Global energy needs will double by 2050, the World Energy Council predicts. In response, to relieve strain on existing energy sources, innovators worldwide are using new technologies and materials to develop “smart roads” that can capture, store and redistribute energy whenever and wherever it is needed. Roads surfaced with strong solar panels – known in this application as “photovoltaic cells”– are springing up worldwide. The first test road opened in Normandy, France, in 2016. In December 2017, the world’s first solar-panel highway opened to public traffic in Jinan, Shangdong, China. And in the United States, Idaho-based start-up Solar Roadways has been working on three contracts over the past five years with the US Department of Transportation, including one that involved building a prototype parking lot in Sandpoint, Idaho.
Each of Solar Roadways’ glass solar panels can generate 67 watts of electricity; that energy can be used to power snow-melting heating elements or LED-illuminated road markings and graphics. A microprocessor also facilitates wireless communication between panels and vehicles. Solar Road ways also is working with a partner to embed technology that would enable its solar panels to dynamically charge electric vehicles as they pass over the panels. “Our panels have undergone all the same tests as conventional roads at multiple civil engineering laboratories across the US and passed with superior results,” said Julie Brusaw, Solar Roadways’ co-founder. “There are over 28,000 square miles [72,520 square kilometers] of paved surfaces in the lower 48 US states alone, and we anticipate that covering these surfaces with our panels would produce over three times the electrical energy that the country uses annually.”
A SUNNY FUTURE?
Not everyone is convinced of the effectiveness of solar-panel roads, however. Inclement weather, shade and dirt can interfere with solar capture. Installing the panels on flat surfaces, rather than on an angle as most solar farms do, also limits their efficiency. For example, Normandy’s 1-kilometer (0.6-mile) road, covered with 2,800 square meters [about 30,000 square feet] of solar panels, was expected to generate 800 kilowatt hours per day, but its actual yield during a pilot phase was only half that.
Then there’s the cost. Normandy’s solar road cost 5 million euros (US$5.6 million). Building 0.6 miles of standard two-lane road in the US costs an average of US$1.2 million to US$1.8 million (1.0 million to 1.6 million euros), based on figures from the American Road and Transportation Builders Association – half the price of the solar road.
“There have been some impressive results engineering-wise, but it’s completely ridiculous to think that solar roads can have a meaningful contribution to the grid compared to standard solar farms or other renewable alternatives,” said Andrew Thomson, renewable energy engineer at energy developer CWP Renewables, based in New South Wales, Australia.
“Long solar roads would be complicated and expensive to build because they’d need hundreds of connection points, so the challenges of making them practical on a large scale are mind boggling. It would be far cheaper and much more effective to install conventional solar panel walls at the side of roads or fit them on rooftops, car parks and in fields, like we’re increasingly doing in Australia. In a couple of years, we’ll have so much energy that we won’t know what to do with it.”
KINETIC ENERGY FROM ROADS
Solar panels aren’t the only option for making roads smart, however. Other projects are exploring the financial and technical feasibility of converting the pressure from vehicles’ weight on roads into electrical energy. The concept involves embedding piezoelectriccrystals into road surfaces. As vehicles drive over the road, their wheels exert a force that deforms the crystals, causing them to generate electricity.
Piezoelectric systems have already had moderate success. In late 2011, a pilot program on a provincial motorway near Hardenberg, Netherlands, carried out by the University of Twente and engineering agency Tauw, showed that the systems generated enough electricity to power roadside sensors and other low-energy applications. However, they did not produce enough power to illuminate traffic lights or streetlights.
Engineers from the UK’s Lancaster University are building on the 2011 research, hoping to develop a piezoelectric system that will produce more energy on a mass scale. The California Energy Commission (CEC), a state government agency, is doing the same in the USA. It has invested US$2 million (1.78 million euros) in two independent piezoelectric projects led by Los Angeles-based energy harvesting technology company Pyro-E and the University of California, Merced.
“Both entities have built prototypes of ultra-high-density piezoelectric generators, which have generated a significant level of electric power output when tested under a compressive load during laboratory tests,” said Prab Sethi, senior project manager at CEC. “Now they’re fabricating integrated power electronics systems for conditioning the harvest electricity so it could be used to power roadside lights and call boxes, charge batteries or electric cars, or be fed into the grid. Field demonstrations will be carried out on private or university roads toward the end of 2019.
Once the pilots are complete, CEC will assess the viability of piezoelectric systems compared to other renewable energy sources in terms of power output, life expectancy, durability, cost and marketing potential.
