In recent years, PPRP has often been asked how much renewable energy capacity could be added to the grid in Maryland and whether the interconnection capacity available on individual transmission and distribution (T&D) lines could be shown in SmartDG+, a screening tool for renewable energy projects in the state. These answers are provided below, along with general information about interconnection analysis. Readers can use the Table of Contents to skip ahead to any section or question of particular interest.
Introduction and Background
Interconnecting at the Transmission Level
Interconnecting at the Distribution Level
Introduction and Background
What is hosting capacity?
Hosting capacity is defined in the Code of Maryland Regulations (COMAR) 20.50.09.02B(17) as the amount of aggregate generation that can be accommodated on the electric distribution system without requiring infrastructure upgrades. Hosting capacity does not represent a hard limit; if distribution upgrades are implemented, the hosting capacity of a system increases. Conversely, if new generation is added at a certain location, the hosting capacity will likely decrease. Although the term “hosting capacity” is used only in reference to distribution systems, questions about available interconnection capacity arise when generation projects request permission to interconnect to the bulk power grid.
How does a new generation project affect the amount of capacity available on the grid?
Each generation project impacts the amount of capacity available for other projects in an area or even in nearby areas, whether on the distribution or transmission grid.
What kinds of issues are considered during interconnection studies?
The ability to keep the grid system running smoothly depends on numerous factors. Four of the most important factors are described briefly below:
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Thermal Capacity – There are limits to the amount of power that electrical lines can carry without suffering heat-related damage, particularly to conductors. Power fed onto the grid can cause lines to exceed their thermal limits.
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Voltage – Electrical lines must maintain voltage within safe ranges. Generation resources may increase voltage levels on a line or the speed at which voltage can change.
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Protection – System operators must be able to detect and isolate abnormalities in electrical current. Generation projects may increase the number of short circuits, fuse blows, equipment malfunctions, etc.
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Reliability/Safety – System operators must ensure that the grid is safe and dependable. One way distributed generation may affect grid safety is by “islanding,” or continuing to feed power into the grid, even when power supply from the local utility has been disrupted. Islanding can be dangerous to line workers and prevent the automatic reconnection of devices.
Are there areas where it has become difficult to interconnect projects in Maryland?
Hosting capacity does not currently appear to be an issue at the distribution level. Under COMAR 20.50.09, the state’s five largest utilities are required to file an annual report with the Maryland Public Service Commission (PSC) that provides the number of interconnection requests received, approved, and denied. Over the past five years, very few interconnection requests (i.e., ~0.2%) have been denied.1
With respect to the bulk power grid, most of the proposed and operating solar projects in Maryland are located on the Eastern Shore, accounting for ~70% of such projects in the state. Over time, it is taking longer for proposed solar projects on the Eastern Shore, in particular, to come online. More details are provided in the following section.
Interconnecting at the Transmission Level
Who determines whether interconnection capacity is available on the bulk power grid?
The PJM Interconnection (PJM), a regional transmission organization (RTO), coordinates and manages the transmission grid in all or parts of 13 states, including Maryland and Washington, D.C. PJM has two distinct processes related to interconnection capacity: conducting studies to determine whether proposed generation or transmission projects can be safely and reliably connected to the grid; and preparing an annual plan, known as the Regional Transmission Expansion Plan (RTEP), that examines transmission needs across PJM’s footprint. Under the RTEP process, PJM identifies both baseline projects, which will ensure compliance with national reliability standards (or increase market efficiency), and network projects, which will help new generation resources connect to the grid.2
Is there information available about interconnection applications in Maryland?
PJM’s New Services Queue is posted online and can be sorted by state and technology. The status of each interconnection request is provided, as are studies that have been completed to date. It is important to note that due to a variety of factors, only about 25% of the generation capacity that enters the PJM queue, regardless of technology, comes online.
How does PJM gauge whether capacity is available for individual projects?
PJM commissions a range of studies to determine whether any thermal loading, voltage, short circuit, stability, or similar engineering problem would be caused by interconnecting and accepting power from a new generation project. These studies evaluate the proposed project’s impact both under normal operating conditions and under contingencies (e.g., single or multiple line outages). Certain studies involve power flow models that simulate generators and loads throughout PJM during summer peak conditions, when the transmission system tends to be most stressed. The studies identify system reinforcements, such as transmission upgrades, that could be used to eliminate or mitigate each potential issue.
Who is responsible for any upgrades that may be required for a project to interconnect?
PJM determines cost responsibility through its interconnection studies. A generation project may be solely responsible for the cost of network and local system upgrades, or the cost may be shared with other generation projects that contribute to the need for network reinforcement(s). (By contrast, transmission owners are responsible for the cost of baseline and network enhancements identified through PJM’s RTEP process. Their costs are passed down to transmission customers through FERC- approved transmission service rates.)
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Is there a map of available interconnection capacity in Maryland?
PJM does not maintain a map of available transmission capacity or a total estimate of available transmission capacity. As discussed earlier, projects seeking interconnection at the transmission level are large and their potential impacts on the grid are complex. Also, the amount of available transmission capacity changes frequently as older generators retire or as new generators come online. For these reasons, transmission-level hosting capacity is sometimes characterized by industry experts as dynamic and unmappable.
What would it take to gauge Maryland’s total available interconnection capacity?
The state's interconnection capacity is dynamic; and therefore, it can only be quantified at a specific point in time. Since available capacity on the grid is constantly changing, preparing such an estimate is unfortunately beyond the scope of Smart DG+.
