nick clark reports from gothenberg in sweden. >> reporter: the port of gothenberg is sweeped's tradingloading and unloading 900,000 containers a year. that's two a minute. 24 hours a day, seven days a week. in fact, 11,000 vessels from all over the world pass through gothenberg every 12 months. but the port lies in the heart of the city's srez reds shall community and shipping is not as clean as you might think. >> shipping has always been stuck with the worst type of oil. heavy fuel oil. heavy fuel oil has the large share of sulfur content, this is just in the recent 10 years lifted up as a problem. >> reporter: armed the world even when ships are docked, they keep their engines running their emissions or big factor in port communities. here in gothenberg they have pioneered a new system, some chips can plug in to green energy generate odd shore so they don't need to burn fuel until they leave. they are taking power from the city. >> from the city grid, feeding the ship. simple as that. >> reporter: just like a plug at home. >> plug in the cord, that's it: recently maritime law change