Energy storage technology is rapidly evolving with various chemistries, technologies and C ratings available, selecting the right battery for the correct application can be complicated. There are many unique advantages and disadvantages when comparing energy storage technology and chemistry and considering the C rating for the specific application requires an understanding of the functional demands to be placed on the storage system. This white paper is a guide and uses modular, fully integrated, AC-coupled industrial energy storage system technology as an example to provide a guide across various applications and will detail how C ratings can be applied. Please contact us if you have any questions

1. WHITE PAPER
Understanding the difference
between energy and power
batteries

2. UNDERSTANDING THE DIFFERENCE BETWEEN ENERGY AND POWER BATTERIES WHITE PAPER | 2
TABLE OF CONTENTS
1. Executive Summary Page 3
2. Introduction Page 3
2.1 Energy and Power Definition Page 3
2.2 Understanding C Ratings Page 4
3. Selecting the Right Solution Page 7
3.1 Hybrid Energy Storage System Page 7
3.2 Load Levelling Page 7
3.3 Peak Shaving Page 7
3.4 Security of Supply Page 7
3.5 Frequency Stability Page 8
3.6 Power Quality Page 9
3.7 Energy Storage Solutions Page 9
4. Utility Solutions Page 9
4.1 Renewables Integration Page 9
5. Microgrid Storage Solutions Page 9
6. References Page 10

3. UNDERSTANDING THE DIFFERENCE BETWEEN ENERGY AND POWER BATTERIES WHITE PAPER | 3
1. EXECUTIVE SUMMARY
Energy storage technology is rapidly evolving with various chemistries, technologies and C ratings available,
selecting the right battery for the correct application can be complicated. There are many unique advantages and
disadvantages when comparing energy storage technology and chemistry and considering the C rating for the
specific application requires an understanding of the functional demands to be placed on the storage system. Key
drivers to the selection of batteries and their respective C ratings vary by the specific requirements that are unique
to each application including the need to control variable renewable energy feed-in to minimise variability and
better match renewable electricity supply with area demand.
This white paper is a guide and uses modular, fully integrated, AC-coupled industrial energy storage system
technology as an example to provide a guide across various applications and will detail how C ratings can be
applied.
2. INTRODUCTION
Two of the most important factors in determining energy system sizing are the amount of peak or average power
required and the amount of time it is required to supply power. Any additional non-intermittent and dispatchable
supply sources available in the system for example generators, must be identified to ensure security of supply.
Energy storage systems can be engineered to fit a range of design parameters, and achieving the right mix of supply
sources can result in significant cost savings as well as increased renewable energy penetration. Conversely,
poorly designed and over or under-specified systems can result in both underutilisation of assets and improper
utilisation of storage systems resulting in damage and degradation.
For example, in the case of a hybrid energy system that is designed to provide a secure supply of energy regardless
of weather conditions, the backup generation must be sufficient to power the site without the use of any distributed
energy resources. The cost and scope considerations for the project should be weighed against the cost of
lost production or plant shut down. Disruptions to power supply can cause expensive damage to equipment and
lost periods of production in factory or processing environments can result in damaged batches, lost revenue,
and significant costs. Individual project requirements should be evaluated to understand the cost of downtime,
production losses, and other potential impacts when designing the system supply.
Energy storage systems power to energy ratio or C rating provides a factor for the duration the energy storage
system can provide its full power ability. For example, a 1MW battery with 2MWh of capacity has a 0.5 C rating
(1MW/2MWh) and can provide its full power capacity for 2 hours. However, site load profiles provide the limiting
factor for energy discharge and a varying or reduced demand (e.g. 0.5MW) allows for a longer discharge time (4
hours in this case).
The pairing of energy storage systems with both dispatchable and non-dispatchable energy sources can drive the
design of the system to meet cost requirements while providing specific site requirements such as uninterrupted
loads, sufficient time for shutdowns, sufficient time for generator start up, and extended cloud events. When
paired with dispatchable sources, the sizing should consider both the time requirements for start-up in unplanned
events as well as regular storage system utilisation. When paired with non-dispatchable sources such as solar
photovoltaic or wind, the storage system should be able to accommodate production disruptions as well as regular
expected drops in profile, for example at night time for solar photovoltaic. Addition of forecasting technologies to
provide intelligence around expected production resource availability increases system robustness and reliability.
When considering energy storage system design, battery cost variations across power and energy profiles are
important factors as are the expected utilisation frequency and degradation of storage capacity from utilisation.
Certain battery technologies are more suited to high-power or high-energy applications and should be considered
when evaluating technology applicability. Additionally, batteries such as lithium-ion based chemistries suffer
degradation from charge and discharge cycling and future replacements or expansions of system capacity need to
be considered as part of the project lifecycle. Other battery technologies such as flow batteries do not suffer similar
cycling damage and therefore may be more suitable for certain applications.
2.1 Energy and Power Definition
Understanding the difference between energy and power can simply be explained as: Power is the ability to do
work, or the rate of doing work. The unit of power is the Watt (W) or kW/MW. A generator has a maximum power
rating, which is the maximum work rate of the unit. Electrical power is the rate at which energy is being transferred
through a circuit. Power is an instantaneous value.

