Community Wind Handbook/Plan Interconnection

From Open Energy Information

Community Wind Handbook

Plan Interconnection

An integral part of any large community wind project is determining how to properly interconnect the project to the high-voltage transmission system or to a local distribution network.

Some large community wind projects will be required to use substations as a part of the interconnection infrastructure. Photo by David Parsons, NREL 06791.

Interconnection processes differ depending on the project size and the utility, so it is important to begin researching and planning early. All costs associated with the required interconnection studies are the responsibility of the project developer and not the local utility.[1] Costs associated with equipment upgrades needed to interconnect a project depend on whether the project is interconnected through the transmission system or to a local distribution network. Upgrades associated with projects that are interconnected through the high-voltage distribution system can typically receive transmission credits for network upgrades. Distribution network-connected projects do not typically qualify for this credit.[2] A knowledgeable team member or consultant must fully understand the study results and be able to assist in negotiating system upgrade responsibilities.

Often systems below a certain size have simpler rules for interconnection, so understanding the utility's regulations is crucial. It can also help determine the interconnection costs and how they will affect the overall project economics.[1]

One- or two-turbine projects can connect at a distribution-level voltage (12.5 to 41 kV, if one is nearby), which generally means the project will not be required to construct a new substation. In this situation, a large community wind project will need the necessary equipment to “step up” the voltage level at the base of the turbine prior to connecting to the distribution-level voltage line. This typically includes a step-up transformer and other appropriately sized collection system components.

If a project is required to interconnect to the transmission system, it will be necessary to construct a substation, which can easily add $1 million to $5 million or more to the total project cost. A substation is a facility that contains equipment utilized to switch, change, or regulate electric voltage.[3] They also regulate the flow of electricity, with breakers as an example, and act as a safety device to protect the project and the grid from the impacts of faults. Substations are also where revenue grade meters are installed to determine financial compensation.

It is important to note that projects in excess of 10 MW will probably have to connect to higher-voltage (above 69 kV) lines because they require more electrical capacity than distribution voltage lines can provide.[4]

If you are interconnecting to a power line owned by a utility that participates as a Regional Transmission Organization (RTO) or is managed by an Independent System Operator (ISO), you must complete steps such as:

  • Interconnection application
  • Interconnection feasibility study
  • System impact study
  • Facility study
  • Optional study
  • Large generator interconnection agreement.[4]

Interconnection applications can be found on a utility’s website and may require additional fees. In most cases, the “fee” is considered an estimated cost of the study (paid up-front by the developer), but note that an additional invoice could be forthcoming if the study costs exceed this estimate. Information needed to complete an interconnection request includes:

  • Project location
  • Proof of land control at the point of interconnection (e.g., copy of signed land lease) and sometimes proof of land control for turbines
  • Estimated in-service date
  • Network resource or energy resource
  • Type of generator and specifications (manufacturer, model name, number, and version)
  • Total number of generators
  • Project size/capacity (MW)
  • Power system load-flow data sheet
  • One-line facility and point of interconnection diagram
  • Transformer specifications.[1]

The initial interconnection feasibility study provides a high-level analysis of whether a project is viable at a point of entry into the grid. The feasibility study also examines how the proposed facility will interact with other facilities that are currently, or will soon be, connected to the grid.[5] Negative impacts that can be revealed from an interconnection feasibility study include circuit breaker faults, thermal overloads, or voltage-limit violations.[1]

The feasibility study will also require a cost estimate that will take into account the generator type, size, and potential impacts based on interconnection standards and criteria.[4] The project could be responsible to pay for upgrades necessary to maintain the safe and reliable operation of the grid. If the feasibility study reveals no negative impacts, the utility may provide an interconnection agreement without requiring any additional steps.[1]

System impact studies further detail electric system impacts from the proposed project, including how it may affect reliability. A detailed system impact study can consist of analyses of potential effects including power flow, short-circuit conditions, voltage drop and flicker, protection and control coordination, and grounding. Results of the system impact study will include an introductory indication of the cost and amount of time that would be required to repair any identified issues.[6]

The final step before an interconnection agreement can be completed is the interconnection facilities study. The interconnection facilities study identifies the necessary equipment, engineering, procurement, and construction work to connect the large community wind project to the grid. The study will include all necessary equipment, estimates of the full interconnection cost, and the time required to complete the construction.[5]

Optional studies can be conducted to determine what impacts, additional system costs, and potential benefits will result from alternate system configurations. Like the other studies, optional studies will involve an initial meeting and a financial deposit for the study. Costs and payment schedule will depend on the extent and estimated costs of conducting the study.[4]

The interconnection agreement is the last step required prior to installing your turbine and officially interconnecting to the local utility’s distribution line. The agreement finalizes payment details for the necessary system upgrades that were noted in the previous interconnection studies and may include operations and maintenance fees.[1]

Completion of all interconnection studies and signing the large generator interconnection agreement only gives you the right to interconnect, not to transmit electrons. Projects may have to go through a transmission service process if the development connects to one utility’s line but sells the power to a different utility. In this scenario, it is important to understand which party (buyer or seller) is responsible for obtaining necessary transmission rights.[7]


  1. 1.0 1.1 1.2 1.3 1.4 1.5  "Energy Trust of Oregon. Community Wind: An Oregon Guidebook"
  2.  "PacifiCorp. Generation Interconnection Process"
  3.  "U.S. Energy Information Administration. Electricity Glossary"
  4. 4.0 4.1 4.2 4.3  "Windustry. Interconnection: Getting Energy to Market"
  5. 5.0 5.1  "National Renewable Energy Laboratory. Generation Interconnection Policies and Wind Power: A Discussion of Issues, Problems, and Potential Solutions"
  6.  "National Renewable Energy Laboratory. System Impacts from Interconnection of Distributed Resources: Current Status and Identification of Needs for Further Development"