Energy Storage Systems

Definition of Energy Storage

• Electrical Energy Storage (EES) is
the process of taking electrical
energy from a power network,
converting it into a form that can be
stored, and then converting it back
into electrical energy when it's
needed.

• This process allows electricity to be

produced during periods of low
demand, low generation cost, or
from intermittent energy sources,
and then used during periods of
high demand, high generation cost,
or when no other generation
options are available.
Application of Energy Storage
 Role of Energy Storage
Capacity Services
In the context of Energy Storage Systems (ESS),
capacity services refer to how an ESS helps balance
electricity supply and demand within a system. This
involves storing excess electricity when demand is
low or supply is high and then releasing it when
demand is high or supply is low. By doing so, ESS
ensures that there is a reliable and consistent
electricity supply, preventing shortages or surpluses
and helping maintain grid stability.
Peak Reduction
To meet rising electricity demand, system planners and operators often build new generation
capacity to match the peak of the demand curve. However, by charging storage assets during low-
demand periods and discharging them during peak periods, it is possible to reduce the overall
maximum system demand. This method, known as 'shaving' the demand curve, decreases the need
for traditional power plants that only operate during peak times, making the system more efficient
and cost-effective.
 Role of Energy Storage
Demand charge reduction
• At the end-user level, large facilities like
factories and data centers often face maximum
demand charges. These charges are paid to
utilities to reserve the right to a specific
maximum demand level needed for their
operations. To secure this right, customers pay
a fixed fee in addition to the charges for the
electricity they consume.

• By using storage assets, these large load

customers can shave the peak off their power
demand, reducing these fixed fees while
maintaining the same overall energy
consumption.
 Role of Energy Storage
Capacity Firming

As more renewable energy sources are

integrated into electricity grids, a common
problem occurs when solar power plants in
the same region simultaneously start
producing electricity when the sun rises, or
wind turbine generation drops at the same
time when the wind stops. Capacity firming
involves using energy storage systems to
smooth out these fluctuations, ensuring a
steady and reliable power supply.
 Role of Energy Storage
Capacity Firming

• During these ramps and drops, an

Energy Storage System (ESS) can be
used to ensure a smooth increase or
decrease in power, allowing generation
assets time to adjust their production
without disrupting grid stability.
• Additionally, the ESS can cover capacity
drops or surges until renewable assets
return to normal operation. This
approach prevents abrupt changes in
power quality and ensures a firm
capacity from otherwise variable
generation sources.
 Role of Energy Storage
Capacity Firming
• Employing an Energy Storage System (ESS) facilitates the flexibility of base load
generating assets to accommodate swift changes in demand profiles, which traditional
power plants find challenging. The ESS functions by storing surplus generation during
periods of low demand, allowing base load plants to operate at high capacity in advance
of anticipated demand increases.
• Furthermore, the ESS can release stored
energy swiftly to address sudden spikes in
demand, thereby maintaining stability
and efficiency in the base load generation
profile. This strategy enables base load
plants to operate efficiently and
consistently while the ESS responds
dynamically to fluctuations in demand,
ensuring a reliable electricity supply
aligned with varying consumer needs.
 Role of Energy Storage
Reserve Margin and Spinning Reserve
• System operators typically require a reserve margin in the total power capacity of a grid to handle
situations where demand exceeds anticipated levels. Historically, this reserve margin has been
met by constructing additional conventional generation assets. However, Energy Storage Systems
(ESS) are increasingly being considered as an alternative.
• Moreover, ESS can serve as a spinning reserve for the network. Traditionally, spinning reserves
were provided by large rotating generators capable of quickly responding to unexpected spikes in
demand. ESS now fulfills this role by offering a fast and, in some cases, nearly instantaneous
response. This function acts as a backup for the grid, providing inertia and ensuring grid stability
during fluctuations in demand or supply.