4. UNDERSTANDING THE DIFFERENCE BETWEEN ENERGY AND POWER BATTERIES WHITE PAPER | 4
Energy is the integral of power over time (sum of all instantaneous power consumption over a period of time).
Energy is the amount of work done. The unit of energy for electrical circuits is the kWh. One kWh is the energy
transferred by one kW of power in one hour. Energy in kWh is what we buy from our electricity utility. Energy is
an accumulated value.
2.2 Understanding C Ratings
Batteries are defined in units of C, for example, a high C rate battery can be charged or discharged very fast and
produce a lot of power. Low C rate batteries have lower power but a higher energy rating, which means the capacity
to deliver power over a longer time-frame. In a battery pack, more cells in parallel lower the peak current in each
cell and allow each cell to operate at a lower C rate. An example of a low C rate battery can be seen in electric
vehicle applications, the desired peak battery pack current can be reached with either a battery pack with more
parallel cells (thus, larger energy capacity) or fewer parallel cells and a higher C rate. With parallel cells, a Low C
battery can stay within its C limit.
Battery manufacturers data sheets typically come with a curve detailed (see chart below) the cell voltage as a
function of charge removed, and report several different curves depending on the discharge rate. The C rate is the
current used to discharge the battery. It is defined as the current divided by the rated capacity. Therefore, if the
discharge current is at the 20-hour discharge rate, the C rate is I20 ÷ q20 × C = 0.05 × C or (C/20). A charge rate
that, under ideal conditions, is equal to the energy storage capacity of an electricity storage device divided by 1
hour.
A C rate of 1C is also known as a one-hour discharge; 0.5C is a two-hour discharge and 0.2C is a 5-hour discharge.
Some high-performance batteries can be charged and discharged above 1C with only moderate stress. The table
over the page illustrates typical times at various C rates.
Image 1. Fully charged cell voltage. The voltage at the given C-rate when
a cell is at its maximum charge

5. UNDERSTANDING THE DIFFERENCE BETWEEN ENERGY AND POWER BATTERIES WHITE PAPER | 5
C Rating Duration Application
5C and above 12 minutes Hybrid P/V integration generation smoothing applications
2C 30 minutes Hybrid P/V integration generation N+1 smoothing applications
1C 1-hour Load levelling and frequency stability control
0.5C 2-hours Peak smoothing and asset protection
0.2C 5-hours Security of supply short term
0.1C 10-hours Energy storage 8-10 hour cycle off grid security of supply
.05C 20-hours Energy storage 24-hour cycle off grid applications
Table 1. C rate service times when charging and discharging batteries
2.2.1 Battery Selection Checklist
There are many factors to consider when scoping a battery solution; the following is a list of criteria that should
form the basis of battery selection;
• Safety
• Performance requirements
• Technology and company track record
• Depth of Discharge
• Installation requirements - space limitations
• Maintenance requirements
• Application
• Critical spares availability
• Warrantee and performance guarantees
• Cost
• Conditions – temperature
• Requirements from network, utility or end user
• Efficiency of chosen chemistry
• Life cycle of battery and overall solution
2.2.2 Battery Life Cycle
The cycle life of a battery is the number of charge and discharge cycles a battery can complete before losing
considerable performance. It is specified at a certain Depth of Discharge and temperature. The necessary
performance depends on the application and relative size of the installation. However, a fully charged battery
that can only deliver 60-80% of its original capacity may be considered at the end of its cycle life. Calendar life
is the number of years the battery can operate before losing considerable performance capability. The primary
parameters are temperature and time. Lithium-ion has a lifespan of no more than 10,000 cycles, which must be
taken into consideration of the life span of the project when calculating the cost befit analysis and the overall design
of the system. [e]
2.2.3 Depth of Discharge
Depth of Discharge directly relates to the life cycle of the battery and is the utilised amount of the batteries capacity.
This is expressed percentage of the batteries full energy capacity 0-100%. If a battery discharges 10% of its full
energy capacity, 90% of the full capacity is unused. This corresponds to 10% Depth of Discharge. Batteries will be
able to complete more charging cycles (defined above in 2.2.1) than a battery cycled at deep discharge, however
each battery type and chemistry reacts differently to variable conditions such as temperature and configuration.
The figure over the page provides an illustration of the effect of Depth of Discharge (the x axis) on cycle life (y axis).

