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The 13 Key Characteristics of Battery Storage Systems

batteries connected

Battery storage systems are an essential part of the future energy market. However, there are so many different types of batteries, it may be hard to compare and understand which one is best for your particular application.

To help you make sense of this, we have broken down the key characteristics that you should look for when selecting a battery storage system.

1. Rated power capacity 

Rated power capacity is the maximum power that the battery can provide in ideal conditions. It is provided by the battery manufacturer and typically measured in kW. A higher rated power capacity means that the battery can provide more power and can be used for a wider range of applications.

Batteries are typically rated for their continuous power rating, which is the amount of power they can provide without being damaged. They are not designed to be at 100% capacity for a long period of time. Therefore, the rated power is typically is not what the battery is expected to provide over a long period.

2. Energy capacity

Energy capacity is the maximum amount of energy that the battery can store. It is typically measured in milliamps × hours (mAH). For example, if a battery has 100 mAH capacity and provides 3 mA for 100 hours, then it has a total energy capacity of 300 mAH.

The higher the energy capacity, the longer your system can run on a single charge. However, batteries with high capacity also tend to be more expensive and larger in size. Therefore, it is important to choose a battery with the correct energy capacity for your application.

3. Storage duration

The storage duration is the amount of time that the battery can store energy without being recharged.

It is typically measured in hours and is a good indicator of how long the battery can power an application before it needs to be recharged. A longer storage duration means that you have more freedom in your energy management plans.

For example, a battery with 2 MW of power capacity and a 10 MWh of usable energy capacity will have a storage duration of five hours.

4. Cycle life/lifetime 

Cycle life/lifetime is the number of times that the battery can be charged and discharged before it needs to be replaced.

It is typically measured in cycles and the number of years that a battery should last and depend on the type of battery, its application, and environmental conditions.

A longer cycle life means that you will need to replace your batteries less often which means saving money in the long term.

5. Self-discharge rate

Self-discharge is the rate at which a battery loses its charge when it has not been used for some time.

A lower self-discharge rate means that the battery can be stored for longer periods of time without requiring a recharge which would definitely have a positive impact on your energy management plan.

For example, batteries with a low self-discharge rate would be better suited for long-term storage applications, such as energy arbitrage applications where the batteries are charged during periods of low energy prices and discharged to cover high demand.

A battery with a high self-discharge rate would not be able to store energy for long periods of time and would need more frequent recharges.

Self-discharge is sometimes referred to as the parasitic load of a battery system. The rate at which it occurs depends on several factors such as the battery chemistry, its application, and environmental conditions.

6. State of charge

The state of charge represents the battery’s current level of charge. It is typically measured in percentage and influences a battery’s ability to provide the required power.

A low state of charge means that a battery is not fully charged and will need to be recharged before being used.

On the other hand, a high state of charge means that you can use the battery immediately and it will not need to be recharged until later.

7. Round-trip efficiency

Round-trip efficiency is the ratio between the energy-charged into the battery and the amount of energy returned by the battery when used. It is typically measured in percentage and will vary depending on several factors such as the battery chemistry and the application.

A high round-trip efficiency means that the battery can efficiently store energy without a large loss of power. Although battery manufacturers typically quote round-trip efficiency figures that only account for the charging and discharging of a battery, it is important to take into consideration all of the losses that occur throughout the lifetime of a battery.

8. Operating temperature

The operating temperature is the range of temperatures at which a battery can be used without any performance degradation. It is typically measured in degrees Celsius or Fahrenheit and it will influence the temperature range that a battery can be used in.

A battery’s operating temperature can also influence its cost because higher temperatures will require materials that are more expensive and can withstand high temperatures.

9. Weight

The weight of a battery system is an important factor to take into consideration because it impacts the cost, handling requirements, and portability factors. A battery’s weight will depend on the size of its cells and their composition.

Every type of battery technology used on the market today has a different power-to-weight ratio. A battery with a high power-to-weight ratio means that it can deliver more power per unit mass than batteries with a low power-to-weight ratio.

Battery technologies used for stationary applications like utility-scale energy storage systems would typically have a higher weight per kWh than batteries used for portable applications. However, battery newer battery technologies coming onto the market are already lighter than older ones. This will further improve their cost and performance characteristics.

10. Nominal cell voltage

The nominal cell voltage is the average voltage of a battery’s cells. It is typically measured in volts and it represents the voltage that an individual cell can provide when fully charged.

Nominal cell voltage is important to consider when calculating the size of a system’s power inverter. Because batteries charge and discharge at different rates, their individual cell voltages will vary.

11. Load Shift Response Time

The load shift response time is the amount of time it takes for a battery to respond when subjected to an increase or decrease in its power demand. It is typically measured in seconds and can impact whether batteries are suitable for use in the power grid.

A long load shift response time means that overshooting voltage levels may occur when batteries are subjected to high rates of fluctuation in demand. The faster a battery’s load shift response time, the better it can accommodate changes to its demand and improve grid stability.

12. Fluctuation suppression

Fluctuation suppression is a battery’s ability to reduce the fluctuations in output voltage when subjected to changes in load. It can be defined as the amount of voltage variation that a load shift can cause.

Fluctuation suppression is important because it affects the quality and stability of electricity that is delivered to customers. A battery with high fluctuation suppression can help improve the voltage profile of electricity that it delivers and contribute towards improving grid stability.

13. Voltage stability

Voltage stability is measured by the amount of voltage variation that a battery can experience during normal operation without impacting its performance. It tends to be measured in percent over-voltage or under-voltage.

Voltage stability is important to consider because it impacts the quality of electricity that a battery system can deliver to customers and it also impacts the cost of energy conversion. A high degree of voltage stability means that a power inverter does not need to be oversized, which can reduce its cost.