A Scale-Related Difficulty in Switching from Fossil Fuels to Renewables: Renewables are Highly Land Intensive

Christopher Green

McGill University

Montreal, Quebec, Canada

The increase in economic progress in the last two centuries owes much to our ability to harness energy. Most energy is produced by fossil fuels - long-stored solar energy. Although renewables such as hydropower, wind, biomass and solar thermal contribute at the margin to the world's energy supply, currently, they are no substitute for fossil fuels for meeting baseload energy needs. One reason for this, Green argues, is that renewables are highly land intensive. Heavy reliance on renewables would increase competition for land, much of which has good alternative uses. Since the desire of an increasing world population for improved economic well-being inevitably means increased energy use, albeit greater energy efficiency will slow the rate of increase in energy consumed, it is predictable that most of the increase will have to be met by fossil fuels in the foreseeable future.

Therein lies a problem. Fossil fuel use causes the emission of greenhouse gases (GHGs), the most important of which is carbon dioxide (CO₂). There is mounting evidence to support the prediction that GHG emissions from a continued high level of fossil fuel use will eventually raise the earth's average temperature. A rise in global average temperature implies a change in global climate, with less predictable effects on local climate and weather, and in turn, on local economic activity, health and social structure.

Scaling Up of Renewable Energy Sources: The Land Intensity Problem

Conversion from fossil fuels to renewable energy sources poses a potentially serious scale-related problem. Fundamentally, the problem involves a little understood facet of renewable energy technologies: in their current form, they are all very land intensive with the obvious exceptions of geothermal, ocean thermal and tidal energy. Thus, what may be technically and economically feasible on a small scale may not be so on a large, global scale, either because there may be insufficient land with the appropriate characteristics or there are better (more valuable) uses of land.

In order to get some idea of the problem posed by large scale use of renewable energy technologies, it is useful to establish some benchmarks. These are set out below in Tables 1.9 and 1.10. Table 1.9 indicates the number of Quads or exajoules (EJ) of energy produced globally in 1988 and 1996, and the least that is likely to be needed in 2100. Table 1.10 indicates what it currently takes to produce one Quad (=1.055 EJ) of energy per year.

Conversion from fossil fuels to renewable energy sources poses a potentially serious scale-related problem: in their current form, renewables are very land intensive.

Sources:

^a U. S. Department of Energy. (1990) National Energy Strategy, Interim Report. Washington, D. C., April 1990;

^b IPCC (1995) WG II Ch. 19, Part I, B.)

^a U. S. consumed 80.8 Quads in 1988 according to U. S. Department of Energy, National Energy Strategy, Interim Report, April 1990

^b At 0.40 actual capacity factor

^c Total U. S. cropland is approximately 600,000 sq. miles (1,554,000 km²)

Source: H. Douglas Lightfoot and C. Green (1992). The Dominance of Fossil Fuels: Technical and Resource Limitations to Alternative Energy Sources. McGill University, Center for Climate and Global Change Research (C2GCR). Working Paper 92-6, May.

What may be technically and economically feasible on a small scale may not be so on a global scale, either because there may be insufficient land with the appropriate characteristics or there are more valuable uses for the land.

It is clear from Table 1.10 that, with the exception of nuclear power, all of the non-fossil fuel energy alternatives are very land using. Essentially it takes many thousands of square miles to produce a Quad (or EJ) of energy from biomass or other vegetation-related energy sources. For solar energy, it takes anywhere from 1,000 to 3,000 sq. miles (2,590 to 7,770 km²) to produce a Quad of energy, the specific amount depending on locale. In the case of wind energy, it takes 4,200 square miles (10,878 km²) in a windy locale to produce a Quad of energy with one turbine per acre (2.5 turbines per ha). If the turbines can be packed more densely (say 2 per acre), it takes an area of 2,100 square miles (5,439 km ²) covered with turbines to generate a Quad of energy.

Hydropower is also land intensive. For example, it is estimated that a huge expanse of Northern Quebec would be inundated if Hydro-Quebec were to build all three phases (only Phase I now exists) of the planned James Bay project; yet delivered energy from all three phases would be less than a Quad. Not only are each of the renewables land intensive, but they are site-specific as well. Only some land, especially in the tropics, but in some mid-latitude sites as well, is appropriate for fast growing plantation biomass that requires substantial water as well as sun and warm temperatures. Few locales have sufficient insolation and suitable terrain with enough water to make large scale solar power operations feasible. Even then there is a storage problem. The same is true of wind energy, which is typically most abundant in locales far from centers with a large demand for energy.

The message of the preceding paragraphs is that the technical feasibility and economic competitiveness of a renewable technology is a necessary but not sufficient condition for its application as a baseload alternative to fossil fuels at a global level. If renewables are to be treated as worldwide substitutes for fossil fuels, it is also necessary to consider their land (area) and site requirements. To Green's knowledge, this has not been done on a systematic basis for any renewable, with the possible exception of biomass, which is considered below. Thus, alternative energy scenarios discussed by the Intergovernmental Panel on Climate Change (IPCC 1995, Working Group II, Chapter 19) such as FFES (Fossil Free Energy Scenario) and LESS (Low -Emissions Supply System) may be prone to a scaling problem. Land constraints may stand in the way of heavy reliance on renewables in a low carbon emission world. The example of biomass is illustrative.

