Can solar power fuel mass transit?

Today’s research is tomorrow’s design. We’re asking researchers within Arup and beyond to describe their work and its potential applications. Tony Bruzzone, a transportation planner in our San Francisco office, spoke with us about his work on solar-powered mass transit.


What are you studying?

Bay Area Rapid Transit (BART) commissioned Arup and the Center for Sustainable Energy (CSE), a San Diego–based nonprofit, to determine whether solar energy could help power its system.

Why is this important? What are the potential implications for the future?

Moving more than 430,000 passengers across 107 miles of track each weekday requires a massive amount of energy, making BART one of Northern California’s top 10 power consumers. The agency has been investigating ways to obtain more of this energy from renewable sources. As part of this effort, it asked Arup to consider the potential impact of placing photovoltaic (PV) arrays on its substantial real estate holdings.

After studying the technical and economic issues for a year, my colleagues and I concluded that BART could increase the amount of on-site solar by means of PV installations on stations, parking lots, maintenance facilities, and other properties.

Illustration of solar potential at the Pittsburg / Bay Point Station. The red areas are available for solar canopies, while the gray areas are off-limits due to development potential.

This has important implications for cities around the nation. Most of the United States receives enough sunshine to generate a substantial amount of solar power. (The country sees far more sun than Germany, which now gets over 7% of its overall power output from solar.) Transit agencies from coast to coast could therefore take advantage of PV generation.

Solar potential across the United States and Germany

But this would require them to contend with the mismatch between peak travel hours (morning and evening commute times) and peak solar hours (midday). Maximizing solar generation’s potential would require energy storage as well as energy “wheeling,” or exporting power around a system’s internal power distribution network.

Our team initially considered this a drawback of solar due to the costs associated with energy storage. Upon further consideration, however, we determined that this solution confers unexpected benefits. By providing an independent power supply in the event of a grid failure, it makes transit systems more resilient.

What are the next steps for the research?

The research team recommended short-, medium-, and long-term strategies for maximizing BART’s solar power potential.

Short-term suggestions included installing solar PV in low-risk, high-reward locations (e.g., parking lots for new stations) and adding energy storage capabilities. In the medium term, we recommended doubling PV installations and working to implement smart-grid technologies. Long-term advice included covering maintenance yards with PV arrays and working with the owners of adjacent properties — the Port of Oakland, for example — to realize mutual benefits through solar generation.

Arup is currently helping BART to pilot energy storage that may ultimately position the system to address misalignments between peak travel times and peak solar hours.


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