High-Tech Solar Roads Could Power Electric Vehicles

Some environmentalists are concerned about the impact of huge solar farms. But what if solar energy could be generated in ways that don’t add to environmental impact … like replacing asphalt surfaces on roadways with solar panels? That’s the idea being proposed by Solar Roadways of Sagle, Idaho. Without using any new real estate for solar powerplants, the company estimates that if solar panels covered all the asphalt surfaces in 48 states – roads, parking lots, driveways, and sidewalks - they could supply several times the country’s electrical energy needs.

The idea isn’t as far-fetched as it might seem. In fact, the Department of Transportation has awarded Solar Roadways a $100,000 contract to demonstrate the first prototype Solar Road Panel, which will consist of building and testing the first 12-foot by 12-foot prototype panel.

Solar Road Panels are composed of three layers. The bottom, or base plate, layer contains data and power lines to distribute electrical power. The middle electronics layer contains a large array of solar cells, supercapacitors to store the electricity, and embedded LEDs. The LEDs ‘paint’ the road lines from beneath for safer nighttime driving and can provide real time warnings.

The top road surface layer is made of translucent high-strength material that lets sunlight through to the solar collector cells. It provides the same traction capability as asphalt while handling heavy traffic and protecting the electronic components below. Besides producing electricity, in colder climates Solar Roads could generate heat to prevent snow and ice accumulation. Thus, parking lots could be a primary first application.

While paving the nation with solar panels is probably too ambitious, it’s not too much a stretch to imagine the technology being used to charge the batteries on electric vehicles while they’re driving or parked. This could be accomplished by combining the Solar Road Panels with an in-road charging technology like that being developed by Ingenieurgesellschaft Auto und Verkehr (IAV) in Germany or the Korea Advanced Institute of Science and Technology (KAIST).

IAV’s design would embed induction loops in roads to transfer energy using Maxwell's electromagnetic laws. Electric current flowing through a conductor generates a magnetic field, and this field can induce a voltage in a second conductor even though the two are not in contact with one another. Using precisely controlled frequencies of alternating current, high-efficiency energy transmission from sending to receiving electrical circuits is possible and a moving vehicle can receive power from buried transmission lines.

While in the IAV system’s transmission losses are relatively low at about 10 percent, the technique is very sensitive to the gap between road and vehicle. IAV says electric vehicles could use active suspension and opto-electronic measurement technologies to automatically maintain the optimum distance.

Fortunately, because of high transmission efficiency only limited stretches of road would need to be used for charging. This means infrastructure investments would be less than might be expected. IAV is planning to build a demonstration section of ‘charging road’ and a full-scale test track in the German state of Lower Saxony.

KAIST is using similar technology for its Online Electric Vehicle (OLEV), which is already in use at factories and large warehouse facilities for powering and remotely controlling robotic materials handling equipment. The OLEV features power cables with energy transferred by magnetic induction without physical contact of any kind. KAIST claims 80 percent efficiency for power transfer across a 1 cm gap, and 60 percent efficiency across a 12 cm gap.