As the Bulk Energy Storage System (BESS) era progresses into discussions about applications rather just about technology, it is becoming clear that there are two primary application types being required by end users. The difference between the so-called High Power BESS and High Energy Bess applications is significant, and each places considerably different demands on the core energy storage components in the system.
High Power BESS applications include Spinning Reserve, Voltage Control, Frequency Stability/Correction, VAR Compensation, Power Smoothing, and Power Factor Correction. These are primarily short term operations, demanding high power outputs for short periods, and fast recovery, meaning high power inputs in short periods for fast recharge. “Short Term” is generally thought of in seconds and minutes, usually limited to less than 1 hour for most applications. High Power BESS applications require an energy storage medium capable of delivering high currents and being recharged with equally high currents, and the storage medium must also be able to operate continuously at less than 100% State of Charge (SOC), typically having a standby state of 70%. This allows for sudden demand to absorb energy as well as deliver. These applications tend to be more prevalent at grid level for Utilities and Energy Providers.
High Energy BESS applications include Peak Lopping/Limiting, Energy Shifting/ Arbitrage, Islanding, and longer term Power Smoothing and Power Factor Correction. These are primarily long term (>1hr) operations, and unlike high power applications, demand an energy storage medium able to deliver very large amounts of energy (eg batteries with high AHr capacities) for long periods. However, like high power applications, it is advantageous if the energy storage medium can be recovered quickly, so it is ready to deliver again when called upon. Operation of high energy BESS often requires the SOC standby state to be 100%, allowing for maximum delivery of energy to the load when required. Subsequent recovery after discharge is usually back to 100% SOC, however, in many such applications, this is not possible due to lack of availability of the continuous energy supply required to achieve this. As such the energy storage medium must be tolerant of operating at partial states of charge, with frequent discharge/recharge cycles to less than 100% SOC.
Whilst traditional Lead Acid Batteries provide the large capacities required by High Energy BESS applications, they do not provide the very high cycle life and thus very high total energy throughput demanded by such applications. Advanced VRLA batteries contain nano-carbon particles in the plates to give more efficient charging, low risk of sulphation (allowing continuous operation at less than 100%SOC), and higher capacity retention during the battery life. AVRLA batteries are designed for use in large energy storage and remote renewable power applications where frequent charge/discharge cycles are encountered. The technology allows in excess of 5000 deep discharge cycles, delivering in excess of 7 MWHrs of total throughput from a single 2V cell. Because of this very high total throughput, it is possible to assemble large energy storage systems with just a few parallel strings, making management of string current imbalances very easy, extending the life of the BESS even further, and dramatically reducing the system footprint.
High Energy BESS Application
Consider two types of energy storage system the average Prosumer is likely to operate – those with renewable technology attached and those without. The goal of those without renewable technology is primarily tariff reduction. The goals of those with renewables are this with the added complications of ensuring there is either sufficient storage to hold the daily energy production for later use, and/or the ability to export this excess to the grid and be paid for this production.
The system without renewables is intended to consume additional energy over and above the load from the grid at times of low load consumption and low tariff, and produce energy to supply the additional demands of the load at times of high load consumption and high tariff, thus reducing the demand on the grid and cost to the consumer. This is the so called peak tariff reduction operation, or energy arbitrage. Both tariffs can be reduced if the control system is capable. Both consumption costs during peak tariff and peak demand charge tariff costs can be reduced, provided the system’s predictive abilities are sufficient.
High Energy BESS applications demanding very large total energy throughputs are now able to be delivered by GS Yuasa’s Advanced VRLA battery solutions.