IPCC Special Report on Emissions Scenarios

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3.4.3.2. Renewable Resources

A review of medium-term (to 2025) and long-term (up to 2100) potentials of renewable energy is given in IPCC WGII SAR (Nakicenovic et al., 1996) and shown in Table 3-6. A summary of the literature of renewable resource development potentials consistent with IPCC WGII SAR, including a detailed regional breakdown, is given in Christiansson (1995) and Neij (1997).

Hydropower currently provides some of the cheapest electricity available in the world, although the potential for new capacity is limited in some regions. WEC (1994, 1995a) estimates the gross world potential for hydroelectric schemes at about 144 EJ per year, of which about 47 EJ per year is technically feasible for development, about 32 EJ per year is economically feasible at present, and about 8 EJ per year is currently in operation. IPCC WGII SAR (Nakicenovic et al., 1996) gives a comparable medium-term potential of between 13 and 55 EJ, and a maximum technical potential above 130 EJ.

Other important renewable energy resources are wind and solar, as well as modern forms of biomass use. Biomass resources are potentially the largest renewable global energy source, with an annual primary production of 220 billion oven dry tons (ODT) or 4500 EJ (Hall and Rosillo-Calle, 1998). The annual bioenergy potential is estimated to be in the order of 2900 EJ, of which 270 EJ could currently be considered available on a sustainable basis (Hall and Rosillo-Calle, 1998). Hall and Rao (1994) conclude that the biomass challenge is not one of availability but of the sustainable management, conversion, and delivery to the market place in the form of modern and affordable energy services. It is also important to distinguish between harvesting and deforestation; the former results in afforestation, and the latter in conversion of forest land for other uses, such as agriculture or urban development.

The use of biomass as an energy source necessitates the use of land. Based on estimates by IIASA-WEC (1995), by 2100 about 690-1350 million hectares of additional land would be needed to support future biomass energy requirements for a high-growth scenario. However, the additional land requirement for agriculture is estimated to reach 1700 million hectares during the same period. These land requirements can be fulfilled if the potential additional arable land is taken into account (at present this is mostly covered by forest). Hence, land-use conflicts could arise, and particularly for Asia which is projected to require its entire potential of arable land by 2100. Africa and Latin America may have sufficient land to support an expanded biomass program. One estimate (WEC, 1994) shows that Africa can support the production of biomass energy equivalent to 115% of its current energy consumption (8.6 EJ).

Some authors stress that increased demand for bioenergy could compete with food production (Azar and Berndes, 1999). They note that the competitiveness between food and bioenergy production is not realistic in most energy-economy models; rather it is treated in an ad hoc fashion with the assumption that enough land is secured for food production. In reality an increasing competitiveness of bioenergy plantations may cause food prices to jump. Some developing regions, in particular Africa, are often assumed in scenarios to become major importers of food (Azar and Berndes, 1999).

Unlike hydropower, most of the technologies that could harness these renewable energy forms are in their infancy and are generally still high cost (although wind power is becoming increasingly competitive in some areas). Conversely, the potential for improvement in technical performance and costs is substantial. Thus, the future resource potential of these renewables is largely determined by advances in technologies and economics (discussed in Section 3.4.4).

Advances in renewable energy technologies could materialize to a significant extent even in the absence of climate policies, albeit conventional wisdom holds that such policies could accelerate their diffusion considerably. According to IPCC WGII SAR (Nakicenovic et al., 1996), in the medium-term (to 2025) the largest renewable energy potentials lie in the development of modern biomass (70 to 140 EJ), solar (16 to 22 EJ), and wind energy (7 to 10 EJ) as indicated in Table 3-6. In the long term the maximum technical energy supply potential for renewable energy is evidently solar (>2,600 EJ), followed by biomass (>1,300 EJ).