g GE Power

State of the Art Hybrid Solutions for Energy

Storage and Grid Firming

James DiCampli, P.E.

Donald Laing CEng FIMechE

POWER-GEN & Renewable Energy World

Europe

28 June 2017

State of the Art Hybrid Solutions for Energy

Storage and Grid Firming

Abstract

The impact of COP21 and growing renewable standards are driving new behaviors and

technologies such as two-way power flows, microgrids, digital analytics, and new transmission

and distribution models. Modern power systems must adapt to large fluctuations in both supply

and demand to maintain grid stability.

One solution recently developed by GE and its partners utilizes a hybrid electric gas turbine

(Hybrid EGTTM) to address these challenges. With the increasing proportion of intermittent

resources supplying the grid, battery storage holds significant promise in coming years. Like

renewable technologies before it, manufacturing scale and technical advances will drive costs

lower. Bulk storage will provide backup power, peak shaving, and ancillary services.

Transmission and distribution investments may be deferred as batteries provide congestion relief

during times of peak demand.

The GE Hybrid EGTTM is the world’s first gas turbine and battery storage hybrid, coupling a 10-

megawatt battery with a 50-megawatt (MW) GE LM6000 Gas Turbine, operated by an

integrated digital turbine control system. Key benefits include “spinning reserve” without firing

the gas turbine utilizing near instantaneous battery power through inverters, enhanced primary

frequency response and voltage support, reduced greenhouse gas emissions, and smooth transient

response with less turbine thermal stress, thereby lowering maintenance costs.

This paper reviews advances in storage technology and the state of the art technology that

integrates thermal and battery power to mitigate the challenges of variable generation.

Background

The bulk electric system in Europe is undergoing a significant transformation. Environmental

regulations and the Renewable Energy Directive 2009/28/EC are driving growth in variable

energy resources, notably wind and solar. These renewable technologies are rapidly achieving

grid parity and will likely be cost competitive in the absence of government subsidies, fueling

their growth.

The large-scale integration of variable renewable resources requires the operation of the grid in a

fast, flexible and responsive manner. To maintain power quality and reliability, the thermal

power generation fleet must provide more frequency support, reactive energy for voltage control,

fast dispatch and ramping. These flexible power solutions are required to maintain a stable

generation-load balance. This has typically been met in the past by spinning reserve. However,

operating plants at these lower outputs reduces the power generation efficiency and requires over

capacity during normal operation. Hence there’s a need for a better solution. To address these

requirements, GE has engineered the LM6000 Hybrid EGTTM (electric gas turbine), an integrated

battery and gas turbine solution, that can change output very quickly to support changes in

demand and support overall grid reliability. Well-designed thermal and integrated battery

systems can provide fast ramping, voltage and frequency support, and reduce the frequency and

duration of outages.

Renewable Energy in Europe

Renewable energy in the EU has grown substantially in recent years. This has been prompted by

the legally binding targets for renewable energy enacted by Directive 2009/28/EC. In 2015,

electricity generation from renewable sources, contributed 27.5 % of the EU-28’s gross

electricity consumptioni. The growth in electricity generated from renewable energy sources

during the period 2004 to 2014 largely reflects an expansion in three renewable energy sources;

wind turbines, solar power and solid biofuels. The quantity of electricity generated from wind

turbines in 2014 was 3.3 times higher as in 2004. The growth in electricity from solar power was

rose from just 0.7 TWh in 2004 to 92.3 TWh in 2014.ii

As noted, this variable power generation growth will significantly increase the need for

flexibility in the electricity grid. Storage could help balance electricity supply and demand,

holding the energy produced when the conditions for renewable energy are good but demand

may be low, then using the stored energy when demand (and price) is high. In February 2017,

the European Commission published a Staff Working Document titled 'Energy storage – the role

of electricity.' This document presents different technologies and discusses possible policy

approaches.iii IHS estimates that 640MW of non-traditional storage (storage other than pumped

hydro or compressed air) capacity is currently operating in Europe, with another 190MW of

projects coming on line in 2017.iv

Reliability Impact

Previously noted, large-scale integration of variable renewable resources requires a mix of

solutions to maintain power quality and grid reliability. The most important elements of

reliability on the grid are managing frequency, net demand ramping and fast dispatch, and

voltage support.

