By Dave Elliott
Urban areas account for around 75% of the world’s energy use and there are ambitious plans to reduce their reliance on fossil fuels. Around the world, cities are beginning to think in terms of meeting their energy needs from renewable sources, so as to limit air pollution and climate change problems. The case for this transition is strong, not least given the likely rise in air-conditioning demand as climate change impacts more, and there have been many interesting initiatives launched around the world, often led by city governments.
In addition to many early initiatives across the EU (including in Freiburg, Germany, and Woking, England), current high-profile examples include new projects in China (Tianjin Eco-City) and the UAE (Masdar City), and initiatives in the US, where existing cities such as San Diego and San Francisco, and many others, have committed to 100 percent clean energy.
A 2105 CDP report noted that globally, 308 cities had participated in a CDP programme aiming to better manage their climate change strategies, with 109 cities setting renewable energy or electricity targets. CDP say that 35% of the 162 cities that had reported details were currently getting 75% of their electricity from non-fossil sources with, in many areas, hydro being a major supplier, producing over 72% of the mains power used in 45 Latin American cities.
For the moment, whatever its generation source or type, including renewables, the electricity cities use is nearly all imported, very little as yet being generated inside cities. However, that is changing, with some cities now getting increasing amounts of their energy from local generation, including some using renewable sources; there are inspiring examples of surplus local PV solar generation in parts of some German cities, which export that surplus to the rest of the city.
That is still rare and relatively small scale. A review of the programmes mounted by 13 cities in the EU Energy Cities initiative found that by 2013 they could meet 44% of their energy needs from locally produced energy, although the renewable proportion (4.38TWh) was only around 16% of the local generation total (26.77TWh), or about 7% of total energy use. It will hopefully be possible to increase the ‘local generation’ total (some of which can be low carbon) and also, crucially, the renewable proportion achieved in initiatives like this: they had actually tripled their renewables share since 2010.
Even so, 7% is quite low and, although much more can be expected in future, there may be limits to very substantial expansion. Certainly cities can get more of their energy from renewable sources within their boundaries, with electricity generated from PV solar and heat from solar collectors, and heat and power from bio-wastes, and in some cases geothermal/ambient sources within cities.
However, given the spatial constraints and the high level of energy usage in cities, it seems unlikely that cities can generate all the energy they need themselves from renewables within their boundaries. Although roof-top PV can provide power for individual dwellings, that’s harder with multi-occupancy high-rise buildings (with one roof shared by many dwellings) and although energy from wastes is an obvious option for cities, which generate a lot of bio-wastes, including sewage and food wastes, there are environmental and siting constraints on converting this into useful energy. Wind projects are usually not well suited to urban environments, with micro-wind turbines being inefficient and urban wind speeds often low and erratic, although some industrial or dockland sites have been used for larger machines. Some industrial and retail units can use PV and solar heating, for daytime loads in summer especially, but although the overall scale of demand can perhaps be reduced, it is large.
Consequently, a study by the International Energy Agency concluded that ‘the high energy densities of some urban areas would require large areas of “catchment” land outside of the city boundary if renewable energy is to be used to increasingly supply the energy needs within the boundaries of a large city’ .
Cities can and should seek to supply as much as possible of the energy they need from local urban sources, including wastes. But, as with water and food production, many urban areas will still be dependent on rural areas, and in some cases marine locations, for some of their renewable energy.
This does not have to be seen as a failure. While self-sufficiency is a good goal, it can become a dogma if applied too single-mindedly to any specific context. Indeed, importing energy may be the most efficient way to achieve 100% renewable energy use within cities. Renewables are mostly variable and will need systems to allow for balancing, including supergrid links, so that local supply and demand variations can be balanced across wide areas. That implies a wider framework than just generation within cities, linking up to where the resources are best available.
Fortunately there are plenty of renewable resources available outside cities, enough to meet all their needs. Many studies now suggest that, if properly developed and combined with energy saving and smart grid systems, renewables could supply the bulk of the electricity needed in most countries and most of their other energy needs by around 2050.
However, there is much work to be done to reach that state, including, along with ambitious national renewable energy development and energy saving policies, in the context of cities, the development of improved building design, urban planning and transport policies, tailored to local conditions. Although that may first need a better understanding of energy use in cities and how to change it.
At the same time, much progress has been made due to grass-roots initiatives. In some cases, individual consumers are becoming ‘prosumers’, using their own roof-top PV solar arrays, many of these projects being in urban or suburban areas. Local community energy projects are also proliferating, along with municipal projects and support programmes. Certainly many of the national ‘low carbon’ energy scenarios that have emerged in recent years assume major local level inputs from such projects, with many of them in urban areas, and involving renewable and low carbon local heat and power generation projects initiated and run by local municipal authorities, including heat networks: http://www.realisingtransitionpathways.org.uk/realisingtransitionpathways/news/distributing_power.html.
Although there may be exceptions, and some cities may be able to sustain independent initiatives, it follows from the analysis above that the cities that are likely to do best, in terms of meeting their energy needs from renewable sources, will be those in countries that are promoting renewables strongly, at the overall national level. Given that renewables of all types are expanding across the world, the prospects for expanding the use of renewables in cities therefore look quite good. In addition, cities can also expand renewable generation within their boundaries, while reducing their energy demand as far as possible. So, it does seem possible, by this double approach, for cities to aim for high renewable energy usage targets.
For a nicely positive view of what’s being done, see www.nuclearpolicy.info/wp/wp-content/uploads/2016/06/Alan_Simpson_DE_energy_without_illusions.pdf