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LESSONS LEARNT FROM ADVANCED ENERGY STORAGE APPLICATIONS

S. HARRIS

Country Club Estates, 21 Woodland Crescent, 2196, Johannesburg, South Africa

sherwin.harris@ge.com

Energy Storage

GE Power

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Contents

1 Background ................................................................................................................................... 3

1.1 Why Energy Storage? ......................................................................................................... 3

1.2 Trends .................................................................................................................................... 3

1.3 Benefits of Energy Storage ................................................................................................. 4

2 Power & Energy Reservoir Storage Solution ........................................................................... 4

3 Primary Reservoir Applications .................................................................................................. 6

3.1 Hybrid Renewable ................................................................................................................ 6

3.1.1 Frequency Response Services .................................................................................. 7

3.1.2 Firming Application ....................................................................................................... 7

3.1.3 Curtailment avoidance ................................................................................................. 7

3.2 Dispatchable Solar ............................................................................................................... 8

3.2.1 AC-Coupled Solar ........................................................................................................ 9

3.2.2 DC-DC coupled Solar .................................................................................................. 9

3.2.3 Comparison ................................................................................................................. 10

3.3 Thermal Hybrid ................................................................................................................... 10

3.3.1 Typical Applications for open cycle gas turbines ................................................... 11

3.3.2 Typical Applications for combined cycle gas turbines .......................................... 12

3.4 Energy Storage Generation Application ......................................................................... 13

3.4.1 Shifting or Arbitrage ................................................................................................... 13

3.4.2 Capacity Reserve ....................................................................................................... 13

4 Conclusion : Energy Storage for South Africa ....................................................................... 14

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1 Background

1.1 Why Energy Storage? The Electricity industry is faced with unprecedented challenges. An aging power grid needs massive

investment while renewable energy sources require a more localized approach to storage and

distribution. The rise of electric cars is further straining the infrastructure. Clean energy, environmental

policy, and technological advances are rapidly reshaping the world’s electrical grids, creating a range

of new challenges but also exciting new opportunities. The latest energy storage solutions deliver

cleaner, more reliable power where and when it’s needed most, to meet industry’s rapidly changing

needs.

1.2 Trends The global energy system is transforming. The change to energy generation and consumption is being

driven by three powerful trends:

• Decentralization: The growing penetration of increasingly affordable distributed energy

resources, including renewables and storage, is creating more “prosumers” (end users who are

active in the power system), greatly increasing distribution grid complexity. Annual Installed

capacity of distributed energy resources is expected to reach 530 GW by 2026 globally;

• Decarbonization: The rapid deployment of low-carbon technologies such as wind and solar is

making it increasingly difficult to forecast variable generation, creating challenges around grid

stability, congestion and market volatility

• Digitalization: A rise in the number of connected devices and smart sensors enables fast

decision-making on dynamic and nodal prices, while intelligent control systems and internet-

enabled software optimize power plants and the grid.

As an example, the California duck curve gives a good illustration of the threat those trends will bring

to the grid (Figure.1).

Figure 1 Increasing Renewable create new pressure on the grid

78% OF THE 9000GW+ OF NEW GENERATION FORECAST TO BE BUILT BY 2040 WILL BE RENEWABLE1

1 Bloomberg - New Energy Outlook Report & Navigant Research - Global DER Deployment Forecast

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The integration of intermittent renewables and distributed energy into an aging grid requires flexible

and resilient technologies, able to ramp up quickly and dynamically adjust to real-time grid signals:

a battery energy storage solution meets those expectations.

1.3 Benefits of Energy Storage

A battery energy storage solution offers unprecedent flexibility in grid optimization, unlocking new

business value across the energy value chain, from conventional power generation, transmission &

distribution, and renewable power, to industrial and commercial sectors. Energy storage supports

diverse applications including firming renewable production, stabilizing the electrical grid, controlling

energy flow, and improving asset operation. Figure 2 is giving a more comprehensive view of what

benefit and value battery energy storage system can bring.

