Reviewed by Lexie CornerAug 7 2024
Recent research published in Earth’s Future suggests that covering all the world's highways with solar panel roofs could significantly reduce carbon dioxide emissions and road accidents.
Benefits of highway solar roofs include reduced traffic accidents, clean energy generation and possible reductions in carbon emissions by replacing fossil fuel energy sources, the study says. Image Credit: Figure 1 of the new study. Jiang et al. (2024) Earth’s Future e2023EF003975
By reducing the demand for fossil fuels, the ambitious projection suggests that placing solar roofs over roadways globally could decrease carbon emissions by almost 28 %.
According to the study, a network of solar panels would be installed over key highways and other roads to generate electricity and protect vehicles from adverse weather. This research was published in the open-access AGU journal Earth’s Future, which features multidisciplinary studies on the past, present, and future of Earth and its inhabitants.
There are some highway photovoltaic roof pilot programs, but not to the scale that we have imagined. Covering Earth’s highways with solar roofs could generate 17.58 PWh of electricity per year, equivalent to more than 60 % of the world’s total electricity consumption in 2023.
Ling Yao, Study Lead Author and Remote Sensing Scientist, Chinese Academy of Sciences
The authors propose that to achieve the 1.5 degrees Celsius (2.7 degrees Fahrenheit) warming target established by the International Panel on Climate Change, innovative methods to reduce carbon emissions are necessary.
Between 2012 and 2021, solar photovoltaics (solar panels) accounted for 40 % of newly installed renewable energy. As the cost of solar panels decreases, innovative solar initiatives like Yao's could significantly aid in the global transition to sustainable energy.
Picturing a Renewable and Safe Future
Yao was driving across an overpass on his nighttime commute when he had the idea for this creative study.
Yao added, “I suddenly looked down at the road, and thought, ‘The roads are connected to each other. It is just like a network–the cars can move freely from one place to another. I thought, ‘Why don’t we turn our roads into a network of photovoltaics?”
Building solar roofs over roadways will generate power using already-developed land, reducing demand for energy that releases greenhouse gases and, eventually, reducing carbon emissions. There are more than 3.2 million kilometers (1.9 million miles) of roads on Earth, enough asphalt to round the equator 251 times.
While solar-roofed parking lots have become more commonplace, photovoltaic-paved and -roofed highways are still relatively new. Although a few countries have initiated small-scale pilot highway photovoltaic projects to demonstrate the technology's potential, long highway sections equipped with solar panels are still a long way off.
The researchers determined the cost to establish and maintain a network of solar panels in each country or region after looking at highways and important arterial routes worldwide. Their analysis was based on polysilicon photovoltaic panels positioned at a 10-degree tilt towards the highway’s outer lanes, with a maximum power production of 250 watts.
According to Yao, 52.3 billion solar panels would be needed to cover all of the world's major roads with solar rooftops. Over four times the annual energy production of the United States, or 17,578 terawatt-hours, could be produced worldwide each year by the highway-covering solar panels. 13,570 terawatt-hours more would be produced annually if solar roofs were installed over large main roadways.
The cost per megawatt-hour and the potential for energy production would differ depending on the location, with the majority of the installations being constructed close to heavily populated regions with lots of highways, including the East Coast of the United States, Eastern China, and Western Europe.
Installing highway photovoltaic roofs worldwide could create enough energy to replace the equivalent of 9.66 gigatons of fossil fuel-generated carbon dioxide per year, or up to two-thirds of the United States' greenhouse gas emissions in 2022.
Yao added, “This really surprised me. I didn’t realize that highways alone could support the deployment of such large photovoltaic installations, generating more than half of the world’s electricity demand and greatly easing the pressure to reduce global carbon emissions.”
According to the study, by protecting vehicles and the road from rain and snow, solar highway roofs could possibly cut traffic fatalities by 10.8 % globally, particularly in areas with heavy precipitation. The financial toll that traffic accidents take would also be decreased by increased highway safety.
An Array of Challenges
The futuristic highway configuration might face obstacles such as costly installations (up to four times more expensive than similar ground-based arrays) and ongoing maintenance expenses. Beyond these difficulties, there are more commonplace issues like how to keep billions of solar panels clean.
Yao, nevertheless, is optimistic that some of these small pilot schemes will gain traction and that large-scale highway solar roof implementation could occur in certain countries. He believes that long, level highways, such as those in the Southwest of the United States, would be the best places to put solar rooftops.
He concluded, “Actually putting this into practice is the best evidence to make someone believe that this idea is practical.”
Journal Reference:
Jiang, H., et. al. (2024) Roofing Highways With Solar Panels Substantially Reduces Carbon Emissions and Traffic Losses. Earth’s Future. doi:10.1029/2023EF003975