The spinning reserve is the extra generating capacity that is available by

increasing the power output of generators that are already connected to
Reserve margin calculates how much extra supply is available
the power system
in a given region above expected peak demand.
 Role of Energy Storage
Arbitrage
• Energy arbitrage involves the process of storing energy
produced at one time in an Energy Storage System
(ESS) and then discharging it into the grid at another
time. A common application of this strategy is price
arbitrage, where market conditions are favorable.
• For instance, in electricity markets with varying prices
over time (hourly, daily, yearly), ESS owners can charge
the storage asset when electricity prices are low and
discharge it when prices are high. This practice enables
private operators to generate revenue and allows
distribution companies to enhance profitability by
purchasing electricity at off-peak costs and supplying it
during peak pricing periods to meet customer demand
efficiently.
 Role of Energy Storage
Generation Shifting
Generation shifting involves aligning on-site generation with
storage to optimize energy use according to demand. For
instance, a factory might integrate solar panels with an
Energy Storage System (ESS) to meet its energy needs.
During the day, the solar panels generate electricity for
immediate use and also charge the battery. Later, during the
evening and night when solar generation is unavailable, the
battery discharges to supply energy, ensuring continuous
operations. This process enhances the value of excess solar
energy that would otherwise go unused during daytime
hours, making it valuable by shifting it to periods of higher
demand, such as nighttime. Thus, generation shifting with an
ESS maximizes energy efficiency and reliability for the
consumer.
 Role of Energy Storage
Renewable Energy Penetration
• Storage assets are increasingly essential for
enabling higher levels of renewable energy
penetration in both traditional grids and mini-
grids. ESS allows operators and customers to
harness renewable energy that might
otherwise be wasted due to curtailment.
• Moreover, ESS facilitates increased integration
of VRE into the grid, allowing these sources to
contribute a larger share of total energy
production. Systems nearing their operational
limits with variable energy sources can benefit
from adding VRE assets paired with ESS,
whether colocated or distributed. ESS enhances
predictability and smooth out energy flows,
thereby optimizing the utilization of renewable
resources across the network.
 Role of Energy Storage
Frequency/Inertia Response
Energy storage plays a crucial role in providing
frequency and inertia response as well as voltage
regulation in electricity grids. For frequency and
inertia response, storage systems can quickly inject
or absorb power to stabilize grid frequency during
sudden changes in supply or demand. This helps
maintain grid stability and reliability.
Ramp Rate Control
Role of Energy Storage
Energy storage systems play a critical role in ramp rate
control within electricity grids. They are capable of quickly
adjusting their charging or discharging rates to manage rapid
changes in power demand or generation.

For example, during periods when renewable energy sources

like solar or wind experience fluctuations, energy storage
can smooth out these variations by absorbing excess power
during high generation periods and releasing stored energy
during low generation or high demand periods. This
capability helps maintain grid stability, prevents sudden
power surges or drops, and supports the integration of
intermittent renewable energy sources into the grid without
compromising reliability. Thus, energy storage enhances grid
flexibility and efficiency by regulating ramp rates and
ensuring smooth transitions in power supply and demand.
 Role of Energy Storage
Step Demand Changes
When a sudden increase or decrease in demand,
known as a step change, occurs at the end of a long
transmission or distribution line, it can lead to
substantial voltage fluctuations that may harm
network equipment.
Energy Storage Systems (ESS) play a crucial role in
mitigating these effects by smoothing out the
power and current fluctuations experienced by the
power line. By absorbing excess power during
sudden increases in demand or releasing stored
energy during decreases, ESS helps maintain a
stable voltage level, ensuring better quality of
service and protecting equipment from potential
damage due to voltage spikes or drops. Thus, ESS
enhances grid reliability and efficiency by managing
step demand changes effectively.
 Role of Energy Storage
Black Start

During a total power outage or blackout, restarting the

network is a challenging and time-consuming task for grid
operators. It involves carefully bringing both generation and
load back online in a stable and balanced manner.

Energy Storage Systems (ESS) play a crucial role in this

process by providing flexible services to assist during what is
known as a black start. ESS can rapidly inject power into the
grid to help kickstart essential generation units or critical
loads. This capability enables grid operators to restore
electricity supply more efficiently and quickly, minimizing
downtime and ensuring a smoother recovery from major
grid disruptions. Thus, ESS enhances grid resilience by
supporting the challenging task of black start operations.
 Energy Storage roles in Smart grid (Summary)
Energy storage systems play several crucial roles in smart grid systems:

• Load Shifting: Energy storage systems can store excess energy generated during periods of low demand and
release it during peak demand times. This load shifting capability helps utilities manage grid congestion and
reduce the need for expensive peaking power plants.

• Renewable Energy Integration: Energy storage enables better integration of intermittent renewable energy
sources like solar and wind into the grid by storing excess energy when generation exceeds demand and
supplying it when generation is low. This helps balance supply and demand, smooth out fluctuations, and
enhance grid stability.