6. UNDERSTANDING THE DIFFERENCE BETWEEN ENERGY AND POWER BATTERIES WHITE PAPER | 6
Exponential zone cell voltage
The cell voltage at the end of the exponential zone, as shown in the Nominal Current Discharge Characteristic
graph above - The cell charge removed at this point is Q
full -It
.
Nominal zone cell voltage
The cell voltage at the end of the nominal zone, as shown in the Nominal Current Discharge Characteristic graph
above -The cell charge removed at this point is Q
full -It
.
Charge removed at exponential and nominal point
Voltage vs discharge curves show that cell-voltage typically undergoes several distinct regions depending on
charge.

7. UNDERSTANDING THE DIFFERENCE BETWEEN ENERGY AND POWER BATTERIES WHITE PAPER | 7
3. SELECTING THE RIGHT SOLUTION
This section of the white paper looks at various applications, provides the user with recommendations for each
application, and relies on the user modelling each application to achieve the desired outcome.
The design of the system must also take into consideration equipment selection including the battery management
system to achieve and maintain, performance, longevity and safety of the battery system.
Choosing the ratio of power and energy for energy storage systems in a microgrid or off-grid environment is highly
dependent on the types of electrical demand in any given application. Depending on the types of load on site and
the mix of supply sources, the energy storage system may provide a range of services include:
• Production profile variability smoothing – provide gap fills for passing clouds
• Back-up power and uninterrupted power source – fill in for short periods to allow for safe shut down or short
network outages
• Pairing with renewable energy resources – shift production from periods of over supply to periods of under
supply
• Peak energy smoothing – eliminate spikes in power demand and power supply and achieve smoothed
balance of power delivery / demand
• Voltage regulation
• Frequency regulation
• Night time / cloudy power supply (in solar-based systems) – sufficient capacity to endure nights (10-18 hour
periods) or extended periods of clouds (days – weeks)
3.1 Hybrid Energy Storage System
The use of hybrid energy storage systems and the integration with existing islanded power stations, photovoltaic,
wind turbines a hybrid power system becomes a viable proposition for the improvement of the power peaks caused
by varying loads.
3.2 Load Levelling
Load levelling usually involves storing power during periods of light loading on the system and delivering it during
periods of high demand.
During these periods of high demand, the energy storage system supplies power, reducing the load on less
economical peak-generating facilities. Load levelling allows for the postponement of investments in grid upgrades
or in new generating capacity.
3.3 Peak Shaving
Peak shaving ideally can be used for reducing peak demand and has some financial incentives to the operator. An
Energy storage system will provide a fast response and emission-free operation, making it the optimal solution for
this application. Power producers and utilities generally own peak shaving systems, with many benefits including:
• Power producers and utilities can offset the operational costs during peak periods; in the case of power
producers, it could mean reduced requirements for additional spinning reserve units
• By reducing peak demand will reduce the power costs to commercial and industrial customers
• Reduction in the investment required for infrastructure as the loads will be flatter and the demand during
peak time will be less
3.4 Security of Supply
The variable, intermittent power output from a renewable power generation plant, such as wind or solar can be
maintained at a committed level for a period.
The energy storage system smooths the output and controls the ramp rate (MW/min) to eliminate rapid voltage and
power swings on the electrical grid.