Frequency regulation involves second to second balancing of generation and load, and restoring

frequency after an event such as the loss of a major resource. The frequency within an

interconnection will immediately fall upon such an event, requiring a very fast response from

other generating resources to slow the rate of fall. That is, a fast increase in power output (or

decrease in power consumption) to stop the fall and stabilize the frequency, then a more

prolonged contribution of additional power (or reduced load) to compensate for the lost units and

bring system frequency back to the normal level. The kinetic energy extracted from the rotating

mass of the grid’s synchronous machines is critical. Some minimum synchronous inertial

response is needed to keep frequency from reaching a low set point within a given time to

prevent load shedding. With more wind and solar on the grid, frequency will fall more quickly

when there is an upset. Lower inertia increases the rate of change of frequency, giving less time

for primary frequency response to arrest frequency decay above under-frequency load shed set

points.

Capacity ramp rates are important in maintaining frequency during normal operations. Changes

in the amount of non-dispatchable resources, load behaviors and the generation mix can impact

the ramp rates needed to keep the system in balance. As renewables increase as a percentage of

total generation, the flexibility of dispatchable resources will become more important to balance

demand and supply. One of the major challenges of managing power quality is dealing with

steeper ramp rates when, for example, the sun sets and/or the wind diminishes.

The injection or absorption of reactive power to maintain voltage levels in the transmission and

distribution system under normal conditions is referred to as voltage support. This control is

local in nature, at individual transmission substations and the distribution system. The concept

of Voltage/VAR (volt-amp reactive) management is essential to electrical utilities’ ability to

deliver power within appropriate voltage limits so that supplied equipment operates properly,

and to deliver power at an optimal power factor to minimize losses. These concepts are affected

by a variety of factors throughout the distribution network including: substation bus voltages;

length of feeders; conductor sizing; type, size, and location of different loads (resistive,

capacitive, inductive, or a combination of these); and the type, size, and location of distributed

energy resources (photovoltaics, distributed wind, various storage technologies, etc.).v

Utility loads require a combination of real power (watts) and reactive power (VARs). Real

power must be supplied by a generator while reactive power can be supplied either by a

generator or a local VAR supply, such as a capacitor. Delivery of reactive power from a remote

VAR supply results in feeder voltage drop and losses due to increased current flow, so utilities

prefer to deliver reactive power from a local source.

Let’s explore storage options to understand their benefits and uses as related to maintaining

power quality and grid reliability.

Storage Options

With few exceptions, electricity cannot be stored in any appreciable quantities, and thus must be

produced as needed. Further, electricity’s inelastic demand does not move with prices. Lacking

storage and responsive demand, operators must plan and operate power plants and the

transmission grid so that demand and supply continuously match.

This requires close coordination of all utility functions, notably the process of determining which

generating units to use, generally prioritized on efficiency (lowest cost generation is dispatched

first). Operators want to commit just enough capacity to ensure reliability, but no more than is

needed. Reserve power can be provided in multiple ways. These include distribution through

interconnecting grids, operating fossil fuel plants on part power, spinning reserve and energy

storage.

Utility scale storage offers a solution to managing these complexities. There are several

technologies available with varying advantages in terms of cost, capacity, technical maturity,

efficiency cycle life.

Fig. 1 below provides a comparative maturity status. Some technologies are displayed with

respect to their associated initial capital investment requirements and technology risk versus their

current phase of development (i.e. R&D, demonstration and deployment, or commercialization

phases). At one end of the scale pumped hydro storage is well proven and in commercial

operation around the world for over 100 years. At the other end is thermochemical storage;

reversible chemical reactions, a technology at the early R&D stage. In between there is indirect

storage including compressed air storage, batteries, fuel cells and mechanical flywheels, and

direct storage such as supercapacitors and superconducting magnets.

Fig 1: Energy Storage Technology Maturityvi

Let’s briefly review some of these technologies.

Pumped storage

Pumped storage hydro power is the most mature of large scale storage methods. It has a high

efficiency (70 – 80%) and fast response rate. There are relatively few suitable locations and the

local environmental impact can be significant. Still, pumped hydro storage dwarfs all other

forms of electricity storage in Europe, accounting for more than 99% of the total. There is 53.2

GW of pumped storage in Europe as of 2016. vii

Underground Pumped storage

With a limited natural locations suitable for pumped storage, underground pumped storage is an

alternative solution. Typically, mines that are no longer viable for their mineral content can be

converted to provide pumped storage. A reservoir above the mine and another at the bottom

along with the hydro plant can utilize the head of the mine shafts and the excavated underground.

