As prices increase, so does the recoverable reserve of fuels. However, extraction of these fuels may be in more remote areas, need new technologies, and may lead to increased pressure on the environment. For example, the extraction of crude oil from the oil sands in Canada and shale in the U.S. not only affects a large land area due to mining, actual oil extraction requires large amounts of energy (heat) and water, and leads to increased emissions of greenhouse gases and air pollutants. Likewise, extraction of oil in remote areas such as the Arctic brings increased risks to the environment. As the boundaries of recoverable reserves change, so too will the environmental impact of the energy supply.

There is a wide body of literature on estimating fuel reserves, which falls outside the scope ofthis chapter. Here it is important to realize that measuring the sustainability of energy supply is dependent on a number of (changing) factors:

• reserves and consumption,

• mix of final energy carriers,

• environmental impact of extraction and conversion.

The future choice of supply mix is strongly affected by the energy usage patterns in society. In the past, major changes in the supply of energy were primarily the result of developments in energy demand technology. For example, electrification of society did not start before the invention and the wide dissemination of the incandescent light bulb and related technology. This growing market was the incentive behind the buildup of a power industry over subsequent decades, one that is still growing strongly.

It is important to note that while there may be no direct limitations to the "reserves" of renewable resources (except for hydropower and biomass), there are indirect factors that may limit the extraction of energy (e.g., available land, water availability). For example, reserves of some metals may limit the types and volume of photovoltaic systems that can be deployed to convert solar energy to electricity (Andersson 2001). The potential estimates of the resource base for solar energy do now exceed the total amount of energy use in the world. However, estimates of the recoverable potential strongly depend on the assessment of the surface area available (e.g., suitable roof area in a given region), efficiency of conversion systems, materials availability, transport, distribution and storage potential, and economic considerations. The same limitations apply to the supply of other renewable resources, such as wind and biomass energy. Furthermore, the choice of biomass conversion technology will affect the environmental impact of extraction (e.g., air pollution, eutrophication, biodiversity).

Moving Boundaries in Energy Demand

Fuels are converted to produce a wide array of energy services throughout society. Generally, during conversion, the largest environmental impact of the energy system occurs, as here the fuel is combusted. Velthuijsen and Worrell (1999) show the major environmental impacts of the energy system, divided into air, water, and solid wastes. Below, we will use emissions of the main greenhouse gas, CO2, as the proxy for environmental pollution. However, other environmental impacts should also be measured to establish the sustainability of the energy system. Due to the development of abatement technology, each pollutant may have different patterns than CO2.

In addition, end use conversion technologies are also responsible for the largest changes in the energy system. Grübler (1998) argues that the invention of the steam engine (and internal combustion engine) precipitated the start of the "grand transition" to fossil fuels, and that the second grand transition of the diversified energy end use technologies and supply sources was the result of the increased use of electricity to provide energy services (e.g., lighting, power). The more rapid increase in electricity demand was mainly caused by an increasing demand for domestic energy services. This demonstrates that moving or changeable boundaries in energy demand (e.g., types of energy services) are the key factor in understanding the changes in the energy supply system.

As energy is used for myriad applications which change over time, in terms of the volume consumed and the type of activities undertaken, understanding energy demand is relatively complex. Generally speaking, energy demand is understood to be a function of volume (of activities/energy services provided), structure (or mix of activities/energy services), and efficiency (with which the services are provided). In its simplest form, structure can be interpreted as the mix of economic sectors, and volume will refer to the level of activities of each sector. In energy analysis, the key end use sectors distinguished are agriculture, industry (including mining), buildings (both residential and residential), and transport. The power sector is not an end use sector but converts primary fuels to a secondary energy carrier. Power is consumed by the end use sectors. Table 21.1 provides an estimate of the breakdown of final and primary energy use by sector.

The main factors affecting growth of energy use and carbon emissions in an economy include the rate of population growth, the size and structure of the economy (depending on consumption patterns and stage of development), the amount of energy consumed per unit of activity, and the specific carbon

Table 21.1 Share of global energy consumption by sector (De la Rue de Can and Price 2008).


Final energy-based

Primary energy-based

Energy conversion


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