, all these components are described in the following subsections. Figure 5.1 shows schematically a typical flywheel system for energy storage.

Figure 5.1. Structure and Components of a Flywheel [1].

Axial Thrust Bearing

Housing

Radial Bearing

Vacuum Pump Axial Thrust Bearing

Flywheel rotor

Electric Motor-generator

Direct current link

INEEL November 2017

There are mainly two options for the energy storage system of flywheels of inertia: -the low speed flywheels (normally up to 10,000 rpm) and -the high speed flywheels (up to 100,000 rpm). The low speed flywheels are usually made of heavier metallic material and are supported by mechanical or magnetic bearings. High-speed flywheels generally use lighter but tougher composite materials and typically require magnetic bearings. In addition, a new class of intermediate-speed inertia flywheels is being developed, benefiting from the low cost of steel materials, but also from a sufficiently high energy density, based on the use of rolled steel. This has the potential to offer low cost options, as well as compact systems.

The electric machine or integrated electric motor-generator is coupled to the rotor of the flywheel to allow the bi-directional conversion of energy and the loading process of the flywheel. The machine, acting as a motor, loads the flywheel by accelerating it and extracts the electrical energy from the source. The energy stored in the flywheel is extracted by the same machine, acting as an electrical generator; therefore, the motor slows down (decreases its speed) during unloading. The common electrical machines used in the energy storage systems of flywheels are: the electric induction machine, the permanent magnet machine and the variable reluctance machine.

The energy conversion in a ESS (Energy Storage System) based on a flywheel (FESS), is done by the electric machine (motor-generator) and a bidirectional power converter. The topologies of the electronic power converters that can be used in energy storage applications by flywheels are DC-AC, AC-AC and AC-DC-AC or a combination of these. The switching devices of the power converters are selected based on their operating characteristics and their application. The most used configuration in the power converters of FESS is the configuration back-to-back (BTB) or AC-DC-AC, connected to a direct current link capacitor.

Bearings are necessary to keep the rotor in the correct place with very low friction, but providing a support mechanism for the flywheel. The bearing system can be mechanical or magnetic depending on the weight, cycle life and minor losses.

The casing/housing has two purposes: one is to provide tightness for obtaining a low gas entrainment and the other is to encapsulate the rotor in case of failure. The casing is the stationary part of the flywheel and is usually made of a thick steel or other high strength material, such as composites. The housing maintains the rotor in a vacuum environment to control the aerodynamic drag losses, maintaining a low pressure inside.

5.1.2. Implementation experiences

The most common applications of flywheels are: power quality, frequency regulation, voltage drop control, uninterruptible power sources (UPS), transportation (electric and hybrid vehicles), spacecraft (positioning control), renewable energies and military applications (pulsating power). As part of the energy storage applications, the flywheels carry out storage applications not only at the electric grid level but also at the customer level.

INEEL November 2017

Energy Quality. As part of the energy quality requirements, the grid frequency and voltage of the electrical system must be maintained at an acceptable level without important deviations. In the electrical grid, when the loads are added or subtracted, the voltage and frequency of the system will also be increased or reduced. Energy storage systems, especially fast-response ones such as flywheels, can quickly add or remove energy from the grid in order to keep the voltage and frequency of the system within the acceptable range.

Frequency Regulation. Frequency fluctuations occur as a result of variations between loads and power supply, when one exceeds the other. When the demand exceeds the energy supply, the power plants are slowed down by the additional load, thus decreasing the frequency of the system. On the other hand, the generators are accelerated and the frequency increases when the generation exceeds the demanded loads. The frequency fluctuates every second, since the demand varies and the generators start and stop or vary the power generation. To avoid this, frequency regulation is applied, which requires generators to maintain capacity in reserve, in order to maintain generation and consumption stability. Due to its rapid response and its frequent loading and unloading capacities, flywheels are suitable in these applications.

