Innovation in the solar energy industry is happening constantly. While panels are typically installed on rooftops or on large plots of land, some in the industry think that roads and highways are a suitable place for solar panels as well. Solar roadways are roads that have integrated solar cells generating power from the sun – in this article, we’ll examine how feasible solar roadways are and what their future might look like.
Solar roadways: what are they?
Most roads in the U.S. are made from asphalt. A solar roadway is any road that has some sort of solar panel technology attached to its surface, thus producing electricity while also supporting the cars and trucks that drive on it. While an interesting and innovative way to generate solar power, solar roadways are far from being a realistic, cost-effective energy production method.
One company in the United States, Solar Roadways, has raised money for prototyping and initial solar road product installations, but the company is still a long way away from scalable solar-power-generating road technology due to a number of challenges that come with altering highway infrastructure.
Could solar roadways power the U.S.?
How much power could realistically come from a network of solar-powered roads? For the sake of example, let’s assume that solar roadway technology is sufficiently advanced and cost-effective enough to install nationwide. Here’s how the math works out:
According to the American Road & Transportation Builders Association, there are about 8,615,000 lane miles of road in the lower 48 states, which equates to approximately 18,000 square miles of land covered by roads. That’s a little bit more than three times the land area of Connecticut.
And according to a 2008 analysis by the National Renewable Energy Laboratory (NREL), roughly 1,948 square feet per person of land is needed to supply enough electricity to run the country on solar power. Multiply that number by the U.S. population (about 325 million people), and a rough estimate of the total land area needed to power the U.S. with solar energy comes to nearly 23,000 square miles. Comparing that number to the square mileage of roads in the U.S., we see that covering the lower 48 states’ roads in solar panels could generate a little less than 80 percent of the nation’s energy needs (78.2 percent to be exact). Adding in the huge amount of space covered by parking lots could probably get us all the way to 100 percent coverage.
These calculations are rough estimates. Factors like panel efficiency, panel angle and tracking capabilities, sunlight hours, temperature, and more all play into the actual production numbers. For this example, the number above gives a good ballpark estimate, but we’ll keep in mind that the calculations are an oversimplification.
How much rooftop space is available for solar panels?
Hypothetically, covering the country’s roads in solar technology gets us most of the way to being completely solar powered. Add in the rooftop space potential in the U.S. and we’re all the way there – NREL estimates that around 39 percent of the country’s energy use could be supplied by rooftop solar panel systems, equaling 1,118 gigawatts (GW) of solar production.
Hurdles to making solar roadways a reality: cost, durability, safety, and energy production
Solar roadways sound like an innovative and effective way to expand solar energy use without taking up new land space, but there are a few major roadblocks to solar roadway technology becoming widespread:
One of the biggest challenges for solar roadways is the high upfront and maintenance costs involved. Solar panels are much more expensive than asphalt on a per square foot basis, and repair costs are also high compared to filling in potholes or repaving sections of road. One estimate puts the cost of replacing the country’s roads with Solar Roadway’s prototype product at $56 trillion. We’ll need innovation to help lower production, installation, and maintenance costs before solar roads can become a realistic and cost-effective solution.
Cars and trucks are very heavy loads for roads to bear, which is why asphalt is such a useful road material – it flexes slightly with weight and won’t shatter under heavy weight or big impacts. Designing a solar roadway product that can let light through to the solar cells while also being durable and resistant to damage is a difficult engineering problem. Solar cells are typically covered in glass to protect them from the elements while letting sunlight through, but withstanding the weight of an 18-wheeler with a full load is an entirely different problem. Any solar roadway solution needs to be highly durable to both weight and impacts, which is something that current prototypes have yet to completely solve.
Imagine driving on a road surfaced with glass in a rainstorm. That’s an accident waiting to happen, and it’s another barrier to widespread installations of solar roadways. One solution to the problem of safety on solar roadways is to texture the glass covering any solar cells used on roads, but that will likely reduce the efficiency of the solar panels.
The calculations above assume a lot, including reliable and predictable energy production from solar roadways, which isn’t always a safe bet. Depending on where in the country they are installed, weather patterns, and tilt, solar cells produce highly variable amounts of energy. Specifically for solar roadways, cells would have to lie flat, which is not the optimal direction for them to capture the maximum amount of sunlight. This also means that snow or debris covering the cells wouldn’t simply slide off, as it usually does for rooftop systems installed at an angle.
Solar roadways case study: China
Solar roadways are a long way from being feasible in the U.S., but China may be much closer. Similar to the U.S. company Solar Roadways, a Chinese company called Pavenergy is spearheading solar roadway development in the country. Pavenergy has benefitted from heavy government financial help, as they partnered with Qilu Transportation, a government-owned construction group, to open the first solar highway in the country in 2017.
In addition to financial advantages, Chinese solar roadway projects have an important technological leg up as well: most roads in China are made with concrete, while roads in the U.S. are usually constructed with asphalt. Asphalt flexes slightly under pressure, meaning that rigid solar cells will easily snap under the weight of cars and trucks. Concrete is a more sturdy foundation, and solar cells on top of a concrete road don’t face the same durability issues as those on asphalt.
Rooftop solar: a proven way to benefit from solar energy
While solar roadways still have a long way to go, there are other ways to repurpose otherwise unusable area to generate solar energy. Specifically, rooftop solar is a proven, cost-effective, and safe way to install solar panels at many different scales. If you’re interested in using your roof to generate power from the sun, the best way to shop for the right solar panel system is to compare quotes on the EnergySage Marketplace. Simply register your property to start receiving free quotes from qualified, pre-vetted installers near you.