Figure 3.37 Urban Energy Supply Sources and Systems: A Stylized Sketch

Figure 3.37 Urban Energy Supply Sources and Systems: A Stylized Sketch

Source: Author compilation (Feng Liu). Note: Many gas-fi red microgeneration facilities produce electricity and provide heating and cooling (using absorption chillers).

the summer if it is economically justifi ed. Distributed energy resources often produce electricity, while off ering heating and cooling services. Natural gas not only represents a cleaner alternative to oil and coal, but also adds more fl exibility to urban energy services through distributed generation facilities. For a large city, fi tting all the pieces together to optimize sustainable energy outcomes is not an easy undertaking. This is especially challenging in developing-country cities in which energy supplies are less well organized or streamlined relative to developed-country cities in which energy supplies are primarily network based.

Advances in centralized and distributed renewable energy supply technologies, such as wind towers, solar water heaters, biomass, and photovoltaic systems, enable cities to source a small, but increasing amount of renewable energy. Heat pumps and shallow geothermal energy sources also provide additional ways to reduce reliance on purchased energy. Considering the energy saved from effi ciency and conservation measures as a valid source of energy supply has become a compelling concept in demand-side management and energy supply planning.

The consumption of solid fuels by households and other dispersed end use points, such as restaurants, tends to decline as gaseous fuels— liquefi ed petroleum gas or natural gas—become available or electricity becomes more abundant. Such a transition may take decades and often requires the construction of regional and national energy infrastructure. In China, the dispersed use of solid fuels in urban areas has decreased dramatically over the last 20 years. Solid fuels have been largely eliminated from cooking and are now mainly used in a falling number of cold climate urban households that have no access to centralized heating or natural gas. This trend has been generated because of the strong support of the national government for boosting the supply of liquefi ed petroleum gas and expanding natural gas transmission networks.

Spatial and temporal concerns are important in developing network-based urban energy infrastructure. Spatial planning entails the layout of networks within existing and planned builtup areas to achieve the most effi cient routing and siting of generation and distribution facilities based on demand and load distribution. Temporal planning addresses system size based on current and anticipated demand and load and, most critically, the size of mains and trunk lines that are diffi cult to rehabilitate once built. This is especially important in rapidly growing cities and has signifi cant fi nancial implications. Owing to uncertainty in predicting demand, using the proper size in infrastructure is part science and part luck. However, decisions on size become more reliable if planners understand urban energy demand patterns and trends and have access to knowledge developed in other cities confronting similar situations.

Urban planners should also consider the constraints of overlapping energy supply networks