2 Power & Energy Reservoir Storage Solution

Globally costs are declining, and global competition is intensifying, leading to large scale manufacturing,

consolidation, improvement and manufacturing processes and technology and commoditization of

products. Hence, modular scalable solutions are the answer to faster deployment and optimization of

system costs.

To meet these needs GE has developed a modular energy storage platform called the ‘Reservoir’. The

Reservoir Solution platform consists in the following components: Reservoir Storage Unit (Battery

Packs, Blade Protection Unit, Battery management system, cells and modules, specialized safety

enclosure), Reservoir Inverter Unit (Power Conversion System or Inverter, Isolation Transformer, and

climate control auxiliaries), Reservoir control unit (Energy Storage Plant controller, Protection and

Monitoring devices, SCADA etc.)

Figure 2 Services provided by energy storage

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Figure 3 Block Diagram of Reservoir Platform

The Reservoir Solution can be designed in a power or energy configuration depending on the

required application. In an energy configuration, the batteries are used to inject a steady amount of

power into the grid for an extended period. In a power configuration, the batteries are used to inject a

large amount of power into the grid over a shorter period. The configuration of power or energy is

determined by the ratio of inverters to batteries.

It is possible to unlock new business value with Reservoir Energy Storage solution:

• Improve Financial Performance: Monetize assets through new revenue streams, increased

asset utilization, improved yield, and reduced operating costs.

• Increase Renewables Integration: Improve integration and maximize utilization of the energy

generated from photovoltaics (PV) and wind turbines.

• Optimize Electrical Grid: Defer upgrades, relieve congestion, control voltage, provide reserves

and ancillary services, and improve reliability with backup power and black start functionality.

• Reduce Energy Costs: Commercial and industrial end users can mitigate demand charges,

optimize differential (Time of Day) energy prices, and benefit from additional onsite PV

generation.

• Develop Microgrids: Create a new and more flexible grid by locally integrating renewable

generation and smart devices with energy storage and real-time communication.

Figure 4 Energy and Power Configurations

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3 Primary Reservoir Applications

Reservoir can have renewable and thermal integrated hybrid solution applications in which it can deliver

new application facility, some of these applications/use cases are explored below.

3.1 Hybrid Renewable

Reservoir coupled with Solar or Wind farm can transform variable generation into predictable and

reliable generation in compliance with local grid code and enable new revenue streams.

Hybrid systems that combine photovoltaics (PV), wind, and energy storage are becoming a feasible

option for large-scale power plants and can have significant economic, environmental, and social

benefits.

Combining wind and solar generation results in significant increase in annual energy production for the

same plant footprint often without creating the need for transmission expansion due to typical temporal

differences in wind and solar resources. Adding energy storage technologies and accurate resource

forecasting tools can transform such hybrid plants into dispatchable and flexible sources of energy

better suited to operate in both day-ahead and real-time energy markets, and to provide existing and

future advanced essential reliability services to the grid.

A combination of renewable generators like wind and solar in the right proportion, when combined with

batteries can be dispatched in constant output or load following modes using smart controls,

optimization and communication architecture.

A system approach rather than a single technology approach is key to this. One key element of the

control of the integrated systems is a hybrid controller that spans across the individual asset controllers

(battery, WTG).

The role of this hybrid controller is to run the integrated system both in the context of revenue

optimization as well as grid code compliance and adherence.

Benefits of the hybrid controller include:

• Faster response time: controllers directly connected to assets instead of third-party link;

• Grid Compliance: hybrid controller coordinates individual systems to meet requirements and

ensure safety

• Intelligent Controls: optimizer consolidates market data to maximize revenue streams

• Flexible: day ahead scheduler enables manual override of bidding strategy

• Coordinated: Hybrid controller prioritizes assets to prevent availability loss

Consolidated SCADA: single interface instead of individual ones per assets Further details are

explained in the below sections.

