Energy Systems

It’s no secret that the electric power industry is undergoing a transformation with utilities scaling up clean energy sources, embracing a new era of consumer participation and choice, and tackling issues of security, efficiency and resiliency in a changing world. As the industry turns to holistic solutions such as AC/DC transmission and distribution technologies, both centralized and decentralized control, advanced inverters, energy storage and microgrids, the challenges of integrating these new technologies into the grid are becoming more complex. To tackle these challenges, utilities, manufacturers and technology solutions providers are increasingly turning to the Energy Department’s Energy Systems Integration Facility (ESIF) located at the National Renewable Energy Laboratory (NREL) in Golden, Colo. 

While NREL is primarily known for its research in renewable energy technologies, the laboratory has always understood that these and other clean energy technologies need to be integrated into the existing energy infrastructure. The ESIF, which opened more than a year ago, provides partners with all the equipment necessary to evaluate the performance of a new piece of equipment under real-world conditions, but before it is connected to an actual grid. Looped buses carrying high-voltage AC and DC power run throughout the building and are monitored in a utility-style control room, complete with a SCADA system.

A power-hardware-in-the-loop (PHIL) capability allows the hardware to be connected to a software simulation, and it can even be connected to a remote facility, allowing researchers all over the world to access the ESIF. The ESIF also includes a thermal distribution bus, integrated fuel distribution buses and specialized laboratories.

Such utility-scale electrical research facilities are ideal for testing advanced inverters that include special features for grid support, such as the ability to keep connected to the grid when the grid voltage momentarily sags. Both Advanced Energy and Solectria have tested advanced inverters with capacities as great as 1 MW at the ESIF.

NREL also used the testing to develop preliminary test procedures for advanced inverters, providing valuable guidance to various national standards-development efforts aimed at easing the integration of high penetrations of distributed resources. In addition, NREL is collaborating with Alstom Grid to implement a comprehensive modeling, analysis, visualization and hardware study of smart inverters, using a representation of a Duke Energy feeder line.

Field testing 

In addition to testing inverters, NREL is also helping to put them to good use. Research with SolarCity, in partnership with the Hawaiian Electric Companies (HECO), is examining how advanced inverters can provide grid support, easing utility concerns about the impacts of high penetrations of photovoltaic (PV) power on reliability. The utility is now working to clear a backlog of thousands of customers requesting net energy metering interconnections.

Utilities are also exploring minigrids and microgrids because of their reliability benefits, but control systems for these new grid solutions are still in their infancy. This year, NREL will be working with San Diego Gas & Electric to examine the potential to form islanded microgrids by adding energy storage and a control system to areas with high penetrations of PV power. This approach can improve reliability by keeping the microgrids operating during a grid outage. The study will examine control systems and optimal energy storage and placement.

And with a growing interest in energy storage – and battery storage in particular – NREL is working with American Vanadium to test and develop its CellCube flow battery, which employs vanadium in redox reactions. Flow batteries have the advantage that their capacity is determined by the size of the tanks that hold the electrolyte, so they can be scaled up to a large size relatively cheaply. American Vanadium’s CellCube is rated at 20 kW.

electric transportation

Research teams at the ESIF are also examining an important convergence of two energy domains that, until recently, were entirely separate: electric power and transportation. In collaboration with Toyota Motor Engineering & Manufacturing North America, the NREL is testing the impact of a high-penetration deployment of plug-in hybrid electric vehicles (PHEVs) on the power grid. 

Name the utility technology – advanced inverters, microgrids, battery storage or whatever – and there’s a place to test it at the ESIF. The ESIF is a designated Energy Department user facility, which means that industry can use the ESIF under a variety of agreements. So bring your challenges, and the researchers at NREL will do their best to solve them. 

Kevin Eber is a senior technical writer at the National Renewable Energy Laboratory. Learn more at http://www.nrel.gov/esi/working_with.html. 

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