These activities focus on enabling solar energy technologies to move from their relatively small role in the energy market to a much larger role in the near future and allow for solar technologies to be deployed at increased speed and scale. For solar technologies to occupy this large role in the grid, these systems must be fully integrated into the planning and operations of the grid. This transition will require collecting data from large-scale systems, developing models based on the data, analyzing the results, and developing solutions to large-scale solar deployments.
The Solar Energy Grid Integration Systems (SEGIS) works with industry to develop advanced photovoltaic systems with intelligent interfaces to seamlessly integrate into the distribution and transmission grid.
Integrating solar energy technologies into the grid requires an analysis of the technical impacts, particularly of high penetrations. Within the Systems Integration subprogram, activities to allow for large-scale solar integration into the grid include developing scenarios of solar systems integrated into the utility transmission or distribution system, identifying barriers to these scenarios, and providing solutions to these barriers. The current electric grid, which was built decades ago, was designed with a centralized generation approach with electricity flowing in one direction to the loads. Renewable energy is often distributed and results in a two-way power flow within the grid. Modeling and simulation tools are used to closely replicate how solar systems and components interact with the current grid system. These types of analysis enable the research and development of new solutions, both technological and systematic, that will enable the integration of solar technologies into the grid. Overcoming the challenges identified by technical modeling, simulation, and analysis enables high levels of solar energy to be developed in the electrical power grid. Additionally, these activities allow for sharing of best practices among multiple stakeholders in the solar industry, which encourages efficiencies and leads to greater amounts of solar energy.
To accomplish this goal, the Systems Integration subprogram efforts encompass the following activities in the Grid Integration research area:
Developing new transmission and distribution system modeling approaches and tools that take into account bi-directional power flow, load control, demand response, distributed energy sources, and energy storage.
Updating models for photovoltaic (PV) inverters and systems to use in commercial load-flow and fault-current calculation software to handle multiple distributed energy sources on the system.
Evaluation of real-world, high-penetration solar case studies throughout the United States and internationally.
Creating a set of benchmark cases to test models and the associated software.
Developing recommended practices and handbooks on integrating high penetrations of solar into the electric power system. This can include screening tools that will evaluate benefits and impacts of solar installations.
Within the Systems Integration subprogram, the Grid Integration efforts are led by the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (SNL).
Distribution System Integration
The Systems Integration team is focusing on developing solutions to reach high penetrations of PV at the distribution level. As distributed renewable energy systems become a larger contributor to the electric power system, the distribution system will need to be changed to accommodate high levels of these systems.
Technical concerns involve voltage regulation, protection and coordination, power quality (harmonics, flicker, dc injection), unintentional islanding, grounding, and cloud induced variability. The current utility grid was designed to accommodate power flows from the central generation source to the transmission system and eventually to the distribution feeders. Operationally, protection systems were not designed to coordinate with power systems that back feed power onto the grid. Key to understanding these impacts is being able to accurately model the performance of PV systems in electrical distribution system modeling packages. Inverters and other controls must also be designed to communicate with utility systems and energy management systems to lessen these technical and operational concerns.
NREL and SNL are developing tools and techniques to study integration of high penetrations of solar into the distribution system.
Renewable Systems Interconnection (RSI) Reports
The first milestone in identifying the technical and analytical challenges is the Renewable Systems Interconnection (RSI) study, completed in 2008. The comprehensive RSI study consists of 14 reports that address a range of issues on grid integration. The reports were developed collaboratively by a team of technical experts with valuable input from across the solar industry.
In 2008, SNL also completed a white paper, Solar Energy Grid Integration Systems—Energy Storage (PDF 546 KB), on integrated storage in high-penetration PV scenarios. The paper describes the concept for enhancing the Solar Energy Grid Integration Systems activities with energy storage in residential and small commercial applications of less than 100 kilowatts. By providing increased value to both customers and utilities, integrated storage can increase penetration of distributed PV systems. Download Adobe Reader.
Future technical modeling, simulation, and analysis projects include:
Developing a database for models of distributed renewable systems and components
Developing a method to integrate solar resource data sets and distributed renewable system models with electrical distribution system modeling
Developing PV/storage system requirements and use profiles through modeling of potential applications and systems, including command-and-control requirements
Conducting an initial study on the integration between plug-in hybrid electric vehicles and PV systems.
Hybrid Power and Microgrid Integration
Hybrid power systems are common in the United States in remote areas that have no grid power connection, adequate sunshine, and are difficult to supply with fuel. Hybrid PV systems often offer a cost-competitive method of reducing expensive fuel deliveries. Microgrids and Minigrids have one or more distributed energy systems operating in parallel with or independent from the electric power system, while providing continuous power to multiple loads. Microgrids can be used to improve system reliability and can be scalable on many service levels—whether for a few customers or for larger applications that include substations. The design and operation of these types of systems are complex, so there is a need for standardized design, integration, and operation requirements.
In the area of hybrid power systems and minigrids, members of the Systems Integration team lend their expertise to the International Energy Agency Task 11 on PV Hybrid and minigrids. This group reports on progress in PV hybrid power systems and minigrids that incorporate PV. The primary benefit of this international collaboration is in understanding how other countries are addressing PV grid integration challenges, and working globally to solve these critical issues.
Both SNL and the National Renewable Energy Laboratory have facilities that can set up to test and evaluate hybrid and microgrid systems.
High penetrations of solar energy also face technical, operational, market, and regulatory challenges at the bulk system level. Utilities are concerned about their ability to adequately integrate large amounts of variable resources while remaining within their systems’ design tolerances. Bulk system integration issues—such as the ability to provide ancillary services, reliability value, and ensuring adequate transmission system expansion—are critical to large-scale deployment. The Transmission Integration area includes work to systematically acquire resource and generation data to develop and validate models, provide support for enhancing utility operations, engage in regional and subregional transmission planning forums, model generator output, and to engage with stakeholders on critical solar-related issues.
As the penetration of the grid increases, the variability of the output of solar systems caused by clouds becomes an important parameter. Current approaches to model solar system behavior calculate the average of the solar input over an hour and treat the system as a point. System output varies naturally with the solar resource, and, especially for large systems, solar resources and system output vary across the system area. Therefore, understanding the dynamic output of both large-scale and distributed systems requires improved models. The Systems Integration team is working with groups such as the Utility Wind Integration Group (UWIG), Solar Electric Power Association (SEPA), and Electric power Research Institute (EPRI) to address such challenges. In 2009, a working group (PDF 18 MB) on the subject of PV variability met to address these challenges.