“If successful, we’ll examine how to increase the power output while lowering capital costs, before testing the technology on major highways,” Sethi said. “This technology could help California achieve its goal of deriving 60% of its electricity from renewable sources by 2030.”
If the technology ever becomes part of California’s vast roadway system, researchers envision it being used to power roadside lights and call boxes, charge batteries or electric cars, or be fed into the grid.
Meanwhile, other researchers are working on generating energy from various technology combinations. The University of Texas at San Antonio, for example, is working on a self-powered hybrid system that converts both vehicle vibrations and the thermal energy from sun-heated road surfaces into electrical power. Designed to be embedded under any road surface, the system works completely independently of the national electric grid, making it ideal for providing energy to remote rural areas. Researchers report that results from pilot systems on roads at the university campus have been promising.
“We’ve optimized the system to function in our warm climate where there are high traffic streams, and we’ve recorded a continuous source of 29 megawatts of power from the heat conversion and 15 megawatts from piezoelectric energy conversion,” said Samer Dessouky, professor in the Department of Civil and Environmental Engineering at the University of Texas at San Antonio. “This is sufficient to operate low-watt LEDs in traffic lights or streetlamps and to activate sensors that collect data about traffic and the road’s structural health, thereby improving safety and cutting maintenance costs.”
That doesn’t mean the system is ready for commercial application, however.
“The system is not, in any capacity, ready to compete with existing green power-generating systems [such as solar panels], and we’re still addressing technical issues for installing our solution in major roadways,” Dessouky said. “We anticipate more optimization after site deployment to maximize long-term functionality; but piezoelectric transducers, thermo-electric generators and phase-change materials are getting chaper as more vendors are producing them in larger quantities with improved efficiency.
AN ALTERNATIVE USE
Elsewhere, researchers are focusing on electrification and electromagnetic induction solutions that enable electric vehicles (EVs) to recharge as they travel. Israel-based firm ElectReon, for instance, is piloting dynamic wireless power transfer technology that can be used to charge EVs as they travel in Tel Aviv.
“Although this electricity is not generated from the road, it provides an ideal method for transferring renewable energy to EVs so they can travel for long periods of time without having to carry heavy batteries or plug into traditional charging stations,” said Noam Ilan, vice president of Business Development at ElectReon. “Tests we carried out with an electric car from vehicle manufacturer Renault-Nissan showed that our robust system can efficiently and stably transfer electric power to cars in different conditions.
A 2019 pilot with Tel Aviv-based Dan Bus Company will test the system’s potential on public buses. ElectReon hopes to be ready for full commercial deployment in 2020, Ilan said.
Sweden, which aims to have a fossil fuel-free transportation infrastructure by 2030, has implemented several innovative projects. Since 2017, hybrid trucks have been able to connect to overhead electrical points to charge as they drive on a stretch of road between Hillsta and Sandviken. In 2018, the world’s first road to charge EVs from an embedded electrified track opened just outside its capital city, Stockholm. Developed by local consortium eRoadArlanda, the system consists of two electrified rail tracks installed beneath the road. The tracks transfer power to moveable arms attached to the underside of EVs as they pass. The initial test road is 2 kilometers (1.2 miles) long, but the second will be 20-30 kilometers (12-19 miles).
Additionally, ElectReon is leading a consortium of companies to electrify a 1.6 kilometer (1-mile) stretch of the 4.1-kilometer (2.5 mile) road between the airport and the city of Visby on the Swedish island of Gotland. It will accommodate wireless loading of electric trucks and buses.
Roads that could produce their own electricity, rather than collecting it from renewable resources, are the ultimate dream. While these roads are currently in the experimental stages, new virtualization, simulation and 3D modeling technologies could help researchers to engineer better performing and more cost-effective materials to bring them closer to reality.
eRoadArlanda’s inventor and research and development manager, Gunnar Asplund, is realistic about the challenges.
“It’s a great idea to have roads generating their own power, but most smart roads will be part of very small, isolated electric grids,” he said.
Solar Roadways’ Brusaw sees that as an advantage, however.
“Building new solar or wind farms takes up land and causes problems for the wildlife inhabiting it, but we already have millions of kilometers of roads,” she said. “Unlike centralized solar or wind farms, solar and other smart roads create a decentralized grid that cannot be shut down during a cyberattack, thereby increasing national security. Road infrastructures and antiquated electrical grids need upgrading to meet future energy demands, and we’re developing the technology to do both.”
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