Microgrid Enabled Distributed Energy Solutions for DoD Installations
Teri Hall | Lockheed Martin Corporation
Objectives of the Demonstration
Currently the U.S. power grid is largely centralized with a handful of large utilities handling the majority of power production. To remedy systemic risk from large-scale blackouts, a new more decentralized system can be used in which a cluster of on-site power generation devices/assets can service local loads in the event of power loss from the utility. A microgrid is a localized set of generation, energy storage, and loads that normally operate connected to a traditional utility grid. There is a single point of common coupling with the utility grid that can be disconnected if the microgrid needs to be able to operate without utility power in the event of utility failure. The primary benefit of a microgrid is energy surety, resiliency, and mission sustainment; however, there can be advantages in energy cost savings depending on the electric rate structure.
This demonstration was the first Department of Defense (DoD) grid-tied microgrid to integrate renewable resources, on-site generation, and energy storage with facility loads and the utility distribution network. Lockheed Martin designed and built the microgrid system, intelligently integrating distributed diesel generation, solar photovoltaic (PV) array, and grid-scale energy storage with the medium voltage utility grid and facility loads at one of the Brigade Combat Team (BCT) Complexes at Fort Bliss. The technical objectives were to demonstrate reduced greenhouse gas (GHG) emissions, lower capital expenditure, lower operating costs, and enhanced energy security via a microgrid consisting of distributed energy resources (DERs) and load management capabilities.
The technology utilized for this project included an intelligent microgrid controls and data acquisition system with distributed diesel generation, a solar PV array, and grid-scale energy storage integrated with the medium voltage utility distribution grid and facility loads of the Enlisted Personnel Dining Facility (EPDF).
The microgrid controls architecture provided a flexible platform to integrate multiple types of DERs, energy storage, and load management. The architecture is comprised of distributed controllers that locally manage each DER connected to the common power bus. The distributed controller also manages load centers to provide monitoring and load scheduling capability. The distributed controllers communicate with the microgrid centralized controller, which provides the overarching control and optimization of the microgrid including Demand/Response (D/R) algorithms, an Advanced Metering Infrastructure (AMI), and Meter Data Management System (MDMS). The centralized controller also provides aggregate real-time monitoring data of relevant DERs, loads, faults, and financial performance.
The microgrid optimization functions were designed to avoid or lower energy costs and increase energy surety with the following features: peak shaving, electricity arbitrage, power factor improvement, renewable smoothing, integration with the existing building management system, and the ability to near seamlessly transition between Grid Tied and Grid Independent modes.
This project can be categorized into three phases of execution: (1) baseline design and performance documentation, (2) technology implementation, and (3) technology performance validation. The baseline design was performed by conducting site surveys and preliminary power flow measurements to document the baseline design. The baseline performance documentation consisted of two tasks: (1) obtaining energy consumption data at the demonstration site by installing power measurement instrumentation and data acquisition systems and (2) obtaining energy consumption data of the larger installation utilizing the existing metering system and performing load surveys. After the baseline design and performance data were captured, the detailed design of the microgrid was developed and major components were procured. The project design, preparation, permitting, and procurement phase started after contract signing in June 2011 and continued until April 2012. Construction was performed from December 2012 to March 2013 with configuration and acceptance testing occurring in April 2013 and final commissioning in May 2013. Performance measurements and verification were continued until the project was concluded in December 2013.
In addition to showing the economic benefits of deploying microgrids at BCT complexes, the EPDF Microgrid demonstration:
- Reduced peak utility demand to 261 kilowatts (kW), which is a 14.4% reduction when compared to the 305 kW peak load observed by Fort Bliss’s Department of Public Works (DPW) in prior years.
- Reduced fuel usage and GHG emissions of backup generators during grid independent operations.
- Increased islanded load from 30-50 kW to 50-80 kW (a 37.5% to 40% increase in load supported during grid independent operations).
- Picked up system load within two cycles of utility interruption enhancing Energy Surety.
- Met economic criteria with a Savings-to-Investment Ratio of 1.51 and a payback of 8.89 years.
- Increased Power Factor (PF) Improvement (> 0.9 PF during peak hours) and power quality assessment.
- Demonstrated an average energy output of 21.35 kilowatt hours (kWh) per day at peak hours for Electricity Arbitrage.
Retrofitting the generators to operate within the microgrid proved to be a significant challenge. Generators at the time of installation are either installed as a standalone backup generator or a paralleling generator. While standalone generator controls reference system voltage and system frequency, parallel generators utilize/manage real and reactive power as well as system voltage and frequency. Generator grounding schemes are also different between paralleling generators and backup generators and a hybrid grounding system suitable for both types of generator installations was developed. Also, standalone backup generators do not have a restricted run time but when using them to parallel with the utility, an air permit must be obtained for the unit from the relevant authority, in this case from the Texas Commission on Environmental Quality. The process for obtaining this permit must be started as early in the process as possible.
Retrofitting the existing electrical infrastructure was a challenge, especially with the existing switchboard layout restricting the addition of motor operators (to allow for load shedding). The project team installed as many motor operators as physically possible in the existing switchboard such that load shed capability was maximized to avoid purchasing a completely brand new switchboard.
There are inherent challenges in integrating multiple DERs because the electrical bus requires a master DER. While grid tied, the utility is always the bus master, but when the microgrid islands, the bus master functionality passes first to the energy storage system until the generator comes online. The handoff of that functionality between the energy storage system and the generator is a high speed, time critical event. The interfaces between DERs have to be carefully coordinated, timed, and tested thoroughly to ensure no conflicts of authority.
Although not a major issue, separate data loggers were used to collect baseline data for the BCT feeders because the DPW Building Operations Command Center data collection did not have the resolution of individual feeders in their energy measurements. As the Fort Bliss power distribution is upgraded, more resolution could be available in these measurements to support future energy projects.
Regulatory hurdles associated with ‘islanding’ microgrid power architectures are being addressed with release of the Institute of Electrical and Electronic Engineers (IEEE) 1547.4 and 1547.8 guidance. The approach will allow DoD end users to implement a proven, consistent solution that addresses renewable energy and environmental mandate compliance, energy cost reduction, and energy security goals.