The roofs of urban underground systems could be transformed into fully functional solar power plants. This proposal was put forward by researchers from Ahsanullah University of Science and Technology, Rajshahi University of Engineering and Technology, and the Military Institute of Science and Technology in Bangladesh. In their study, they calculated that just one metro line in the country’s capital Dhaka could generate more than 25,500 MWh of electricity annually and prevent the emissions of approximately 235,000 tons of carbon dioxide over 20 years.
The metro remains one of the most environmentally friendly modes of transport, but its operation requires enormous amounts of electricity. It is needed not only for train movement but also for station lighting, escalator operation, ventilation, air conditioning, safety and communication systems. In many countries, this energy is still produced at power plants that use fossil fuels. Thus, the metro serves as a clear example of the indirect contribution of electric transport to greenhouse gas emissions.
To reduce the metro’s dependence on external power supply, the researchers from Bangladesh proposed using an almost entirely untapped space, specifically the roofs of stations and depots. As a case study, they examined Dhaka Metro’s Line 6. According to calculations, over an area of nearly 70,000 square meters, more than 34,000 solar panels with a total capacity of about 20 MWt could be installed.
Based on the estimated generation potential of one line, a digital model of the entire metro power system was created, taking into account solar radiation, seasonal weather variations, air temperature, battery operation, grid connection, and operational economics.
The modelling showed that the solar power plant would be able to produce about 25,500 MWh of electricity annually. Approximately half of the infrastructure’s needs can be covered directly by solar generation, while about 48% would come from batteries storing energy during daylight hours. The share of electricity that has to be drawn from the main grid would amount to only about 2%.
According to the researchers’ calculations, the project’s payback period would be approximately six years, with the cost of generated electricity at about 7.6 US cents per kilowatt-hour – making the system competitive with traditional energy sources.
A significant climate benefit is also expected. Since Bangladesh’s power system relies heavily on natural gas, coal, and diesel fuel, shifting part of the metro system to solar generation would avoid approximately 235,000 tons of carbon dioxide emissions over 20 years. Even when accounting for emissions associated with the production of solar panels and equipment, the net reduction would amount to about 215,000 tons of CO₂.
