Applications

The increasing penetration of variable or inflexible low-carbon electricity generation increases the need for power system flexibility. Electricity storage is one option that can provide this flexibility. As a result, there is a wide range of applications for electricity storage that increase power system flexibility. These applications can be characterized along three qualitative categories:

Type of economic value
Location in the power system
Relation to variable renewable electricity (RE)

The type of economic value describes the actual service electricity storage provides to the power system and how it creates economic value. The four fundamental services are:

Power quality: Keeping frequency and voltage within permissible limits
Power reliability: Providing electricity in case of supply reduction
Increased utilisation: Optimising use of existing assets in the power system
Arbitrage: Exploiting temporal price differentials

The location in the power system describes at which point in the electricity network the service is most likely required. This affects the voltage level at which electricity storage has to provide electricity.

Generation: at generator-site (front-of-the-meter), match voltage output of generator
Network: at substation of transmission or distribution network (front-of-the-meter), 1-200 kV
Consumption: at consumer-site (behind-the-meter), <1 kV

The relation of electricity storage applications to variable renewable electricity generation can be characterized as:

Direct: For example, self-consumption increases the share of consumed variable RE and would not exist as a service without variable RE generation.
Indirect: For example, frequency regulation, which contains frequency fluctuations as a result of supply and demand imbalances, is a common power system service. However, more variable RE likely increase supply-demand imbalances.
Unrelated: For example, black start is required when parts of the electricity system fail, regardless of the reason for the failure.

A comprehensive overview of electricity storage applications is provided in Figure 1 where the 23 most common applications are listed along these three categories.

Figure 1 – Overview of the 23 most common electricity storage applications along the dimensions: location within power system (x-axis) type of economic value (y-axis) and relation to variable renewable electricity generation (colour). The selection of 23 applications is based on a review of reports from research institutes, international organisations, industry, and academia. A detailed description of all 23 applications can be found in Table 1. Schematic is inspired by Malhotraa.

Table 1 provides a more detailed description of the 23 most common electricity storage applications and alternative names that are commonly used for them. It also allocates the applications to 13 archetype applications based on similar requirements for discharge duration and annual charge-discharge cycles.

Table 1 - Detailed description of the 23 most common electricity storage services, including alternative names and allocation to archetypical applications based on quantitative technical requirements, i.e. discharge duration, annual cycles.

Figure 2 displays the 12 archetype applications with explicit discharge duration and annual cycle requirements (excluding voltage support). In addition, a currently hypothetical service at very high charge-discharge cycle frequency is displayed (named high cycle). Naturally, the exact requirements for these applications vary by market. For example, resilient power systems may have a black start event every decade while more fragile systems see multiple a year. Here, annual cycle and discharge duration requirements are chosen from within common ranges observed in various markets to cover the entire spectrum of cycle and discharge duration requirements.

Figure 2 – 13 electricity storage applications with illustrative requirements. The annual cycle and discharge duration requirements are chosen from within the common range of each application such that the entire spectrum for these parameter combinations is represented. Annual cycles refers to full equivalent charge-discharge cycles. Size in MW refers to the nominal power capacity of a typical electricity storage system serving the respective application.