Energy Storage Toolkit

Energy storage technologies absorb energy from an external source to be discharged at a later time. The Energy Storage Toolkit offers curated resources and guidance on integrating commercially available energy storage technologies into the power system.

Welcome to the Energy Storage Toolkit. On these pages, you will find resources that have been expertly curated and annotated to assist you in navigating key topics related to deploying and integrating energy storage into electric power systems. 

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Background and Context

Energy storage technologies are capable of absorbing energy from an external source and discharging this energy at a later time. The emergence of lower cost storage technologies—in particular, electrochemical storage technologies—has created new opportunities for shifting energy supply and demand in the power system. As developing countries continue to deploy increasing levels of renewable energy, energy storage can facilitate the integration of these renewable energy resources through the provision of various types of grid services. Furthermore, energy storage can provide additional services to support grid reliability and enhance resilience.

What is the Energy Storage Toolkit?

The Energy Storage Toolkit focuses primarily on those commercially available technologies that are currently most likely to be deployed in developing countries—predominantly pumped-storage hydropower and electrochemical batteries (typically lithium-ion). Thermal energy storage and other energy storage technologies that are used in more unique power sector applications are not featured because they are not commonly used in developing countries. The Energy Storage Toolkit includes information on key topics, including:

Storage Types and Location

Energy storage systems can be broadly categorized based on (1) where they are interconnected (e.g., as front-of-the-meter, behind-the-meter, or off-grid systems); and (2) the medium for energy storage (e.g., electrochemical, thermal, mechanical, etc.). The type of technology selected and the point of interconnection greatly affect whether energy storage is a viable option. Different energy storage technologies can have dramatically different operating characteristics (such as the speed at which they can charge or discharge, and the power or energy density), which in turn influences the services that energy storage can best provide. Where storage systems are interconnected influences various aspects such as appropriate technology selection, system sizing, and relevant energy and reliability services offered. There are four main categories for energy storage based on where they interconnect to the power system:

  • Behind-the-meter (BTM) — these are small systems located directly at the customer premises, connected on the customer side of the meter. Often, these systems are used to provide backup power or power-quality-related services to the system owner. However, as communication, telemetry, and inverter equipment improve, these systems are increasingly being used to provide distribution-level services in a more coordinated fashion to utilities. In some advanced markets, BTM systems are also being aggregated to provide transmission-level services.
  • Front-of-the-meter (FTM) — these systems are much larger than BTM systems and supply services to the distribution or transmission system, such as ancillary services, load shifting and/or voltage support. They are directly connected to the distribution system rather than located behind a given customer’s meter.
  • Utility-scale — these systems, which are the largest, are connected at the transmission level to provide services such as system frequency regulation, load following and/or other ancillary services. 
  • Off-grid systems — these systems are isolated from, and operate independently of, the centralized grid, although they may provide many of the same critical services as storage interconnected to the centralized grid such as load shifting and voltage support, among others.

Grid Integration

Power system flexibility is necessary to safely and reliably integrate high levels of variable renewable energy. Although energy storage technologies can increase power system flexibility, storage is not required to integrate variable renewable energy, and there are no universally applicable methods for determining how much storage is necessary. Instead, a power system’s specific characteristics—including its generation mix, demand profiles, and interconnections with other power systems, among other factors—influence whether and to what extent storage technologies are necessary and appropriate, or whether other sources of flexibility should be considered instead.

 Interested in partnering through Greening the Grid to receive technical assistance on energy storage? Please contact us to learn more and explore opportunities for collaboration.  

Reading List and Case Studies

Energy Storage Requirements for Achieving 50% Solar Photovoltaic Energy Penetration in California

National Renewable Energy Laboratory, 2016

This report estimates the storage required for high PV penetration on the grid (up to 50% annual solar PV penetration in California with total annual renewable penetration over 66%), and quantifies the complex relationships among storage, PV penetration, grid flexibility, and PV costs due to increased curtailment. The authors find that storage needs depend strongly upon the amount of other flexibility resources deployed and the penetration of solar PV on the system. Lower levels of power system flexibility require relatively higher levels of energy storage to achieve the same level of PV penetration while ensuring that PV remains cost-competitive with conventional combined-cycle gas generators. Without energy storage to shift energy supply and demand, and assuming constant levels of power system flexibility, increasing levels of PV penetration lead to additional PV curtailment, reducing the overall value of the next PV system to the grid (measured in the study as the net marginal levelized cost of electricity). Thus, energy storage can play an important role in preserving the value of solar PV to the power system, especially at higher penetrations of solar PV.

 The Value of Energy Storage in Decarbonizing the Electricity Sector

Argonne National Laboratory and Massachusetts Institute of Technology, May 2016

This paper examines the value of energy storage in grid decarbonization efforts by using forecasts of hourly electricity demand in Texas in 2035. The authors determine the optimal mix of thermal and renewable resources given various operational limits and assuming different scenarios of installed energy storage capacity and CO2 emission limits. Results suggest that the value of short duration (2-hour) energy storage is only economical at today's costs under strict emission limits, while longer duration (10-hour) energy storage could provide value at costs similar to pumped storage hydropower. Longer duration energy storage systems were also better able to maintain their value as the penetration of energy storage in the grid increased, whereas short duration energy storage saw declining marginal value under higher penetration scenarios.

Battery Storage in New Zealand

Transpower New Zealand Limited, September 2017

This study by New Zealand’s grid owner and system operator explores the value of battery energy storage to electricity consumers and the New Zealand electricity system. Findings specific to New Zealand’s electricity market suggest that:

  • The greatest value is in behind-the-meter applications
  • Existing market tools limit consumer participation in the various energy markets
  • The potential value of each service provided by storage varies widely based on physical location
  • Dynamic retail tariff design such as time-of-use pricing could improve the economic value of batteries
  • Behind-the-meter batteries and grid-scale batteries are expected to be economically viable by 2020 and 2022, respectively. 

Flexibility in 21st Century Power Systems

National Renewable Energy Laboratory and others, 2014

This paper discusses the role that flexibility plays in power systems, as this provides the ability of a power system to respond to changes in demand and supply. Flexibility is especially prized in twenty-first century power systems, with higher levels of grid-connected variable renewable energy (primarily wind and solar). Energy storage, while more expensive than interventions in markets and system operating practices, is among the flexibility options considered.


The Storage Energy Toolkit is supported by the United States Agency for International Development (USAID).

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