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Energy storage has a broad scope of application: it covers not only the entire field of power generation, transmission, and distribution but also extends to mobile applications in sustainable mobility.
Stationary energy storage systems are used for a variety of functions in power supply: for load leveling, for frequency regulation, as a spinning reserve, for peak shaving, or for capacity firming. Load leveling refers to an energy storage system (ESS) saving energy at times of low demand for subsequent use when demand is at its highest. In frequency regulation the ESS is charged or discharged to compensate for an increase or decrease of grid frequency following a sudden imbalance of electricity supply with demand. Use as a spinning reserve means the ESS is kept in a charged state that suffices to respond to a failure in generation and transmission and to inject power into the grid within milliseconds. Peak shaving is frequently a topic for large power consumers, for instance in industry. They use energy storage systems to reduce their peak demand from the grid. Finally, capacity firming refers to keeping the unstable supply of renewable generated power at a certain (desired) level.
Several of these applications can be illustrated with the example of solar power. The power supply from photovoltaic plants (PV plants) fluctuates (is irregular), making it difficult to adjust to demand. When coupled with suitable energy storage systems, solar power can be transformed into a source of electricity that can be easily controlled and planned.
Capacity firming and ramping
In order to maintain the integrity of the electrical grid and ensure power quality, voltage and frequency must constantly be kept at specified levels. However, with utility-scale PV plants, the ability to maintain these levels can be quickly compromised by the passing of clouds, an abrupt change in the weather or a crack in a solar PV panel. These variations can cause rapid fluctuation of the PV power output, resulting in deviations in the desired voltage. Even a second of cloud coverage can cause the voltage to drop, destabilizing the local network. The sudden drop in voltage and power can also cause deviations in frequency levels, disrupting the overall operating characteristics of the grid. By quickly absorbing or injecting power in response to grid control signals, the ESS can ensure that the correct frequency and voltage levels are maintained. Not only can energy storage provide this capacity firming for the PV system, but it can also make sure that the PV power output increases and decreases at a rate specified by the grid operators (ramping support) to ensure that the PV plant abides by local grid codes.
In areas with a high penetration of solar generation, the local utility network is susceptible to resource adequacy issues when demand and PV generation are out of balance – specifically, in the early morning and evening hours when demand begins to increase but solar sources are not producing enough power to accommodate this demand. This is where energy storage can help the system operator maintain grid integrity through load-shifting capabilities. By coupling solar power with energy storage, the ESS can charge when generation is higher than demand and discharge when demand begins to spike, yet the sun is setting.
Storage systems offer similar advantages from the perspective of owners of PV plants on buildings: the new solar energy keywords are self-consumption (the consumption by the household of locally produced solar energy) and self-sufficiency (the capability to autonomously meet the energy demand of the household). To achieve these two aims, the misalignment between the daily solar power profile and the household demand must be overcome. This is achieved by adding energy storage capability to the traditional PV system.
A vital application for energy storage systems in the grid is frequency regulation. System operators often use large-scale generation facilities to not only provide bulk power to the end users, but also to provide the ancillary services needed to maintain the integrity of the electrical grid. One of the more pertinent of these services is real-time frequency regulation. Around the world, the electrical grid needs to operate at either 50 or 60 Hz in order to ensure that the facilities and critical equipment used in manufacturing are properly powered. This requires the instant and continuous balancing of electricity supply with demand.
The ESS can be used for second-by-second frequency regulation in real time. In this capacity, the ESS is charged or discharged in response to an increase or decrease of grid frequency. This approach to frequency regulation is a particularly attractive option due to its rapid response time and emission-free operation.
Battery storage for electric vehicles
Along with stationary use in the power grid, energy storage systems are increasingly being employed as mobile solutions. For example, modern electric buses fitted with a battery storage system can recharge at stops along the way or at the depot, allowing them to operate without an overhead line. They can help further electrify public transit and thereby reduce CO2 emissions.
Geneva, for instance, recently started operating 12 electric buses in its TOSA system. The buses’ batteries are recharged ultra-quickly at stops along their routes. The advantage of the system is that it requires no large heavy batteries, so it saves space and weight. The charging time at the end of the route is also shortened, which is especially advantageous for tightly scheduled operational intervals at peak traffic times. The system can save as much as 1,000 tons of CO2 on a line covering 600,000 kilometers per year.
The ultra-fast charging procedure is carried out safely in just 15 to 20 seconds with a charging output of 600 kW at points where the bus stops anyway to let passengers on and off. It takes less than one second to connect the bus to the charging point, making it the world’s fastest flash-charging connection technology.
A key challenge in battery integration for the bus lay in predicting the rate at which the battery would degrade and in creating specifications that would ensure availability of power throughout the life of the product and system. The solution was to make a model informed by experimental results and a fundamental understanding of the key physical and chemical processes of the battery.
Dispensing with overhead lines means that they disappear from the cityscape and that installation costs are also saved because no elaborate construction work is necessary. Moreover, buses can operate with greater flexibility when road construction work is going on. There is a reduction in the need for maintenance, which makes up a substantial part of the costs for operating conventional buses with overhead lines.
All in all, energy storage systems can make an important contribution to tackling various challenges in the future: they help overcome the intermittent nature of renewable energy, bringing it into line with more traditional energy sources in terms of dispatchability, stability, controllability, etc. What is more, they increase the flexibility and efficiency of sustainable mobility solutions.
About the author: Dr. Daniel Chartouni is the Head of the Energy & Materials Department at the ABB Corporate Research Center in Baden-Dättwil, Switzerland. The department focuses on developing and applying new materials for ABB’s power products and on physics-related research topics in energy transition and energy management. Parallel to leading the department, he was the Global Program Manager for the Energy Storage Research Program within the ABB Corporate Research organization. From 2008 to 2012, Dr. Chartouni was Group Leader of the Applied Physics Group within the Electrotechnology Department at ABB Corporate Research. This group develops novel cooling solutions for power devices and supports the ABB Group in developing energy storage solutions. He joined ABB as a scientist in 2000 after a one-year post doc on fuel cells at the Osaka National Research Institute, Japan. He earned his graduate degree and PhD in solid-state physics from the University of Fribourg, Switzerland.
ABB (ABBN: SIX Swiss Ex) is a pioneering technology leader in electrification products, robotics and motion, industrial automation and power grids, serving customers in utilities, industry and transport & infrastructure globally. Continuing a history of innovation spanning more than 130 years, ABB today is writing the future of industrial digitalization and driving the Energy and Fourth Industrial Revolutions. As title partner of Formula E, the fully electric international FIA motorsport class, ABB is pushing the boundaries of e-mobility to contribute to a sustainable future. ABB operates in more than 100 countries with about 136,000 employees, thereof 6,000 in Switzerland.