energy harvesting

Capturing small amounts of ambient energy — vibration, movement, heat, light — and converting it into usable electricity. A genuine engineering discipline, and the umbrella term covering piezoelectric, photovoltaic and triboelectric devices.

It is also among the most oversold ideas in urban infrastructure. No city anywhere has adopted electricity-generating pavement as working infrastructure. Every installation on record is an event demonstration, a grant-funded pilot, a vendor showcase, or a failure that was removed.

Documented real-world example: the California Energy Commission commissioned an independent assessment of piezoelectric roadway harvesting (CEC-500-2013-007, 2014). It measured system output at 44 to 440 watts per kilometre of road, against vendor claims of more than 100 kilowatts per kilometre — a gap of two to three orders of magnitude. Washington DC installed 194 kinetic pavers at Dupont Circle in November 2016 for roughly $300,000 and has never published an evaluation. Sandpoint, Idaho’s solar roadway averaged 0.25 kWh a day in its best month, about one sixth of a single rooftop panel, and shut down in December 2018. A €5m solar road at Tourouvre-au-Perche in France saw annual output fall from 150,000 to 38,000 kWh before sections were destroyed and removed. A solar expressway in Jinan, China opened on 28 December 2017 and closed within days after panels shattered under traffic.

A note on vocabulary, because the marketing and the engineering use different words. Energy harvesting, photovoltaic pavement and triboelectric nanogenerator are engineering terms. Kinetic pavement, smart street and solar roadway are trade names. Pavegen’s tiles, frequently described as piezoelectric, in fact work by electromagnetic induction. And footstep harvesting is parasitic: the electricity comes from the extra work the pedestrian does compressing the tile.

Related terms: piezoelectricity

Sources: Assessment of Piezoelectric Materials for Roadway Energy Harvesting, CEC-500-2013-007 — California Energy Commission; This Dupont Circle sidewalk turns footsteps into power — Washington Post; Solar Roadways — Wikipedia; China’s solar highway was a victim of heavy traffic and bad design — South China Morning Post