In Germany, the 600 meter (1,969 foot) deep Prosper-Haniel coal mine is about to be turned into

a 200 MW pumped-storage hydroelectric reservoir to help provide uninterrupted power in

support of the renewables.viii

Compressed Air Storage

Compressed air energy storage (CAES) can store large amounts of energy like pumped storage

and has potential for large-scale, cost-effective storage. It has a fast rate of response but requires

sealed caverns. In CAES, excess power from the grid is used by an electric motor to drive a

compressor. The compressed air is cooled and stored at pressures of typically 60-70 bar. At

times of high electrical demand, the air is drawn back from the store, heated and then supplied to

a modified gas turbine. The energy from this high-pressure air, along with some thermal input,

drives the turbine generator to supply electrical energy to the grid. The first CAES plant with

290MW capacity has been operating in Huntorf, Germany, since 1978 and another 110MW plant

has also been operating in the US since 1991. New developments in adiabatic and underwater

CAES look promising. Underwater storage involves a balloon-like vessel made of stretched

fabric, anchored to a sea- or lakebed. When energy is needed, its compressed air can be released

to drive turbines.

Thermal storage

Thermal storage entails storing energy in form of heat. Storing large amounts of heat can be

achieved by simply heating an insulated mass or through phase changing of materials. Some

materials can hold large energy amounts when changing from one phase into another. Molten

salt storage (a combination of sodium and potassium) offers such capability. Gemasolar in

Seville, Spain is the first commercial scale solar thermal power plant. It can produce 19.9 MW

for 24 hours a day. While it has the benefit of high efficiency, high life cycle and low cost, it

needs to be coupled with concentrated solar power which is expensive.ix

Flywheels

A flywheel is a rotating mechanical device that is used to store rotational energy. The amount of

energy stored in a flywheel is proportional to the square of its rotational speed. For power

generation, a flywheel releases stored energy by applying torque to a generator. Flywheels are

well suited for shorter-duration frequency regulation.

Electromagnetic Energy Storage

Electromagnetic energy storage systems store electricity “directly” in the electromagnetic fields

without transformation. The two main technologies are supercapacitors and superconducting

magnetic energy storage (SMES) technologies.

Supercapacitors

The capacitive energy storage is based on the parting of positive and negative electrical

charge carriers. Supercapacitors are basically double-layered versions of normal

capacitors but with considerably higher electrode surfaces and a fluid electrolyte.

Compared to lead-acid batteries, supercapacitors have lower energy density but they have

longer cycle lives and faster charge and discharge capabilities than batteries. However,

large-scale commercial supercapacitors are still under development, with cost being the

greatest hindrance to date.

Superconducting Magnetic Energy Storage (SMES)

Superconducting magnetic energy storage (SMES) systems store electrical energy in the

magnetic field of a coil. They typically consist of a superconducting coil, a power

conditioning system, a refrigeration system for cooling of the coil and a cryostat/vacuum

vessel. The superconducting material itself has very little resistive losses, but must be

cooled down by the cryogenic system to extremely low temperatures (~ 5 K). This

cooling is mainly done with liquid helium, which leads to considerable high operational

costs. The major advantages of SMES systems are their high efficiencies (~ 95%) and

their ability to provide very high output and fully recharge in minutes. SMES systems

are relatively new technologies with only a few prototypes developed.

Batteries

The battery storage industry is growing quickly, particularly Lithium-ion (Li-ion). Electric cars

are largely responsible, with increasing demand driving a large-scale manufacturing. As

manufacturing capacity grows, prices for lithium-ion batteries have fallen fast—by almost half

just since 2014. Three massive battery storage plants—built by Tesla, AES Corp., and Altagas

Ltd. are being built in southern California. Combined, they amount to 15 percent of the battery

storage installed planet-wide last year. x China leads the world in Li-ion production, followed by

South Korea, the U.S., and Poland.xi Some of the competing battery technologies:

Lead acid

Lead-acid remains the least-cost battery technology and has a well proven track record,

but it’s very low cycle life keeps it from being competitive in most grid applications.

Lithium ion

Lithium-ion is a higher-cost option today, but as noted, costs are falling rapidly. These

batteries use lithium as an electrolyte and have a very high energy density and both cycle

life and efficiency are superior to lower-cost options.

Sodium -Sulphur

Sodium-sulfur batteries have historically been the least-cost battery option. They are cost

competitive with lithium ion, but are currently only available with a six/seven hours’

duration, operate at high temperatures (300 – 350oC) and costs have not declined much in

over a decade of deployment.

