DC Microgrid Building Energy Management Platform for Improved Energy Efficiency, Energy Security, and Operating Costs
John Saussele | Robert Bosch LLC
Conventional alternating current (AC) building-level electrical power distribution systems require a reliable utility grid connection and do not use locally generated renewable energy in the most cost-effective manner, resulting in excess life-cycle costs and energy security concerns. These systems suffer from AC-to-direct current (DC) conversion losses when powering many common devices, as well as DC-to-AC losses when using locally produced DC power. They also require an unreliable and expensive grid-tie inverter, which prevents the use of solar photovoltaic (PV) power when grid power is lost. This project will demonstrate the performance and value of the DC Microgrid by overcoming these limitations through real-world demonstration at Fort Bragg, North Carolina. The DC Microgrid applies a novel approach that utilizes mature and reliable DC technology to dynamically manage power sources, loads, and energy storage system interaction to minimize total cost-of-ownership and grid reliance.
Two DC Microgrid architectures will be demonstrated: (1) a core system that most effectively uses solar PV energy for common high energy use building loads, and (2) an enhanced system that integrates energy storage to dramatically increase the facility’s energy security and load-leveling capabilities.
The core system includes a solar PV array, DC power supply, DC high-bay induction lighting system, and large-diameter DC ceiling fans (to reduce heating and cooling system use). This core system is relatively small and is sized to match the DC loads, such that all solar PV power production is immediately used, eliminating the need for a grid-tie inverter and utility interconnection study. A Bosch Energy Management Gateway remotely manages each component to minimize utility grid energy usage. Historical energy usage data and lighting output measurements will be collected to quantify the DC Microgrid’s advantages relative to the base case and a small reference AC lighting system representing current state-of-the-art AC lighting.
The enhanced system includes a GreenStation battery energy storage system from Green Charge Networks and additional solar PV elements to improve the facility’s energy security and mission assurance capabilities during power outages. The GreenStation also performs building electrical load leveling/peak load reduction under normal operation to reduce utility usage demand and associated charges. The performance assessment will include the same data collection and analysis protocols used for the core system. The testing will also assess the DC Microgrid’s load-leveling, islanding abilities (by simulating blackout situations), and energy-security benefits resulting from the energy storage and additional solar PV capacity.
This flexible, DC-based building-level energy management tool enables direct, on-site usage of DC-based renewable energy sources without the efficiency losses inherent to AC systems. Load-leveling and islanding functionality are also integrated. The DC Microgrid system offers significantly enhanced energy security, greater renewable energy utilization, and improved economic benefits over conventional systems. (Anticipated Project Completion - 2016)