• Grid Stability and Reliability: Energy storage systems provide fast-response capabilities to help stabilize the
grid by quickly injecting or absorbing power to maintain frequency and voltage within acceptable limits. This
is particularly important as more variable renewable energy sources are integrated into the grid.
 Energy Storage roles in Smart grid (Summary)
• Microgrid Support: Energy storage systems play a vital role in supporting microgrids, which are smaller-
scale power systems that can operate independently or in conjunction with the main grid. Energy storage
helps microgrids manage local generation and consumption, enhance reliability, and support islanding
operations during grid outages.

• Demand Response: Energy storage systems can enable demand response programs by storing energy
during off-peak times when electricity prices are low and supplying it during peak times when prices are
high. This encourages consumers to shift their energy usage patterns, reduce peak demand, and lower
overall electricity costs.

• Voltage and Frequency Regulation: Energy storage systems can provide rapid response to changes in
voltage and frequency, helping to maintain grid stability and reliability in the face of sudden fluctuations
in demand or supply.

Overall, energy storage systems enhance the flexibility, resilience, and efficiency of smart grid systems by
providing valuable services for grid optimization, renewable energy integration, and demand management.
 Energy Storage Technologies
• The table is a general overview and
comparison of existing energy storage
technologies, sorted by their relative sizes
and discharge times. The technologies are
listed in the order that they are presented in
the table above: starting with the highest
system power ratings, module sizes and
discharge times, and ending with
technologies that are still being developed
for utility-scale use.

• Energy storage can be used for multiple

purposes, including energy arbitrage,
generation capacity deferral, ancillary
services, ramping, renewable integration,
electric transportation, maintaining power
quality, and end-user applications. Figure 1: Comparison of existing energy storage technologies
(source: Sandia National Laboratories)
 Energy Storage Technologies
Pumped Hydroelectric Storage

Pumped Hydroelectric Storage systems are widely

used globally on both commercial and utility scales.
These systems typically operate by utilizing off-peak
electricity to pump water from a lower-elevation
reservoir to a higher-elevation reservoir. Later, during
peak electricity demand periods, water from the
upper reservoir is released downhill through
turbines, generating electricity.

This configuration involves two reservoirs situated at

different elevations, enabling power generation as
water moves downhill (discharge) through turbines.
Conversely, the system requires electricity to pump
water back uphill from the lower reservoir to the
upper reservoir (recharge), completing the cycle of
energy storage and generation.

Video credit: https://www.youtube.com/watch?v=xQWL3vUNjS8

 Energy Storage Technologies
Compressed Air Energy Storage (CAES) uses
electricity when prices are low to compress
air and store it either in underground
geologic features or in pipes.

When demand for electricity rises, the

compressed air is mixed with natural gas,
heated, expanded and directed through a
turbine to generate electricity. Other than
pumped hydro, this is the only commercial,
bulk-energy storage plant deployed today.

Video credit: https://www.youtube.com/watch?v=IzuItB_lK6I

 Energy Storage Technologies
A lithium-ion (Li-ion) battery is an advanced battery
technology that uses lithium ions as a key component
of its electrochemistry which has quickly emerged in
applications such as electric vehicles and plug-in
hybrids, and in these applications can be used to
discharge to the grid through Vehicle-to-Grid (V2G)
technology. They also are used for grid services and
larger storage projects.

Video credit: https://www.youtube.com/watch?v=VxMM4g2Sk8U A typical lithium-ion battery system can store and regulate
wind energy for the electric grid
 Energy Storage Technologies
Lead-Acid Batteries

A lead acid battery is a rechargeable battery that uses

lead and sulphuric acid to function. The lead is
submerged into the sulphuric acid to allow a controlled
chemical reaction.

This chemical reaction is what causes the battery to

produce electricity. Then, this reaction is reversed to
recharge the battery.

Video credit: https://www.youtube.com/watch?v=j_rNjiIiBKE

 Energy Storage Technologies
Hydrogen/Fuel Cell
A fuel cell is an electrochemical device that converts hydrogen fuel and oxygen into electricity, heat, and
water through a non-combustive process. It operates similar to a battery, generating electricity continuously
as long as there is a supply of fuel.
Hydrogen, stored in a pressurized container, is combined with oxygen from the air within the fuel cell.
Importantly, this process produces no harmful emissions, with the only by-product being pure water. This
clean energy technology offers a sustainable alternative for power generation, particularly in applications
where reducing environmental impact is critical.