Control of Voltage Drop. Voltage drop problems like sags or swells are created due to unbalanced loads or failures in the grid, causing a decrease or sometimes increase in the magnitude of the voltage. Voltage losses due to unbalanced loads occur when large amounts of energy, during a short period of time, are absorbed by the load; therefore, the voltage will decrease and cause voltage drop problems. The FESS, with their excellent characteristics, can be a viable storage alternative for this cases. Particularly, a fast response, a high power density and a frequent loading and unloading capacity are the best attributes of the flywheels for voltage compensation applications.

Uninterruptible Power Sources (UPS). A short-term energy storage device (seconds to minutes) with control electronics is known as an Uninterruptible Power Supply and is one of the most successful existing application markets for high-power flywheels. They supply energy in periods that normally do not last more than 15 seconds. The uninterruptible power supply sources, such as standby storage, are a bridge to save the dead time that exists between the loss of power from the electrical grid and the start of operation of the energy backup sources during an interruption. In those cases where the ESS based on flywheels is working alone, as an uninterruptible source of electrical power, the electric machine working as generator, supplies enough electrical power for the electrical system to work, until the power grid is restored or a backup power source is connected.

Transportation. (A) FESS are used in hybrid and electric vehicles to store energy. The regenerative braking energy during the vehicle slowdown is stored in the flywheels and this will be supplied by the flywheel again to provide a boost during accelerations or hill

INEEL November 2017

climbing. (B) In the energy recovery systems of railway trains, FESS are installed in stations or substations to recover energy by means of regenerative braking systems and then supply it back to the system for traction purposes when needed. In addition, these FESS allow the control of the voltage drop of the transmission and distribution lines, without increasing the capacity of the railway's electric line. (C) The use of hybrid storage systems with flywheels in motor sports, has shown great developments, starting with Formula 1 and followed by the highest class of the Endurance World Championship.

Space Vehicles. The flywheels ESS have also applications in space vehicles where the primary source of energy is the sun and where the energy needs to be stored for some periods when the satellite is in the darkness.

Renewable Energies. The FESS can help in the penetration of the wind and solar energies into the power systems, by improving their stability. The fast response characteristics of flywheels make them suitable for applications that include renewable energies to stabilize the frequency of the electrical grid (regulation). Energy oscillations due to solar and wind sources are compensated by storing the energy during sunny or windy periods and this is returned to the electrical grid when it is required. Inertial flywheels can be used to rectify wind oscillations and to improve the frequency of the electrical grid; while, in solar systems they can be integrated with batteries to improve the energy output of the system and extend the useful life of the batteries.

Military Applications. In the military field, there has been a recent trend towards the inclusion of electricity in military applications, such as in ships and other land vehicles, as well as in weapons, navigation, communications and associated intelligent systems. The use of electrical energy at different machine speeds and different power levels requires energy storage to respond quickly and reliably to this demand for variable energy demand. Hybrid electric power is essential for future combat vehicles, based on their electrical applications, therefore, flywheels appear as an energy storage technology suitable for such applications as they are combined with super-capacitors to provide power to high speed systems that require some power in less than 10 μs.

INEEL November 2017

5.1.3. Advantages and disadvantages

Table 5.1.1 shows the applications, advantages and disadvantages of flywheel energy storage

systems.

Table 5.1.1. Applications, Advantages and Disadvantages of Flywheels as an ESS.

Applications. Advantages. Disadvantages.

Energy Quality. High Power Density (5 to 130 W-h/kg).

High Investment Cost (Compared to Batteries).

Frequency Regulation. High Return Energy Efficiency (90 to 95%).

Control of Voltage Drop. Long Useful Life (More than 20 Years).

Uninterruptible Power Source (UPS).

High Load and Discharge Cycles.

Transportation (Electric and Hybrid Vehicles).

High Response Capacity (s).

Space Vehicles (Position Control).

Minimum Maintenance.

Renewable energies. High Response Capacity (s).

Military Applications (Pulsing Power).

High Peak Power without Overheating.

Modular Technology.

INEEL November 2017

5.1.4. Technology Readiness Levels (TRL)

The international technology readiness level for some of the technological developments of the

flywheel ESS is 9, as indicated in Table 5.1.2 (Reference: Annex 0 of the Joint Call CONACYT -

British Council Mexico which is based on in the TRL methodology of NASA).

