The scramble for alternatives is on. High oil prices, growing concerns over energy security, and the threat of climate change have all stimulated investment in the development of alternatives to conventional oil.
“Alternative energy” generally falls into two categories:
..Substitutes for existing petroleum liquids (ethanol, biodiesel, biobutanol, dimethyl ether, coal-toliquids, tar sands, oil shale), both from biomass and fossil feedstocks.
..Alternatives for the generation of electric power, including power-storage technologies (wind, solar photovoltaics, solar thermal, tidal, biomass, fuel cells, batteries).
The technology pathways to these alternatives vary widely, from distillation and gasification to bioreactors of algae and high-tech manufacturing of photonabsorbing silicon panels. Many are considered “green” or “clean,” although some, such as coal-to-liquids and tar sands, are “dirtier” than the petroleum they are replacing. Others, such as biofuels, have concomitant environmental impacts that offset potential carbon savings.
Unlike conventional fossil fuels, where nature provided energy over millions of years to convert biomass into energy-dense solids, liquids, and gases–requiring only extraction and transportation technolgy for us to mobilize them–alternative energy depends heavily on specially engineered equipment and infrastructure for capture or conversion, essentially making it a high-tech manufacturing process. However, the full supply chain for alternative energy, from raw material to manufacturing, is still very dependent on fossil-fuel energy for mining, transport, and materials production. Alternative energy faces the challenge of how to supplant a fossil-fuel-based supply chain with one driven by alternative energy forms themselves in order to break their reliance on a fossil-fuel foundation.
…1. Scalability and Timing
For the promise of an alternative energy source to be achieved, it must be supplied in the time frame needed, in the volume needed, and at a reasonable cost…
Closely related to the issue of scalability and timing is commercialization, or the question of how far away a proposed alternative energy source stands from being fully commercialized…
Ideally, an alternative energy form would integrate directly into the current energy system as a “drop-in” substitute for an existing form without requiring further infrastructure changes…
…4. Material Input Requirements
Unlike what is generally assumed, the input to an alternative energy process is not money per se: It is resources and energy, and the type and volume of the resources and energy needed may in turn limit the scalability and affect the cost and feasibility of an alternative…
Modern societies expect that electrons will flow when a switch is flipped, that gas will flow when a knob is turned, and that liquids will flow when the pump handle is squeezed. This system of continuous supply is possible because of our exploitation of large stores of fossil fuels, which are the result of millions of years of intermittent sunlight concentrated into a continuously extractable source of energy. Alternative energies such as solar and wind power, in contrast, produce only intermittently as the wind blows or the sun shines, and even biomass-based fuels depend on seasonal harvests of crops…
…6. Energy Density
Energy density refers to the amount of energy that is contained in a unit of an energy form…The consequence of low energy density is that larger amounts of material or resources are needed to provide the same amount of energy as a denser material or fuel. Many alternative energies and storage technologies are characterized by low energy densities, and their deployment will result in higher levels of resource consumption…
Water ranks with energy as a potential source of conflict among peoples and nations, but a number of alternative energy sources, primarily biomass-based energy, are large water consumers critically dependent on a dependable water supply…
…8. The Law of Receding Horizons
An often-cited metric of the viability of alternatives is the expected break-even cost of the alternative with oil, or the price that crude oil would have to be to make the alternative cost competitive. Underlying this calculation, however, is an assumption that the input costs to alternative energy production would remain static as oil prices rise, thereby providing the economic incentive to development. This assumption, however, has not always proved to be the case, particularly for those alternatives for which energy itself is a major input. Because of price linkages in the energy (and now energy and biomass) markets, rising oil prices tend to push up the price of natural gas as well as coal; for processes that are heavily dependent on these fuels, higher oil prices also bring higher production costs.
…9. Energy Return on Investment
The complexity of our economy and society is a function of the amount of net energy we have available. “Net energy” is, simply, the amount of energy remaining after we consume energy to produce energy. Consuming energy to produce energy is unavoidable, but only that which is not consumed to produce energy is available to sustain our industrial, transport, residential, commercial, agricultural, and military activities. The ratio of the amount of energy we put into energy production and the amount of energy we produce is called “energy return on investment” (EROI)…
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