December 2015, No. 3 Vol. LII, Sustainable Energy

Over the last 20 years, urban areas have experienced dramatic growth. Currently, over 3.5 billion people inhabit urban areas (approximately half of the global population). Developing countries in particular are undergoing rapid change from rural to urban-based economies as they are transformed by their urbanizing populations (UN-HABITAT, ICLEI, and UNEP, 2009, p. 7). Although the extent of urbanization in developing countries differs in magnitude and pace, their challenge is to stabilize a growing hunger for secure energy supplies, construct bridges of access, equity and empowerment, minimize environmental degradation, enhance human health and livelihoods, and craft new development directions (Droege, 2008, p. 1).

Global population has doubled since 1960 and is expected to surpass 9 billion by 2050. 99 per cent of this population growth, as well as 50 per cent of urban growth, is expected to occur in developing countries (Chu and Majumdar, 2012; Curry and Pillay, 2012). According to the United Nations Environment Programme (UNEP), Latin America and the Caribbean are highly urbanized, with 78 per cent of the population living in cities in 2007. By 2050, that number is expected to increase to 89 per cent. While Africa and Asia are less urbanized, with approximately 40 per cent of the current population living in cities, they have also experienced high rates of growth, and their urban population is projected to increase to 62 per cent by the year 2050 (as cited in UN-HABITAT, ICLEI, and UNEP, 2009, p. 7). The United Nations projects that by 2050, 6 billion people will live in cities.

The global energy crisis, coupled with the threat of climate change, demands innovation in the energy sectors, and responsible consumption for both developed and developing countries. In Urban Energy Transition: From Fossil Fuels to Renewable Power, it was stated that by 2030, global energy demands are expected to increase by 60 to 85 per cent. According to the Intergovernmental Panel on Climate Change (IPCC) recommendations, if we are to limit global warming to no more than 2°C above pre-industrial levels, we cannot exceed an atmospheric greenhouse gas concentration level of 450 parts per million (ppm). In March 2015, however, NASA revealed that the 400 ppm level had been surpassed. 

To ensure a viable, healthy and environmentally sound future, the world needs another industrial revolution, where development is fuelled by affordable, accessible and sustainable energy resources. In an attempt  to reduce resource inputs and environmental impacts, some developed nations have already successfully managed to decouple economic growth from energy consumption. This has been achieved by closing the energy loop in production, such as recapturing released heat for power generation (UN-HABITAT, ICLEI, and UNEP, 2009, p. 7). Energy efficiency and conservation, as well as decarbonizing energy sources, are essential to this revolution.

Although fossil fuels-based energy generation still plays a major role in cities, it is increasingly apparent that sustainable energy is the only choice moving forward. For example, in cities, the share of fossil fuels may remain substantial, though they often employ co-generation and district heating characterized by high fuel efficiency. Implementing renewable energy strategies in city environments is rapidly becoming “energetically imperative”. Making the transition involves not only switching the energy source, but making sure it is cost-effective, sustainable and beneficial for development. Cities around the world are pledging to make use of 100 per cent clean energy; Copenhagen pledges to be carbon-neutral by 2025, Aspen, Colorado, is expected to use 100 per cent renewable energies by 2015, and Munich is planning to have 100 per cent of its electricity powered by renewables by 2025.

Anaerobic digestion

Urban waste generation and disposal is becoming a critical issue due to increasing urbanization and population growth. Anaerobic digestion, where biodegradable waste is decomposed in the absence of oxygen producing a methane-rich biogas suitable for energy production, could provide a critical solution to growing waste issues, while simultaneously reducing external energy requirements (Curry and Pillay, 2012). The biogas can be combusted to produce both heat and electricity using internal combustion engines or microturbines and hot water heaters, where the generated heat is used to warm the digesters or heat buildings (Ibid). If municipal waste could be utilized for biogas production, thus reducing the demand for landfill, sustainable and renewable energy could be produced alongside a beneficial by-product of bioslurry which can be used as fertilizer. A study by Curry and Pillay in the journal Renewable Energy found that the number of biogas plants is increasing each year by about 20 to 30 per cent, proving that anaerobic digestion is becoming an important sustainable energy source (2012).

