Roadside Resiliency

It’s an occupational hazard I suppose, this compulsion I have to examine roadside infrastructure everywhere I go. Street lights, traffic signals and control cabinets, bus and rail stops… they all smell of underutilization, and there are a lot of them. Why not repurpose? Why not leverage that real estate like American Tower Corporation did when they ingeniously bought up strategically located real estate in the 90s, stood up towers and waited for cellular and broadband companies to pay them for placement? Instead of delivering connectivity, however, this roadside infrastructure could be delivering energy. What’s more, because this infrastructure resides along the low-voltage, secondary distribution end of the electricity grid – the edge as it were – energy delivered here offers unique benefits.

Resiliency is one such benefit. Grid resiliency is a fundamental tenet of the smart grid, and one whose import swells along the eastern seaboard, which is still reeling from Superstorm Sandy. In October of 2012 Sandy delivered a wallop that caused nearly $62 billion in carnage and 13 days without power, punctuating the fragility of our nation’s electrical system. The situation would have been different had roadside infrastructure been upgraded with solar generation and battery storage. Imagine an outdoor lighting microgrid, or a traffic intersection microgrid?

Wait a minute, what’s a microgrid? A microgrid is a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid and that can operate in either grid-connected or “island” mode. Translating, that means an outdoor lighting microgrid is a lighting circuit with an Automatic Transfer Switch (ATS) at the head end interconnection point to the grid, with solar generation, battery storage and lighting loads all residing behind the switch on the same circuit. When properly sized for a particular location’s solar generation capability and then islanded, the solar plus battery microgrid can power the lighting system load indefinitely even though the broader electrical grid is down.

Outdoor Lighting Microgrid

In a similar fashion, a traffic intersection microgrid is a low-voltage circuit on the secondary distribution system that is fronted by an ATS and includes solar generation, battery storage and loads in the form of traffic signals, red light cameras, pedestrian crossing signals, overhead lights, etc. With the right amount of battery storage for the loads and available sunshine, this intersection can also remain functional until grid power returns. Together, outdoor lighting and traffic intersection microgrids would have allowed vehicles and pedestrians to safely get around for all 13 days of Superstorm Sandy’s grid calamity, had they been in place.

Traffic Signal Microgrid

How hard is it to repurpose an already standing outdoor lighting system or traffic intersection into a microgrid? Today, it’s not as hard as you might think, though it does require some unique experience, a healthy dose of ingenuity and an ecosystem of key partners. One of the technical innovations that have emerged recently to simplify such infrastructure reuse is the grid-tied AC battery storage device. Companies like STEM and CODA Energy play in this space, solving the problem of high demand charges in places like California. Being grid-tied AC devices, these battery systems can be added to an existing AC circuit where they will source or sink energy on the circuit using cloud-based predictive analytics. When reducing peak demand charges the algorithm lowers monthly energy bills by predicting energy usage patterns and then deploying stored energy at precise times to reduce peak loads.

When put to use in a roadside microgrid the predictive analytics would be different, but the concept is the same. Predicting energy usage patterns is easy for outdoor lighting since there is very little variance in the load characteristics across a set of luminaires. A traffic intersection may be a bit more challenging to the extent energy usage depends on traffic, but this level of prediction pales in comparison to a commercial energy customer’s load characteristics, so it is well within scope. A roadside microgrid, however, presents a different challenge on the energy releasing side. The goal is no longer reducing peak demand but instead, ensuring there is as much energy as possible to power the microgrid’s loads should the broader electrical grid go down.

By itself that goal is easy; continuously top off the battery storage and then anything else can be released through the interconnection point to the broader electrical grid. Unfortunately the situation is not that simple. These distributed generation and storage assets can be used to help manage the efficiency and utilization of the distribution system, which may be at cross purposes with keeping the microgrid loads on as long as possible. Happily, predictive analytics can help. Storms like Superstorm Sandy do not materialize instantaneously. They evolve. Incorporating meteorological data is already part of the predictive analytics. When mated with rooftop solar, these AC battery storage devices predict how much sunshine and therefore how much energy a system will generate in the hours and days to come. This same technique can be used with roadside microgrids to prioritize storage over distribution system management in the hours and days preceding a widespread weather event.

Because of my compulsion, when I hear and read about the “smart grid” I imagine roadside resiliency – underutilized roadside infrastructure transformed into microgrids that help distribution system operators manage their systems in their spare time but then step up to deliver safe locomotion during emergencies. Now isn’t that smart?

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