Among mushrooming PV power devices, a result of dropping cost, an innovative option is solar panel-covered streets or highways, which can not only generate power and melt snow but also charge cars traveling on them, but technological difficulties remain to be overcome before the idea can be materialized.

While solar-panel road can solve the problem of land acquisition and power demand, it is still faced with a number of difficulties, including load-bearing capacity of panels, high cost, and low power-generation efficiency.

Power generation capacity would be compromised by the weight and shadow of numerous cars constantly rolling over the road, as merely 5% shadow would cut power output by 50%. Given its low light conversion rate, cost effectiveness of solar-panel road is significantly lower than rooftop PV power devices or ground-mounted stations now.

The problems have been manifested by the world's first solar-panel road WattWay in France, built by Colas, under European giant construction group Bouygues, at 5 million euros. The road was projected to generate 767 kWh of power daily or 280 MWh a year, equivalent to 17 euros/kWh each for a total of 2,880 panels, 13 times that of large-sized rooftop solar panel (1.3 euros/kWh). In fact, according to statistics released in Jan. 2018, power output of Wattway reached only 409 kWh daily in the first year, only half of projected output.

High cost is also a major problem plaguing a smart solar-panel road constructed by Solar Roadways in the U.S., which is furnished with smart sensors and LED light, capable of showing up traffic warning or other messages, such as "look out for deer." An experimental project on a sidewalk in Sandpoint of Idaho shows that it cost US$48,734 for installing 1.529 KW solar panel on a space sized 13.9 square meters, or US$32,366 per KW, 20 times of large-scale stations.

Market players noted that LED and heating system would consume 106 MWh and 2.28 MWh of power per mile, respectively, compared with 415 MWh output of solar panel under normal condition. In practice, the experimental road only generated 52.397 kWh of power during a six-month period.

Moreover, investors have to worry about theft, threatening the secret of their patented technology. In the case of a solar-panel section on a freeway in Jinan of China, the first such project worldwide, a whole chunk of solar panels was stolen in mere five days after its inauguration in Dec. 2017, which some suspected was a work of industrial espionage.

It is evident that there is still a long way to go before the commercialization of solar-panel road.

(First photo courtesy of Solar Roadways, written by Daisy Chuang)