As the sun rises and sets each day, the availability of solar power comes and goes. Cloud cover, weather patterns and more also impact reliability. This variability makes it challenging for many to count on solar power to meet their energy needs. To expand solar energy use in the United States, scientists must find an efficient and cost-effective way to combat the natural intermittency of photovoltaic (PV) power.

Researchers at the National Energy Technology Laboratory (NETL) are working to devise a solution using three-port transformers for combined solar and battery grid integration. The project is funded through the SunShot National Laboratory Multiyear Partnership (SuNLaMP) program, managed by the U.S. Department of Energy’s (DOE) Solar Technologies Office. Partners include Eaton Corp., North Carolina State University, Carnegie Mellon University and NASA’s Glenn Research Center.

Three-port transformers allow a PV energy source to hook into the same transformer as an energy storage or battery device – rather than connecting each energy source to separate alternating current-coupled transformers, which then connect to the electric grid. The design of the transformers can vary, but NETL researchers and their partners have reconfigured the windings in a scheme that maximizes power flow and enhances flexibility. The transformers are also designed to transfer electrical energy at a higher frequency (10-50 kilohertz versus 60 hertz), which makes them smaller and increases power density substantially.

Combined PV/battery grid integration helps manage the inherent variability of solar power by storing energy during peak periods of sunlight for future use, allowing for a constant average power delivery and smoothing sudden spikes in voltage. Leveraging this unique topology with the high-frequency, three-port transformer and connecting PV and energy storage on the direct current side achieves key advantages in efficiency, power density, lifetime savings and reliability. Initial estimates suggest an increase in power density by 10 times or more for commercial-scale installations as compared to traditional technologies.

Prototype converters up to 10 kilowatts (kW) were built using this technology and demonstrated with successful power flow, increased power density and efficiencies approaching 99 percent versus traditional efficiencies of about 94 percent. Prototype converters of 30kW and 50kW are being built and tested for demonstration in ongoing research under the project, and system-level simulations demonstrated the potential for successful operation of full-scale 1-megawatt combined solar/energy storage inverter architecture for utility-scale grid-tie inverter applications.

The project’s continued success will enhance the reliability of solar power systems, while also cutting costs and boosting efficiency as compared to more traditional inverters. Technological innovations like those being developed at NETL will enable more widespread commercial and residential use of solar through combined PV/energy storage integration into America’s electric grid.

For more information about SuNLaMP and the Systems Integration subprogram, please click here.