A quiet revolution has taken place in the Oresund Strait between Sweden and Denmark where two of the world's largest battery-powered ferries ply the waters after being converted from polluting diesel power.
Four containers on top of the ships now store 4.1 MW of batteries, propelling the ferries across the 4km between Helsingor and Helsingborg at the same speed as before.
They then recharge automatically each time they dock.
Shipping is thought to account for more than 2% of world CO2 emissions, and the firm running the ferries says the conversion has cut its carbon footprint by 65%.
Find out more in the video above.