A pair of reports from the National Renewable Energy Laboratory presents resources to aid developers and utilities with the integration of solar power to the grid by using battery energy storage to mitigate interconnection costs.
The project, Use of Operating Agreements and Energy Storage to Reduce Photovoltaic Interconnection Costs, was done under the auspices of the Solar Energy Innovation Network and comprises two reports, a Technical and Economic Analysis report by researchers at the National Renewable Energy Laboratory and Lawrence Berkeley National Laboratory and a Conceptual Framework report authored by the national laboratory researchers, as well as staff from the Rhode Island Office of Energy Resources, National Grid, and the Rocky Mountain Institute.
The researchers set out to address the problem that connecting solar photovoltaic systems to the grid can result in time consuming and expensive upgrades. Developers usually either pay the cost of the grid upgrades, which can delay construction and interconnection, or reduce the capacity of the solar system to eliminate the risk of grid violation fees and reduce interconnection costs. A third option, controlling the generation exported to the grid, can be achieved through curtailment or the addition of equipment such as battery storage.
To minimize time from project conception to operation, developers often downsize the size of their solar system in order to maintain proper voltage and power quality requirements on a feeder, the researchers said.
However, because of decreasing land availability and increasing public concern over the visual impact of many small solar power systems, there may be benefit to a shift in strategy, the researchers said. Instead of maximizing the number of solar systems, “there may be future emphasis on maximizing the revenues (and perhaps grid benefit) of each PV system by providing electrons during expensive hours and near large load centers,” they said.
In addition, instead of grid upgrades on an as-needed, project-by-project basis, “focus could shift to using advanced controls and storage technology at the point of interconnection to increase the hosting capacity for distributed resources,” the researchers said.
The two reports examine how controlling exported solar generation at critical hours can be a viable alternative to downsizing a solar project.
The technical report explores the viability and economic feasibility of pairing energy storage to mitigate solar system grid violations. The second report develops an Operating Envelope Agreement that can serve as the conceptual framework for a contractual agreement between a solar system owner and an electric utility on how to operate the paired solar and storage system.
The technical report concluded that an Operating Envelope Agreement that “specifies technical parameters by which a developer can avoid downsizing a proposed PV system and avoid paying expensive infrastructure upgrade costs can be an economically attractive option under select conditions.”
In the second report presents the parameters for developing an Operating Envelope Agreement (OEA). In the future, the researchers said they hope “to produce a follow-on report with real-world examples of OEAs, or interconnection service agreements that include OEA concepts.”