Greenpeace UK has created a virtual tool that can be used to find out how cities can reduce greenhouse gas emissions and save energy: 'EfficienCity'. The tool promotes a so-called decentralised energy system. Combined heat and power (CHP) forms the basis of such a system. CHP plants are located in cities and towns where electricity and heat will also be used, so that little energy is lost in transmission. 'EfficienCity' virtually illustrates how the CHP system can be applied in cities. Moreover, it shows how local renewable energy sources can be used. The tool clearly explains how energy can be saved in different urban settings, such as football stadiums, supermarkets and houses. It also gives concrete examples of already existing projects in the UK by providing video material and pictures.