Zinc

Two zinc-based batteries on the cusp of commercialization are the next-lowest-cost

option. Their materials are abundantly available; however, they must still build up a track

record and are challenged by both cycle life and efficiency.

Flow Batteries

Flow batteries have a much longer cycle life and lower cost than lithium-ion but lack

efficiency and to date are much more expensive.

The Li-ion battery was selected for the GE Hybrid EGTTM due to its high efficiency, high energy

density and rapidly falling costs. Combining a large-scale battery system and a gas turbine

combines the benefits of both, the first of which has been deployed in California, USA. Let’s

examine the case study there and how the benefits apply in Europe.

EGTTM Case Study

Grid Requirements

The California Independent System Operator (CAISO) is a nonprofit public benefit corporation

and manages wholesale electricity markets through much of California, centrally dispatching

electricity generation facilities. In managing the grid, CAISO provides open access to the

transmission system and performs long-term transmission planning. CAISO’s peak load is

around 50MW. System capacity is ~60% gas fuel powered, with much of the balance nuclear

and renewables. CAISO manages a day ahead market, a real-time spot market and ancillary

services. The real-time market uses final day-ahead schedules for resources within the network

as a starting point, then operates a fifteen-minute market to adjust resource schedules, and then a

five-minute market to balance generation and loads.xii CAISO procures four ancillary services in

the day-ahead and real-time markets, including:

• Regulation up: units providing regulation up must be able to move quickly above their

scheduled operating point in response to automated signals from the ISO (equivalent to the

Transmission System Operator (TSO) in Europe) to maintain the frequency on the system by

balancing generation and demand.

• Regulation down: units providing regulation down must be able to move quickly below their

scheduled operating point in response to automated signals from the TSO.

• Spinning reserve: Resources providing spinning reserves must be synchronized with the grid

(online, or spinning) and can respond within 10 minutes. This is more reliable than non-

spinning reserves because generating capacity is already online and synchronized.

• Non-spinning reserve: Resources providing non-spinning reserves must be able to

synchronize with the grid and respond within 10 minutes.

Regulation up and regulation down are used continually to maintain system frequency by

balancing generation and demand. Spinning and non-spinning resources are used to maintain

system frequency and stability during emergency operating conditions (such as unplanned outage

of generation or transmission facilities) and major unexpected variations in load. Spinning and

non-spinning resources are often referred to collectively as operating reserves.xiii

Supply and Demand Challenge

Within CAISO, Southern California Edison (SCE) is the primary electricity supply company

for much of Southern California. It provides 14 million people with electricity across a service

territory of approximately 50,000 square miles. SCE selected GE to partner on a new battery

energy storage system (BESS), to help avert grid issues related to gas shortages caused by a

gas leak at the Aliso Canyon storage facility, the second largest of its kind in the United

States. The leak, discovered on October 23, 2015, resulted in shutdown of the facility, and the

unavailability of gas storage in the region resulted in insufficient delivery of gas to power plants,

leading to a strained electricity grid. Load pockets that are chronically constrained include San

Diego, Los Angeles Basin, and North Coast/North Bay area (San Francisco).

Even prior to the leak, California was leaning forward on energy storage. In 2013 the

California Public Utilities Commission enacted the nation's first energy storage mandate,

directing investor-owned utilities to buy 1.325 GW of energy storage capacity by 2020.

Storage is expected to play an important role in meeting the state's 50% renewable energy

mandate and a recently passed goal to cut greenhouse gas emissions 40% from 1990 levels

by 2030.

The Equipment

The EGTTM project utilizes a 10 MW battery energy storage system supplied by GE Current,

and an existing LM6000PC gas turbine with control system upgrades provided by GE’s

Power Services (Fig. 2).

Fig 2: LM6000 Hybrid EGTTM

Gas Turbine

The CF6 family of GE Aviation’s aircraft engines is packaged by GE Power for industrial use as

the LM6000 in power generation or mechanical drive applications. The LM6000 gas turbine is a

dual-rotor, concentric drive-shaft, gas turbine capable of driving a load from the front and/or rear

of the low-pressure (LP) rotor. Introduced in 1961, there have been more than 1,100 LM6000’s

in operation around the world, adapted to dynamically demanding applications using a broad

range of liquid and gaseous fuels. Combustor configurations include steam or water injection for

emissions control, or a Dry Low Emissions (DLE) option. Wet compression power

augmentation is also offered through Sprint™.

