An international research team led by the University of Utah has explored the potential of installing onsite solar power generation and energy storage at existing bus depots.
The research is based on a case study from Beijing. The Chinese capital is home to the world’s largest public transportation system, with 27,000 buses of which more than 90% are low or no-emission vehicles. The battery-powered buses recharge through a network of more than 700 bus depots spread across 6,500 sqm. The infrastructure runs in parallel with, and can cause strain on, the city's electricity grid.
The research combined a computer model of the Beijing bus network, consisting of 2020 data on air temperature and solar irradiance at each depot, with the rooftop surface area of each depot, to predict the electric output of solar panels that could be installed there.
The scientists found that solar PV could reduce the grid’s net charging load by 23% during electricity generation periods and lower the net charging peak load by 8.6%. Variation in supply and demand between depots was noted, with busier depots better placed to utilize a day’s sunshine, while more remote depots would need to store or redistribute their excess electricity.
Integrating energy storage would amplify reductions to the grid’s net charging load by 28% and lower the net charging peak load by 37.4%, the researchers found. A cost analysis concluded that unsubsidized solar installations would yield profit 64% above costs, while adding battery storage would cut profits to 31%.
“We found energy storage to be the most expensive factor in the model, so smarter and strategic charging schedules would need to be implemented,” said Xiaoyue Cathy Liu, one of the report’s authors. “That responsiveness is critical, as variable energy pricing schemes have such a large impact on the overall economics.”
The study also highlights economic benefits and CO2 emissions reductions as other advantages for transforming public transport depots into profitable energy hubs.
“This study propels our understanding of the synergistic benefits of combining these technologies and provides actionable insights for policymakers, urban planners and the renewable energy community at large,” the academics added. “By demonstrating such a model’s viability and economic advantages, policymakers may be encouraged to prioritize similar renewable energy strategies, possibly accompanied by incentive mechanisms, to fast track urban decarbonization efforts.”
The researchers say they are planning to further generalize the proposed model, to offer other areas a method for estimating the return on investment of transforming bus depots, or other pieces of civic infrastructure, into energy hubs.
Their findings are available in the study “Transforming public transport depots into profitable energy hubs,” which was recently published in nature energy. The team also included academics from China’s Beihang University, Sweden’s Chalmers University of Technology and Germany’s Fraunhofer Institute for Systems and Innovation Research ISI.
