Battery C-Rates for Commercial Battery Storage Systems?|Alternergy

Commercial Battery Storage Systems C-Rates 

Battery Energy Storage Systems (BESS) are emerging as a key player in modern energy infrastructure, particularly for integrating renewable energy sources and enhancing grid stability.

In commercial and industrial applications, they can offer clean, emissions-free power supply.
There are key parameters which are crucial for optimising the design and operation of a BESS:  power capacity (MW), energy capacity (MWh), and charging/discharging rates (C-rates).
Batteries are essential elements of an energy storage system and their charging and discharging rates are an important indicator of their performance.

What is a C-Rate and why Does it matter?

In simple terms, the C-rate (¹) indicates the time it takes to fully charge or discharge a battery.
The C-rate represents the rate at which a battery charges or discharges relative to its maximum capacity. It is a critical factor in battery performance and safety as it ensures that the battery operates within its design parameters to prevent overheating, damage, and capacity degradation.
The higher the rate, the faster the battery can be charged and discharged. 
However, charging and discharging at maximum power can reduce the battery's service life. Therefore, choosing an optimal rate can protect the battery cells.
The maximum C-rate also depends on the technology used. Lithium iron phosphate (LiFePO4) batteries typically can provide higher rates than lead-acid batteries.

How is “C” Calculated?

C-rate is defined as the reciprocal of the time (in hours) needed to fully charge/discharge the battery - a higher rate means a faster charging/discharging time, and vice-versa.

  • A 1C battery c-rate means that it takes an hour for the battery to will either be fully charged or discharged (the reciprocal of 1 equals 1)
  • A 0.5C battery c-rate means a battery charge/discharge rate of 2 hours (reciprocal of 0.5 equals 2)
  • A 0.25C battery c-rate means a battery charge/discharge rate of 4 hours (reciprocal of 0.25 equals 4)


The charging and discharging rate (C) of a battery = the charging and discharging current of the battery ÷ the rated capacity of the battery. So, for a 1000mAh battery, 0.2C represents 200mA (0.2 times the capacity of 1000mAh):

0.2C=200mA/1000mAh


Another example is if a fully charged battery with a capacity of 100 kWh is discharged at 50 kW, the process takes two hours, and the C-rate is 0.5C or C/2.

0.5C=50kW/100kWh

The C-rate can compare the charging and discharging capacities of two batteries with the same total battery capacity under the same conditions. So, if one battery can achieve 3C and the other one 1C, then the first battery can handle sudden, high demands  in charging and discharging better than the second battery.

How to choose the appropriate C-Rate?

The appropriate rate will depend on the energy demands of the application, costs, and the balance between power output and battery health. 
Although a battery with a faster charging and discharging capacity appears to be more appealing, if the C-rate is too high, it will impact on the service life of the battery - a larger charging and discharging rate will increase chemical reactions within the battery, leading to faster capacity loss and degradation.
On the other hand, very low C values, such as 0.1C, 0.2C, and 0.3C commonly seen in lead-acid batteries, offer slower charging currents and speeds, providing better battery protection but reducing output power.

Commercial Battery Storage Systems C-Rates

In industrial and commercial energy storage systems, 0.5C is the most common rate.
Both 0.5C and 0.25C rates are preferred in C&I Battery Energy Storage Systems applications as they prioritise energy capacity and longer discharge periods, contributing to extended battery life and improved efficiency.

 

Why Is 0.5C the Most Common Rate in BESS?

Choosing the right C-rate is important for optimising the Battery Storage System’s performance and longevity.
In commercial and industrial energy storage projects that target the benefits from peak-valley price differences during peak, valley, and flat periods, the 0.5C rate strikes a good balance. For example, for a single-cabinet system with a capacity of 215 kWh, when paired with a 100 kW PCS, it can be fully charged or discharged in 2 hours, which is quite in line with the length of peak and valley periods defined by various power grid companies. It can just perform charging and discharging within the corresponding periods, without wasting power or too much time, and still achieving the expect daily earnings and prolonging the payback period. 

Commercial Battery Storage Systems At Alternergy

We offer a variety of high-performance commercial energy storage for every business. 

Browse our new range of commercial battery storage systems: Dunext and Huawei FusionSolar - all systems are 0.5C Rate. (Sungrow coming soon)

Alternergy also supplies a wide range of residential battery storage solutions, designed to provide efficient and reliable energy storage for homes.

 

Shop Commercial Battery Energy Storage Systems


Shop Dunext Commercial Battery Storage


Shop Huawei FusionSolar Commercial Battery Storage


Browse our Residential Battery Storage Systems

 

(¹)  “C” is the initial letter of the unit of electric charge, Coulomb, which is defined as the amount of electricity passing through the cross-sectional area of a wire within one second.