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Ancillary services are crucial components in the energy sector, designed to maintain grid stability and efficiency. They ensure a reliable electricity supply by managing the balance between electricity supply and demand, thus supporting the continuous flow of energy. These services include various functions such as regulating frequency, providing reserve power, and managing voltage levels. Their importance cannot be overstated, as they help in preventing power outages, ensuring the grid's operational reliability, and facilitating the integration of renewable energy sources, making them indispensable in modern power systems.
Battery Energy Storage Systems (BESS) emerge as a dynamic and robust solution for providing essential ancillary services critical to the operation and stability of the power grid. These systems are renowned for their versatility, enabling them to store and release energy on demand, thereby ensuring a reliable match between energy supply and demand. BESS's flexibility and efficiency in energy management make them indispensable tools in the modern energy landscape, facilitating the smooth integration of renewable energy sources and enhancing grid reliability and performance.
Regulation helps manage short-term differences in power generation and consumption. It smooths out these fluctuations, as illustrated in Figure 1, where the demand line shows variations indicating an imbalance. Regulation, depicted by a thicker line, results in a steadier system response by mitigating these discrepancies. Online generating units adjust their output for regulation—increasing power to address shortfalls (up regulation) and decreasing it when there's excess generation (down regulation). This dynamic response ensures grid balance and reliability.
It's crucial to note that large thermal generation units used for regulation can experience increased wear and tear. This is because they frequently adjust their power output to meet the demands of regulation duties.
When using storage for down regulation by charging, it draws energy from the grid, and the operator incurs costs for this energy. This aspect is particularly significant for less efficient storage systems where the expense of the consumed energy might surpass the financial returns from providing the regulation service.
The quick response capability of most storage systems, known as fast ramp rate, greatly enhances their value as a resource for regulation. These systems should be equipped to react to specific signals, such as the area control error (ACE) or automatic generation control (AGC) signals, from their Balancing Authority. Unlike traditional plants that typically respond to AGC signals, advanced storage technologies like flywheels, capacitors, and certain batteries can more accurately track these signals. This precision enables them to offer double the regulatory benefit of conventional generators, reducing wear on other generation assets.
Managing an electric grid necessitates reserve capacity to address unexpected shortfalls in electricity supply. Typically, reserves match or exceed the capacity of the largest single supply resource, constituting 15% to 20% of the normal supply. Different grid operators have distinct definitions for reserves, depending on the operational context. For clarity, this discussion simplifies into three types of reserve, showcasing the role of storage in this critical service.
Spinning Reserve (Synchronized) refers to online, yet idle, generation capacity ready to activate within 10 minutes for addressing generation or transmission outages. A subtype, 'Frequency-responsive' spinning reserve, acts within 10 seconds to stabilize system frequency. This reserve is the primary resource utilized during immediate shortfalls.
Non-Spinning Reserve (Non-synchronized) involves generation capacity that can be offline or consists of adjustable loads, ready to be utilized within 10 minutes.
Supplemental Reserve refers to generation resources available within one hour to address load demands, acting as a backup to spinning and non-spinning reserves and, occasionally, for commercial energy sales. Unlike spinning reserves, supplemental reserves aren't synchronized with grid frequency and are deployed after spinning reserves are fully utilized. For storage, unlike generation which must be operational at a part load, storage for reserve capacity is not actively discharging but must be ready to do so when called upon.
Electric grid operators are tasked with maintaining voltage within specific limits, often requiring reactance management due to the reactive properties of grid-connected equipment. To stabilize the grid, voltage support resources are necessary to counteract reactive effects. Traditionally, certain power plants have produced reactive power (VAR) for this purpose. However, strategically placed energy storage systems within the grid can serve as an alternative or complement to these plants, offering VAR support either centrally or distributed near large loads for enhanced grid stability.
The Power Conversion System (PCS) in storage systems for voltage support must operate at a non-unity power factor to manage reactive power (VARs), a feature present in all modern PCSs. This operation mode does not require real power from the battery, making discharge duration and cycle frequency irrelevant. It involves either absorbing or providing VARs to balance voltage without needing real power injection or absorption, catering specifically to the grid's requirements.
Black start is the process of restoring operation to an electric power station or part of a grid without relying on external power transmission. Some grid operators mandate regional transmission organizations (RTOs) to maintain at least two strategic black start facilities per zone for quicker restoration during widespread outages or blackouts.
To initiate a black start, some power stations deploy small diesel or gas generators to kick-start larger generators. These larger generators then power up the main station generators. However, many of these black start assets are aging, prompting RTOs to issue requests for proposals (RFPs) or implement new tariffs to encourage black start capabilities in generation facilities, ensuring system reliability.
Concurrently, declining prices of lithium-ion (Li-ion) battery technology have made Battery Energy Storage System (BESS) projects more economically viable for various grid functions, including black start.
Electricity storage effectively smooths out the variability inherent in wind and photovoltaic (PV) systems, making it a popular choice for this purpose. The operational requirements for a storage system stabilizing renewable energy sources are akin to those for managing fluctuating load profiles. Specifications often include maximum expected ramp rates in megawatts per minute and the duration of these ramps. Both load following and renewable ramp support share similar design considerations, highlighting the adaptability of storage systems in aligning electricity supply with variable demand patterns.
It's worth noting that the aforementioned points primarily relate to utility-scale BESS projects. However, when considering commercial and industrial scale projects, there are additional benefits that can help facilities save money and enhance operations. We invite you to reach out to us for a discussion on how we can assist you in implementing your BESS project.
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