Table 5.1.2. Technology Readiness Levels of the Flywheel ESS

Level of

technological

maturity

Description Deliverables Commercial

Deliverables

Precompetitive

development:

9

Proven

technology

through

implementation

in an operating

environment.

The application

of technology

under real

conditions, such

as those found

in evaluations

and operational

tests.

Main

deliverable:

Product tested

under real

operating

conditions.

Results of the

application and

evaluation of

the product

under operating

conditions.

Feasibility analysis

that includes:

a) market analysis,

b) industry analysis,

c) benchmarking and

d) analysis of

intellectual property.

Business model

(preferably

CANVAS).

5.1.5. National Context

National Knowledge Gap

Although, the technology and equipment of the flywheels energy storage systems can be acquired as turnkey by recognized international manufacturers that have already installed and tested equipment in commercial operation, the national knowledge gap on FESS is currently big, due to the fact that only electrochemical energy storage systems (batteries) have been installed in Mexico.

Opportunities for Mexico.

Mexico needs to install ESS to improve the stability and quality of the electrical grid, due to the recent installation, of a large number of power generation units based on renewable energies,

INEEL November 2017

such as: wind and solar. For this reason, the Mexican government considers priority the installation of ESS and has published in the Official Gazette of the Federation (DOF: 02/12/2016) the Energy Transition Law, where establishes a Transition Strategy policy to Promote the Use of Cleaner Technologies and Fuels and specifically in point 7.4.2 that refers to Energy Storage, and dictates their action lines in Table 17 of that document, which is presented below in Table 5.1.3. Table 5.1.3. Energy Storage Actions (Table 17 DOF: 02/12/2016).

Categories: Lines of Action:

Regulations and

public policy:

Develop specific regulations for the interconnection of energy storage systems in

the Grid Codes.

Include the specific treatment for the contribution of related services of the

storage systems in the Basis of the Electrical Market, considering the needs and

opportunities of the grid for their integration.

Develop specific regulations for the construction, performance and removal of

energy storage systems.

Institutions: Develop a Technology Roadmap that identifies objectives, needs, challenges and

convergent priorities for the deployment of energy storage systems.

Publish information about the Electrical Market that eases the modeling of energy

storage systems.

Technical capacities

and human

resources:

Integrate the energy storage issues into the Strategic Program for the Training of

Human Resources in Energy.

Markets and

financing:

Promote the development of business models to impulse the technology, products

and services for the energy storage value chain.

Research,

development and

innovation:

Promote calls for the funding of the sector for the development of studies,

research projects, technological development and innovation in energy storage.

Promote national and international collaboration in research, development and

innovation in storage technologies, considering present collaboration agreements

such as Mission Innovation.

INEEL November 2017

5.1.6. Challenges

It is necessary to overcome four barriers or obstacles to expand and implement, in a general way, the technology of energy storage, as indicated in Table 5.1.4. Table 5.1.4. Barriers to be overcome and Challenges of Energy Storage Systems based on

Flywheels of Inertia.

No. Barriers Challenges

1. Energy Storage Systems at

Competitive Costs

The achievement of this goal requires to pay attention to

factors such as the cost of cycle life (charging and

discharging) and the energy efficiency of the technology

used for storage (increasing efficiency, energy density and

time duration of discharge).

2. Validated Performance

and Safety Tests

The validation of the security, reliability and performance of

energy storage is essential for the confidence of users.

3. Equitable Regulatory

Environment.

The value propositions for the storage in the electrical grid

depend on the reduction of institutional and regulatory

barriers to levels comparable with those of other resources

of the same electrical grid.

4. Acceptance by Industry Adoption by the industry requires greater confidence in the

energy storage systems; performing as planned and

promised.

INEEL November 2017

5.1.7. Guiding Questions for the Workshop Panelists

What is the state of the art of flywheel technologies?

Which are the main applications and requirements for this technology and the benefits?

What is the necessary infrastructure for the application of flywheel systems?

What are the experiences of applying flywheel systems in the world?

