As more than two-thirds of us will be living in cities by 2050, scientists and tech firms are looking at new ways to harness renewable energy within the built environment. But at what cost?
One day, your office windows will be harvesting energy from the sun, while the lamp-post down in the street is storing energy in its concrete.
Vertical wind turbines will spin as traffic whooshes past, and pavements and roads will generate small amounts of energy from all those commuter feet and heavy buses and lorries pounding down them.
New materials certainly show promise. Cement mixtures made from power station waste could turn buildings in to batteries, for example. These potassium-geopolymetric (KGP) composites are cheaper than ordinary cement and can store electricity. A six-metre tall lamp-post made from KGP and equipped with a small solar panel could hold enough energy to power itself throughout the evening, researchers say.
Another solution from Turkish firm Devici Tech is to use vertical wind turbines along roads where they can be powered by the slipstream from passing traffic.