PNNL

Electricity is unique among commodities in that its supply chain was developed without a storage component. Every other resource commodity has the ability to store excess quantities built into its supply chain in the form of granaries, warehouses, reservoirs, etc. This embedded storage creates a buffer for mismatches between supply and demand, stabilizing prices, and protecting customers. 

The lack of embedded storage in the electric grid has ramifications for its design, operations, and costs. Without a buffer, electric grid operators must maintain generation (supply) and customer load (demand) in constant balance—a responsibility that requires constant precision with very little margin for error. To account for unpredictability in loads, generation, weather, and mechanical outages, operators must maintain significant amounts of reserve generation that can quickly respond to changing grid conditions and preserve the balance. It also means that grid components must be sized and built based on peak demand, resulting in a grid that is larger (and more expensive) than what average load would require. When contrasted with the natural gas system, which has ubiquitous storage built into its delivery system, the benefits of embedded storage become clear. 

White Papers

Regulatory Implications of Embedded Grid Energy Storage

Recent advances in flexible and scalable electrical energy storage technologies have made the concept of embedded storage on the electric grid feasible, but complex regulatory issues must be resolved before it can be practical. The U.S. energy regulatory structure, which bifurcates authority between federal and state levels, has resulted in a fragmented approach to grid planning, involving multiple processes subject to different jurisdictions, each of which considers different grid functions under different time horizons. 

This regulatory structure also creates two classes of resources: regulated assets subject to fixed rates set by regulators, and competitive assets subject to market rates. Transmission and distribution assets, the electric grid’s delivery infrastructure, are almost universally regulated assets subject to fixed-rate recovery. As a grid asset used to manage the flow and delivery of power, embedded storage would most likely fall into the category of a regulated asset, identified through a regional transmission planning process or a single utility’s distribution planning process and would be subject to fixed-cost recovery. 

But before embedded storage can fit within this regulatory paradigm, five key issues must be resolved: the lack of underlying standards, barriers in planning processes, ownership model, compensation structure, and metrics. The objective of this paper is to identify the regulatory questions raised by the concept of embedded storage and explore potential pathways forward. Read the White Paper.

The Use of Embedded Electric Grid Storage for Resilience, Operational Flexibility, and Cybersecurity 

In recent years, bulk energy storage has been applied to electric power systems as an auxiliary device for the support of grid reliability via grid services. This approach is useful but only extracts value from storage on a marginal basis because grid services involve only a tiny fraction of the power flowing in a grid. While storage is flexible enough to perform many services, assessing its value on a stacked-services basis obscures its real value: storage is a buffer for electric energy flows. All of its capabilities stem from this one fundamental property. Limiting storage to use as an ancillary services device leaves this primary value untapped. 

The real value of storage is to provide a key characteristic missing from power grids: the ability to absorb stresses with little or no loss of performance—the essence of resilience. Storage applied systematically throughout the grid can provide the missing “shock absorber” springiness that the grid is missing. To provide this value, storage must be incorporated into the grid as core infrastructure and must be deeply integrated into grid operations. Doing so will provide far-reaching benefits to users of electricity at all levels, including vastly increased system resilience, expanded system operational flexibility, support for critical lifeline functions during critical events, and even improved cybersecurity. In this model, embedded storage is used to address operational issues such as the following: 

• Flatten demand curves 
• Avoid/mitigate outages 
• Manage apparent load volatility 
• Reduce exchange of volatilities between the bulk and the distribution system 
• Mitigate system ramping constraints 
• Facilitate source/load matching and decoupling 
• Defend against edge-based volatility attacks 
• Support electric vehicle charging 
• Facilitate microgrid adoption 
• Maximize verified emission reduction energy extraction to avoid curtailment 
• Support distributed energy resource integration 
• Enable energy banking to facilitate energy networking and congestion management 
• Support generation black-start 
• Manage volatility exchange between bulk natural gas and electric generation systems. 

Improving grid infrastructure with embedded storage will improve transmission-level and distribution-level resilience, support critical lifeline capabilities for emergencies such as critical load outage ride-through and generator black-start, and improve joint operating characteristics of natural gas/electric generation systems. Read the White Paper.

Control of Embedded Bulk Electric Storage Networks for Operational Flexibility and Grid Resilience 

When bulk energy storage units are located at transmission/distribution interface substations system-wide and are operated collectively, such an arrangement can be made to improve intrinsic grid operational characteristics and dynamic grid behavior. This schema requires specialized but practicable control of the storage devices, along with appropriate grid observability (sensing capability). The method is aligned with present approaches to transmission system observability via Synchrophasor measurements and with modern architectures for using storage as core infrastructure. Control of the storage units in such an arrangement is unlike control of storage used for grid services. It is more akin to primary and secondary real-time grid control, operates on grid sensor data, and must function on time scales far too short for market-based or security-constrained economic dispatch methods. 

This paper describes four nested control schemes operating on different time scales. They enable operation of coordinated storage networks to improve intrinsic operational flexibility and resilience of the grid to facilitate integration of variable (stochastic) resources on a regional scale in an equitable manner. These control schemes are not market dispatch functions for ancillary services—rather, they use real-time grid state feedback and advanced control algorithms that function autonomously inside the grid. A coordinated storage network involves system-wide deployment of bulk reflexive storage at a large number of transmission/distribution substations, with the storage units electrically connected to a power bus (engineering details determined in part by the substation bus structure).

Using storage as core infrastructure requires a suite of control algorithms, such as volatility decoupling control, inertia augmentation and control, short-term planned event management, net load regulation, and diurnal net load profile control. Read the White Paper.