Enhancing Zero-Emission Transit with Microgrids

The adoption of zero-emission buses (ZEBs) has been on a remarkable upswing in the United States, witnessing a substantial 66% increase from 2021 to 2022 alone. According to a recent report by Chard, the total number of full-size transit ZEBs funded, ordered, and/or delivered nationwide reached an impressive 5,480 last year. While most of these buses are battery-electric, their reliance on the utility grid for electricity poses challenges to future grid management, especially for larger fleets. This also raises concerns about the detrimental consequences during utility grid outages.
In light of this growing concern, a groundbreaking report introduces a potential game-changer in the form of microgrids, offering numerous benefits for zero-emission bus fleets over conventional approaches to resiliency. Microgrids are capable of disconnecting entirely from the utility grid and continuing to generate power using a variety of distributed energy resources (DERs) such as solar panels, wind turbines, and stationary fuel cells, along with energy storage assets like batteries.

One of the most significant advantages of microgrids is peak shaving, a process that involves storing self-generated energy during periods of low demand and deploying it when buses require charging. By reducing power demand further, microgrids can significantly cut operational costs, leading to substantial financial implications for transit agencies.

Illustrating the cost-effectiveness of microgrids, the report presents a hypothetical scenario for a sample 65-bus fleet. Under a traditional utility rate structure, the fleet’s annual expenses amount to approximately $1.97 million. However, implementing a microgrid system, where batteries are charged solely with solar energy, would reduce the utility bill to $1.18 million annually, saving the fleet $791,000 per year. The savings could soar to about $810,000 annually if demand charges increase as expected in the coming decade.

While microgrids are a novel approach for zero-emission transportation, several transit microgrid projects are already underway across the nation. An outstanding example is the Blue Lake Rancheria (BLR) in California, which frequently experiences natural disasters. BLR successfully deployed DERs in the form of a microgrid with a low-carbon backup power system, saving around $200,000 in utility costs annually. During a series of recent blackouts caused by a 6.4-magnitude earthquake and winter storms, BLR’s microgrid proved its resilience by providing power to essential facilities, including an American Red Cross-certified evacuation center and a six-building campus, for over 24 hours.

Transit agencies looking to adopt microgrids for their ZEB fleets must consider five high-level factors on a project-by-project basis, as outlined in the report. By determining the purpose, identifying critical loads, selecting appropriate energy assets, calculating energy consumption and power demand, and optimizing microgrid components, agencies can ensure an effective and efficient transition to this revolutionary technology.

As the United States strives to meet its sustainability goals and tackle the challenges posed by the increasing demand for electric buses, microgrids emerge as a promising solution that not only boosts resiliency during utility grid outages but also offers substantial financial benefits for transit agencies. With real-world examples already showcasing the potential of microgrids, their integration is set to shape the future of zero-emission public transportation.

Source: CALSTART

A bar graph titled "Figure 1. Power Demand Comparisons" shows peak load in kW for various electric vehicles. From left to right: 100 electric cars (700 kW), 100 medium-duty electric vans (1,500 kW), Chrysler building (2,400 kW), Ellen electric ferry vessel (3,500 kW), 100 electric school buses (5,000 kW), and 100 electric transit buses (10,000 kW). Each vehicle type is represented visually.
Source: CALSTART
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