Solar power

The initial benefit of utilizing solar power as an energy resource, compared to biomass, hydropower, or nuclear, is that it requires no water and therefore eliminates environmental concerns regarding increasing water consumption and subsequent shortages. Recent cost reductions in the implementation of solar technologies (both concentrated and photovoltaic solar power) made them cost-competitive with fossil fuel-based power generation in both mid to high latitudes. Globally, solar photovoltaic power grew the fastest of all renewable technologies between 2006 and 2011, increasing by 58 per cent annually, followed by concentrated solar power, which increased by almost 37 per cent, and wind power which grew by 26 per cent, as reported in an energy policy study (Purohit, Purohit and Shekhar, 2013). Solar power for urban application is effective as panels and photovoltaic materials can be placed on the roofs of buildings, where they are non-obstructive, efficient and low maintenance. It is estimated that global concentrated solar power capacity will be 147 GW in 2020, 337 GW in 2030 and 1089 GW in 2050 (Ibid).

Efficient infrastructure

In the future, the development of on-site renewable energy production could lead to zero emission buildings and highly energy efficient low carbon eco-cities (Lund, 2012). New innovative technologies are advancing every day, making cities more energetically sustainable. For example, a wind, solar and rainwater harvester is being developed for application in urban high-rise buildings to optimize energy production. It helps to minimize issues with current urban wind turbine applications.


With advancing technology, there has been a rise in the number of eco-cities around the world. Examples of such “sustainable urban areas” are Masdar City in Abu Dhabi and PlanIT Valley in Portugal. Aiming to be the largest of its kind, Tianjin Eco-city is a collaborative project between China and Singapore that by 2020 will provide homes to over 350,000 residents in a low-carbon, green environment around half the size of Manhattan. These cities include infrastructure with water-saving fittings, insulated walls, double-glazed windows, south-facing orientation to optimize passive heat, solar photovoltaic roofs and walls, and on-site energy generating stations.

The implementation of renewable energies in urban environments is sometimes constrained by the mismatch between supply and demand, and their integration within the energy system. Smart grids could provide the necessary interconnections and control to manage power provision effectively. The implementation of such measures in the urban environment provides several benefits, including improved energy security and reliability, reduced transmission costs through bringing local energy supply closer to demand, employment of existing infrastructure and minimizing demand for land (Ibid).


Large-scale renewable energy use in urban environments is of high importance as a future sustainable energy option in both meeting increasing urban energy demand and reducing emissions (Ibid). As technology continues to advance, renewable energies will become ever more efficient, user-friendly, cost-effective, accessible and sustainable.



Chu, Steven, and Arun Majumdar (2012). Opportunities and challenges for a sustainable energy future. Nature, 488, (August), pp. 294-303. Available from

Curry, Nathan, and Pragasen Pillay (2012). Biogas prediction and design of a food waste to energy system for the urban environment. Renewable Energy, vol. 41 (May), pp. 200-209.

Droege, Peter, ed. (2008). Urban Energy Transition: From Fossil Fuels to Renewable Power. Oxford: Elsevier Ltd.

Lund, Peter (2012). Large-scale urban renewable electricity schemes—Integration and interfacing aspects. Energy Conversion and Management, vol. 63 (November), pp. 162–172.

Purohit, Ishan, Pallav Purohit, and Sashaank Shekhar (2013). Evaluating the potential of concentrating solar power generation in North-western India. Energy Policy, vol. 62, pp. 157-175.

UN-HABITAT, Local Governments for Sustainability, and the United Nations Environment Programme (2009). Sustainable Urban Energy Planning: A handbook for cities and towns in developing countries. Nairobi: UNEP. Available from