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3.1.1 Frequency Response

Services Energy storage can raise the frequency

of the grid by discharging to push real

power or to lower the frequency by

charging, State of charge (SOC) of the

batteries is controlled through advanced

algorithms which manage continuous

frequency regulation. This enhances the

power systems responsiveness to

frequency changes. It can add to the

ancillary service revenue and ensure

grid code compliance.

Figure 5 Frequency Response with Energy Storage

3.1.2 Firming Application

Energy storage can be used for

firming of variable solar or wind

output. Firming is the process of

using energy storage to charge or

discharge in response to variation

in solar output to provide firm,

predictable power during discrete

operating time intervals. This

application can be used to avoid

balancing charge and ensure grid

code compliance. Below example

shows a solar firming application.

Figure 6 Firming of Solar Output with Energy Storage

3.1.3 Curtailment avoidance

Curtailed energy captured by storage provides flexible management of oversupply and constrained grid

system capacity or avoids negative power prices. By avoiding curtailment, storage has a direct impact

on the revenue stream optimization from generated energy by increasing the load factor and hence

increasing the annual energy production.

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Figure 7 Curtailment avoidance with Energy Storage

3.2 Dispatchable Solar

Dispatchable generators can be turned on to adjust their power output at the request of the power grid

operators. Non-dispatchable renewable resources, such as solar PV cannot typically be controlled by

operators. Combining storage with solar enables dispatch capabilities that can be used to serve peak

demand periods and follow loads. This can enable revenue streams like time of day price premium and

increased capacity factor.

Figure 8 Dispatchable generation with Energy Storage

These hybrids offer a stack of benefits beyond conventional PV solutions, such as synthetic inertia,

frequency response, ramp-rate control, curtailment avoidance, energy shifting and peak management,

as well as two main approaches: AC Coupled and DC Coupled.

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3.2.1 AC-Coupled Solar In an AC-Coupled solution, the PV and Energy Storage (ES) plants are separate, joined only at the grid

connection. To charge the batteries, solar energy passes from the solar strings through the solar

inverters, transformers, cables and switchgear to the coupling point and then passes the cables,

transformers, and battery inverter to reach the battery. When this energy is needed, the energy passes

back through the battery inverter, transformer, cables and switchgear to be delivered onto the grid.

Through this tortuous path, over ~13% of the energy can be lost due to conversion efficiencies and

other system losses.

With this topology, you also need the AC scope of the project (inverters, transformers, switchgear) to

be sized for the nameplate ratings of the PV and the ES portions of the project. This can mean double

the AC equipment and installation costs on some solar hybrid projects and double the associated O&M

costs over the life of the project.

3.2.2 DC-DC coupled Solar

With this topology, the PV and ES plants are fully integrated on the DC side. The output of the PV

strings can be directly coupled to the Reservoir Storage units with the integrated combiner option. To

charge the batteries, solar energy passes from the solar strings through the solar optimizer to reach the

battery. When this energy is needed, the energy passes back through the battery inverter, transformer,

cables and switchgear to be delivered onto the grid. With this simplified configuration, the losses are

nearly cut in half to ~7% being lost due to conversion efficiencies and other system losses.

It is possible to eliminate the redundant AC scope of the project (inverters, transformers, switchgear)

because the solar and storage energy both share a common set of AC equipment. This can mean half

the AC equipment and installation costs on some solar hybrid project and half the associated O&M

costs over the life of the project.

Furthermore, while conventional PV systems are established with DC:AC ratios (inverter loading ratio)

of about ~1.3, DC coupling can enable DC:AC ratios of 2.0 or higher (2.5, 2.6) to significantly increase

the overall capacity factor of the project. This configuration can enable more energy sales in grid

Figure 9 AC Coupled Solar plus Storage

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constrained projects. For example, it is possible to connect 10 MWdc of PV though a 5MWac grid

connection resulting in a 40-50% capacity factor.