The technical feasibility and economic competitiveness of a renewable technology is a necessary but not sufficient condition for its application as a baseload alternative to fossil fuels at a global level.

The IPCC (1995) Working Group II, in its chapter 19, "Energy Supply Mitigation Options," gives extensive attention to low CO₂-emitting energy supply systems - ones that ostensibly could replace fossil fuels by the end of the next century. Various versions of a Low-Emissions Supply System (LESS) were constructed, one emphasizing the role of biomass, another nuclear, another natural gas. The estimated energy use under these scenarios is in the range of 600-700 EJ in the year 2100 (IPCC 1995, II, 19-8:624). In each of the IPCC scenarios, fossil fuel use declines and biomass increases significantly over the next century.

It is useful to probe the land requirements for biomass under the LESS constructions. The IPCC provides estimates of the number of hectares covered by biomass energy plantations, by region, under the alternative LESS constructions (IPCC 1996, II, 19 -11:627). The estimates imply that major sections of Africa, South America and Australia would need to be planted in biomass in each of the scenarios. In the biomass-intensive scenario, by the year 2100, 572 million hectares would be planted in biomass globally or 2.2 million sq. miles (5.7 million km²). Assuming the required amount of land is still available, and it is economically sensible to convert it to biomass plantation, the LESS construction suggests that the world could be largely weaned from its dependence on fossil fuels.

The large substitution away from fossil fuels in a biomass-intensive world would, in principle, allow for a large reduction in CO₂ emissions (IPCC 1995, II, 19-13: 629). It is estimated that world production of energy in 2100 will total around 720 EJ (almost double the present 380 EJ). According to the LESS estimates, the conversion to biomass and other renewables would result in annual CO₂ emissions falling to 1.78 GtC per year (by 2100) compared to the 6.5 GtC emitted in 1990. The resultant 70 percent decline in emissions from current levels (and more than 90 percent from a business-as-usual baseline) would be sufficient to stabilize the atmospheric concentrations of carbon dioxide. In the LESS scenario, the major factor in the decline in CO₂ emissions is the production of 325 EJ from biomass. The 325 EJ are produced from 572 million hectares of plantation biomass. Another 250 EJ would be produced from "intermittent" renewables (solar, wind) and solar hydrogen. But as shown earlier, all of these, too, are land intensive.

The LESS biomass-intensive construction is a rosy scenario, and taken at face values seems so simple it doesn't even require any major technological advance. In fact, it seems to solve the energy-climate change problem by turning back the clock. But it is too simple. In an increasingly populated world, LESS requires enormous amounts of land to be devoted just to energy production. Even assuming there is sufficient land, along with the soil water and temperature to produce rapid growth vegetation convertible to biomass energy, converting to biomass may not be economically sensible . Land with the qualities just described has an opportunity cost in the form of good alternative uses. One measure of available land for plantation biomass is the estimate of cropland in the recent study of the value of the world's ecosystem services and natural capital (Costanza et al., 1997). There, it is estimated that the world's cropland is 1.4 billion hectares. The LESS biomass-intensive scenario would devote 572 million hectares (or 41 percent of cropland) to biomass production. This is a significant shift of cultivable land resources from food to fuel. It implies important opportunity costs when biomass is promoted on a global scale.

Even assuming there is sufficient land, along with the soil water and temperature to produce rapid growth vegetation convertible to biomass energy, converting to biomass may not be economically sensible.

In sum, what may appear as technically and economically feasible at a micro, or local, level may not be economically sensible when scaled up to a macro, or global, level. Converting from fossil fuels to renewables implies devoting large amounts of land to energy production. But land has alternative uses, the more so in an increasingly populated world. These alternative uses will compete with energy production and the former may turn out to be more highly valued than the latter. In any event, the widespread conversion of land, even if it is possible, will increase the price of land. These possibilities do not, however, seem to be recognized in the literature on a "renewables future." Yet, the issue of alternative uses of land is crucial to how we should think about disconnecting the climate from our overwhelming need to use energy.

Perhaps it is time to look to the development of new non-fossil fuel energy technologies that are not heavily dependent on relatively fixed or scarce factors such as land.

Conclusions

The threat of greenhouse warming and global climate change will produce increasing calls for reductions in fossil fuel energy use. A growing world population bent on increasing economic and social well being will require increased energy supplies. Although there is a widespread belief that the potential conflict between environment and energy can be resolved by progressive conversion to renewables, the land-intensity of renewables stands as an important barrier to large scale conversion. Perhaps it is time to look in an altogether different direction - to the development of new non-fossil fuel energy technologies that are not heavily dependent on relatively fixed or scarce factors such as land.

References

Costanza, R. et al. (1997). The Value of the World's Ecosystem Services and Natural Capital. Nature, 387:253-260.

Lightfoot, H. D. and C. Green (1992). The Dominance of Fossil Fuels: Technical and Resource Limitations to Alternative Energy Sources. McGill University, Center for Climate and Global Change Research (C2GCR) Working Paper 92-6.

Watson, R. T., M. C. Zinowera and R. H. Moss, Eds. (1996). Climate Change 1995: Impacts, Adaptations and Mitigation of Climate Change , Contribution of Working Group II. Ch. 19: Energy Supply Mitigation Options. Cambridge University Press. pp. 587 -648.