This project developed and demonstrated the key enabling methodologies and technologies for energy microgrids. Specific performance objectives were to:
- Develop power conversion and power electronics technologies that could (a) be universally used for plug & play interconnection of renewable and non-renewable energy sources and energy storage, and (b) lead to large-scale deployment of distributed power systems, fully integrated with building loads and the external grid at the building or district level.
- Demonstrate the capability to integrate multiple energy sources that could provide continuous power to critical loads while maintaining stable integration with the grid.
- Develop an energy management system (EMS) that could provide optimal power setpoints to individual sources of energy and provide supply as well as demand response commands, integrated with both the grid and the building energy management systems (BEMS).
- Demonstrate the value of both energy microgrids and EMSs by demonstrating the capability to outperform current systems.
To accomplish these objectives, United Technologies Research Center (UTRC) installed an energy microgrid system at the McGuire Air Force Base medical clinic. The microgrid consisted of a universal power converter (UPC), its control board, and an EMS.
Scalable power conversion and switching technologies, power electronics, local controls algorithms, and a supervisory system were developed that could be universally applicable to energy microgrids. These technologies were developed, integrated, and tested with a system comprising an 80kW solar photovoltaic (PV) emulator and a 40kW lithium-ion energy storage battery. After tests were successfully completed, the system was integrated with a 76.5 kW solar PV and the electrical AC bus at McGuire AFB medical clinic. UTRC hardware and software managed the flow of energy from the grid, the roof mounted solar PV, and the lithium-ion battery, and is ready for scalability to multiple alternative sources and storage and power levels ranging from kW to MW. The power switch and local controls developed enable seamless transitions between grid-connected and island operating modes.
Key results from this energy microgrid system demonstration include:
- About 1.6% measured total harmonic distortion, compared to 5% required by IEEE1547.
- Anti-islanding (i.e., power outage) detection, seamless and stable connection and reconnection with the external grid, and uninterrupted power supply to critical loads.
- Seamless and stable transition between solar PV, battery, and external grid energy supply (and any combination of all of them).
- Safe system operation even under loss of communications with the EMS.
- Potential to achieve at least 30% energy savings and CO2 reduction with paybacks lower than 6 years. This result could be achieved with an adequate selection of microgrid topology including energy storage and cogeneration (CHP) equipment, and depends on weather and loads conditions, and assumed installed, maintenance, and replacement cost of the microgrid components.
These technologies, when adopted, will provide the infrastructure and controls required for efficient and reliable use of renewable energy sources. The energy microgrid systems can help reduce external grid utilization and the environmental impact associated with the use of non-renewable sources, and they represent an important step toward improving energy security at Department of Defense (DoD) installations.
There are a number of considerations for implementing energy microgrid systems. Existing regulations applicable to solar PV systems and high voltage/energy batteries are not clear in microgrid applications. The same holds true for IEEE1547 interconnection and islanding standards, which do not directly address energy microgrid applications. Although payback periods look promising, a high initial investment is required to cover the cost of renewable-based energy microgrid systems. The use of electrical energy storage technologies is essential to fulfill the economic benefits of renewable-based energy microgrids; these technologies are not ready for large power/energy applications. Lastly, communications with EMSs, local utilities, and weather sites are essential to achieve full potential economic benefits of energy microgrids. The use of optimization-base energy systems may add up to 20% energy savings; however, these savings cannot be achieved if the information required by the supervisory system is not available, which is the case in DoD installations because of communications and networking constraints.