Storage Plant Controller

GE's Energy Storage Plant Controller (ESPC) is a supervisory control and data acquisition

(SCADA) system for energy storage plants and renewable hybrid plants. The ESPC is built on

GE’s MarkVIe Control System, a mature platform that is used worldwide to monitor and control

GE's gas turbine, wind, and solar energy fleets. The MarkVIe controller is installed in over 400

global locations with more than 16 million hours of combined operation. GE's ESPC monitors

and controls inverter-and plant-level functions and provides real-time and historical operational

data for performance analysis. It includes a variety of grid-friendly controls for managing plant-

level active power, reactive power, voltage, and frequency. These controls can be configured to

meet operating requirements under a variety of conditions such as grid connect mode and

islanded mode, and to allow GE's Battery Energy Storage System (BESS – Fig. 3) to connect to

the grid at one point rather than at several inverters.

Battery Enclosure

Purpose Built Enclosures for the batteries are low maintenance and modular. They are designed

for 20 years of life and offer more than 25 percent higher power and energy density than

standard shipping containers. Aisle widths of 48 inches meet National Electrical Code (NEC)

requirements. Integrated Fire Suppression System, cooling and insulation are also included.

Brilliance Inverter

GE's Brilliance Inverter includes features such as voltage ride-through, frequency response, and a

variety of reactive power configurations. There are more than 23,000 GE Renewables Inverters

installed on GE's wind turbines and solar installations around the world. Each 1.25 MW inverter

is capable of charging and discharging at 1.25 MW, has 50/60 Hz options and a peak conversion

efficiency >98%. It includes an integrated 3000 amp dc disconnect and 1600 amp ac circuit

breaker and provides zero, low and high voltage ride through capabilities.

Fig 3: Battery Energy Storage System

Lithium-Ion Battery

This battery technology was chosen for several reasons. It can reach the minimum on-line load

commitment without burning fuel or adding wear on the plant. It is greenhouse gas free, it

reduces the fuel expense for peaking and mid-merit power operation and it also increases the

plants utilization for peaking and mid-merit operation. Previously noted, Lithium-ion costs are

falling rapidly. These batteries have a very high energy density and both cycle life and

efficiency are superior to other battery options.

GE partners with several of the world’s Tier 1 Li-ion battery manufacturers to provide fully

tested and integrated solutions. Each manufacturer and candidate cell must pass stringent

performance and quality inspections. GE Energy Storage performs a comprehensive Safety Risk

Assessment for our equipment based on ISO 12100, the Recommendations for Safety Risk

Assessments and ISO 13849, Functional Safety.

Operation and Benefits

Reduce System Costs to Create Ratepayer Value

The largest value is typically captured by load serving entities or transmission system operators

(TSO), with savings that can be passed to ratepayers (Fig 4a and 4b). The GE LM6000 EGTTM

Hybrid system provides transient response and provides high-fidelity frequency regulation with

GT fuel burn, and 50MW of rapid response contingency reserve with zero fuel burn, including

primary frequency response and voltage support services.

In the United States, this has been made possible by the Federal Electric Regulatory Commission

(agency that regulates interstate electric transmission) rules that allow energy storage systems to

qualify as spinning reserve. Key sections of the rule:

• FERC Order 789 Section 48: BAL-002-WECC-2 R2

o “The Commission determines that non-traditional resources, including electric

storage facilities, may qualify as ‘Operating Reserve—Spinning’ provided those

resources satisfy the technical and performance requirements in Requirement R2.”

• R2 Requirements:

o 2.1 Reserve that is immediately and automatically responsive to frequency

deviations through the action of a governor or other control system;

o 2.2 Reserve that is capable of fully responding within ten minutes.

The EGTTM battery system provides the immediate response. Within ten minutes, the gas turbine

can be on line at full power. This frees up resources lower in the bid stack (e.g., curtailed solar

and negative priced assets such as CCGT otherwise used for capacity) to generate power at

higher efficiencies. Since more energy is generated by these base assets, fewer expensive peak

resources need to be called upon, both saving fuel burn and lowering the overall market clearing

price for energy.