8. UNDERSTANDING THE DIFFERENCE BETWEEN ENERGY AND POWER BATTERIES WHITE PAPER | 8
3.5 Frequency Stability
Variable loads, intermittent load shedding and the integration of large photovoltaic (PV) systems power generation
from renewables and other sources, along with variable loads cause deviations from nominal frequency in the grid.
Energy storage systems are an attractive way to restore the balance between supply and demand, featuring rapid
response and emission-free operation. The energy storage system is charged or discharged in response to an
increase or decrease of grid frequency and keeps it within pre-set limits.
3.6 Power Quality
The demand for high-quality power has grown with the emerging digital world and the augmentation of delicate and
sensitive equipment and microprocessor-based controls, there are some electrical grids that have not provided up
to date protection for their customers, exposing them to disturbances such as voltage dips/sags and short supply
outages.
Batteries offer accurate and rapid response, energy storage systems improve power quality and protect downstream
loads against short-duration disturbances in the grid, affecting their operation.
3.7 Energy Storage Solutions
The advent of volatile and decentralised power generation from renewable sources and unpredictable consumers
like electric vehicles, as well as obstacles for reinforcing the grid infrastructure, accentuate the unbalance between
production and consumption of electrical energy in the power system.
This results in grid instabilities, for example, voltage and frequency deviations affecting consumers. Energy storage
solutions can make a major contribution in alleviating these effects.
4 UTILITY SOLUTIONS
Substations facilitate the efficient and reliable transmission and distribution of electricity. Utilities today are under
extreme pressure to meet consumer and regulatory demand for high-quality power supply at competitive prices
while lowering environmental impact. Trends towards decentralised power generation from renewable sources
further challenge established grid structures and require flexible and intelligent substations [b]. As a single-source
solution provider, Vector Energy manages these complexities, minimises risks and interfaces, while ensuring timely
and on-quality delivery of turnkey substations and engineered equipment packages.
4.1 Renewables Integration
Integration of decentralized power generation from renewable sources necessitates careful analysis and adaption
of the power system as well as the construction of collection grids for wind farms or solar power plants.
Vector Energy offers a range of scalable substation solutions that help to efficiently integrate renewable energy into
the transmission grid and distribution network. Our in-depth knowledge of renewable power generation technologies
and comprehensive experience with grid codes and utility practices in use around the world enables us to provide
turnkey grid connection solutions for all types and sizes of renewables power plants. The customized systems are
based on proven and state-of-the art technologies, and are designed to meet the requirements of customers with
a global market presence as well as local specifications.
Vector Energy presence ensures support throughout the lifecycle of the project, and our turnkey project capabilities
allow us to support customers with permitting applications and system studies for commissioning and maintenance.
Advantages range from, scalable grid connection substations for all types and sizes of renewables power plant and
enhanced reliability and quality of power supply.

9. UNDERSTANDING THE DIFFERENCE BETWEEN ENERGY AND POWER BATTERIES WHITE PAPER | 9
5 MICRO-GRID STORAGE SOLUTIONS
“A micro-grid is a group of interconnected loads and distributed energy resources within clearly defined electrical
boundaries that act as a single controllable entity with respect to the grid” [c].
A microgrid system, depending on the circumstances, can operate either in parallel with the upstream grid or
island mode. Micro-sources that comprise the microgrid include technologies such as diesel generators, fuel cells,
micro-turbines, photovoltaic panels and wind turbines. Energy storage systems play a key role in the operation
of microgrids. Vector Energy has successfully installed an energy storage systems battery in a utility substation,
effectively reducing the stress on the existing infrastructure and provided peek shaving solutions [d]. Vector Energy
installed the energy storage systems and stores energy during high availability periods and re-dispatch it when
there is a power shortage or peak shaving requirement. An energy storage systems can utilise time of use tariff by
purchasing power from the grid during the off-peak hours and selling it back to the grid during the peak demand
hours. Other benefits of using storage systems in microgrids include the provision of ancillary services and power
quality improvement. Because of the crucial role played by the storage systems, their sizing is essential for assuring
the correct operation of the microgrids. Therefore, sizing the system and selecting the correct C-rating for the
battery is critical.

10. UNDERSTANDING THE DIFFERENCE BETWEEN ENERGY AND POWER BATTERIES WHITE PAPER | 10
6 REFERENCES
• [a] Developed from - System Advised Model (SAM) version 2017.1.17
• [b] ABB utility solutions - http://new.abb.com/substations/utility-solutions
• [c] College of Engineering Munnar - https://www.scribd.com/document/262505431/Micro-Grid
• [d] International Journel of Electrical Power & Energy SyetemsOptimal scheduling of a microgrid with a fuzzy
logic controlled storage system Juan P. Fossati, Ainhoa Galarza, Ander Martín-Villate, José M. Echeverría, Luis
Fontán Department of Electronics and Communications, CEIT and Tecnun (University of Navarra), Paseo de
Manuel Lardizábal N 15, 20018 Donostia-San Sebastián, Spain http://dx.doi.org/10.1016/j.ijepes.2014.12.032
• [e] https://wiki.epfl.ch/ess/documents/IRENA_Battery_Storage_report_2015.pdf