How can a large city’s transit system become electrified without causing issues with its power grid? Recent studies on Beijing’s extensive fleet of 27,000 buses examine the potential for depots to produce solar energy.
Electric buses are a powerful tool in the fight against climate change: they promote efficient urban population density, remove numerous polluting vehicles from the roads, and do not emit harmful tailpipe gases.
However, the growing popularity of electric buses brings its own challenges; cities are able to roll out these buses quicker than their electricity grids can handle the rising demand.
For Xiaoyue Cathy Liu, an engineering professor at the University of Utah, this presents a chance not only to address the issues of grid stability but also to rethink how public transportation interacts with other urban infrastructure.
“By incorporating solar power generation and energy storage within bus depots, we create a new model for renewable energy production and management,” Liu remarked. “This transforms a transport depot into an energy center that generates more electricity than it uses.”
A faculty member at the Price College of Engineering’s Department of Civil & Environmental Engineering, Liu recently conducted a study published in the journal Nature Energy, which examines this innovative solution using data from Beijing’s electric bus network. This project involves collaboration with researchers from Beihang University in China, Sweden’s Chalmers University of Technology, and the Fraunhofer Institute for Systems and Innovation Research ISI in Germany.
Beijing has the world’s largest public transportation system, consisting of 27,000 buses. As of 2022, over 90% of these are low or zero-emission vehicles. These battery-operated buses get recharged via a network of more than 700 depots across 6,500 square miles, which forms a significant infrastructure parallel to the region’s electrical network. The considerable power needs of these vehicles mean the depots exert significant pressure on the grid, increasing the risk of localized power outages or other issues.
By using sophisticated data science techniques, Liu and her team are investigating whether solar energy generated locally could effectively meet this growing demand. Importantly, they are also considering the complex economic aspects that will influence the viability of this approach.
“Our simulations indicate that rather than just being energy consumers, these depots could actually become energy producers, which would help stabilize the grid,” Liu stated.
The research is based on a computer simulation of Beijing’s bus network, utilizing real-time data on air temperature and solar irradiation for each depot, collected throughout 2020. By factoring in the rooftop area of each depot, the researchers were able to estimate how much electricity solar panels on each site might produce.
The model’s complexity increases with variations in energy supply and demand among the depots. Busier depots with more vehicles to charge can maximize sunlight on busy days, while depots that are more isolated would need to store or redistribute their surplus electricity to avoid waste.
“We discovered that energy storage represents the highest cost in the model, necessitating smarter and more strategic charging schedules,” Liu explained. “Being responsive to energy prices is vital as varying rates greatly influence overall economics.”
The team plans to refine their model further, paving the way for other nations to assess the potential return on investment for transforming bus depots and other municipal facilities into energy hubs.