3.2.3 Comparison DC-Coupled solar-storage hybrids enable a premium solar product that provides firm dispatchable

power to deliver cost effective, clean energy during peak demands in a new and exciting way. These

solutions are an ideal approach to mitigate the duck curve, address clean peak standards or to capture

arbitrage value in hourly price strips.

In most greenfield applications DC coupled solutions are the clear winner, but AC-Coupled can be best

under certain conditions when the storage size is <20% of the PV plant capacity. These may include

systems designed to provide grid code compliance such as frequency response and/or ramp-rate or

applications when a relatively small portion (<15%) of the solar energy will be shifted, but many result

in superior economics when designed from the ground up as an integrated DC coupled solar-storage

hybrid Increasingly, the value of midday solar lowers, while the premium. Reservoir technology is

equally suited for both AC and DC coupled solar-storage hybrids and can be scaled to best suit the

project needs.

3.3 Thermal Hybrid Steam and gas turbines can be combined with energy storage and digital controls to reduce fuel costs

and gas emissions, by improving the use of existing generation sources and enabling applications such

as frequency response, black start, shifting and capacity markets. While services such as frequency

response already covered in section 3.1.1 are applicable, some specific examples for synthetic inertia,

contingency reserves and improved operations are given in the following paragraphs: The core of the

Lower Capex Reduced Opex

Increased Annual Energy Production (EAP)

More Premium Power

Increased IRR%

Figure 11 DC coupled solar benefits

Figure 10 DC Coupled Solar plus Storage

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hybrid solutions is the integrated control system approach that makes the two assets like one single

asset operated on the grid. The single integrated control system ensures also improvement in speed of

executing the commands and the level of system reliability thanks to a -1 level of control instruction

exchange. The integrated control system approach is also able to ensure the optimum battery state of

charge not subject to grid availability. The integrated control system provides also the advantages to

automatically manage the correct load split between the battery system and the gas turbine for each

service (start-up, frequency control, peak capacity, etc.). In addition, thanks to a tuning of the gas turbine

the integrated control system is also able to increase the overall asset loading gradients without

maintenance impact and emissions. For integration with open cycle gas turbines, the integrated control

system ensures a continuous 0MW turndown capability without storage limitation and reliability impact.

3.3.1 Typical Applications for open cycle gas turbines

Below typical examples of improved services and new services enabled by the integration of the battery

technology into an existing gas turbine in open cycle configuration.

• Blacks tart: There exists possibility to start the gas turbine without importing energy from the

grid and without additional fuel burnt. Storage systems are well suited to serve as black start

assets because, unlike generators they do not need special equipment to start up. The power

to dispatch can be made available immediately (there is no need to keep it running in standby

mode) ES systems can be used to boot strap the grid by enabling the startup of additional

assets like natural gas plant.

Figure 12 Blackout event mitigated by energy storage

• Ultra-fast start-up capability & lifetime improvements:

for open cycle gas turbine operating as peakers or

spinning grid support, the battery system can be sized

to cover up to the full gas turbine baseload in less

than 1 second. As soon as the gas turbine is started

and loaded the control system automatically split the

load between the GT and the batteries to ensure a

constant output on the grid. Thanks to the ultra-fast

start-up capability the operators can have access to

new market opportunities or they can switch from

spinning reserve support to a non-spinning reserve

operating profile. In this latest scenario, the

hybridization can reduce the fuel consumption and

the emissions while improving the quality of the

service provided to the grid. in case the event that

triggered the activation of the battery is closed within

the battery storage capability an unnecessary start can be also avoided

TIme

Battery

GT

Total

Figure 13 Ultra-fast Start-up Capability using Energy Storage, useful in peakers

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• Increasing ramp rates: batteries can be used to improve the GT ramp rates without additional

maintenance impact and emissions.