Fig 4a: Rate Payer Savings Illustration without GT

Fig 4b: Rate Payer Savings Illustration with GT

The GT can reach max power in a minimum of 5 minutes if needed. The hybrid EGTTM delivers

the commanded net-output on a blended basis from the Battery and/or Gas Turbine at the most

optimal ratio given both internal and external system requirements. The desired hybrid power

demand is calculated automatically by the EGTTM control system based on net power demand

and required frequency control contribution subject to the BESS max power limits, ramp rate

limits and stored energy capacity.

When the GT is not running, the BESS system supplies all demanded power until the demand

exceeds the BESS capacity. Once the GT is running, the GT power demand is calculated using a

combination of EGTTM net power demand, hybrid frequency droop power demand and hybrid

charge power demand subject to GT MW and ramp rate constraints.

The BESS operates across the complete MW range providing high-fidelity frequency regulation.

Figure 5 indicates an actual example of a highly variable power output the hybrid EGT will to

produce through a blended combination of the BESS and the GT. The GT provides the overall

power with its output increasing and decreasing gradually to meet the overall demand. At the

same time the BESS provides the highly variable and transient output, thereby evening out the

load on the GT. Thus, there’s considerably less stress on the GT and consequently there’s a

considerable reliability and availability benefit.

Fig. 5: EGT Response

Each battery is equipped with a battery management system (BMS) that monitors and maintains

the battery for the optimal performance per system guidelines. The BMS controls and protects

the battery, and relays information on temperature of the cells, voltage and current parameters,

and reports on the health of the battery. The BMS can open contactors to electrically isolate a

battery module from the rest of the battery rack as necessary. When conditions improve or when

the battery status returns to normal, the BMS reconnects the battery module to the rest of the

rack. In addition, each BMS also includes a fuse that can protect against over-current events if

the BMS’s control of the battery is compromised.

The ESPC is connected to these devices through a communication protocol. It serves as the main

interface for retrieving all system information, communicating with remote locations, performing

grid services, providing data for HMI and SCADA units, and monitoring the system.

Conclusions

The bulk electric system in Europe is undergoing a significant transformation. Growth in

renewable energy capacity will require flexible thermal power systems that will maintain grid

reliability and power quality. Reserve dispatching favors low cost providers and often requires

assets to run at non-optimum, minimum loads. Additionally, the market needs fast transient

response and low emissions; meeting this dichotomy poses new challenges to grid operators and

generators alike.

To address these challenges, GE has developed the LM6000 Hybrid EGTTM, coupling a 10 MW

battery with a 50 MW GE LM6000 Gas Turbine, operated by an integrated digital control

system. The first plant was made operational 17 April 2017 in California, USA. Key benefits

include “spinning reserve” without firing the gas turbine utilizing near instantaneous battery

power through inverters, enhanced primary frequency response and voltage support, reduced

greenhouse gas emissions, and smooth transient response with less turbine thermal stress,

thereby lowering maintenance costs.

i Gross national electricity consumption includes the total gross national electricity generation

from all fuels (including auto-production), plus electricity imports, minus exports. Auto-

production is defined as a natural or legal person generating electricity essentially for his/her

own use. Gross electricity generation is measured at the outlet of the main transformers, i.e. it

includes consumption in the plant auxiliaries and in transformers. ii "Energy from Renewable Sources." Energy from Renewable Sources - Statistics Explained.

European Commission, Mar. 2017. Web. 18 Mar. 2017. iii European Commission - Fact Sheet, http://europa.eu/rapid/press-release_MEMO-15-

5181_en.htm iv Mann, Deborah. European Grid Storage, Technology Options Beyon Batteries. Rep Houston:

HIS, 2017. Print. v Web: https://www.nema.org/Policy/Energy/Smartgrid/Documents/VoltVAR-Optimazation-

Improves%20Grid-Efficiency.pdf vi Web:

https://www.iea.org/publications/freepublications/publication/TechnologyRoadmapEnergystorag

e.pdf vii IBID, part 2, page 8 viii Web: https://www.bloomberg.com/news/articles/2017-03-17/german-coal-mine-to-be-

reborn-as-giant-pumped-hydropower-battery ix Web: https://en.wikipedia.org/wiki/Gemasolar_Thermosolar_Plant x Web: https://www.bloomberg.com/news/articles/2017-01-30/tesla-s-battery-revolution-just-

reached-critical-mass xi Web: http://www.visualcapitalist.com/china-leading-charge-lithium-ion-megafactories/ xii Energy Primer: A Handbook of Energy Market Basics, November 2015. Rep. Washington,

DC: Federal Energy Regulatory Commission, 2015. Print. xiii IBID