PNNL

Small hydropower projects—those that generate less than 20 megawatts (MW) of power—have been the predominant source of hydropower growth in the United States since the 2010s. However, small hydropower developers often face challenges plugging new projects into the electrical grid. These challenges typically come up during interconnection, the process by which project developers apply to connect their project to the grid. During interconnection, owners of the electrical distribution or transmission system review the project application and request necessary system upgrades to increase the capacity of the electrical circuit. This process can generate unexpected costs and scheduling delays for developers—posing a challenge to small hydropower projects.

With support from the Department of Energy Water Power Technologies Office, Pacific Northwest National Laboratory (PNNL) and Oak Ridge National Laboratory (ORNL) reviewed the status of small hydropower interconnection across the United States in 2021 to identify current challenges and recommend best practices to achieve successful interconnections. The results of this work were described in a series of four white papers with the main findings summarized below.

Most new hydropower development projects in the United States are small and generate less than 20 MW of power

Between 2016 and 2018, over 4,300 MW of new, small hydropower projects were under development in the United States. The majority of these new projects were rated to have an power output below 5 MW. There were four types of small hydropower development projects, the majority of which were non-powered dams:

1. Non-powered dam – retrofitting existing dams to add hydropower generation
2. In-conduit hydropower – adding small hydropower generation to existing water conveyance, distribution, or collection infrastructure
3. Pumped storage hydropower – pumping water uphill to store as potential energy and then releasing it through a hydropower generator when electricity is needed
4. New stream reach development – adding new infrastructure for hydropower generation in streams

More information on the type, size, and location of new small-sized hydropower development projects in the United States is described in "Small Hydropower Interconnections: Small Hydropower in the United States."

State processes for interconnecting small hydropower vary significantly

The interconnection of new generators to the grid is governed by state-level processes. These processes vary in complexity and requirements from state to state, which can result in different timelines and costs for project developers. The inconsistency in these standards across state or utility boundaries may limit or incentivize development in certain jurisdictions. The interconnection process is often particularly unclear and difficult to navigate for small hydropower developers in areas that do not already have many existing distributed energy resources—such as solar or wind power. A summary of state interconnection processes is described in “Small Hydropower Interconnections: State Interconnection Processes."

Interconnection studies reveal the timeline and cost necessary to secure a grid connection

PNNL researchers evaluated the costs and timeline for interconnection upgrades by drawing on over 150 recent interconnection study reports of small hydropower projects. Proposed interconnection upgrades were categorized into five groups: electrical cables, substation, protection and control, communication, and metering. The types of upgrades necessary to complete the interconnection process varied by project size, with new substations more common for projects over 10 MW and upgraded cables or protection and control more common for projects under 5 MW. A review of the interconnection is provided in “Small Hydropower Interconnections: Analysis of Interconnection Processes."

Improving interconnection processes can help reduce risk and uncertainty

Currently, interconnection costs for small hydropower projects exceed those for solar and distributed wind. Reducing uncertainties and surprises during the interconnection process could help lower these costs for small hydropower projects and facilitate future development.

PNNL researchers identified best practices for interconnecting small hydropower projects from states that have seen successful development of other distributed energy technologies, such as small-scale solar photovoltaics. Providing information to developers earlier in the interconnection process can lower the risk and uncertainty associated with an interconnection application and allow developers to design projects that fit within the electrical system’s capabilities. A review of best practices is available in ”Small Hydropower Interconnections: Best Practices.”