• Additional capacity: battery can be used to provide

additional peak capacity on top of gas turbine base

load without maintenance impact. The battery can also

be used to provide frequency support on top of gas

turbine base load. Batteries can also be used during

summer time to compensate GT power output derating

due to hot ambient air. These features can ensure a

flat output across all the year maximizing the capacity

payments and revenues during peak energy price.

• Turndown improvement: with the integration of the

battery the gas turbine can be dispatched with a 0MW

turndown capability. Battery can be sized to cover the

gas turbine minimum load. The combination of this

with ramp rates improvement will further enhance the flexibility of the gas turbine in ancillary

service market.

3.3.2 Typical Applications for combined cycle gas turbines

• Black start: possibility to start the gas turbine without importing energy from the grid and without

additional fuel burnt, as explained above.

• Increasing ramp rates: batteries can be used to improve the overall combined cycle ramp rates

without additional maintenance impact and emissions.

• Additional capacity: battery can be used to provide additional peak capacity on top of gas

turbine base load without maintenance impact. Batteries can also be used during summer time

to compensate GT power output derating due to hot ambient air. These features can ensure a

flat output across all the year maximizing the capacity payments and revenues during peak

energy price.

• Frequency support improvements: batteries can be used to improve the overall combined cycle

flexibility by:

o Unlocking MW typically reserved for frequency

support. Battery can be used to provide up to 100% of

required frequency support even on top of plant rated

baseload.

o Improving combined cycle turndown by moving up to

100% negative frequency response to the battery. This

allows operators to park the combined cycle at real

technical minimum load and reduce the fuel

consumption while improving at the same time the

operating band of the combined cycle.

o Fast frequency response, the batteries react

in less than 1 second to any frequency

deviation. The batteries can enable the fast

frequency response capability at plant level

by providing up to 100% of the frequency

response while the GT is loaded without the

need of fast ramp limiting in this way the

thermal stress on HRSG and steam turbine

in case of combined cycles. This functionality can also enable the plant merit order on

the grid where applicable.

Figure 14 Additional Capacity without maintenance Using Energy Storage

Figure 15 Combined Cycle Baseload Plant Energy Storage Support

Figure 16 Combined Cycle Cycling Plant Energy Storage Support

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• Start-up costs reductions: batteries can be used to reduce the energy import during the start-

up process until the GT is synchronized to the grid. During the start-up process, batteries can

also be used to compensate the load unbalancing due to process delays due to HRSG or steam

turbine.

3.4 Energy Storage Generation Application Energy Storage installed at the generation level can help maintain a robust and resilient electricity

delivery system by improving the operating capabilities and reliability of the grid while generating new

revenue systems. While services such as frequency response already covered in section 3.1.1 are

applicable, some specific examples for black start, shifting and capacity market are given below:

3.4.1 Shifting or Arbitrage Shifting or Arbitrage may be done to increase the revenue stream by time-shifting wholesale electric

energy. This is buying at low price and selling at high price. Shifting is typically about maximizing the

price delta whereas peak management is about reducing peak demands to drive asset deferral or

reduced demand charges.

Figure 17 Shifting using energy storage

3.4.2 Capacity Reserve A utility or other electricity supplier is required, always to have the resources to meet its customers

demands plus a reserve. Suppliers can meet the requirement with generating capacity they own, with

capacity they purchase from others, through demand response, or with capacity obtained through

capacity market auctions.

Figure 18 Capacity Value of Storage

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4 Conclusion: Energy Storage for South/Southern and Sub-Saharan

Africa.

A battery energy storage solution offers new application flexibility and unlocks new business value

across the value chain, from power generation, transmission & distribution, and renewables, to industrial

and commercial sectors. The ability to offer highly customized solutions through the platform offers

customers unprecedented levels of flexibility, resilience and operational efficiency in hybrid generation,

grid operation and energy management. The Reservoir platform also enables higher levels of renewable

power by providing efficient grid stabilization and peak management system. Considering wide spread

adoption of renewables and to provide reliable power in South, Southern and Sub-Saharan Africa.