Accounting the urban energy consumption raises some issues:
– Electricity is often provided by several private companies that do not disclose detailed information. Gas delivered by pipe is in the same situation. Despite that, you can (theoretically) obtain a figure at the household level.
– Fuels are rather complex, but for deliveries to big clients. How to count the automotive fuels, at the pump, at the owner’s address, or in the road sections where they are burnt? And the bottled gas sometimes sold in some filling stations? Or wood?
– Renewable energy can be decentralized generation; if it is later delivered to the general grid its accounting is more complex (but you an always think of a citywide balance)
And there is another problem: efficiency. What matters is not just how much energy you use, but rather how efficient that use is. The district heating systems that are common in northern Europe often begin as isolated power stations, but gain in efficiency as they are integrated in grids, as well as a home can be more efficient if the wall insulation is upgraded. So there is not just an issue of consumption, but also of the benefit that derives.
The energy part of the Green City Index, by Siemens, gave in 2009 the highest mark to Oslo (8,71), while London was 10th (5,64) and Madrid 12th (5,52) among the 30 studied European capitals. These marks resulted from 3 quantitative criteria: energy consumption (Gj per capita), energy intensity (Mj per unit of real GDP), renewable energy consumption (% of total consumption); and a fourth qualitative element addressing energy policies.