What are the most important challenges facing this technology?

In which applications flywheels, have a greater advantage over the other ESS?

In which applications flywheels must be operating in conjunction with other ESS?

What are the lines of research and development of this technology that could bring the most

benefits?

What are the gaps in current research that should be tackled to achieve the best results?

What previous studies are necessary for the application of flywheels in Mexico?

Are there flywheel systems that could be implemented in a pilot plant in Mexico and which will

be their capacity?

What are the immediate impacts that a technology of this type can be develop?

Which institutions are currently responsible of the development of flywheel applications?

Are there linkage opportunities between research and business that promote the integration

and development of flywheels storage in Mexico?

How long would it take to implement a flywheels pilot system?

5.1.8. Bibliography

1. Steitz D. E., Rink C.; NASA Looks to Go Beyond Batteries for Space Exploration. NASA News, features & press releases. RELEASE 14-103, April 9, 2014.

2. Samuel Wicki, Erik G. Hansen, Clean Energy Storage Technology in the Making: An Innovation Systems Perspective on Flywheel Energy Storage, Journal of Cleaner Production, May 2017

3. Ankita Shinde1, Kratika Singh Rawat1, Ruchi Mahajan1, Veeraj Pardeshi1, Balbheem Kamanna2 and Sachin Sheravi1; Design and Analysis of Flywheel for Different Geometries and Materials, DOI: 10.18311/gjeis/2017/15872

INEEL November 2017

4. A.A. Khodadoost Arani, H. Karami, G.B. Gharehpetian, M.S.A. Hejazi; Review of Flywheel Energy Storage Systems structures and applications in power systems and microgrids; Renewable and Sustainable Energy Reviews, 2017

5. Flywheel Energy Storage, An alternative to batteries for uninterruptible power supply systems; Federal energy Management Program. DOE/EE-0286, www.eere.energy.gov/femp/

6. Hongliang Li, Jiangwei Chu, Jialu Li, Pengfei Cui and Zhanzhong Wang; Energy recovery data characteristics extraction of flywheel energy storage control system for vehicular applications. Advances in Mechanical Engineering 2017 Vol.9(4) I-II

INEEL November 2017

5.1.9. Structure of the mechanical ESS panel based on flywheels

November 14, 2017

PANEL: (TABLE 5) PANEL A- Flywheels

Schedule Activities Scope of Discussion Guiding Questions

11:45 Leader intervention Introduction and presentation of panelists

General aspects of flywheels technology.

State of the art, characteristics and classification.

Advantages and disadvantages of this application.

State of maturity, TRL

Costs of technology.

Challenges

Institutions involved

What is the state of the art of flywheel technologies? Which are the main applications and requirements for this technology and the benefits? What is the necessary infrastructure for the application of flywheel systems? What are the experiences of applying flywheel systems in the world? What are the most important challenges facing this technology? In which applications flywheels, have a greater advantage over the other ESS? In which applications flywheels must be operating in conjunction with other ESS?

12:00 Panelist presentation 1

12:30 Panelist presentation 2

13:00 Leader questions to the panelists

14:00 FOOD

15:00 Intervention of the Leader

R+D+i Opportunities Challenges

State of the art.

Benefits and Impact.

Approach Method / steps

Objective and Goals: 2, 3 and 4 years.

Stakeholders.

Possible National and International collaborators.

Possible barriers to the development of initiatives.

What are the lines of research and development of this technology that could bring the most benefits? What are the gaps in current research that should be tackled to achieve the best results? What previous studies are necessary for the application of flywheels in Mexico? Are there flywheel systems that could be implemented in a pilot plant in Mexico and which will be their capacity? What are the immediate impacts that a technology of this type can be develop? Which institutions are currently responsible of the development of flywheel applications? Are there linkage opportunities between research and business that promote the integration and development of flywheels storage in Mexico? How long would it take to implement a flywheels pilot system?

15:10 Panelist intervention 1

15:30 Panelist intervention 2

15:50 Leader questions to panelists

16:45 BREAK

17:00 Compilation of information

Conclusions