Interconnecting at the Distribution Level
Who determines hosting capacity?
Each of Maryland’s 13 electric distribution utilities determines the hosting capacity of its systems.
4 The five largest utilities—Baltimore Gas and Electric Company (BGE), Delmarva Power & Light Company (DPL), Potomac Electric Power Company (Pepco), The Potomac Edison Company, and Southern Maryland Electric Cooperative (SMECO)—collectively represent over 97% of the state’s customer load.
5 At present, there is no public distribution planning process in Maryland.
Is there information available about interconnection applications in Maryland?
COMAR 20.50.09 governs the interconnection of small generators. In addition to providing general interconnection requirements, this section contains information about interconnection request processing fees, certified equipment, and the various levels of review. The state’s largest utilities are required to provide an interconnection queue, updated monthly, with information about interconnection requests from all facilities with a nameplate capacity greater than 500 kW.
How do utilities gauge whether capacity is available for individual projects?
When an electric distribution utility receives an interconnection request, it determines whether the new resource meets IEEE Standard 1547, which specifies a set of distributed energy resource (DER) system requirements (such as voltage regulation capability) necessary to maintain grid reliability. As of January 1, 2022, DERs will be required to use “smart inverters” designed to detect islanding (described earlier) and immediately cease producing power.
The utility also determines whether it can accommodate additional DER capacity on the feeder in question. Three primary approaches that can be used to assess hosting capacity (HC):
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Static HC – Does not fully capture the behavior of grid devices or controls; assumes the “worst-case scenario” and plans accordingly; devices are granted a firm connection with no risk of curtailment (Example: HC maps used in California);
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Uncoordinated Dynamic HC – Assumes autonomous “smart inverters”; captures time- dependent behavior of PV, loads, and grid devices; and
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Coordinated Dynamic HC – Assumes “smart inverters” in communication with a utility; also captures time-dependent behavior of PV, loads, and grid devices; devices may be coordinated/curtailed (Example: New York Flexible Interconnect Capacity Solution).
Naturally, the methodology used impacts the results, with simpler methods tending to yield more conservative results.6
Who is responsible for any upgrades that may be required for a project to interconnect?
Individual generation projects greater than 100 kW are typically responsible for any distribution system upgrades required to maintain power quality and reliability after a system is connected.
How long does it take for a project to come online?
The timeline for a project to come online can vary, as the size and complexity of a project determine the level of review it will undergo to ensure reliability. Smaller interconnection projects will undergo lower levels of review which result in a quicker turnaround time. Larger and more complex interconnection projects will undergo higher levels of review which will result in a longer turnaround time.
One indication of the speed with which projects come online comes from distribution utility annual interconnection reports. In these reports, each utility must indicate the number of interconnection requests that were not processed within the deadlines established for Level 1 (15 days), Level 2 (20 days), Level 3 (25 days), and Level 4 (no deadline) review. Over the past five years, roughly 4% of applications were not processed within the allotted time frame. After an interconnection request is deemed appropriate by the utility, the applicant has 30 days to sign the approved interconnection agreement or the request is considered withdrawn. Once the agreement is signed by both the utility and the applicant, another 20 days are allotted for the issuance of permission to operate.
Are hosting capacity maps available for Maryland?
Hosting capacity maps are currently not available on a state-wide level, although two utilities in Maryland, Pepco and DPL, provide hosting capacity maps. Both are subsidiaries of Pepco Holdings, Inc. (PHI) which models hosting capacity across all its service territories. PHI states that hosting capacity modeling is not an exact science and that space on a feeder is subject to change with new interconnections. Therefore, the map may over- or understate the actual hosting capacity of a distribution line.
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Several of Maryland’s distribution utilities maintain restricted circuits maps, which show circuits that have limited (or no further) capacity for additional interconnections. These include BGE,
8 Choptank Electric Cooperative,9 and Pepco and DPL.
10 Each utility states that circuit restrictions are complex and constantly evolving, so the maps should only be used for discussion purposes.
What would it take to gauge Maryland’s total hosting capacity?
Maryland could ask each electric distribution utility in the state to gauge the total hosting capacity of its system periodically, such as monthly or annually. However, making hosting capacity estimates is not an exact science and should be considered a guide. Also, hosting capacity is constantly in flux, as Maryland’s electric distribution utilities receive interconnection requests on a weekly basis and the status of interconnection projects in each utility’s queue can change at any given time.
Why isn’t hosting capacity shown in SmartDG+?
As stated earlier, only two PHI utilities, DPL and Pepco, provide hosting capacity maps in Maryland. Through consultation with PHI, it was determined that weekly updates would be required to mirror PHI’s hosting capacity maps in SmartDG+. Instead, SmartDG+ links to PHI’s map via a supporting document titled “Useful resources related to SmartDG+.”
1 Based on a review of Annual Small Generator Interconnection Reports filed pursuant to COMAR 20.50.09.14C.
3FERC = Federal Energy Regulatory Commission.
4 A&N Electric Cooperative; BGE; Berlin Municipal Electric Company; Choptank Electric Cooperative, Inc.; DPL; Easton Utilities; Hagerstown Municipal Electric Light Plant; The Potomac Edison Company; Pepco; Somerset Rural Electric Cooperative; SMECO; Thurmont Municipal Light Company; and Williamsport Municipal Light Plant.
